About the SA Blog Network

Tetrapod Zoology

Tetrapod Zoology

Amphibians, reptiles, birds and mammals - living and extinct
Tetrapod Zoology Home

Marsupial ‘dogs’, ‘bears’, ‘sabre-tooths’ and ‘weasels’ of island South America: meet the borhyaenoids

The views expressed are those of the author and are not necessarily those of Scientific American.

Email   PrintPrint

A selection of borhyaenoid crania (with neck vertebrae), illustrating some of the diversity within the group. From Argot (2004a).

I’ve decided to republish – in slightly updated form – the borhyaenoid text posted on Tet Zoo ver 2 back in July 2008. The text was originally published as three separate articles. It makes more sense to have it all together in the same place, so here are all those articles combined.

Just a few of the fantastic beasts that inhabited Cenozoic South America: astrapotheres, a phorusrhacid, and a giant sloth. Click to enlarge.

Even to novices with no special interest in the extinct wildlife of the Cenozoic, it should be obvious that ancient South America had what we might technically call a Really Awesome Faunal Assemblage. Astrapotheres, sebecosuchians, phorusrhacids, teratorns, gigantic caimans, madtsoiid snakes, sloths, glyptodonts… and this is only half of it, there’s so much more. It seems only fair and proper that yet another of South America’s extinct Cenozoic groups gets appropriate coverage on Tet Zoo, and yet again it’s a bunch of animals on which comparatively little information is freely available: the borhyaenoids, a long-lived and diverse group of carnivorous marsupials (or are they?). And it’s a particularly good time to bring this group to wider attention because, in a series of excellent recent papers, one worker has, almost single-handedly, done the most amazing job of bringing these animals to life.

Florentino Ameghino (1854-1911), Argentine palaeontologist, naturalist, zoologist, anthropologist. Namer of many borhyaenoids.

Borhyaenoids were first recognised during the 1880s when Florentino Ameghino (1854-1911) described some new Patagonian fossil mammal remains dating to the Miocene. They were carnivores of some sort, with jaws and teeth reminiscent of those of carnivorous or omnivorous mammals like dogs or raccoons. He grouped them together in the newly recognised ‘family’ Acyonidae Ameghino, 1889 and suggested that they descended from opossums and included the ancestors of canids. That’s right – Ameghino thought that the similarities present between South American mammals and their Northern Hemisphere counterparts were not the results of convergent evolution, but indicative of actual evolutionary relationships (Simpson 1980). Another name that Ameghino coined later on (in 1894) – Borhyaenidae – ended up superseding Acyonidae, and the name we’re using for the group here (Borhyaenoidea) is based on that one*. Borhyaenoids have also been called sparassodonts (for Sparassodonta Ameghino, 1894), and while this name is used by some recent authors it hasn’t been used as much. They’ve also been called Borhyaeniformes Szalay, 1962 and Borhyaenomorphia Archer, 1984.

* Marshall et al. (1978) petitioned the ICZN to suppress Acyonidae, and asked, while they were at it, that the spelling Borhyaena Ameghino, 1889 be formally recognised over Boryhaena [sic], the name that Ameghino originally used – apparently accidentally – in 1887.

Borhyaenoids within the marsupial radiation… or not

Virginia opossum (Didelphis virginiana), photographed in the wild by Daniel W. Holth. Like many mammals thought to be short-legged, you can see here that opossums aren't really short-legged at all. Photo by Daniel W. Holth, from wikipedia. Released into public domain.

Most borhyaenoids have been characterised as ‘dog-like marsupials’, and if any common name is used for the group it’s this one. As we’ll see, at least some borhyaenoids were superficially dog-like, but others certainly weren’t, and if you want to find a more zoologically accurate way of describing these animals it might be to think of them as giant predatory opossums. It used to be thought that the dog-like marsupials of Australasia, the thylacines, were close kin of borhyaenoids, but anatomical and molecular data shows that this is not the case: thylacines are part of the exclusively Australasian marsupial clade that includes the dasyures. Borhyaenoids have also been considered allied to the stagodontids, a Cretaceous group of mostly North American omnivores or carnivores (some of which had bulbous teeth that look suited for crushing or breaking hard objects), to the deltatheroidans of Cretaceous Asia, and to the pediomyids of Cretaceous North America.

An extensive literature discusses these various proposals, most of it focusing on detailed characters of the braincase and ear region. Muizon et al. (1997) and Muizon (1999) showed that the stagodontid, deltatheroidan and pediomyid proposals were not supported by good character evidence, and argued that borhyaenoids should be united with opossums (didelphids) and their relatives in the clade Didelphimorphia. The key characters that unite these animals are found in the back of the skull.

If borhyaenoids are part of Didelphimorphia, then they’re part of the marsupial crown-group and can properly be considered part of Marsupialia. If they’re not part of Didelphimorphia, the competing hypothesis puts them outside the marsupial crown-group, meaning that they’re stem-marsupials, or non-marsupialian metatherians. Note that Metatheria is more inclusive than Marsupialia, and that the name Marsupialia is restricted to the crown-group (e.g., Rougier et al. 1998, Asher et al. 2004). In a large and inclusive analysis of metatherians and other mammals, Rougier et al. (1998) found borhyaenoids and other alleged stem-didelphimorphians to be outside of Marsupialia; Asher et al. (2004) found a similar result for the supposed early borhyaenoid Mayulestes.

Pucadelphys andinus specimen, (c) MNHN, Paris. A 2011 discovery points to strong sociality in this species, with 35 associated specimens suggesting to some that this was a 'pack-living' animal. Might this tell us about sociality in borhyaenoids?

Let’s suppose, however, that borhyaenoids are didelphimorphians for a moment. While it might be difficult to imagine that a group of small, superficially rat-like predators are close kin of one of the most spectacular dynasties of big-bodied mammalian macropredators, note that Palaeocene proto-opossums, like Pucadelphys, are really very similar to taxa regarded by some as the most basal of borhyaenoids, like Mayulestes [Pucadelphys shown in adjacent image, from Paleocene Mammals of the World, but original is © MNHN]. The characters that distinguish borhyaenoids from other didelphimorphians are mostly minor cranial details like the absence of prootic canal, the form of the tympanic sinus, and the presence of nasal bones that don’t overhang the narial opening. Borhyaenoids are also characterised by specialised shearing teeth (Muizon 1999).

A selection of borhyaenoids that we'll meet later on in the article. Top to bottom: the proborhyaenid Callistoe (from Babot et al. 2002), the thylacosmilid Thylacosmilus (from Riggs 1933), and the proborhyaenid Arminiheringia (from Simpson 1932).

Were borhyaenoids pouched? That’s not a dumb question, as pouches have been repeatedly lost within metatherian evolution, and particularly within opossums. Articulated borhyaenoid skeletons lack the epipubic bones used in other metatherians to support the pouch, so pouches might have been absent. However, some marsupials (like Thylacinus) that lack ossified epipubic bones have cartilaginous ones, so we can’t be sure.

While people have often made proposals about how certain borhyaenoids lived and hunted, detailed comparative work that analyses the anatomical details of these animals and compares them with those of living carnivorous mammals has generally been lacking. Indeed, harking back to comments I made about the CEE Functional Anatomy meeting, the widely held view that this sort of work is old-fashioned, outdated and redundant ignores the massively under-appreciated fact that, in an absurdly high number of cases, it’s never been done at all. Thanks almost entirely to one worker – Christine Argot of the Muséum National d’Histoire Naturelle (Paris) – we now have a very robust, incredibly detailed literature on borhyaenoid functional anatomy. Argot’s papers contain so much information that I’m only going to be reviewing but a fraction of the areas she covers. Given that lengthy papers on functional anatomy of any type are pretty rare, it cannot be over-emphasised how important studies like this are. What’s also of special interest as goes borhyaenoids is that Argot’s work has shown how various taxa, repeatedly depicted in the popular and semi-technical literature, seem to have been quite different from their ‘conventional’ image.

Mayulestes and Allqokirus

Mayulestes ferox from the Santa Lucía Formation of Tiupampa, Bolivia, has typically been regarded as the sister-taxon to the rest of the borhyaenoid radiation (Muizon 1994). However, Rougier et al. (1998) didn’t find Mayulestes to be part of Borhyaenoidea, and this was followed by Forasiepi et al. (2006). Tiupampa gives its name to the Tiupampan Land Mammal Age, a time span dated to the early Palaeocene.

Reconstructed skeleton of Mayulestes ferox in hypothesised life posture, from Argot (2004a), modified after Muizon. Scale bar = 50 mm.

A second Tiupampan borhyaenoid, Allqokirus australis, has been regarded as close to Mayulestes and both have been regarded as part of the ‘family’ Mayulestidae Muizon, 1994. The fact that Allqokirus is known only from teeth makes this difficult to verify, however. Mayulestes was weasel-sized and weighed less than 1 kg: probably, in fact, less than 500 g. By comparing its pelvis and hindlimb with those of extant marsupials, Argot (2002) showed that this animal had a mobile lumbar region and was agile and well able to climb and move with agility across uneven surfaces. However, the forelimb has features more suggestive of a climbing lifestyle (Argot 2001). It wasn’t a cursorial animal, running around in open habitats, nor was it good at leaping. It should probably be imagined as scansorial: as a predominantly terrestrial denizen of cluttered, three-dimensional habitats like tangled forest floors, but well able to climb.

The Tiupampan fauna includes an assortment of opossums and mioclaenids, and there are also some real oddballs in the fauna, like the pantodont Alcidedorbignya and the opossum-like Szalinia and Jaskhadelphys. It’s been hypothesised that Mayulestes preyed on frogs, small marsupials, and the eggs of crocodilians, turtles and birds (Argot 2004a). As the potential ‘most basal’ member of Borhyaenoidea, Mayulestes might show us what the ancestral lifestyle and morphology of the group was. However, as we’ve just seen, there is now doubt as to whether Mayulestes is definitely a borhyaenoid.

With Mayulestes and Allqokirus out of the way, the remaining borhyaenoids have been recognised as a clade (unnamed, so far as I know) united on the basis of braincase details, palatal morphology and an incisor compliment reduced to four uppers and three lowers* (Muizon 1994, 1999). Conventionally, these ‘higher borhyaenoids’ have been grouped into five ‘families’: Hathlyacynidae, Prothylacynidae, Proborhyaenidae, Borhyaenidae and Thylacosmilidae. These have also been regarded as ‘subfamilies’ in those classification schemes where the group here termed Borhyaenoidea has been regarded as a ‘family’. Of these groups, hathlyacynids (which differ from other borhyaenoids in possessing a pneumatised squamosal) appear to form the sister-taxon to a clade that includes the remaining taxa (Muizon 1994, 1999).

* The primitive condition for marsupials is five upper incisors and four lowers.

Long-snouted marsupial martens and false thylacines

Maxillary dentition of Patene simpsoni, from Marshall (1981). Regarded by Marshall as the "most generalized of known borhyaenoids", its whole lower jaw was c. 70 mm long.

Hathlyacynidae is the biggest and longest-lived borhyaenoid clade, with members that range in age from Late Palaeocene (Patene) to Early Pliocene (Notocynus and Borhyaenidium). Notocynus might even have made it to the Late Pliocene, but this is debatable. Incidentally, there are two ways of spelling the name of this group, with some authors spelling it Hathliacynidae. Most of the 17 or so hathlyacynid genera are known only from jaw fragments, and these show that members of the group were conservative over their long history: in fact Marshall (1981) described hathlyacynid genera as “monotonously alike”.

Skull of the hathlyacynid Cladosictis patagonica. No reason for thinking it's 'otter-like' as the books say.

While often characterised as dog-like, those taxa known from good remains show that at least some hathlyacynids were marten-like predators with good climbing abilities. So far as we know they were all long snouted, with short gaps in the toothrow both between the premolars, and between the first premolar and the canine. Their teeth suggest that they were carnivorous or even omnivorous generalists, though there is a trend for later members of the group to have more specialised carnassials (Marshall 1981). Two hathlyacynids in particular, Sipalocyon gracilis and Cladosictis patagonica (both from the Santacrucian beds of Early Miocene Patagonia), have been subjected to detailed functional analyses.

Charles Knight's well-known and oft-reproduced reconstruction of Cladosictis hunting the lagomorph-like notoungulate Pachyrukhos, from W. D. Scott's 1913 A History of Land Mammals in the Western Hemisphere. As so often happens, the hypothetical pigmentation here became the 'standard' livery forever adopted by all artists that followed. Out of copyright in the USA.

Based on its divergent hallux and semi-opposable pollex, Sinclair (1906) thought that Sipalocyon was plantigrade and probably arboreal, and comparison of its bones with those of extant mammals suggest that it was probably scansorial (Argot 2003a, 2004a). Its mobile thumb suggests that it was good at grabbing and manipulating prey. Cladosictis has been repeatedly depicted in the popular and semi-technical literature as an amphibious, otter-like predator. This idea appears to come from Savage’s (1977) statement that the forelimbs of Cladosictis recall those of an otter in their proportions. However, otter-like forelimb proportions do not mean an otter-like lifestyle, and in fact the forelimb proportions of otters aren’t really reliably different from those of other (non-swimming) mustelids.

Reconstructed skeleton of Cladosictis patagonica, from Argot (2004a).

Cladosictis was about 20-25 cm tall at the shoulder and weighed 4-8 kg; it was relatively short-legged with limb details suggesting a good climbing ability [adjacent skeletal reconstruction from Argot 2004a. Image © C. Argot. Scale bar = 10 cm]. It also had a semi-opposable thumb, and hence was able to grasp branches and manipulate prey. The closest analogue is perhaps the Tayra Eira barbata, a tropical American mustelid that forages terrestrially but is also a good climber (Argot 2003a, 2004a). Based on contemporary fossils and morphology, Cladosictis probably predated on small mammals, birds, reptiles and frogs. The neck was about similar in length to that of a modern canid (c. 37% of thoracolumbar length); large ventral processes on the neck vertebrae demonstrate that the musculature here was powerful. Reasonably long and powerfully muscled necks of this sort are typical of borhyaenoids.

All the other hathlyacynids

Hathlyacinid lower jaw dentitions drawn to scale, with teeth in labial (A), occlusal (B), and lingual (C) views. From Marshall (1981). Click to enlarge.

Do we know if other hathlyacynids were doing the same sort of thing as Sipalocyon and Cladosictis? Unfortunately we don’t know enough about them to be sure. The forelimb bones of little Pseudonotictis pusillus (also from the Santacrucian) indicate climbing abilities, but this taxon had particularly slender bones, suggesting that it was doing something unusual… but just what we’re not sure (Argot 2003a). The lower jaw of P. pusillus is about 4 cm long, suggesting a weasel-like size of less than 40 cm. It’s the smallest hathlyacynid known, but its probable close relative Notictis ortizi from the Huayquerian (= Late Miocene) of Argentina was nearly as small (Marshall 1981). Marshall (1981) and Villarroel & Marshall (1983) further proposed that Santacrucian Perathereutes pungens shared an ancestor with Pseudonotictis, and that Perathereutes was close to the ancestry of Borhyaenidium from the Huayquerian. In both Perathereutes and Sipalocyon the first lower premolar is set at an angle relative to the other teeth, leading Marshall (1981) to suggest that both shared an ancestor. Marshall (1981) also regarded Notocynus hermosicus from the Montehermosan (= late Late Miocene) as a close relative or descendant of Sipalocyon as the two share tooth cusp characters.

One of several mandibular specimens referred to Sipalocyon gracilis by Marshall (1981). This specimen is the type of Protoproviverra manzaniana Ameghino, 1891.

However, Sipalocyon was regarded as closely related to Notogale by Forasiepi et al. (2006), as both possess a transverse canal in the auditory region. This character is also present in Cladosictis, however (Muizon 1999). Santacrucian and Laventan (= Middle Miocene) Acyon – resurrected from the synonymy of Anatherium by Forasiepi et al. (2006)* – shares a single tooth character with Cladosictis and might be closely related to it, and Chasiocostylus castroi is also similar and probably close to Cladosictis.

* The type species of Anatherium, A. defossus, was referred to Cladosictis sp. by Forasiepi et al. (2006).

Sallacyon hoffstetteri has been regarded as a basal hathlyacynid (Muizon 1999, Forasiepi et al. 2006), as has Patene (Marshall 1981). Procladosictis anomala from the Mustersan (= middle Eocene) resembles Patene. Several other genera, including Agustylus, Ictioborus, and Amphithereutes, continue to be listed by some authors (e.g., McKenna & Bell, 1997), but are regarded as synonymous with other taxa by others (e.g,. Marshall 1981). Palaeocladosictis mosesi, sometimes listed as a hathlyacinid, was based on an ungulate tooth according to Marshall (1978).

Prothylacinids: climbing thylacine-hyaena-binturong hybrids

Character evidence indicates that hathlyacynids are the sister-group to a borhyaenoid clade that includes all the remaining taxa. Among these ‘remaining taxa’, we begin with the prothylacinids (or prothylacynines): an Oligocene-early Pliocene group regarded by some as part of Borhyaenidae: both groups share characters not seen in other borhyaenoids (Muizon 1999). However, prothylacinids and borhyaenids are more usually imagined as sister-groups, which, if true, means that prothylacynids must have a ghost-lineage going back to the Early Eocene at least (as there are apparently borhyaenids this old, like Argyrolestes and Angelocabrerus).

Excellent skeleton of Lycopsis longirostrus, from Marshall (1977).

Lycopsis from the Santacrucian and Friasian (= late Early Miocene) has conventionally been regarded as one of the most basal prothylacinids (Marshall 1979). However, more recent studies have failed to recover this position, and have instead found it to be the sister-taxon of, or basal member of, a ((prothylacinid + borhyaenid) + (proborhyaenid + thylacosmilid)) clade (Muizon 1999, Babot et al. 2002, Forasiepi et al. 2006). Again, the characters involved are all trivial details of the back of the skull and if I explain them I can see myself adding 1000 words to this article.

Thanks to a wonderfully near-complete skeleton of L. longirostrus* from the Friasian of Colombia [shown above] we have a reasonably good idea of the morphology and functional anatomy of this animal (Marshall 1977a, Argot 2004b). About 35 cm tall at the shoulder and weighing about 15 kg (Argot 2004a), it possesses an unusual combination of features. The relatively elongate, straight-boned forelimb and semi-digitigrade manus indicate a trend towards cursoriality, but the semi-opposable thumb, short metatarsals and prominent hallux are at odds with this. Lycopsis doesn’t appear to have been a particularly good climber, but it could probably clamber in trees if need be, and Argot (2004b) noted that this might have been necessary given the densely forested environment it inhabited and the presence of a diverse crocodilian assemblage. Perhaps it was an ambush predator of small and mid-sized prey, able to engage in some running and some climbing, but not specialised for either. While previously imagined as thylacine-like in lifestyle, it probably mostly preyed on small rodents, and indeed we know it did at least sometimes, as rodent bones and a tooth were preserved adjacent to the pelvis of one specimen (Marshall 1977a).

* Argot (2004b) mistakenly spelt it L. longirostris [sic].

Moving on to prothylacinids proper, Argot (2003b) showed that Prothylacinus patagonicus from the Santacrucian had a powerful neck, short, muscular limbs and a flexible body. Its manual phalanges were proportionally long, its manual unguals were deep, sharply curved and with large flexor tubercles, and it probably had a fairly large, pseudo-opposable pollex.

What we know of its tail indicates that the organ was long (incorporating 20-30 vertebrae) and gradually tapering. Its metapodials were proportionally short and its feet were plantigrade, with a long first metatarsal probably supporting a long plantar pad that would have enabled the foot to grip curved surfaces.

Captive Binturong, photo by Tassilo Rau, from wikipedia. Licensed under Creative Commons Attribution-Share Alike 3.0 Unported license.

Combined, these features strongly suggest that Prothylacinus was another scansorial borhyaenoid: a powerful, agile climber that used flexible hands in gripping branches and a muscular neck and large skull to support the weight of large prey items. No living carnivorous mammal is exactly like this, but the strongest similarity is with binturongs Arctictis (Argot 2003b) [adjacent binturong by Tassilo Rau]. Binturongs are large, slow, agile climbers, with robust, muscular limbs and long tails. They’re predominantly frugivorous, so (so far as we know) are unlike Prothylacinus in this respect. Argot (2004a) speculated that the prey of Prothylacinus might have included rodents, caenolestoids and some of the smaller sloths. Incidentally, Prothylacinus was relatively large, with an estimated weight of 27-37 kg. However, such a size is not at all incompatible with a scansorial lifestyle, as demonstrated by living wolverines, sun bears, clouded leopards and leopards. Prothylacinus was from the Santacrucian fauna, so did it complete with the also scansorial Cladosictis and Sipalocyon? The difference in size between the hathlyacynids and prothylacinid indicate that they occupied different niches.

Lower jaw fragment of the prothylacinid Stylocynus paranensis, from Marshall (1979).

The crowded cheek teeth, shortened premolars and molars and tightly fused mandibular symphysis indicate that Prothylacinus was a specialised carnivore less suited for omnivory than other prothylacinids. Indeed, scars indicating large masseter muscles, combined with evidence from tooth cusp morphology, have led other prothylacinids (like Montehermosan Stylocynus paranensis: shown here, from Marshall 1979) to be regarded as omnivores with a bear-like diet (Marshall 1979).

The largest prothylacynid is Dukecynus magnus from La Venta in Colombia. Charactised by a particularly narrow, elongate rostrum (Goin 1997), its teeth suggest that it was more carnivorous than some of the other taxa, and its molars suggest close affinities with Pseudolycopsis cabrerai from the Chasicoan. Pseudothylacinus from the Colhuehuapian was thought by Marshall (1979) to be close to the ancestry of Pseudolycopsis.

The not so bear-like borhyaenids

Shabby ghetto-scan of some notorious borhyaenoid (and necrolestid) reconstructions from a well-known prehistoric animal book. The plantigrade pseudo-bear in the middle is Borhyaena (but read on). Illustrations by Graham Allen.

Borhyaenids (yes, borhyaenid borhyaenoids) include about ten genera of superficially dog- or thylacine-like borhyaenoids. The oldest (Nemolestes) is from the Early Eocene or possibly Late Palaeocene while the youngest (Eutemnodus) is from the Early Pliocene (Marshall 1978)*. Easily the best known member of the group is Borhyaena tuberata from the Santacrucian (= Early Miocene). Like the contemporary Cladosictis, it has frequently been depicted in the popular and semi-technical literature. As is also the case with Cladosictis, its ‘conventional’ image is – so it turns out – pretty far off the mark.

* An alleged borhyaenid from the Late Miocene or Early Pliocene – Parahyaenodon argentinus from Argentina – was reidentified as a procyonid (a member of the raccoon family) by Forasiepi et al. (2007).

The best known life restoration of this animal (that produced by John Long for Mammal Evolution: An Illustrated Guide) depicts it as something like a long-tailed bear, and I can recall thinking that Borhyaena was giant; perhaps similar in size to a brown bear. In fact, weight estimates (Argot 2003b) put it at 19-29 kg, which is about equivalent to a small hyaena or wolf, or a large thylacine. However, its robust skull, with its particularly broad zygomatic arches, indicate a disproportionately large amount of skull and neck musculature, and mass estimates for the whole animal based on skull proportions alone (and assuming body proportions resembling those of extant carnivorous mammals) give Borhyaena an inflated mass of 74 kg, a vivid illustration of why knowing the overall proportions of an animal are important when estimating its weight (Van Valkenburgh 1985, 1987). The substantial neck musculature suggests an ability to carry heavy loads.

A semi- or fully digitigrade manus, short, blunt claws, and forelimbs that were restricted to parasagittal movement and exhibit reduced distal musculature indicate that Borhyaena was terrestrial and cursorial – in fact, the most cursorial of all borhyaenoids. However, its limbs weren’t as proportionally elongate as those of extant cursorial predators. That might not have been such a problem, because virtually all the potential large-bodied prey (a assortment of xenarthrans, astrapotheres, notoungulates and big rodents) were not cursorial either: in the Santacrucian fauna, only proterotheriid and macraucheniid litopterns can be considered cursorial (Argot 2004a). While previously depicted as being plantigrade, what is known of ankle morphology and forelimb proportions show that Borhyaena was more likely digitigrade in the hindlimb (Argot 2003b) [life restoration and skeletal reconstruction above © C. Argot; skull photo below by Ghedoghedo].

Skull of Borhyaena tuberata as displayed at NHM (London). Photo by Ghedoghedo, licensed under Creative Commons Attribution-Share Alike 3.0 Unported license.

Whether the other borhyaenids were like ‘new-look Borhyaena’ remains to be shown. Fredszalaya hunteri from the Deseadan (Late Oligocene) of Bolivia was suggested by Shockey & Anaya (2008) to be closely related to Borhyaena on the basis of the form of the alisphenoid, but the unreduced shelves and cusps on its molars suggest that it was omnivorous while the shape of its calcaneum suggest possible climbing abilities (Shockey & Anaya 2008). Fredszalaya is smaller than Borhyaena and with a much shorter snout.

Proborhyaenids, the ‘marsupial bears’

Fantastic, articulated skeleton of the proborhyaenid Callistoe vincei. In total length, the specimen is c. 2.1 m long. Image courtesy of C. Argot.

Proborhyaenids have usually been thought of as as a group of hyaena-like or bear-like borhyaenoids. Marshall (1977b) thought that proborhyaenids might be the most basal of borhyaenoids (while at the same time the most specialised), but it has more recently been argued that proborhyaenids share derived characters with the sabre-toothed cat-like thylacosmilids (Muizon 1994, 1999, Babot et al. 2002). One of the most interesting characters present in both proborhyaenids and thylacosmilids is the presence of ever-growing, open-rooted upper canines. Both groups also exhibit strongly projecting occipital condyles, indicating that they were capable of greater rotation and movement at the head-neck joint than other borhyaenoids. Babot et al. (2002) suggested that the presence of fine ridges and grooves on the canine roots might be diagnostic for proborhyaenids, but the fact that thylacosmilids have such strongly modified canines raises the possibility that thylacosmilids had this character ancestrally but later reversed it. Babot (2005) found Proborhyaenidae of tradition to be paraphyletic, but I haven’t seen this (unpublished) study and don’t know the details.

Holotype specimen (partial lower jaw) of Proborhyaena gigantea, from Patterson & Marshall (1978). Scale bar = 50 mm.

Proborhyaenids are unique to the Eocene and Oligocene: there are only four recognised genera (Callistoe, Arminiheringia*, Paraborhyaena and Proborhyaena). Proborhyaena in particular has often been referred to as huge and bear-like, with there being estimates here and there of skulls perhaps 60 cm long [P. gigantea holotype lower jaw shown here, from Patterson & Marshall (1978). From top to bottom, the specimen is shown in labial, occlusal and lingual views. Scale bar = 50 mm].

However, as has turned out to be the case for other archaic carnivorous mammals (example: hyaenodontids), big, bear-sized skulls do not necessarily mean big, bear-sized bodies, and an articulated proborhyaenid skeleton (read on) shows that these animals had big heads for their size.

* Arminiheringia was originally given its own ‘family’, Arminiheringiidae Amegino, 1902.

As is the case with most borhyaenoid genera, proborhyaenids are mostly known from fragmentary jaws and other parts of skulls. The 2002 discovery of a fantastic, near-complete proborhyaenid skeleton was thus a major boon to our understanding of these animals. The skeleton [shown above] represents the new taxon Callistoe vincei and is from the Casamayoran (= Early Eocene) Lumbrera Formation of Salta, Argentina (Babot et al. 2002). The generic name comes from Callisto, the Arcadian nymph loved by Zeus and changed by him into a bear to protect her from Hera’s wrath (Jupiter has a moon called Callisto).

Articulated left and right hand skeletons of Callistoe vincei, from Argot & Babot (2011). Note the relatively long, weakly curved claws. The arrows point to what seems to be a healed fracture.

In contrast to other proborhyaenids, Callistoe has a gracile, narrow snout and might have superficially resembled a thylacine in facial shape. In overall proportions, it most resembles marten-like mustelids and red pandas (Argot & Babot 2011): unlike those animals, however, it lacks limb and vertebral characters associated with climbing. Instead, the form of its limb joints, the presence of an ossified patella and the shapes of its limb bones show that it was restricted to a parasagittal gait, possessed little flexibility in its elbow, wrist, knee and ankle, and hence was specialised for terrestrial walking and running. Argot & Babot (2011) described how its very long, gently curved manual claws – totally unlike those of other borhyaenoids – suggest a digging ability. Intriguingly, what appears to be a healed fracture on one digit suggests ‘heavy use’ of its hands. Meanwhile, the slender outer toes on its very short hindfeet indicate cursoriality. It probably weighed about 23 kg. Callistoe lived alongside a variety of armadillos, rodents and small notoungulates, so perhaps it needed to cover large distances on foot before digging for such prey when it discovered them. Remember that this animal lived during the Early Eocene: it long pre-dated the digging mustelids and other such placental carnivores than evolved elsewhere.

Arminiheringia had unusual procumbent lower canines: there has actually been some disagreement as to whether this is natural or not (Bond & Pascual 1983), but it does appear to be according to Babot et al. (2002) (A. auceta shown here, from Simpson 1932). Paraborhyaena also had somewhat procumbent lower canines and, unlike other members of the group, it had only a single pair of lower incisors (Shockey & Anaya 2008) – a character seen elsewhere in thylacosmilids. After Thylacosmilus, Simpson (1932) regarded Arminiheringia auceta (one of three species in the genus) as the most specialised borhyaenoid, and also one of the largest, “about the size of the great Pharsophorus lacerans” (Pharsophorus is a borhyaenid). Exactly how big Pharsophorus was, however, I have no idea – and was it supposed to be bigger than, say, Proborhyaena?

The marsupial sabre-tooths

Finally, we come to the superficially cat-like thylacosmilids, the only borhyaenoid group that are at all familiar, and all thanks to the incredible Thylacosmilus atrox Riggs, 1933 of the Late Miocene and Early Pliocene of Catamarca, north-western Argentina. In contrast to other borhyaenoids, thylacosmilids were short-faced and some of them, at least, had a complete bony postorbital bar. T. atrox is the only thylacosmilid we ever hear about, but it isn’t the only one.

Life restoration of Thylacosmilus, by Rom-diz. From wikipedia, released into public domain.

Achlysictis Ameghino, 1891, known only from mandibular fragments and teeth (three species have been named), was smaller than T. atrox and differed from it in tooth cusp characters. Similar comments can be made about Hyaenodonops Ameghino, 1908, known only from teeth (though postcrania has been referred to it). Notosmilus Kraglievich, 1960, named for a maxilla and canine, was only about half the size of T. atrox. Marshall (1976) regarded all of these taxa as distinct, but Goin & Pascual (1987) and McKenna & Bell (1997) regarded them all as synonyms of Thylacosmilus. Of course, if that’s true, then the generic name Thylacosmilus is pre-dated by both Achlysictis and Notosmilus and the ICZN would have to be petitioned if we want to preserve Thylacosmilus (which we do). Incidentally, Riggs (1933) named a second species of Thylacosmilus, T. lentis, but this was argued by Marshall (1976) to be synonymous with T. atrox.

Most recently, Goin (1997) named the Middle Miocene species Anachlysictis gracilis from the La Venta site in Colombia. This animal differed from the other thylacosmilids in smaller size, in possessing a flattened skull roof, and in lacking a postorbital bar. And another thylacosmilid, Patagosmilus goini, has since been named from the middle Miocene of Argentina (Forasiepi & Carlini 2010). The form of the one preserved hand bone and shape of the manual claw suggest that Patagosmilus was able to climb, but this is uncertain given the poor nature of the material. It otherwise seems to have been similar to Thylacosmilus.

Replica skull of Thylacosmilus atrox, as displayed at the AMNH. Photo by Claire Houck, licensed under Creative Commons Attribution-Share Alike 2.0 Generic license.

You might think you know Thylacosmilus, but (as is so often the case) it’s rather stranger than usually thought. [Adjacent photo by Claire Houck]. Based on Riggs’s skull reconstruction, some authors (and artists) have concluded that it had no upper incisors at all, in which case you really have to wonder how it pulled tissue from prey after killing it. Such a configuration would be so unusual compared to other predatory mammals that Churcher (1985) cautioned against it, and it all rests on the fact that the critical regions of the premaxillary bones are absent. Furthermore, there’s enough space between the huge upper canines for small incisors, and there are wear facets on the single pair of lower incisors that can only have been caused by interaction with upper incisors (Churcher 1985).

Churcher's (1985) reconstruction of the Thylacosmilus skull seen from the front. Upper incisors are shown as absent, even though Churcher argued for their presence.

The laterally compressed, ever-growing upper canines were not just rooted in maxillary sockets as they are in sabre-toothed cats, but arced up and over the orbits, forming a notably convex skull roof. The premolars and molars were narrow lineal blades, specialised for slicing. Huge, laterally flattened flanges – sometimes called genial flanges – grew downwards from the lower jaw, and the sabre teeth would have rested against their sides when the jaws were closed. Riggs (1934) illustrated these diverging laterally toward their tips, and several artists followed his lead. However, other authors have considered this inaccurate (Turnbull 1976, Marshall 1976, Churcher 1985), and the flanges were more likely fairly parallel.

Protuberances, rugosities and excrescenses at the back and base of the skull show that a substantial amount of musculature allowed both great power and fine control to be exerted over the head, and large muscle attachment sites on the neck vertebrae also show that the neck was very strong and flexible. Several studies have looked at these features: Marshall (1976) discussed skull function and its possible role in behaviour, Turnbull (1976) reconstructed the cranial musculature, and Turner & Antón (1997) and Argot (2004c) analysed postcranial morphology.

How exactly did thylacosmilids live? Again, Argot’s (2004c) detailed functional analysis provides us with a huge amount of information. With its semi-plantigrade hindfeet, stout fibulae and curved tibiae, Thylacosmilus looks poorly suited for fast running. A massively powerful upper arm and a reinforced and relatively inflexible lumbar region imply that it was an ambush predator that attacked prey after a short dash.

It’s now widely thought that sabre-toothed predatory mammals used their elongate and delicate weapons for precise attacks inflicted on the ventral surface of the neck, and for this to work the predator has to be able to physically manipulate and restrain the prey, and use coordinated and precise neck and head movements to attack in the right place. A semi-opposable thumb and tremendous forelimb strength suggest that Thylacosmilus could pin down and restrain prey, and its elongate, powerful neck demonstrates the presence of a ‘neck-driven’ precision biting style. In their study of bite forces seen in various mammalian predators, Wroe et al. (2005) found bite forces of Thylacosmilus to be very low. This is also the case for sabre-toothed cats like Smilodon, and it indicates that these animals were not ‘power biting’ like short-toothed predators, but driving their unusual killing style with their neck musculature. Most thylacosmilid reconstructions make the animals look far too cat-like, and also give them completely incorrect limb details [brilliant illustrations below by Carl Buell: be sure to check out - and 'like' - Carl Buell Illustration at facebook].

Beautiful comparison by Carl Buell of the cat Smilodon (at top) with the borhyaenoid Thylacosmilus: compare and contrast. They're not quite to scale: as Carl points out, Thylacosmilus is somewhat smaller than shown here.

Here’s an interesting thing to consider within the context of thylacosmilid biology and behaviour. Given that sabre-toothed biting appears to have been specialised and difficult in actual, practical terms, it’s inferred that sabre-toothed predators have to go through a very dangerous ‘apprenticeship’ in which they learn how to successfully inflict a bite without getting smacked in the head or breaking a tooth. But, for this to occur, juveniles and adults must stay together for an extended post-weaning period. In marsupials* in general, this is rare, with juveniles rarely staying with their parents for more than a few weeks once weaning is finished. Were thylacosmilids a major exception? That is, did they have some sort of extended system of parental care? Unfortunately, we just don’t know.

* Remember that borhyaenoids may not actually be marsupials, but members of the more inclusive clade Metatheria.

What were thylacosmilids preying on anyhow? Argot (2004c) proposed that mesotheriid notoungulates, litopterns and big rodents like capybaras were among the prey of Thylacosmilus. And it’s also interesting to note that thylacosmilids were living alongside other borhyaenoids: in the Huayquerian, Thylacosmilus was sharing its habitat with late-surviving hathlyacinids, the probably omnivorous prothylacinid Stylocynus, and the borhyaenid Eutemnodus. Phorusrhacids were around too: did they compete with borhyaenoids, or did the groups occupy different niches and avoid competition? So many animals, so many questions.

One final point. I hope it’s clear by now that there’s quite a bit of very good technical literature on borhyaenoids. But what if you want semi-technical or popular stuff, preferably well-illustrated with nice photos and life restorations? Sad to say, we’re still at the stage where such a work simply does not exist. This is despite the recent publication of some very good volumes on the fossil fauna of Cenozoic South America (e.g., Sánchez-Villagra et al.’s  2010 Urumaco & Venezuelan Paleontology and Patterson & Costa’s 2012 Bones, Clones & Biomes: The History and Geography of Recent Neotropical Mammals). Takehome point: there is still a gap in the market. We need a good, non-technical, well-illustrated volume on the Cenozoic fossil fauna of South America.

Many thanks to Christine Argot for her kind assistance with this  article.

Refs – -

Argot, C. 2001. Functional-adaptive anatomy of the forelimb in the Didelphidae, and the paleobiology of the Paleocene marsupials Mayulestes ferox and Pucadelphys andinus. Journal of Morphology 247, 51-79.

- . 2002. Functional-adaptive analysis of the hindlimb anatomy of extant marsupials and the paleobiology of the Paleocene marsupials Mayulestes ferox and Pucadelphys andinus. Journal of Morphology 253, 76-108.

- . 2003a. Postcranial functional adaptations in the South American Miocene borhyaenoids (Mammalia,Metatheria): Cladosictis, Pseudonotictis and Sipalocyon. Alcheringa 27, 303-356.

- . 2003b. Functional adaptations of the postcranial skeleton of two Miocene borhyaenoids (Mammalia, Metatheria), Borhyaena and Prothylacinus, from South America. Palaeontology 46, 1213-1267.

- . 2004a. Evolution of South American mammalian predators (Borhyaenoidea): anatomical and palaeobiological implications. Zoological Journal of the Linnean Society 140, 487-521.

- . 2004b. Functional-adaptive analysis of the postcranial skeleton of a Laventan borhyaenoid, Lycopsis longirostris (Marsupialia, Mammalia). Journal of Vertebrate Paleontology 24, 689-708.

- . 2004c. Functional-adaptive features and palaeobiologic implications of the postcranial skeleton of the late Miocene sabretooth borhyaenoid Thylacosmilus atrox (Metatheria). Alcheringa 28, 229-266.

- . & Babot, J. 2011. Postcranial morphology, functional adaptations and palaeobiology of Callistoe vincei, a predaceous metatherian from the Eocene of Salta, north-western Argentina. Palaeontology 54, 411-480.

Asher RJ, Horovitz I, & Sánchez-Villagra MR (2004). First combined cladistic analysis of marsupial mammal interrelationships. Molecular phylogenetics and evolution, 33 (1), 240-50 PMID: 15324852

Babot, M. J. 2005. Los Borhyaenoidea (Mammalia, Metatheria) del Terciario inferior del Noroeste argentino. Aspectos filogenéticos, paleobiológicos y bioestratigráficos. Unpublished PhD thesis, Universidad Nacional de Tucumán, Tucumán, Argentina, 454 pp

- ., Powell, J. E. & de Muizon, C. 2002. Callistoe vincei, a new Proborhyaenidae (Borhyaenoidea, Metatheria, Mammalia) from the Early Eocene of Argentina. Geobios 35, 615-629.

Bond, M. & Pascual, R. 1983. Nuevos y elocuentes restos craneanos de Proborhyaena gigantea Ameghino, 1897 (Marsupialia, Borhyaenidae, Proborhyaeninae) de la Edad Deseadense. Un ejemplo de coevolución. Ameghiniana 20, 47-60.

Churcher, C. S. 1985. Dental functional morphology in the marsupial sabre-tooth Thylacosmilus atrox (Thylacosmilidae) compared to that of felid sabre-tooths. Australian Mammalogy 8, 201-220.

Forasiepi, A. M. & Carlini, A. A. 2010. A new thylacosmilid (Mammalia, Metatheria, Sparassodonta) from the Miocene of Patagonia, Argentina. Zootaxa 2552, 55-68.

- ., Martinelli, A. G. & Goin, F. J. 2007. Revisión taxonómica de Parahyaenodon argentinus Ameghino y sus implicancias en el conocimiento de los grandes mamíferos carnívoros del Mio-Plioceno de América de Sur. Ameghiniana 44, 143-159.

- ., Sánchez-Villagra, M. R., Goin, F. J., Takai, M., Shigehara, N. & Kay, R. F. 2006. A new species of Hathliacynidae (Metatheria, Sparassodonta) from the middle Miocene of Quebrada Honda, Bolivia. Journal of Vertebrate Paleontology 26, 670-684.

Goin, F. J. 1997. New clues for understanding Neogene marsupial radiations. In Kay, R. F., Madden, R. H., Cifelli, R. L. & Flynn, J. J. (eds) Vertebrate Paleontology in the Neotropics: The Miocene fauna of La Venta, Colombia. Smithsonian Institution Press (Washington, D.C.), pp. 187-206.

- . & Pascual, R. 1987. New on the biology and taxonomy of the marsupials Thylacosmilidae (late Tertiary of Argentina). Anales de la Academia Nacional de Ciencias Exactas, Físicas y Naturales 39, 219-246.

Marshall, L. G. 1976. Evolution of the Thylacosmilidae, extinct saber-tooth marsupials of South America. PaleoBios 23, 1-30.

- . 1977a. A new species of Lycopsis (Borhyaenidae: Marsupialia) from the La Venta fauna (Late Miocene) of Colombia, South America. Journal of Paleontology 51, 633-642.

- . 1977b. Cladistic analysis of borhyaneoid, dasyuroid, didelphoid, and thylacinid (Marsupialia: Mammalia) affinity. Systematic Zoology 26, 410-425.

- . 1978. Evolution of the Borhyaenidae, extinct South American predaceous marsupials. University of California Publications in Geological Sciences 117, 1-89.

- . 1979. Review of the Prothylacininae, an extinct subfamily of South American “dog-like” marsupials. Fieldiana Geology New Series 3, 1-50.

- . 1981. Review of the Hathlyacyninae, an extinct subfamily of South American “dog-like” marsupials. Fieldiana Geology New Series 7, 1-120.

- ., Clemens, A., Hoffstetter, R. J., Pascual, R., Patterson, B., Tedford, R. H. & Turnbull, W. D. 1978. Acyonidae Ameghino, 1889 (Mammalia): supplement to proposal to suppress this name. Bulletin of Zoological Nomenclature 35, 12-14.

McKenna, M. C. & Bell, S. K. 1997. Classification of Mammals: Above the Species Level. Columbia University Press.

Muizon, C. 1994. A new carnivorous marsupial from the Palaeocene of Bolivia and the problem of marsupial monophyly. Nature 370, 208-211.

- . 1999. Marsupial skulls from the Deseadan (late Oligocene) of Bolivia and phylogenetic analysis of the Borhyaenoidea (Marsupialia, Mammalia). Geobios 32, 483-509.

- ., Cifelli, R. L. & Paz, R. C. 1997. The origin of the dog-like borhyaenoid marsupials of South America. Nature 389, 486-489.

Patterson, B. & Marshall, L. G. 1978. The Deseadan, Early Oligocene, Marsupialia of South America. Fieldiana Geology 41, 37-100.

Riggs, E. S. 1933. Preliminary description of a new marsupial sabertooth from the Pliocene of Argentina. Geological Series of Field Museum of Natural History 6, 61-66.

- . 1934. A new marsupial saber-tooth from the Pliocene of Argentina and its relationships to other South American predacious marsupials. Transactions of the American Philosophical Society 24, 1–32.

Rougier, G. W., Wible, J. R. & Novacek, M. J. 1998. Implications of Deltatheridium specimens for early marsupial history. Nature 396, 459-463.

Savage, R. J. G. 1977. Evolution in carnivorous mammals. Palaeontology 20, 237-271.

Shockey, B. J. & Anaya, F. 2008. Postcranial osteology of mammals from Salla, Bolivia (Late Oligocene): form, function, and phylogenetic implications. In Sargis, E J. & Dagosto, M. (eds) Mammalian Evolutionary Morphology: A Tribute to Frederick S. Szalay. Springer Science (Dordrecht, The Netherlands), pp. 135-157.

Simpson, G. G. 1932. Skulls and brains of some mammals from the Notostylops beds of Patagonia. American Museum Novitates 578, 1-11.

- . 1980. Splendid Isolation: the Curious History of South American Mammals. Yale University Press, New Haven and London.

Sinclair, W. J. 1906. Marsupialia of the Santa Cruz beds. In Scott, W. B. (ed) Reports of the Princeton University Expedition to Patagonia, 1896-1899. Princeton University, pp. 333-460.

Turnbull, W. D. 1976. Restoration of masticatory musculature of Thylacosmilus. In Churcher, C. S. (ed) Athlon, Essays in Palaeontology in Honour of Loris Shano Russell. Royal Ontario Museum (Toronto), pp. 169-185.

Turner, A. & Antón, M. 1997. The Big Cats and Their Fossil Relatives. Columbia University Press, New York.

Van Valkenburgh, B. 1985. Locomotor diversity within past and present guilds of large predatory mammals. Paleobiology 11, 406-428.

- . 1987. Skeletal indicators of locomotor behaviour in living and extinct carnivores. Journal of Vertebrate Paleontology 7, 162-182.

Villarroel, C. & Marshall, L. G. 1983. Two new late Tertiary marsupials (Hathlyacyninae and Sparassocyninae) from the Bolivian Altiplano. Journal of Paleontology 57, 1061-1066.

Wroe, S., McHenry, C. & Thomason, J. 2005. Bite club: comparative bite force in big biting mammals and the prediction of predatory behaviour in fossil taxa. Proceedings of the Royal Society B 272, 619-625.

Darren Naish About the Author: Darren Naish is a science writer, technical editor and palaeozoologist (affiliated with the University of Southampton, UK). He mostly works on Cretaceous dinosaurs and pterosaurs but has an avid interest in all things tetrapod. His publications can be downloaded at He has been blogging at Tetrapod Zoology since 2006. Check out the Tet Zoo podcast at! Follow on Twitter @TetZoo.

The views expressed are those of the author and are not necessarily those of Scientific American.

Rights & Permissions

Comments 76 Comments

Add Comment
  1. 1. Cameron McCormick 7:08 pm 07/12/2012

    the neck was also long – proportionally, twice as long as that of any living canid, for example

    Are they sure? Dog cervicals take up over a quarter of the torso’s length, and the reconstruction of Cladosictis shows a neck around a third the length of the torso.

    Link to this
  2. 2. Bird/tree/dinosaur/etc. geek 8:20 pm 07/12/2012

    Great post, as usual. The *Thylacosmilus* restoration reminds me of the *Holophoneus* skeleton at the AMNH. Ecological similarities, anyone?

    Also, I happen to have the well-known book with illustrations by Graham Allen, and it’s wrong in so many ways (don’t even get me started on the overly-broad usages of “carnosaur” and “coelurosaur”, and the lack of feathers on the maniraptorans, and the tail-dragging sauropods with necks bent at impossible angles, etc.).

    P.S.: I read your links to previous posts about cool South American animals. As an aspiring paleornithologist, I loooooooove *Argentavis magnificens*. The phorusrhacids article was awesome, awesome, awesome. Sebecosuchians are my favorite NDAs*–they’re so cool that I actually based one of the creatures in my speculative zoology project on them (loosely). Now I’ve really got to stop being a sycophant.


    Link to this
  3. 3. Bird/tree/dinosaur/etc. geek 8:49 pm 07/12/2012

    Also, on the topic of *Thylacosmilus*; another good analogue is probably *Barbourofelis*. Any other suggestions?

    Again, awesome post and associated links. I’ve been reading your blog for over four years, and it never gets anything less than fantastic.

    Link to this
  4. 4. Wilbert Friesen 3:53 am 07/13/2012

    Fantastic post. I’ve re-read this many times because there’s nothing quite out there concerning this highly interesting group of carnivorous and omnivorous marsupial ‘dogs’. It is often stated that the Borhyaenids died out because of competition with the placental carnivores but I read somewhere that this might be not the case. The article stated that the borhyaenids died out before the great N-S migration of Smilodon, Canis dirus etc etc etc. I don”t know whether this is true or not because -as usual- the information is limited or only accesible when you spend your monthly earnings. I often wondered why ? Why is this information not accessible for everyone. Why the extreme conservatism ? It goes -imo- against the essence of science. To teach, learn, discuss, expand our knowledge etc.

    My library is full of palaeontological books which I read over, over, over and over again and so I also bought the quite expensive “Urumaco & Venezuelan Paleontology”. My advise. Don’t buy it. It’s one of the few palaeontological books (maybe even the only one) I’ve read once and that’s it. I expected soo much because the Cenozoic of South America is still shrouded in tantalizing mysteries but I was deeply disappointed.
    Don’t waste your money.

    Link to this
  5. 5. naishd 5:33 am 07/13/2012

    Thanks for comments. On the comparative neck length of Cladosictis (comment 1), I’m not sure why, but I screwed up: Argot (2003a) clearly states that the neck of Cladosictis “is approximately as long as in living canids, relatively to the thoracolumbar length” (p. 348). That is, the neck is about 37% as long as thoracolumbar length. A similar value (c. 36%) is present in Prothylacinus. I’ll go correct the main text.


    Link to this
  6. 6. naishd 5:50 am 07/13/2012

    And one very brief comment (WRT comment 4): don’t be hard on the Urumaco book – it is, after all, meant to be specific to Venezuela, not to the South American Cenozoic record as a whole. I’ve had a copy for a while, will be reviewing it here at some stage.


    Link to this
  7. 7. Bird/tree/dinosaur/etc. geek 9:35 am 07/13/2012

    William Friesen (comment 4) has a good point, though. We really do need a comprehensive and accurate work on the South American Cenozoic.

    For the third time, this article was great. I never even imagined that known borhyaenids were this diverse!

    Link to this
  8. 8. David Marjanović 1:08 pm 07/13/2012

    There’s a correlation between ossified kneecaps and parasagittal gait? Interesting. Why don’t any dinosaurs other than Ornithurae-sensu-strictissimo-or-so have them? And don’t monotremes have kneecaps?

    * Argot (2004b) mistakenly spelt it L. longirostris [sic].

    No wonder. Grammatically, -rostrus is plain wrong and makes no sense.

    [Callistoe] probably weighed about 23 kg.

    Wait. A 2.1-m-long animal that weighs just 23 kg? Is that a typo for 230?

    For the third time, this article was great. I never even imagined that known borhyaenids were this diverse!


    Link to this
  9. 9. ohnosir 1:30 pm 07/13/2012

    Thanks for reposting this article, it has been a while since I read your articles on borhyaenoids and I don’t think I ever read all of them! I can never get enough of those big carnivorous marsupials.

    @Wilbert, #4: I did a quick Google search and found at least Argot’s (very well-illustrated) 2009 paper on Borhyaena and Prothylacinus to be freely available on Wiley Online. I would look for the rest but frankly this is my version of slacking off and I need to get back to work on other things…

    I am wondering though, did Argot do those illustrations herself? And is there anywhere I might find higher-resolution versions of her reconstructions other than the texts themselves?

    Link to this
  10. 10. Bird/tree/dinosaur/etc. geek 1:55 pm 07/13/2012

    @ Wilbert;
    Sorry for messing up your name. I’ve figured out how to turn off the auto”correct”–although how it mistook Wilbert for William in the first place, I don’t know.

    @ ohnosir;
    Good find. Those illustrations are great. The paper is here, if this useless hunk of silicon will let me copy things now:

    Link to this
  11. 11. Bird/tree/dinosaur/etc. geek 1:57 pm 07/13/2012

    Hey, it even lets me do links now! It only took six weeks of on-and-off tinkering!

    Link to this
  12. 12. naishd 5:17 pm 07/13/2012

    Thanks for further comments – glad borhyaenoids are so appreciated around here (smiley). Need to revisit astrapotheres and phorusrhacids at some stage, and articles on notoungulates and litopterns are still sitting, unfinished, in my files…

    Re: “correlation between ossified kneecaps and parasagittal gait?” (comment 8). We’re only talking about metatherians here – they generally lack ossified patellae (bandicoots are a weird exception), and the presence of them in these borhyaenoids is consistent with other evidence from the limbs for joints where little rotation was possible.

    “Wait. A 2.1-m-long animal that weighs just 23 kg? Is that a typo for 230?” (also comment 8).

    I roughly guesstimated 2.1 m from figures of Callistoe‘s skeleton – it could be inaccurate. But – if you look at the masses of extant carnivorous mammals – I don’t think that c. 23 kg for c. 2.1 m is unreasonable. That looks about right for extant canids and similarly shaped carnivorans. One example: Ethiopian wolf = c. 1.6 m in total, c. 19 kg. Another: an African hunting dog c. 1.4 m long = c. 17 kg. These figures from Walker’s Mammals of the World (6th edition).


    Link to this
  13. 13. naishd 7:51 pm 07/13/2012

    One more thing on the overlap – or non-overlap – of borhyaenoids with placental carnivores (see comment 4). At the moment, it doesn’t seem that borhyaenoids were still around when carnivorans used the Central American landbridge to get into South America – they’d already become extinct a few million years beforehand. Claims that borhyaenoids were “decimated by competition from cats (including sabretoothed cats), dogs, bears, raccoons, and weasels” (Prothero 2006, p. 253) are no longer regarded as accurate. Why did borhyaenoids become extinct then?

    Prothero, D. 2006. After the Mammals: the Age of Mammals. Indiana University Press (Bloomington & Indianapolis).


    Link to this
  14. 14. Tayo Bethel 1:28 am 07/14/2012

    Great articleon borhyaenids–am I the sixth or seventh? LOL Why are bandicoots weird in having kneecaps?

    Link to this
  15. 15. Tayo Bethel 1:31 am 07/14/2012

    And how much is known about metatherian locomotion?

    Link to this
  16. 16. Wilbert Friesen 2:04 am 07/14/2012

    Thanks for the tip Ohnosir.
    Bird/Tree/Dinosaur you may call me what you want. In Eire they call me Liam, in England William and most people in Holland Willy, Willem, Wil etc. All fine by me.:)

    Indeed why did the borhyaenids die out ? It couldn’t be the competition with the (probably not so terror-like) Terror birds for they lives millions of years together. Could it be climat change ? Forests and woodlands making way for dry plains ? But can climate change alone be responsible for the extinction of this once diverse group in a large landmass such as South America ? And if the borhyaenids died out before the Great Interchange, what took over their predatory role in the meantime ?

    When I look through my McKenna & Bell bible I see there are actually procyonids in South America in the late miocene and early pliocene like Cyonasua, Chapalamania and Parahyaenodon (which is classified as a borhyaenid in McKenna). So at least the ‘true’ borhyaenid Eutemnodus should have coexisted with carnivores (and the Hathliacynids Borhyaenidium, Notocynus and the iconic sabre-toothed Thylacosmilus itself)
    So how can this be ? Riddles, riddles, riddles…

    Link to this
  17. 17. naishd 6:27 am 07/14/2012

    Thanks for additional comments. Kneecaps (comment 14): a general characteristic of marsupials is the absence of a bony patella – there’s a fibrocartilaginous structure in the same place, generally termed a patelloid. Bandicoots are an exception – they have a true, bony patella (and, for this reason, some people have suggested that they might not be marsupials, but close to placentals! This is one of several non-standard hypotheses about marsupial evolution that I hope to write up at some stage).

    Borhyaenoid extinction: I have a vague memory of evidence for an apparent bolide impact in Neogene South America being used to explain the extinction of borhyaenoids and some other endemic groups – can anyone remember any more? And, yes, some procyonids did get to South America before the formation of the landbridge, but they weren’t part of the major invasion that occurred late in the Pliocene. But, then, we now know that the continental exchange was fairly complicated, with some animals (like sloths) making the crossing before the landbridge formed. A really exciting discovery on the timing and nature of the exchange is due to be published soon, I hope. However, it doesn’t change the fact that borhyaenoids were extinct before placental cats, dogs, bears etc. made it onto the continent.


    Link to this
  18. 18. Andreas Johansson 6:32 am 07/14/2012

    Are there any extinctions we can with reasonable confidence ascribe to novel competition caused by the Faunal Interchange?

    Link to this
  19. 19. David Marjanović 9:22 am 07/14/2012

    Thanks for the info on kneecaps and body sizes.

    I have a vague memory of evidence for an apparent bolide impact in Neogene South America being used to explain the extinction of borhyaenoids and some other endemic groups – can anyone remember any more?

    No. I saw it on TV once (long ago), and IIRC they said the impact was only 300,000 years before the Interchange; that’s all.

    Link to this
  20. 20. Tayo Bethel 10:39 am 07/14/2012

    Thanks for the info. Bandicoots seem to be weird all round

    Link to this
  21. 21. Bird/tree/dinosaur/etc. geek 11:51 am 07/14/2012

    Among weird bandicoots, Pig-footed takes (took) the cake. Of course, we humans introduced a bunch of nice alien predators, sheep, rabbits, and sheep, which ate the bandicoot and its habitat.

    I seem to remember Loren Coleman’s “Cryptozoology A to Z” having a page on “saber-toothed cat” reports from South America; Coleman seemed to think that these reports were of thylacosmilids, based on size (reportedly a little smaller than a jaguar) and the fact that the reports were from montane forests only. It seemed a little hard to believe, but some of the reports felt just a little more credible than your typical Bigfoot/Mothman/Nessie stuff. I tried a Google search, but to no avail. There was a reference in Coleman’s book to a book by someone named Mathiessen; do you guys know anything about that?

    On borhyaenoid extinction, I really need more resources. You could probably pin it on rapid aridification after the salinity crisis, though. Less trees=easier for giant killer ground birds, harder for short-legged mammal predators. Not that all phorusrhacids were speed demons, but still.

    Finally, the sycophant in me wants to say that the links in this post left me in a three-hour journey of awesomeness through ver. 2 and ver. 1. The *Harpagornis* (which, ICZN rules aside, sounds a whole f*cking lot better than *Hierattus*, which I can’t even spell) post was totally awesome. The sebecids post reminded me (again) why I made my favorite speculative future predator a land croc (complete with teeth on the palate, symbiotic lethal bacterium, and more teeth than anything has any right to have). Land crocs are awesome.

    Link to this
  22. 22. Wilbert Friesen 2:01 pm 07/14/2012

    Darren wrote: “However, it doesn’t change the fact that borhyaenoids were extinct before placental cats, dogs, bears etc. made it onto the continent”
    Darren is rightof course though I thought that Cyonasua was a ‘doglike’ procyonid of about 23,7 kg and that Chapalmalania was a ‘bearlike’ creature. I don’t know exactly whether Parahyaenodon was doglike but it’s weight was estimated around 19,5 kilo.
    Still, compared with the plethora of foxes, mustelids, cats etc which entered the scene after the borhyaenids where all dead and gone, the competition of the few late miocene/early pliocene placental carnivores probably couldn’t be such that it could completely wipe out the remnants. Esp. the fate of Thylacosmilus itself is puzzling.
    On the other hand, it appears that a lot of endemic herbivores also died out at the L-Mioc/E-Plioc border. Again before their so-called modern ‘counterparts’ arrived on the scene.

    I’m wondering. Is it perhaps possible that members of the Didelphidae could be on of the factors in the extinction ? Especially Hyperdidelphys of Late Miocene – Late Pliocene seems a large opossum which was more carnivorous than the living Didelphys. In the Early Pliocene other species arose like the even larger Thylophorops. It seems possible that these large more carnivorous species where the real victims of the arrival of the placental carnivores.

    Link to this
  23. 23. llewelly 3:39 pm 07/14/2012

    12. naishd 5:17 pm 07/13/2012 :
    “I roughly guesstimated 2.1 m from figures of Callistoe‘s skeleton – it could be inaccurate. But – if you look at the masses of extant carnivorous mammals – I don’t think that c. 23 kg for c. 2.1 m is unreasonable. That looks about right for extant canids and similarly shaped carnivorans. One example: Ethiopian wolf = c. 1.6 m in total, c. 19 kg.”

    Mass scales roughly as the cube of length (slightly more, actually, because supporting limbs must thicken faster.)

    I get:

    (* 19 (cube (/ 2.1 1.6)))

    That is, the length ratio between a 2.1m animal and 1.6m animal is about 1.3 , the cube of 1.3 is about 2.26 , and 19 kg multiplied by 2.26 is about 43 kg . In other words, if the 2.1m animal is really only 23 kg, it must be very lean compared to the 1.6m animal.

    Link to this
  24. 24. naishd 5:03 pm 07/14/2012

    I just knew that someone would bring in an argument from the mathematics of scaling…

    Given that Callistoe looks to have been a fairly robust animal – not an especially gracile one – I think the most likely possibility is that my guesstimated 2.1 m is incorrect. Unfortunately, neither of the two papers on Callistoe include a total length estimate, so you’re left working it out from the scale bars – in coming up with 2.1 m, I measured (along the curves) to the end of what looks like the tail, but this isn’t figured in the line diagrams. I just measured it again: from the line diagram in Babot et al. (2002) without the tail, total length is c. 1.1 m; with the tail it’s more like c. 1.4 m. New conclusion: c. 2.1 m was too long.


    Link to this
  25. 25. vdinets 5:54 pm 07/14/2012

    1.6 m for Ethiopian wolf is clearly an error. Wiki gives 142 cm including tail as maximum length, and 19.5 kg as maximum weight.Visually it is like a coyote or slightly smaller.

    Link to this
  26. 26. Mythusmage 8:49 pm 07/14/2012

    Fuzzy gorgonopsid (

    Thought I’d share. :)

    Link to this
  27. 27. David Marjanović 6:19 am 07/15/2012

    *Hierattus*, which I can’t even spell

    Hieraetus? But it’s probably Aquila anyway.

    a land croc (complete with teeth on the palate, symbiotic lethal bacterium, and more teeth than anything has any right to have)

    Crocs never have teeth on the palate. It’s normal for toothed vertebrates to have teeth on the palate (and for that matter on the coronoids and the prearticular in the lower jaw), but both sides of the archosaur tree have lost them. The Early Permian terrestrial temnospondyl Acheloma will be more to your liking, I’m sure; or try a varanopid with teeth paving the floor of its braincase.

    Why bacteria and not simply poison? After all, that’s what Komodo dragons do.

    Link to this
  28. 28. Christopher Taylor 6:46 am 07/15/2012

    Hieraaetus, with two a’s.

    Link to this
  29. 29. Bird/tree/dinosaur/etc. geek 11:00 am 07/15/2012

    @ Christopher Taylor: Thanks a lot!

    @ David Marjanović: What?? Archosaurs don’t have palate teeth??? WHY DIDN’T I KNOW THAT BEFORE??????? Maybe spontaneous mutation? I’ve heard that it sometimes happens in bats; young bats occasionally have basic mammal front limbs.
    Also, bacteria are much cooler, and venom doesn’t work as well for the creature. It has heavy-duty prey and a low metabolism, so it can afford to wait a few days. Furthermore, injector fangs would probably break–the prey animals are built like *Toxodon* with osteoderms and keratinous horns. The predator’s only ten feet long, so it really needs an effective first strike.

    Link to this
  30. 30. Tayo Bethel 11:03 am 07/15/2012

    What does Hieraaetus mean?

    Is there any readily accessible information on the Australian dasyuromorphian radiation?

    Link to this
  31. 31. Tayo Bethel 11:13 am 07/15/2012

    Venomous archosaurs seem to have never existed.

    Komodo dragons and other varanids dont really have specialized fangs “injector fangs” as far as I know–just grooves on serrated teeth–think Gila monster. And septic bacteria can kill–maybe not quick enough though.
    A reconstruction of baurusuchid predatory behavior would be somethin’ to look forward to if it ever happens.

    Link to this
  32. 32. puppygod 11:33 am 07/15/2012

    Are there any scavengers to speak of on the Komodo island? Because it seems like Komodo dragon hunting tactic (bite & wait until bleeding, venom and septic shock does it’s prey) is only possible in environment lacking numerous scavengers. I imagine that trying it, say, on mainland Africa would mean the prey stripped to the bare bone within hour by vultures, hyenas, jackals and lions.

    Link to this
  33. 33. naishd 11:59 am 07/15/2012

    Palatal teeth in Archosauria (comment 27 and others): they’re apparently present in non-archosaurian archosauriforms (here using Archosauria for the croc-bird crown clade); Euparkeria has them on the pterygoids and palatines. Pterosaurs – recovered as crown-archosaurs by some/most authors – have pterygoid teeth, or Eudimorphodon does, at least. Massospondylus was described as having palatal teeth loosely attached to palatal soft tissues, but some authors (Sereno, I think) say that these are actually fish teeth, washed on to the specimen prior to burial.


    Link to this
  34. 34. Bird/tree/dinosaur/etc. geek 1:41 pm 07/15/2012

    Tayo Bethel, good point. I forgot that completely.

    The symbiotic bacterium is faster-moving than *Streptococcus pyogenes*, which can kill a healthy human adult in 4 days. It has a protective capsule that constantly sloughs off and is replenished; the sloughed-off fragments are cytotoxic. Three different exotoxins, the cell wall is endotoxic, the bacterium has a doubling time of fifteen minutes under optimal conditions, and over a billion can contaminate a single bite. The low metabolism of the croc allows it to wait up to two weeks between meals.

    Link to this
  35. 35. Bird/tree/dinosaur/etc. geek 1:54 pm 07/15/2012

    It should be obvious that I really like land crocs. My personal favorite speculative animal is a bipedal, carnivorous croc that I call a spinetail. Spinetails hunt in packs, led by a female (like raptors, the females are bigger than the males), and kill their prey by taking turns to leap onto its back and use their hooked foreclaws and large anterior teeth to secure their jaws in the prey’s flesh while their smaller posterior teeth, which are kept sharper than obsidian by constant replacement, shred the skin. The prey eventually dies of blood loss. To fend off attacks by larger predators, such as the fleshreaver (the already-described creature with the symbiosis), spinetails have venomous, featherlike barbs all along their tails. Protofeathers cover the body, which is about a foot and a half long (the total length is about three feet, including the tail). Spinetails are endothermic, and are about as intelligent as a conure (a type of small parrot, larger and smarter than a budgie, but smaller and less intelligent than an African Gray or a macaw).

    Link to this
  36. 36. Bird/tree/dinosaur/etc. geek 1:56 pm 07/15/2012

    And now, I take advantage of this marvelous resource of brilliant paleontologists to have my ideas critiqued…

    Dr. Naish, thanks for the info. I wasn’t aware of any of those examples.

    Link to this
  37. 37. Heteromeles 2:07 pm 07/15/2012

    Ummm, can I point out that building a land bridge between two continents is kind of erm, an explosive event? Even a volcanic one?

    I spent a few minutes trying to see if there’s an accepted chronological sequence for the Andean orogeny. There isn’t, except that it started in the Cretaceous and jerked its way forward to the present, with long quiescent periods. Presumably geologists actually know better, but it’s also certain that I’m not going to blow a few hundred dollars getting the articles to educate myself.

    So far as I can tell, the Andes didn’t erupt in a blazing fountain of death for the Borhyaenids. Rather, they replaced a very ancient landscape (now left in the tepuis) with a very young landscape. While I don’t entirely believe that metatherians are inherently better adapted to ancient terranes (e.g. Australia) than are eutherians, I do see that as a problem, especially for the larger animals. Growing mountains are disruptive, as are large volcanoes. This is going to cause problems for large animals, especially if they are large specialists rather than small generalists. Think massive climate change on a local scale.

    The other problem for South America’s indigenous biota is that the Panamanian isthmus provides an troublesome environmental filter. It’s volcanic and highly changeable too. Any animal that makes it down through this bridge, even traveling over-water, will be pre-adapted to the geological changes that were increasingly happening in South America. Since they arrived pre-adapted, as it were, to weedy new habitats on the slopes of volcanoes, they might have represented direct competition to indigenous animals trying to adapt to those same conditions.

    Yes, this is vague, but I’m playing with the notion that the geological history of the Andes and the Panamanian land bridge may have ultimately doomed the borhyaenids, just as it favored the interchange.

    Link to this
  38. 38. AndrewD 3:22 pm 07/15/2012

    Heteromeles this link may be of help as it is free.

    Link to this
  39. 39. Heteromeles 3:48 pm 07/15/2012

    Thanks Andrew. Reading that link, it looks like there’s no “smoking gun” of volanic activity springing up about the time the Borhyaenids were thought to be checking out, and it looks like volcanoes were going off in different parts South America throughout the entire Cenozoic. Oh well, another idea shot down. Onward!

    Link to this
  40. 40. naishd 4:35 pm 07/15/2012

    One brief comment on the above… the more we learn, the more it’s seeming that the ‘Great American Interchange’ was a long, drawn-out affair, not a brief, catastrophic event. Consider that (1) animals were moving north and south for some time prior to the completion of the landbridge, (2) the geologic history of Central America is proving to be messy and complex: the landbridge was formed in piecemeal fashion, with some sections (e.g., eastern Panama, if memory serves) existing in stable fashion long before others, and (3) molecular data from extant taxa shows that many lineages of both North and South American mammals, traditionally regarded as post-interchange endemics, actually diverged prior to the exchange event.


    Link to this
  41. 41. Bird/tree/dinosaur/etc. geek 6:06 pm 07/15/2012

    My money’s on the Mediterranean salinity event as the main cause.

    Link to this
  42. 42. Bird/tree/dinosaur/etc. geek 6:27 pm 07/15/2012

    The cause of borhyaenoid extinction, not the interchange.

    Link to this
  43. 43. Bird/tree/dinosaur/etc. geek 6:35 pm 07/15/2012

    Of course, if the borhyaenoids survived into the Pliocene without significant loss of diversity, that would refute my hypothesis, leaving us back at Square One. Any other ideas, anyone?

    Link to this
  44. 44. Heteromeles 9:15 pm 07/15/2012

    @Bird/: What’s the mechanism?

    Link to this
  45. 45. llewelly 9:33 pm 07/15/2012

    Why the salinity crisis?

    Is there any consensus on its global effects, other than a ~10m sea level rise?

    Link to this
  46. 46. David Marjanović 8:28 am 07/16/2012

    Presumably geologists actually know better, but it’s also certain that I’m not going to blow a few hundred dollars getting the articles to educate myself.

    Write to the authors and ask them. There are people who just never reply to their e-mails, but the others will gladly send you all their work. Remember: authors are not paid when their publications are sold; they have no financial or other interest in paywalls.

    molecular data from extant taxa shows that many lineages of both North and South American mammals, traditionally regarded as post-interchange endemics, actually diverged prior to the exchange event

    I’m contractually obliged to ask how those datings were calibrated.

    Link to this
  47. 47. David Marjanović 8:31 am 07/16/2012

    Massospondylus was described as having palatal teeth loosely attached to palatal soft tissues, but some authors (Sereno, I think) say that these are actually fish teeth, washed on to the specimen prior to burial.

    Ah, good to know.

    Isn’t Eoraptor supposed to have pterygoid teeth, too? Or am I just misremembering?

    Didn’t know about Eudimorphodon, but it’s not surprising if (!) any dinosaurs had pterygoid teeth, too.

    Link to this
  48. 48. Michał 9:28 am 07/16/2012

    “Isn’t Eoraptor supposed to have pterygoid teeth, too?”

    Apparently it is. According to the description of Pampadromaeus barberenai: “A medial ridge on the ventral
    surface of the pterygoid holds a row of about 15 positions
    for small rudimentary teeth, as previously recognized only
    in E. lunensis and Eodromaeus murphi among dinosaurs
    (Martinez et al. 2011; Nesbitt 2011).”

    Palatal teeth are also present in Turfanosuchus which may (Nesbitt, 2011) or may not be pseudosuchian.

    Link to this
  49. 49. Bird/tree/dinosaur/etc. geek 1:56 pm 07/16/2012

    Massive drying, possibly global cooling. Late Miocene was savanna, at least in NAm, Pliocene was more steppe (based on information in Donald R. Prothero’s “After the Dinosaurs: the Age of Mammals”).

    “I’m contractually obliged to ask how those datings were calibrated.”
    Nice one. Molecular “clocks” can be tricky, in my limited experience.

    On pterygoid teeth in *Eoraptor*: Support at last for my idea!

    Link to this
  50. 50. naishd 4:23 am 07/17/2012

    Palatal teeth in Eoraptor and Pampadromaeus: oh, those are so familiar I figured I wouldn’t need to mention them.

    How were molecular dates (pertaining to S. American mammal lineages) calibrated? (see comment 45 and others). The dates I had in mind come from rodents (Melanomys, Heteromys and others), canids (the maned wolf-bush dog lineage diverged from ‘other S. American’ canids before the landbridge formed), mustelids (both Pteronura and Eira diverged from other S. American taxa long prior to the formation of the landbridge), and procyonids (all ‘generic’ lineages diverged in the Miocene). Calibration points? Given that we aren’t talking about fossil taxa, there are numerous calibration points derived from work on other extant lineages.


    Link to this
  51. 51. Heteromeles 12:21 pm 07/17/2012

    The Messinian salinity crisis doesn’t look like a good candidate for affecting South America. It appears to be a multi-step process involving:
    –tectonics (the Gibraltar Strait closed, until erosion opened the area repeatedly until it finally reopened)
    –Milankovic cycles, which controlled how much fresh water flowed into the basin. Less water flowed during the cool phase of the cycle, letting it dry down more. Still, these cycles are pretty eternal, so they’re not a great candidate for causing a mass extinction by themselves.

    The loss of the Mediterranean probably raised ocean levels by ~10 m and decreased oceanic salinity by some small amount. Neither of these would seem to have caused a major lineage extinction in South America.

    Link to this
  52. 52. Heteromeles 12:35 pm 07/17/2012

    Actually, looking at it, I’d say that the dominance of C4 grasses might be a better candidate for the extinction factor. According to one paper (, C4 grasses (which dominate prairies, llano, cerrado, etc.) originated 25-32 myr ago (on the molecular clock), but don’t start producing characteristic, grass-dominated ecosystems until 5-6 myr ago, very crudely at the time that the Borhyaenids are thought to have gone extinct, if I understand it right.

    Basically, going from a forest and savanna matrix to a prairie is one of those things that tends to cause faunal turnovers. It’s going to be particularly hard on short-legged carnivores that depend on stalking, as compared with longer-legged, more cursorial species. Why the borhyaenids didn’t make the switch, I don’t know, but it’s a suggestive correlation.

    Link to this
  53. 53. David Marjanović 2:09 pm 07/17/2012

    On pterygoid teeth in *Eoraptor*: Support at last for my idea!

    Uh, no. There’s still no crocodylomorph, indeed nothing closer to crocodiles than Eoraptor or Turfanosuchus, with pterygoid teeth.

    Palatal teeth in Eoraptor and Pampadromaeus: oh, those are so familiar I figured I wouldn’t need to mention them.

    Is that the new “I was just checking if you were paying attention”? :-)

    Calibration points? Given that we aren’t talking about fossil taxa, there are numerous calibration points derived from work on other extant lineages.

    What are they, and are there both old and young calibration dates both inside and outside the clades of interest?

    Link to this
  54. 54. Bird/tree/dinosaur/etc. geek 3:05 pm 07/17/2012

    @ David Marjanović : Yeah, but pterygoid teeth are still present in at least some awesomes.

    @ Heteromeles, THAT’S WHAT I MEAN!!!!!!!!! The salinity crisis and ensuing aridification helped the spread of C4 grasses.

    Link to this
  55. 55. Bird/tree/dinosaur/etc. geek 4:34 pm 07/17/2012

    Last part of my comment was mysteriously deleted.
    (grasses, thereby causing the extinction of the forest-adapted borhyaenoids. Of course, my dates are probably off, but it’s an idea[period mysteriously spared])

    Link to this
  56. 56. Heteromeles 5:47 pm 07/17/2012

    @Bird/: I’m pretty sure you’ve got the tail wagging the dog here. Admittedly, I’m not an expert on the so-called Messinian Crisis, but:

    a) it looks like it primarily affected Africa and Asia. The so-called crisis was how it affected the Mediterranean basin, and how African and Eurasian biota mixed across the drying sea, and

    b) everything I’ve read to date suggests strongly that the Messinian crisis was a consequence of continental drift (Africa colliding with Europe, and the Antarctic being isolated by ocean at the south pole, enabling it to become a freezer. This caused worldwide climate changes, including the Messinian changes in the Mediterranean basin. Also,

    c) You haven’t proposed a mechanism for moving drought from the drying Mediterranean to a South America ringed by ocean. If anything, the Mediterranean drying means that there was more water for the rest of the world to parcel out, not less.

    Instead, you have to look at GLOBAL climate changes as the reason why grasses took off pretty much everywhere in the world in this period. AFAIK, the big dryer at that point was the building ice cap in Antarctica, not the loss of water from the Mediterranean. Please correct me if I’m wrong.

    Link to this
  57. 57. Bird/tree/dinosaur/etc. geek 8:29 pm 07/17/2012

    @ Heteromeles: Yeah, good point. Prothero does seem to say, though (and I should know this, as I read “After the Dinosaurs: the Age of Mammals” at least once per week) that the crisis affected the world; please correct me if I’m wrong, though. Also, I really need a better understanding of these phenomena, or I’m going to really look like an idiot. Does anyone know a quick-and-easy guide to general Cenozooic paleoclimatographic events? *resigns self to looking stupid, as this one is a real long shot*

    Link to this
  58. 58. Bird/tree/dinosaur/etc. geek 8:32 pm 07/17/2012

    In a nutshell, I have a really good memory, limited resources, keen interest, no formal training, and no credentials. I’m trying to learn by discussion, because the people who comment on Tet Zoo a lot know what they’re saying.

    Link to this
  59. 59. Jerzy v. 3.0. 7:38 am 07/18/2012

    Since we are already talking about Messinian crisis, anybody knows what biota existed on the dried Mediterranean seabed?

    I recently stumbled upon the description that dried Meds was environment unlike any on present-day Earth, and wonder what could live there.

    Imagine depression up to 4km below sea level, with drying river deltas, hypersaline lakes, increased air pressure and: “a theoretical temperature of an area 4 kilometres (2.5 mi) below sea level would be about 40°C (72°F) warmer than the temperature at sea level. Thus one could predict theoretical temperature maximums of around 80°C (176 °F) at the lowest depths of the dry abyssal plain “

    Link to this
  60. 60. John Scanlon FCD 9:12 am 07/18/2012

    Off-topic but closer here than on the suboscine post, another washed-up mystery beast to identify here. I’m pretty sure it’s not a raccoon or a sloth this time.

    [from Darren: will add comment here, since I currently can't login to leave a new comment. I said back in 2007 that this is a beluga. Apparently, however, some data indicates that it's actually a false killer whale Pseudorca.]

    Link to this
  61. 61. Dartian 12:34 pm 07/20/2012

    Darren (OP):
    Note that Metatheria is more inclusive than Marsupialia, and that the name Marsupialia is restricted to the crown-group

    Surely that should be: “Some people would prefer Metatheria to be more inclusive than Marsupialia, and that the name Marsupialia be restricted to the crown-group.” I don’t believe there is any real consensus on this issue yet. (Besides, let’s not forget that the phylogenetic nomenclatural code is, as of today, still not ‘the official one’.)

    the forelimb proportions of otters aren’t really reliably different from those of other (non-swimming) mustelids

    It doesn’t surprise me very much if that’s the case. However, could you give me a reference, please?

    such a size is not at all incompatible with a scansorial lifestyle, as demonstrated by living wolverines, sun bears, clouded leopards and leopards

    And chimpanzees, and orangutans. And gorillas – if, indeed, you can consider them to be ‘scansorial’. Just because an animal can climb trees doesn’t, of course, mean that it should be considered ‘scansorial’ (that is, specialised for climbing). For this reason, I wouldn’t consider, for example, the wolverine to be truly scansorial any more than I would consider the lion or the brown bear to be so (even though they all three can climb trees).

    19-29 kg, which is about equivalent to a small hyaena or wolf, or a large thylacine

    Or (to pick something rather closer to home for most people) a Dalmatian dog.

    ever-growing upper canines

    In a mammalogical context, that is something that’s just frikkin’ bizarre! What, exactly, wore down or otherwise prevented those canine teeth from growing too long? And why did they evolve to be ‘ever-growing’ in the first place? Has anyone ever offered a plausible explanation for that?

    Regarding the weight of Callistoe: Babot et al. (2002) give the length of the (virtually complete) skull of the type specimen, which is 232 mm. In other words, Callistoe had a skull that was similar in size to that of a large grey wolf Canis lupus or a small American black bear Ursus americanus. Even taking into account the fact that metatherians tend to have relatively larger heads than similar-sized carnivores, this suggests that your original 23 kg size estimate was rather too low. Callistoe probably weighed at least twice as much – and possibly quite a bit more, considering how robustly built it was.

    Are there any scavengers to speak of on the Komodo island?

    A huge (possibly flightless) marabou/adjutant stork lived there as recently as during the Pleistocene.

    Link to this
  62. 62. Wilbert Friesen 12:39 pm 07/20/2012

    Some interesting life-like reconstructions of Borhyaenids, including Dukecynus, Borhyaena, Proborhyaena and Arminiheringia

    Link to this
  63. 63. Dartian 1:04 pm 07/20/2012

    Slight correction to my previous comment. Fossils of that extinct giant marabou/adjutant stork have so far only been found on the island of Flores, and not on Komodo (at least AFAIK). However, there were/are Komodo dragons on Flores too.

    Link to this
  64. 64. Bird/tree/dinosaur/etc. geek 7:16 pm 07/20/2012

    Nice find, Wilbert!

    Link to this
  65. 65. David Marjanović 3:35 pm 07/21/2012

    Surely that should be: “Some people would prefer Metatheria to be more inclusive than Marsupialia, and that the name Marsupialia be restricted to the crown-group.” I don’t believe there is any real consensus on this issue yet.

    While not everyone seems to use Marsupialia for the crown-group, most people now do AFAIK; and while Metatheria has been used for the total group for a long time, Marsupialia never seems to have been. At a minimum it excludes the deltatheroidans (which are sheer untold awesomeness, BTW).

    Link to this
  66. 66. Dartian 1:57 am 07/23/2012

    while Metatheria has been used for the total group for a long time, Marsupialia never seems to have been

    At least as far as Thylacosmilus is concerned, there is a long tradition – starting with Riggs’ original descriptions in the 1930ies – of referring to it as a ‘marsupial’. Nowadays, of course, Thylacosmilus is a well-established textbook example of convergent evolution, and it’s one of the very few fossil metatherians that everyone* has heard of. For this reason, IMO, it would be somewhat unfortunate if Marsupialia would be defined in such a way that borhyaenoids are not part of it.

    * For a certain value of ‘everyone’, obviously.

    Regarding canine growth in Thylacosmilus; as I just noticed, Turnbull (1978) suggested that the upper canines were honed against the lower canines, apparently thus providing the necessary wear that prevented them from growing too long.

    Turnbull, W.D. 1978. Another look at dental specialization in the extinct sabre-toothed marsupial, Thylacosmilus, compared with its placental counterparts. In: Butler, P.M. & Joysey, K.A. (eds.): Development, Function and Evolution of Teeth, Academic Press, London • New York • San Fransisco, 399-414.

    Link to this
  67. 67. naishd 5:45 am 07/23/2012

    For this reason, IMO, it would be somewhat unfortunate if Marsupialia would be defined in such a way that borhyaenoids are not part of it.

    But – in the Metatheria via Marsupialia system of nomenclature I allude to above (that is, where Marsupialia is used only for the crown-clade), the problem as it exists for borhyaenoids is caused by controversy over their phylogenetic position: are they close kin of opossums and other undoubted marsupials, or are they outside this clade? If they are outside the crown clade, it isn’t clear to me why we should want them to be called marsupials.


    Link to this
  68. 68. Dartian 6:55 am 07/23/2012

    If they are outside the crown clade, it isn’t clear to me why we should want them to be called marsupials.

    Because that’s what they’ve been called ever since they were discovered and brought to public and scientific attention?

    Link to this
  69. 69. naishd 7:05 am 07/23/2012

    Well, things are not this clear-cut. Many authors have in fact referred to borhyaenoids (or sparassodonts) as metatherians, with the understanding that Metatheria and Marsupialia are not synonymous. I’d provide a list but I don’t have time to compile it.


    Link to this
  70. 70. Dartian 7:21 am 07/23/2012

    Many authors have in fact referred to borhyaenoids (or sparassodonts) as metatherians, with the understanding that Metatheria and Marsupialia are not synonymous.

    Perhaps, but George Gaylord Simpson who, historically speaking, has surely been the most influental author on this subject by far, treated them as de facto synonymous in his “The principles of classification and a classification of mammals” (1945). And most later workers, at least until very recently, have followed him.

    Link to this
  71. 71. David Marjanović 1:34 pm 07/23/2012

    …where “very recently” means “1988″, IIRC.

    Link to this
  72. 72. Dartian 3:06 am 07/24/2012

    …where “very recently” means “1988″

    Well, in the very title of an article (re-)published on the blog Tetrapod Zoology on July 12, 2012, the eminent palaeozoologist Darren Naish refers to borhyaenoids collectively as “marsupials” – without scare quotes. So I’d say that the idea that borhyaenoids are marsupials is still somewhat entrenched in people’s minds… ;)

    Link to this
  73. 73. naishd 4:06 am 07/24/2012

    That’s cheating (smiley), (1) since I specifically said that they’re marsupials IF they’re close relatives of opossums, but non-marsupials if they fall outside the metatherian crown clade. And, (2) when (the first part of) this article was first published on Tet Zoo ver 2, it was titled “Invasion of the marsupial weasels, dogs, cats and bears… or is it?” – a deliberate nod to the idea that borhyaenoids might not be marsupials. But I couldn’t include a reference to that idea in the title this time round since the title was already too long (and title length is one of those factors that helps determine whether people will read and link to an article).


    Link to this
  74. 74. cargot 3:30 am 07/27/2012

    Darren clearly deserves congratulations for this great job, a very exhaustive synthesis of an amazing and bushy group of metatherian predators. It is probably the best destiny for a scientific work to make it available to everybody, so I am obviously grateful (I precise that I did not pay him for that and that we even never met!). Other native South American Cenozoic groups clearly deserve the same publicity and I hope that the blog will continue, or that a popular book on this enigmatic fauna will come out one day!

    I had a quick look to the comments left by readers and I can answer a few of them:
    - As rightly mentioned in one of them, Callistoe vincei, an Eocene species, was not two meters long but 70-80 cm from the tip of the nose to the sacrum. It was a quite small animal – all borhyaenoids very relatively small in comparison to extant Carnivores, but they had a massive head, which disturbs the estimation of body weight. Darren mentions a 2002 discovery for the specimen illustrated but 2002 is the year of the first publication about it by J. Babot and C. de Muizon, something like the birth certificate of the species (that was thought first to belong to the genus Arminiheringia). A long time had spent between the discovery and the study, like very often in paleontology, and things changed when this specimen of Callistoe became the main element of J. Babot’s PhD dissertation.
    - in the Cladosictis part there is one sentence suggesting that otters do not differ significantly in their morphology from non-swimming mustelids, it could be not true. A graduate student of our lab is currently doing morphometric analyses on mustelid postcranium, and swimming and fossorial taxa appear really distinct from those with other adaptations. It’s only a preliminar result but I hope that the following ones will confirm it. Mustelids are astonishing in their diversity in size and adaptations and borhyaenoids clearly recall me them.
    - about the great American biotic interchange (that we called GABI), also mentioned in one comment: obviously nothing is hidden about it, many scientific publications are focused on it, but the conclusions are probably not accessible to everyone. Although I am not at all specialist of that period, far too recent for me, what I can tell you in the context of the blog is that borhyaenoids came to extinction before the GABI and there is no paleontological proof that they meet placental carnivores and competed with them. A short time ago, an American and Japanese TV team came in Paris for an interview about this topic; they absolutely wanted to hear from us that Thylacosmilus and Smilodon were once in competition but there is absolutely no proof about it and it is more likely that a long time separates the extinction of the metatherian species and the arrival of the placental one. Moreover, Thylacosmilus was a dwarf in comparison to the Pleistocene Smilodon populator that was a true monster, so…

    I am glad to see that such an esoteric subject is a matter of interest for so much people, and I hope that new discoveries will improve our knowledge of this vanished world!

    Christine Argot

    Link to this
  75. 75. ohnosir 6:22 pm 07/31/2012

    @Bird/: I meant to thank you a while ago for the link that article, and apparently forgot, so thanks!
    Also very nice speculative zoology. Clearly you are fan of land crocs, but what leads to the expansion and specialization of various land crocs as opposed to other or even new groups?
    I’m a huge nerd for creature design. If we were located nearby in the real world I would say we should hang out.

    Link to this
  76. 76. morphospaceman 11:56 am 10/13/2013

    “The premolars and molars were narrow lineal blades, specialised for slicing.”

    The postcanine teeth of thylacosmilus are smallish but I wouldn’t go calling them linear blades. Aren’t they lophodont… (As a side note: Why can’t people upload occlusal pictures of teeth!)

    Link to this

Add a Comment
You must sign in or register as a member to submit a comment.

More from Scientific American

Email this Article