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Phenacodontidae, I feel like I know you

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


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One day in the not-too-distant future there will be a Tet Zoo Guide to Paleogene Mammals. I’m not kidding – it really will happen one day… hey, I’ve only been promising it since 2007 or so. Until then, here’s a very short excerpt from that project (YES, it does exist,  as does tons and tons and tons of stuff that I just never have time to finish).

Phenacodus primaevus, photographed at the AMNH by Ghedoghedo. Image in public domain.

An enormous number of Paleogene eutherians have traditionally been grouped together in Condylarthra, a group that represents a classic ‘taxonomic wastebasket’ (that is, a storage area for taxa that can’t confidently be placed elsewhere). At the core of the condylarth concept are the phenacodontids, periptychids and hyopsodontids but numerous other Paleogene groups later became added, including arctocyonids and mesonychians. Affinities with such groups as pantodonts, taeniodonts, tillodonts, cetaceans and aardvarks have also been suggested. Anatomical characters that might link all of these animals to the exclusion of other eutherians are non-existent and hence there has been widespread recognition of the fact that Condylarthra is a grade, not a clade.

Cranial and mandibular remains of the phenacodontid Ectocion osbornianus (one of several Ectocion species), from Thewissen (1990).

However, occasional evidence has been presented that might link certain condylarth groups together. Furthermore, large-scale phylogenetic analyses have also led to proposals that some condylarth lineages might be nested within eutherian clades originally recognised following molecular studies, most notably Afrotheria (Tabuce et al. 2007). Tabuce et al. (2001) drew attention to a possible close relationship between a Microhyus + Macroscelidea clade and Proboscidea, Hyracoidea, Perissodactyla and Phenacodontidae. A clade containing all of these taxa corresponds to the group Taxeopoda recognised by Archibald (1998): it is mostly congruent with molecular data apart from the inclusion of perissodactyls. For reviews of the condylarth concept see Prothero et al. (1988) and Archibald (1998).

Phenacodontids are one of those ‘classic’ Paleogene eutherian groups that get featured in the majority of books on fossil mammals; this is due to the fact that Phenacodus from the Paleocene and Eocene of North America and Europe is represented by near-complete remains, and that it has often been imagined as possibly close to the ancestry of perissodactyls. Indeed, phenacodontids share several ankle, humeral and braincase characters with tethytheres and perissodactyls (Prothero et al. 1988).

Charles Knight's 1898 reconstruction of Phenacodus. The flora perhaps looks a bit too modern. Image in public domain.

Possible phenacodontids have been reported from the Paleocene of South America and Eocene of Asia but these records were considered doubtful by Thewissen (1990). Phenacodontids have bunodont or bunolophodont cheek teeth, spatulate lower incisors and large, pointed canines. They were reasonably long-bodied, long-tailed mammals with pentadactyl hoofed hands and feet; their proportions and body size are indicative of semi-cursoriality. Sexual dimorphism in canine size is present in some members of the group and the snout morphology of one species (Phenacodus intermedius) suggests the presence of a short proboscis (Thewissen 1990).

For previous Tet Zoo articles on Paleogene mammals, see…

Refs – -

Archibald, J. D. 1998. Archaic ungulates (“Condylarthra”). In Janis, C. M., Scott, K. M. & Jacobs, L. L. (eds) Evolution of Tertiary Mammals of North America. Volume 1: Terrestrial Carnivores, Ungulates, and Ungulatelike Mammals. Cambridge University Press, pp. 292-331.

Prothero, D. R., Manning, E. M. & Fischer, M. 1988. The phylogeny of the ungulates. In Benton, M. J. (ed) The Phylogeny and Classification of the Tetrapods, Volume 2: Mammals. Clarendon Press (Oxford), pp. 201-234.

Tabuce, R., Coiffait, B., Coiffait, P.-E., Mahboubi, M. & Jaeger, J.-J. 2001. A new genus of Macroscelidea (Mammalia) from the Eocene of Algeria: a possible origin for elephant-shrews. Journal of Vertebrate Paleontology 21, 535-546.

- ., Marivaux, L., Adaci, M., Bensalah, M., Hartenberger, J.-L., Mahboubi, M., Mebrouk, F., Tafforeau, P. & Jaeger, J.-J. 2007. Early Tertiary mammals from North Africa reinforce the molecular Afrotheria clade. Proceedings of the Royal Society B 274, 1159-1166.

Thewissen, J. G. M. 1990. Evolution of Paleocene and Eocene Phenacodontidae (Mammalia, Condylarthra). University of Michigan Papers on Paleontology 29, 1-107.

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 darrennaish.wordpress.com. He has been blogging at Tetrapod Zoology since 2006. Check out the Tet Zoo podcast at tetzoo.com! Follow on Twitter @TetZoo.

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





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  1. 1. Oenitholestes 6:27 pm 08/8/2013

    I was kinda hoping for sphenacodontids when I glanced at the title, but this is just as good!

    Link to this
  2. 2. Yodelling Cyclist 6:58 pm 08/8/2013

    Great stuff. Any estimate of the size of these animals?

    Link to this
  3. 3. Heteromeles 7:04 pm 08/8/2013

    fascinating sternum in Phenacodus, so unconnected to the ribs in the mount. How’d that work for breathing and such? Or was the chest actually much smaller than portrayed?

    Link to this
  4. 4. Christopher Taylor 7:12 pm 08/8/2013

    Any estimate of the size of these animals?

    The smallest were about cat-sized, the largest were about sheep-sized (http://taxondiversity.fieldofscience.com/2011/04/phenacodontidae.html).

    Link to this
  5. 5. Andreas Johansson 7:23 pm 08/8/2013

    Are there any books about (or at least substantially covering) Palaeogene mammals newer than Rose’s The Rise of Placental Mammals (2005) anyone here would to like to recommend?

    Link to this
  6. 6. Gigantala 7:53 pm 08/8/2013

    It’s almost certain that the south american forms are notoungulates. Or maybe xenungulates, depending on who you ask.

    Link to this
  7. 7. Michael_Blonde 1:56 am 08/9/2013

    Of course then the question is what notoungulates were.

    Link to this
  8. 8. Dartian 4:27 am 08/9/2013

    Darren:
    Phenacodontids are one of those ‘classic’ Paleogene eutherian groups that get featured in the majority of books on fossil mammals

    Or got featured, anyway. It’s my (admittedly subjective) impression that after circa the 1980ies, Phenacodus became increasingly less often shown in such books. I suspect that this coincided with the realisation that ‘Condylarthra’ probably doesn’t really exist. Perhaps publishers (at least publishers of books meant for a general public) thought that it might be a bit embarrassing to show a fossil animal that’s been long known from entire preserved skeletons but which cannot currently really be confidently placed anywhere in the mammalian evolutionary tree*? Maybe it was thought that it’s easier to just ignore it?

    * There is possibly a similar case in the fossil primate literature. Oreopithecus, the peculiar ape from the Miocene of Italy, is, by fossil primate standards, known from astonishingly plentiful remains; for example, a virtually complete skeleton has been known since the 1950ies. You’d therefore expect that Oreopithecus would be highlighted and extensively treated in all textbooks about early hominoids and human evolution – but you’d be wrong. Amazingly often Oreopithecus is given minimal attention or even ignored completely in such publications. (At the same time, entire chapters might be devoted to other fossil apes known from much more fragmentary remains.) I strongly suspect that this is mainly due to the fact that the phylogenetic position of Oreopithecus has been (and, indeed, still is) so enigmatic. It’s obviously not a direct human ancestor, but it’s not obvious what it is instead. It’s been easier to ignore this taxon than try to answer such awkward questions.

    I dunno, maybe my impressions about the choice of subject matter in palaeontological textbooks are biased, and maybe I’m too cynical. But I can’t help suspecting that, at least sometimes, certain taxa are deliberately left out from publications just because their taxonomic position is incertae sedis.

    Link to this
  9. 9. BrianL 5:15 am 08/9/2013

    @Dartian:
    I’d second that. Another clade of mammals that hardly gets treated anywhere is Ptolemaiida, despite these generally being recognised as a separate ‘order’ of mammals. Even ‘The origin and evolution of placental mammals’ by Kemp, published in 2005, does not even mention them! Maybe I’m being harsh, but I feel that a book with that scope and title should cover all known fossil mammalian clades even if they are very obscure.
    Ptolemaiidans, by the way, have also been considered afrotherians in some studies. They’ve come out as stem-aardvarks. Wikipedia begrudgingly acknowledges that, but insists on classifying them in Cimolesta, which is barely a better thing than Condylarthra.

    Reference:
    2007. A new estimate of afrotherian phylogeny based on simultaneous analysis of genomic, morphological and fossil evidence.BMC Evolutionary Biology 7:224; doi:10.1186/1471-2148-7-224.

    Link to this
  10. 10. naishd 5:24 am 08/9/2013

    Argh, ptolemaiidans!! If ONLY you could see the >major< text I'm working on right now. Ptolemaiidans are done.

    All to be revealed in time…

    Darren

    Link to this
  11. 11. naishd 5:32 am 08/9/2013

    On Ptolemaiida… Possible affinities with creodonts, pantolestans, macroscelideans and tubulidentates have all been proposed, with the macroscelidean- and tubulidentate-like features leading some to suggest potential inclusion in Afrotheria (Simons & Bown 1995).

    Ref – -

    Simons, E. L. & Bown, T. M. 1995. Ptolemaiida, a new order of Mammalia – with description of the cranium of Ptolemaia grangeri. Proceedings of the National Academy of Sciences 92, 3269-3273.

    Darren

    Link to this
  12. 12. Andreas Johansson 6:36 am 08/9/2013

    Maybe it’s an artefact of the (online) company I keep, but I get the feeling mammalian phylogeny gets surprisingly little attention compared to dinosaurian (incl avian) phylogeny. If anything one’d expect a bias the other way, what with us being mammals and all.

    Link to this
  13. 13. Chabier G. 7:06 am 08/9/2013

    A Guide to Palaeogene Mammals sounds really great. It would be extremely difficult to know phylogenetical relationships of many taxa like Phenacodontidae, at a first glimpse, they don’t exhibit very special morphological traits (compared with contemporaneous oddities like Uintatherium, e.g.).
    Heteromeles: I think it’s improbable to see a fossil mammal skeleton with the ribs reaching the sternum, because, in mammals, the ribs have cartilaginous distal ends. It´s not the case for birds and other dinosaurs, that possess dorsal and ventral bone ribs.

    Link to this
  14. 14. BrianL 9:21 am 08/9/2013

    @Andreas Johansson:
    Count yourself lucky, in the company I keep phylogeny of any sort gets very little attention. :) Just yesterday, I somewhat lost my patience when my brother-in-law kept insisting on okapis being ‘some sort of zebra’ or at least ‘some sort of zebra hybrid’ despite me having told him they’re giraffes (I know, giraffids, but …) three times already. Some minutes later he also felt like ‘teaching’ me that hyenas are dogs…

    @Darren:
    I love it that you’ll apparently feature ptolemaiidans on TetZoo. Were you referring to a blog article or a textbook article, though?

    Link to this
  15. 15. Heteromeles 10:12 am 08/9/2013

    @Chabier: Thanks for the clarification. I kind of got that about the cartilage, but it’s unclear from the standard picture why the sternum is hanging so far away from the ribs. Presumably it’s a best guess based on rib curvature, and on the assumption that none of the ribs were distorted by fossilization. Unfortunately, when artists uncritically use that side view to create their fully fleshed illustrations, you end up with a torso that may be blobbier than it was in life.

    Link to this
  16. 16. Heteromeles 10:46 am 08/9/2013

    @BrianL: just remember that okapi remark when people start talking about “black” people. Most genetic diversity is in Africa, but we only look a badly defined skin color character when categorizing people into races. Phylogenetics is a real discipline, is it not? And brothers-in-law can be a real nuisance, especially when they get in the way of enjoying the zoo.

    Just remember: okapis are giraffids in zebra drag, while hyenas are felids who’ve had clade-reassignment surgery to look like the dogs they’ve always felt themselves to be. If he can BS, so can you, and if he doesn’t want the kids hearing that kind of talk, so much the better.

    Link to this
  17. 17. David Marjanović 2:00 pm 08/9/2013

    fascinating sternum in Phenacodus, so unconnected to the ribs in the mount. How’d that work for breathing and such? Or was the chest actually much smaller than portrayed?

    Don’t take museum mounts literally on such things. The sternal ribs may have been cartilaginous; or perhaps the skeleton is actually incomplete, the missing parts were sculpted for the mount, and nobody bothered to reconstruct the sternal ribs because they’re sorta kinda obvious anyway (if you know 10 x as much anatomy as the average of the general public). Gastralia, sterna, sternal ribs, clavicles, carpals and so on are regularly omitted from museum mounts.

    Oreopithecus, the peculiar ape from the Miocene of Italy, is, by fossil primate standards, known from astonishingly plentiful remains; for example, a virtually complete skeleton has been known since the 1950ies.

    I thought the complete skeleton was only found (or prepared?) in the 90s or later? I’ve read earlier papers about O., and they make clear that not much was known.

    Ptolemaiidans are done.

    *Homeric drool*

    Link to this
  18. 18. David Marjanović 2:09 pm 08/9/2013

    Gastralia, sterna, sternal ribs, clavicles, carpals and so on are regularly omitted from museum mounts.

    …in dinosaurs. *facepalm* Mammal carpals are not omitted anywhere I’ve seen. Mounted dinosaur skeletons, however, often have the metacarpals jammed against radius and ulna with hardly any space for articular cartilage even.

    Link to this
  19. 19. Dartian 3:13 am 08/10/2013

    David:
    I thought the complete skeleton was only found (or prepared?) in the 90s or later?

    Johannes Hürzeler found and described the skeleton in 1958 (the first remains of Oreopithecus had been found already in the 19th century, but these were quite fragmentary). The skeleton, while nearly complete, was also rather crushed, but that didn’t stop other scientists from publishing studies of, e.g., its cranial morphology (for example, Straus & Schön, 1960; Szalay & Bersi, 1973). Later, in the 1990ies, re-examination of the original material showed that the previous studies had overestimated the cranial capacity of Oreopithecus (Clarke, 1997) – perhaps this is what you’re thinking of?

    I’ve read earlier papers about O., and they make clear that not much was known.

    How early papers? As mentioned, in principle at least a substantial amount of information about the gross anatomy of Oreopithecus was out there in the form of published literature from the late 1950ies onward. (Hürzeler, to his credit, AFAIK never tried to restrict other researchers’ access to ‘his’ fossils.) The phylogenetic position of Oreopithecus has, of course, still remained enigmatic to this day. But at least nowadays everyone agrees that it was indeed an ape and not a monkey that had convergently evolved ape-like traits. ;)

    References:

    Clarke, R.J. 1997. First complete restoration of the Oreopithecus skull. Human Evolution 12, 221-232.

    Hürzeler, J. 1958. Oreopithecus bambolii Gervais: a preliminary report. Verhandlungen der Naturforschenden Gesellschaft Basel 69, 1–47.

    Straus, W.L. & Schön, M.A. 1960. Cranial capacity of Oreopithecus bambolii. Science 132, 670-672.

    Szalay, F.S. & Berzi, A. 1973. Cranial anatomy of Oreopithecus. Science 180, 183-185.

    Link to this
  20. 20. BrianL 8:18 am 08/10/2013

    What was the ecology of *Oreopithecus* anyway? Should I imagine it as a slowmoving, squatting herbivore? Something like a hominid panda, chalicothere or ground sloth?

    Link to this
  21. 21. Dartian 8:43 am 08/10/2013

    Brian: Relatively slow-moving (or rather, sluggish) and herbivorous, yes, and presumably more terrestrial than most extant primates. If you want to compare Oreopithecus with some currently living taxon, perhaps you could imagine it as a scrawny, semi-bipedal, small-brained and small-toothed orangutan that spends most of its time on the ground.

    Link to this
  22. 22. Squiddhartha 1:43 am 08/11/2013

    I might be slow-moving or sluggish too, if I never ate anything but Oreos.

    …what do you mean, that’s not what Oreopithecus means?

    Link to this
  23. 23. llewelly 2:00 am 08/11/2013

    Wasn’t Oreopithicus an island ape that went extinct shortly after the island (Sardinia-Tuscany?) reconnected with Africa, presumably due to large predator invasions?

    It seems there are a great many Miocene apes and near-apes from around the Tethys. I wonder how much of that speciation was provoked by all the geographical changes, particularly shoreline changes, taking place during the Miocene.

    It’s interesting that we seem to have an example of extensive ape diversity in the presence of changing shorelines, and yet, so far none show any evidence of greater aquatic activity than seen in modern primates. (Discounting human technology-aided activity – modern humans are by far the most aquatic primate I can think of.)

    Does anyone know where the claim that there were “Approximately 100 species of apes” during the Miocene comes from? (Yes, that number seems to include /all/ apes, not just those near the Tethys.)

    Haha, Squiddhartha! Whenever I see “Oreopithicus” or “Oreodont” I am SO TEMPTED to make jokes about their habitat being the snack-foods aisle, and so forth.

    By the way, Squiddhartha, did you know “oreos” were named that because they were designed to make the eater hill-shaped?

    Link to this
  24. 24. AlHazen 3:33 am 08/11/2013

    Count me as one refer eagerly awaiting your guide to Paleogene mammals!

    Does anyone know when the photo of the AMNH’s Phenacodus above was taken, or whether the specimen(*) is currently on display? It was displayed in the PREVIOUS fossil mammal exhibit, but I think put in storage when the fourth floor (= fossil halls) was redone a few years back.

    (*) A good one: virtually complete, discovered largely in articulation (so the posture and body depth– as shown by position of sternum– may be off, but the bones themselves– and, relevant to questions of how the critter was related to Afrotherians and/or Perissodactyls, things like the number of dorsal vertebrae– are definitely correct). It’s described in an issue of AMNH “Novitates”, available free on-line.

    Link to this
  25. 25. AlHazen 3:45 am 08/11/2013

    Citation:
    Remounted skeleton of Phenacodus primaevus ; Comparison with Euprotogonia. Bulletin of the AMNH ; v. 10, article 9.
    Osborn, Henry Fairfield, 1857-1935.

    (Sorry: “Bulletin,” not “Novitates.” Both tiles available on-line from AMNH.)

    Link to this
  26. 26. Dartian 5:47 am 08/11/2013

    Squiddhartha:
    I might be slow-moving or sluggish too, if I never ate anything but Oreos.

    What a terrible, terrible joke.

    I wish I had thought of it. ;)

    Llewelly:
    Wasn’t Oreopith[e]cus an island ape

    Yes.

    that went extinct shortly after the island (Sardinia-Tuscany?) reconnected with Africa

    Again, yes, although the island reconnected with Europe, not Africa. (In fact, it’s likely that Oreopithecus was the very last European species of hominoid – at least until the dispersal of early humans to that continent in the Pleistocene.)

    Does anyone know where the claim that there were “Approximately 100 species of apes” during the Miocene comes from?

    Don’t know about any exact figures, but that’s probably a realistic estimate – and it may even be an underestimate; the Miocene lasted for a long time.

    Link to this
  27. 27. David Marjanović 11:28 am 08/12/2013

    How early papers? As mentioned, in principle at least a substantial amount of information about the gross anatomy of Oreopithecus was out there in the form of published literature from the late 1950ies onward. [...] The phylogenetic position of Oreopithecus has, of course, still remained enigmatic to this day. But at least nowadays everyone agrees that it was indeed an ape and not a monkey that had convergently evolved ape-like traits. ;)

    I’ve read papers all the way back to Hürzeler’s. I need to look them up again, but, as you say, little enough was known – at least in sufficiently uncrushed form – that many people thought O. wasn’t even an ape.

    O. was pretty clearly bipedal and stood under trees, reaching up to eat leaves much like a minuscule ground sloth or chalicothere or homalodothere. Its molars are outright lophodont (they have shearing crests instead of separate blunt cusps), fitting evidence from enamel microwear that O. was a folivore. It was an ape, at home somewhere around gibbon/great ape dichotomy ( = the origin of the crown-group).

    Wasn’t Oreopithicus [sic] an island ape that went extinct shortly after the island (Sardinia-Tuscany?) reconnected with Africa, presumably due to large predator invasions?

    Well, probably, but I don’t think enough fossils are known to date its extinction with such precision.

    Link to this
  28. 28. Dartian 6:06 am 08/13/2013

    David:
    “O. was pretty clearly bipedal

    For the record, some workers, notably Randall Susman (e.g., 2005) would disagree with that.

    It was an ape, at home somewhere around gibbon/great ape dichotomy

    Harrison & Rook (1997) consider Oreopithecus to have been merely an unusual dryopithecine, which makes sense at least in terms of biogeography.

    References:

    Harrison, T. & Rook, L. 1997. Enigmatic anthropoid or misunderstood ape? The phylogenetic status of Oreopithecus bambolii reconsidered. In: Begun, D.R., Ward, C.V. & Rose, M.D. (eds.), Function, Phylogeny, and Fossils: Miocene Hominid Evolution and Adaptations, Plenum, New York, pp. 327-362.

    Susman, R.L. 2005. Oreopithecus: still apelike after all these years. Journal of Human Evolution 49, 405-411.

    Link to this
  29. 29. Basandere 2:33 pm 08/13/2013

    okapis are giraffids in zebra drag, while hyenas are felids who’ve had clade-reassignment surgery to look like the dogs they’ve always felt themselves to be.

    Squeeeee! Never mind I don’t have a brother-in-law — I’ll tell this story to anybody in earshot from now on. :D

    Link to this

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