ADVERTISEMENT
  About the SA Blog Network













Tetrapod Zoology

Tetrapod Zoology


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

Monstersauria vs Goannasauria

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


Email   PrintPrint



Heloderma suspectum, the Gila monster. Photo by Dave Hone.

ResearchBlogging.org

The Gila monster Heloderma suspectum and its close relative the Mexican Beaded lizard H. horridum are the only two extant members of Helodermatidae, the gila monster clade.  It’s been agreed for a considerable time that, among living lizards, helodermatids are most closely related to monitor lizards (varanids) and to the weird Bornean earless monitor Lanthanotus borneensis. All of these lizards (and their close fossil relatives) are grouped together in Platynota. The name Varanoidea has also been used for Platynota, but it’s been restricted specifically to the monitor lineage within Platynota at times, and hence, annoyingly, means different things to different authors.

Beaded lizard, photographed by Ltshears, from wikipedia. Released into public domain.

Helodermatids are stocky, proportionally short-limbed, short-tailed lizards with deep, robust snouts, dermal armour, osteoderms fused to the skull surface, venom grooves in the dentary teeth, and venom glands located in the lower jaw. Their teeth are formidable – check out the fantastic image below from digimorph. Gila monsters are normally 30-50 cm long in total while Beaded lizards can reach 70 cm or even nearly 1 m (Pianka & Vitt 2003). They prey on a diversity of invertebrates and small vertebrates, do a lot of digging for prey, and are sometimes regarded as specialised nest-seekers: they eat the eggs of other lizards as well as those of snakes and birds, and also prey on rodent nestlings. Gila monsters have been known to locate hen’s eggs buried 15 cm below the ground surface (Pianka & Vitt 2003). Needless to say, their olfactory and vomeronasal senses are highly developed. The venom is used for self-defense – not in subduing prey. They are surprisingly good climbers (albeit slow, cautious climbers) and may regularly forage in trees, bushes and even on cacti.

In general, these are slow, sluggish lizards that may spend about 95% of their time resting and hiding in burrows, but they are known to have one of the highest aerobic scopes of all lizards – this is higher in males than in females and is presumably a sexually selected trait related to the prolonged and metabolically costly wrestling that males engage in (Beck et al. 1995). In Beaded lizards at least, this behaviour is pretty spectacular and similar to the wrestling practised by some monitors: the animals lever off the ground with their heads and tails, forming an arch shape. The aim is then to push the opponent onto his back before biting him on the jaws (Beck & Ramírez-Bautista 1991). While we know that males engage in ‘sexual wrestling’, relatively little is known about social behaviour in general and more work is needed.

Gila monster skull, with numerous osteoderms, from digimorph (c).

Unambiguous fossil helodermatids are known from the Eocene-Oligocene of France (Eurheloderma) and the Oligocene and Miocene of the USA (Lowesaurus and H. texanum). A number of additional taxa from the Cretaceous, argued by some authors to belong together as the ‘gobidermatids’ (Lee 1997), have at times been included within Helodermatidae but are here excluded from that clade following Conrad (2008). In proportions and probably overall appearance, unambiguous fossil helodermatids seem to have been similar to the extant ones, and Eurheloderma and Lowesaurus definitely have venom grooves on their dentary teeth (Nydam 2000).

Skull of Cretaceous monstersaurian Estesia, photographed at the AMNH by Ghedoghedo. Released into public domain.

A number of additional fossil taxa group closer to helodermatids than to other platynotans, and yet don’t necessarily look helodermatid-like. Estesia mongoliensis from the Late Cretaceous of Mongolia, for example, had a shallow snout compared to gila monsters and probably looked superficially more like a monitor. Anatomical characters that link it and other species with helodermatids include tall, narrow neural spines and a distinctive form of tooth implantation.

Platynotan phylogeny plotted against time, from Conrad (2008). The clade shown at the top (the one including Heloderma) is Monstersauria. The one in the middle (including Varanus) is Goannasauria. See Conrad (2008) for a huge amount of additional detail. Mosasaurs and kin may or may not be part of Platynota.

In differentiating this ‘gila monster lineage’ from other groups within Platynota, Norell & Gao (1997) decided to name it.  They went with Monstersauria. Their original definition was node-based (Gobiderma + Heloderma), but Conrad (2008) more recently co-opted the name for the entire gila monster branch (an intention hinted at by Norell & Gao (1997), though not expressed in their node-based definition). So, Estesia, the ‘gobidermatids’, and of course helodermatids proper are monstersaurians.

Monstersauria is the sister-group to the lineage that includes monitors, Lanthanotus and a large number of fossil taxa. Perhaps surprisingly, this lineage has no name unambiguously associated with it, and one was needed. Varanoidea has been applied to it by some authors, but the use of this name for the entire gila monster + monitor clade seems more appropriate. Conrad (2008) therefore came up with a new name for the monitor branch, and opted for Goannasauria. So, Varanoidea – the entire gila monster + monitor clade within Platynota – consists of two major lineages, Monstersauria and Goannasauria.

And this, again, is why I suck at producing ‘picture of the day’ posts. Dammit.

For previous Tet Zoo articles on platynotans, see…

Mosasaurs – historically associated with monitors or even with snakes – have been included within Platynota by some authors (e.g., Lee 1997). This position is looking increasingly unlikely. That is, mosasaurs are probably not platynotans. Nevertheless, if you want to see some Tet Zoo articles on them, go to…

Refs – -

Beck, D. D., Dohm, M. R., Garland, T., Ramírez-Bautista, A. & Lowe, C. H. 1995. Locomotor performance and activity energetics of helodermatid lizards. Copeia 1995, 577-585

- . & Ramírez-Bautista, A. 1991. Combat behavior of the beaded lizard, Heloderma h. horridum, in Jalisco, Mexico. Journal of Herpetology 25, 481-484.

Conrad, J. (2008). Phylogeny And Systematics Of Squamata (Reptilia) Based On Morphology Bulletin of the American Museum of Natural History, 310, 1-182 DOI: 10.1206/310.1

Lee, M. S. Y. 1997. The phylogeny of varanoid lizards and the affinities of snakes. Philosophical Transations of the Royal Society of London B 352, 53-91.

Norell, M. A. & Gao, K. 1997. Braincase and phylogenetic relationships of Estesia mongoliensis from the Late Cretaceous of the Gobi Desert and the recognition of a new clade of lizards. American Museum Novitates 3211, 1-25.

Nydam, R. L. 2000. A new taxon of helodermatid-like lizard from the Albian-Cenomanian of Utah. Journal of Vertebrate Paleontology 20, 285-294.

Pianka, E. R. & Vitt, L. J. 2003. Lizards: Windows the Evolution of Diversity. University of California Press, Berkeley.

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.





Rights & Permissions

Comments 40 Comments

Add Comment
  1. 1. David Marjanović 7:58 am 05/3/2012

    Their teeth are formidable – check out the fantastic image below from digimorph.

    Those of Anguis fragilis are actually scarier. They look the same, but they’re proportionally bigger.

    and the Oligocene and Miocene of the USA (Lowesaurus and H. texana)

    H. texanum.

    an intention hinted at by Norell & Gao (1997), though not expressed in their node-based definition

    Ah, yeah. That occasionally happened in those stupid times. Laurin & Reisz (1995) submitted a manuscript with branch-based definitions in it, but at least one reviewer didn’t allow them to keep them in; they had to replace them all by node-base ones.

    And this, again, is why I suck at producing ‘picture of the day’ posts. Dammit.

    :-) :-) :-) :-) :-)

    Link to this
  2. 2. naishd 8:05 am 05/3/2012

    Scary slow-worm teeth: go here.

    Darren

    Link to this
  3. 3. Tomasz Skawiński 8:41 am 05/3/2012

    It’s been agreed for a considerable time that, among living lizards, helodermatids are most closely related to monitor lizards (varanids) and to the weird Bornean earless monitor Lanthanotus borneensis.

    Well, it has recently been questioned on the basis of molecular evidence that suggest that Varanus and Lanthanotus are more closely related to Shinisaurus while Heloderma is closer to Anguidae (among extant taxa). This result stands when both morphological and molecular characters are used (Conrad et al. 2011; very good paper btw).

    Conrad JL, Ast JC, Montanari S, Norell MA. 2011. A combined evidence phylogenetic analysis of Anguimorpha (Reptilia: Squamata). Cladistics 27 (3): 230–277. http://dx.doi.org/10.1111/j.1096-0031.2010.00330.x

    Link to this
  4. 4. BrianL 9:54 am 05/3/2012

    Are there any fossils known from *Lanthanotus*’ side of the family, by the way? Given its likely age and present distribution, surely it would be a relict? This is just as true of monstersaurians themselves, of course.

    Link to this
  5. 5. naishd 10:19 am 05/3/2012

    I just realised that I changed Heloderma texana to H. texanum on David’s suggestion – but is this definitely right? I see other authors using H. texana.

    Fossil record of Lanthanotus lineage (comment 3): great question. While Cherminotus from the Late Cretaceous of Mongolia used to be regarded as the sister-taxon of Lanthanotus, this is now in doubt – they might be close, but not that close. As you can see from Conrad’s figure above, there are essentially no fossils linking Lanthanotus with its Late Cretaceous relatives, so it has a conspicuously long ghost lineage.

    By the way, I should have noticed the cute way Daniel Beck described helodermatids in the mostly varanid-focused Varanoid Lizards of the World: “Their demeanor, gait, and general body form are sufficiently reminiscent of Varanus that many familiar with H. horridum called it the “Mexican monitor”. For this work, the Helodermatidae might thus be informally referred to as the “Helodermonitor” lizards” (Beck 2004, p. 517).

    Darren

    Ref – -

    Beck, D. D. 2004. Overview of the family Helodermatidae for varanophiles. In Pianka, E. R., King, D. R. & King, R. A. (eds) Varanoid Lizards of the World. Indiana University Press (Bloomington & Indianapolis), pp. 517-520.

    Link to this
  6. 6. Therizinosaurus 6:11 pm 05/3/2012

    Conrad et al. (2011) recently added data to the Conrad lizard analysis and found Platynota to be diphyletic. Instead, monstersaurians are sister to anguids+xenosaurids, then to shinisaurs. The relationships within Monstersauria were also changed, in large part due to new Gobiderma material.

    Conrad, Rieppel, Gauthier and Norell, 2011. Osteology of Gobiderma pulchrum (Monstersauria, Lepidosauria, Reptilia). Bulletin of the American Museum of Natural History. 362, 88 pp.

    Link to this
  7. 7. naishd 6:24 pm 05/3/2012

    Dammit, I’m so out of touch. There’s also this…

    Mead, J. I., Schubert, B. W., Wallace, S. C. & Swift, S. L. 2012. Helodermatid lizard from the Mio−Pliocene oak−hickory forest of Tennessee, eastern USA, and a review of monstersaurian osteoderms. Acta Palaeontologica Polonica 57, 111–121.

    … though it’s a bit weird in saying that Estesia is a helodermatid.

    Darren

    Link to this
  8. 8. naishd 7:18 pm 05/3/2012

    Ok, thanks to Mickey I’ve now seen Conrad et al. (2011) (I can’t download AMNH publications at the moment, no idea why). If Platynota is understood to be the monitor + gila monster clade, they don’t find it to be diphyletic – rather, they find shinisaurians and all members of the xenosaur + anguid clade to be within Platynota, and closer to Monstersauria than to Goannasauria. That’s heterodox in view of most previous morphology-based phylogenies, and they note that it’s surprising and indeed that their new phylogeny is poorly resolved (p. 67).

    The topology they recovered for Monstersauria is the same as what’s described in the article above: there’s a grade of ‘gobidermatids’ outside an Estesia + Helodermatidae clade.

    Darren

    Link to this
  9. 9. Therizinosaurus 7:38 pm 05/3/2012

    Ahhh, but (just to be pedantic) Platynota is defined in Conrad (2008) as “All taxa sharing a more recent common ancestor with Varanus varius and Heloderma horridum than with Anguis fragilis or Xenosaurus grandis.” Thus it can never include anguids or xenosaurids and does not exist in Conrad et al.’s combined data trees. It’s due to using molecular data in addition to morphological data in the later analysis.

    Link to this
  10. 10. naishd 8:35 pm 05/3/2012

    Nuts, I missed that definition. Thanks. Well, I’ll just fall back on the argument that the PhyloCode hasn’t been implemented yet, and that Platynota should = the clade that includes Varanus varius and Heloderma horridum, no matter what the contents :) Oh yeah, and that the topology in Conrad et al. (2011) likely doesn’t represent the True Tree anyway :)

    Darren

    Link to this
  11. 11. Riggi 6:56 am 05/4/2012

    Since you said mosasaurs in a snippet, here is something to laugh about. Unless I read this wrong, he suggested that mosasaurs were the ancestors of whales. http://www.macroevolution.net/evolution-of-whales.html

    Anyhow what, if anything, are mosasaurs?

    Link to this
  12. 12. Riggi 6:57 am 05/4/2012

    *meant to say this “guy” not “he”.

    Link to this
  13. 13. David Marjanović 9:54 am 05/4/2012

    but is this definitely right? I see other authors using H. texana.

    I don’t doubt that. But Article 31.2 and 34.2… well… don’t give a shit.

    The corrected spelling must be attributed to the original author(s), says Art. 50.4.

    rather, they find shinisaurians and all members of the xenosaur + anguid clade to be [...] closer to Monstersauria than to Goannasauria

    Indeed, part of Monstersauria, if Monstersauria and Goannasauria have reciprocal branch-based definitions.

    Anyhow what, if anything, are mosasaurs?

    Stem-pythonomorphs. And Pythonomorpha is the sister-group of Anguimorpha. And forty-five wrongs make a right (Gatesy & Baker 2005 in the references).

    Link to this
  14. 14. Frits B 1:23 pm 05/4/2012

    Re #4: “skin” in ancient Greek is “to derma” so “it”, not “she”. The Texan variety should therefore be texanum.

    Link to this
  15. 15. Halbred 3:30 pm 05/4/2012

    Mosasaurs are related to varanids through a group called agilisaurs (which themselves were semi-aquatic live-birthers). So I guess they’d be platynotids.

    Link to this
  16. 16. Hai~Ren 4:56 pm 05/4/2012

    Halbred: Surely you mean aigialosaurs? After that Agilisaurus is an ornithischian from the Middle Jurassic of China.

    It’s like that whole confusion between dryosaurs and dyrosaurs…

    Link to this
  17. 17. Halbred 5:59 pm 05/4/2012

    Yup, totally meant aigialosaurs. *headdesk*

    Link to this
  18. 18. Peteykins 7:18 pm 05/4/2012

    Oh! Thanks for this. I grew up in Gila Monster territory, outside Tucson, Arizona. My friends and I saw all kinds of wildlife all the time, but Gila Monsters were always the rarest of the rare sightings. I believe I only ever saw one in the wild twice. They are really beautiful animals.

    At my middle-of-the-desert grade school, we were always reminded to be very respectful of these enticing, candy-like beasties, and were told horror stories about their bite, about how the lizard would clamp on and start grinding to work the poison into the wounds, and that the only way to get it off was to decapitate it. Yikes!

    Link to this
  19. 19. llewelly 11:08 pm 05/4/2012

    “Yup, totally meant aigialosaurs. *headdesk*”

    DAMN YOU AUTOCORRECT!!

    Link to this
  20. 20. naishd 10:41 am 05/5/2012

    Thanks for the many interesting and worthy comments. Aigialosaurids (see comment 15) have conventionally been identified as a paraphyletic assemblage of basal mosasaurs (Mosasauroidea or Mosasauria, whatever your preference), or as a clade close to Mosasauridae (s. l.), as (typically) have dolichosaurids. While some analyses do indeed find the topology (varanids + (aigialosaurids + mosasaurids)), it may be that mosasaurs in the most inclusive sense are not especially close to varanids after all (and, by varanids, I mean goannasaurians. Conrad (2008) also used the name Varaniformes for the monitor branch).

    Darren

    Link to this
  21. 21. Metridia 9:39 pm 05/5/2012

    Darren- I’d be interested to hear about how one might explain biogeographical overlap between early Cenozoic animals of Europe and North America. For example, we have prosimians of a similar grade distributed across Europe and North America, and now members of an apparently Cenozoic-restricted clade of lizards; however, Eurotamandua is the anteater that wasn’t, and am not sure if there are other convergences that appear to be dispersal events. How were these things dispersing? If they appear in Europe does that imply they also ranged across all of Eurasia and across the Bering land bridge? Some of these animals don’t seem very polar; but even for the trans-South-Atlantic monkey dispersal that we know had to have happened, it’s not clear to me (or anyone?) how that happened since Africa and South America were already far apart by the Cenozoic.

    Link to this
  22. 22. Heteromeles 10:13 pm 05/5/2012

    I’m not Darren, but I spent a bit of time looking at the split between Greenland and Europe during the Paleocene for a project I was working on.

    The thing to remember is that Europe in the modern sense didn’t exist in the Paleocene. It was a varying archipelago of islands (number varies depending on the time we’re talking about), separated by water from Russia and the rest of Asia. It was closer to Greenland than Eurasia. To the west of the European archipelago was the rapidly opening Atlantic ocean, and to the south was the Tethys sea.

    Here’s the deal: it’s not clear (to me, at least) when the north Atlantic finished opening up into the Arctic Ocean, or whether it went through an open/close/open routine during the Cretaceous and early Cenozoic. There’s also a roving hotspot in this mix that wandered west to east across Greenland and finally settled where Iceland is now. There’s also the possibility that something (perhaps the hotspot) burned a large deposit of hydrocarbons in the North Atlantic Rift system, and helped precipitate the Paleocene/Eocene Thermal Maximum (PETM).

    What this implies (but does not prove) is that there was most likely a land bridge from North America, across Greenland, to Europe. This hypothetical land bridge would have been very temporary, and formed by flood basalts from the hotspot that today sits under Iceland. I haven’t seen this explicitly mentioned in the geological literature, because it depends on lands that would have been eroded away to form the present connection between the Atlantic and the Arctic. However, it seems implicit in a number of paleomaps I’ve seen.

    From my perspective of having done a bit of reading on Paleocene geology of the north Atlantic, the issue is that the people talking about the Atlantic geology are mostly petroleum geologists interested in the North Sea and other hydrocarbon resources off Greenland and Norway, while the Arctic Sea geologists seemed more interested in figuring out the Arctic geology for geopolitical reasons related to the Cold War. Any land bridge would have cut right across both domains, and if someone’s studying it, I haven’t seen their papers yet.

    Hope this helps. If you’re trying to bridge from North America to Europe in the Paleocene, I’d suggest focusing on Greenland, not Siberia.

    Link to this
  23. 23. Dartian 2:17 am 05/6/2012

    Metridia: What Heteromeles said; the Early Paleogene biotic interchange between North America and Europe mostly took place across the (present-day) northern Atlantic.

    we have prosimians of a similar grade distributed across Europe and North America, and now members of an apparently Cenozoic-restricted clade of lizards

    There are actually quite a lot of terrestrial vertebrate taxa that were common to North America and Europe in the Paleocene and Eocene. Various early perissodactyls, ‘condylarthrs’, flightless gastornithid (a.k.a. ‘diatrymid’) birds, and semi-terrestrial pristichampsid crocodiles, just to take a few examples.

    Link to this
  24. 24. BrianL 5:25 am 05/6/2012

    @Metridia:
    What’s also important to realise about Europe being an archipelago in the Paleocene/Eocene is that it was hardly uniform biologically and that separation from Africa and Asia was not absolute, even for flightless taxa. Certainly there seems to have been a western province and an eastern province, at least. The west is (as usual) better known.
    Whereas the western province seems to have shared many of its taxa with North America (including the likes of *Eurotamandua* if it’s indeed a palaeanodont or close to them), the eastern fauna was somewhat different and seems to have included non-arsinoitherid embrithopods (phenacolophids, if I’m not mistaken) that were simply absent in the west, as far as is known. Also, ‘anthracotheres’ probably arrived in the archipelago from Asia and managed to push into the western archipelago as well as into Africa as did protocetids. Phenacolophids and anthracobunids (Asian relatives of proboscideans and possibly ancestral to desmostylians)might well have gone the opposite way: from Africa, via eastern Europe to Asia. They would presumably have done so via island hopping. Given that their closest living relatives are hippos (for anthracotheres) and sirenians and proboscideans (for the others) and these are aquatic or known to be proficient swimmers and island colonisers, they might well have done so by swimming rather than using landbridges.
    On the other hand, the western archipelago may well have been connected (either via islands or a direct passage) to northern Africa in the Paleocene. Rodents, primates and metatherians would seem to have gone south, while hyaenodonts and hyopsodontids (if indeed stem-macroscelideans) would have gone north. It’s hardly inconceivable that rodents island-hopped or rafted and entered Africa the ‘anthracotherian’ way though.

    Link to this
  25. 25. David Marjanović 7:23 am 05/6/2012

    Phenacolophids are embrithopods now? Reference, please!

    There’s also a roving hotspot in this mix that wandered west to east across Greenland and finally settled where Iceland is now.

    Its flood basalt eruptions formed the Thule landbridge: Greenland-Iceland-Rockall-Scotland. It’s mentioned a lot in discussions of Eocene biogeography, and I’ve seen paleomaps that show it.

    There’s also the possibility that something (perhaps the hotspot) burned a large deposit of hydrocarbons in the North Atlantic Rift system, and helped precipitate the Paleocene/Eocene Thermal Maximum (PETM).

    Huh. Interesting.

    There are actually quite a lot of terrestrial vertebrate taxa that were common to North America and Europe in the Paleocene and Eocene.

    Especially in the Eocene! Before the PETM, it seems that the Thule landbridge – or perhaps rather the connection between Ellesmere Island and Greenland – was too cool for some taxa.

    Link to this
  26. 26. BrianL 10:47 am 05/6/2012

    @David:
    The idea that phenacolophids were related to arsinoitheres is not exactly new; phenacolophids have been proposed as allies to them repeatedly. It’s mentioned in ‘Cenozoic Mammals of Africa’ (Sanders and Werdelin) and if I’m not mistaken it’s mentioned in ‘The rise of placental mammals’ (Archibald and Rose) too. It’s also one of those obscure theories that have a web presence. I actually thought the idea was a pretty standard one and generally considered valid, to be honest. I could perhaps have expected you would point out the absence of words like ‘maybe’, ‘possible’ or ‘thought by some to be’, though.

    Link to this
  27. 27. Heteromeles 10:59 am 05/6/2012

    @David: Yes, I’ve seen mention of the land bridge. Based on the limited reading of the geology literature I did, it’s not clear to me that said land bridge actually followed the route you suggested, although (as you noted) it makes sense on biogeographic grounds.

    The basic issue is that Greenland rifted apart from Scandanavia, the North Sea started to form (a separate split) and stalled, then (in the Paleocene) the western side of Scotland formed, along with Iceland, but under two different volcanic regimes. It’s this last bit that gets messy, because with all the splitting and vulcanism (think East African Rift zone, only wider), it’s hard for me to tell what was connected when and where.

    If I understand it properly, the Atlantic rift connected to the Arctic Ocean, lost that connection (due to the Thule land bridge, which was presumably due to volcanic land formation) then opened it again as continued rifting and erosion disassembled the bridge.

    The key question is where the land bridge touched land. It could be through Iceland and Scotland (although that both were forming at this point), but looking at the map, it could also be through Jan Mayen Island and Norway, or even potentially earlier through Svalbard. Unfortunately, there’s been a fair amount of subsequent rifting, sedimentation, and glacial erosion in the area since to confuse the evidence.

    Presumably geologists are much less confused than I am about how the Arctic Ocean formed.

    As for the European Paleocene archipelago, sea levels varied a fair amount during the Paleocene (due to plate tectonics, not climate), so I’m pretty sure the boundaries of the islands varied too, until they joined up as a continent a bit later in the Cenozoic.

    Link to this
  28. 28. naishd 12:51 pm 05/6/2012

    Hi – no time to comment at length here, but, historically, two proposed routes have been used to explain how Paleogene taxa moved between Europe and North America. The ‘de Geer route’ suggests movement in the far north, via northern Greenland and involving Fennoscandia. The ‘Thulean route’ suggests movement across submerged islands in the direction of southern Greenland and the UK. There were certainly enough warm spells in the Paleocene and Eocene to allow even small ectotherms to use one or both routes. A paper last year discussed how giant formiciine ants must have done exactly this.

    Darren

    Link to this
  29. 29. Andreas Johansson 1:06 pm 05/6/2012

    Dartian wrote:
    Various early perissodactyls, ‘condylarthrs’, flightless gastornithid (a.k.a. ‘diatrymid’) birds, and semi-terrestrial pristichampsid crocodiles

    My eyes made a quick one here and read “flightless pristichampsid crocodiles”. Which should be unremarkable but …

    Link to this
  30. 30. llewelly 9:57 pm 05/6/2012

    “My eyes made a quick one here and read “flightless pristichampsid crocodiles”. Which should be unremarkable but …”

    It is rumored that a certain noted paleontologist (who shall remain nameless) spent many years investigating the possibility that crocodilians were descended from pterosaurs. Eventually, after many rejected papers, he was forced to conclude the theory would never fly.

    Link to this
  31. 31. David Marjanović 2:21 pm 05/7/2012

    I actually thought the idea was a pretty standard one and generally considered valid, to be honest. I could perhaps have expected you would point out the absence of words like ‘maybe’, ‘possible’ or ‘thought by some to be’, though.

    I have no reason to doubt the idea a priori, I had just never encountered it before. I’m not familiar with phenacolophids beyond their being “condylarths” *barf*.

    From what you say, though, it seems like it’s just another old speculation that has never been tested by phylogenetic analysis…

    Eventually, after many rejected papers, he was forced to conclude the theory would never fly.

    *cringe*

    Link to this
  32. 32. Metridia 5:43 pm 05/7/2012

    I can contribute this http://www.pnas.org/content/102/6/1821/F8.expansion.html which shows the Thulean/de Geer routes nicely

    Link to this
  33. 33. John Scanlon FCD 11:12 am 05/8/2012

    For lulz, I quote the following from Garth Underwood’s 1957 review of McDowell and Bogert (1954):

    “Bogert himself has apparently had second thoughts on some of the work for Bogert and Martin del Campo (1956:209) state “…McDowell and Bogert (1954) have managed to obfuscate the relationships of virtually all the Squamata”. This is unduly harsh, I would put the fraction at about half of the Squamata.”

    I’ve been reminded of this frequently by developments in squamate phylogenetics over the last six years or so, that seem to represent a new cycle of obfuscation. In particular, the purely molecular-based Toxicofera hypotheses with basal polytomy in which snakes are no more closely related to anguimorphs than to iguanians; and the snakes-as-scincomorphs hypothesis, which was so obviously wrong every other time it was proposed, but now requires someone (with a lot of time) to completely reanalyse Conrad’s (2008) character set to see how much of the signal is just superficial convergence.

    Certainly the molecular results have overturned the morphology-based pattern where snakes appeared to be nested within Varanoidea, but are consistent with Platynota (the goanna-monster clade) and Pythonomorpha (the snake-mosasaur clade) being successive sister groups to Anguoidea (or whatever we call the ‘other crown anguimorph’ clade). If that’s true, the varanoid-snake LCA is also ancestral to all those slightly-less-awesome skinky-looking anguids, while at the same time being only a node away from the base of Iguania. Surprising, but important if we’re interested in understanding the origin of modern diversity and adaptations (which DNA alone cannot address).

    Link to this
  34. 34. John Scanlon FCD 11:27 am 05/8/2012

    And while on goannas and such, today I saw a photo of an adult Varanus giganteus (Perentie) in the act of swallowing a V. panoptes that’s not a whole lot smaller than itself (these are two of the three biggest extant lizards in Australia). I’ve sent a copy to Darren and hope he can share it here. Must find out if there’s more than one photo…

    Link to this
  35. 35. David Marjanović 6:32 pm 05/8/2012

    the purely molecular-based Toxicofera hypotheses with basal polytomy in which snakes are no more closely related to anguimorphs than to iguanians;

    Well, the original papers did suggest morphological synapomorphies (the venom glands) and of course toxicological ones. Have they held up?

    and the snakes-as-scincomorphs hypothesis, which was so obviously wrong every other time it was proposed, but now requires someone (with a lot of time) to completely reanalyse Conrad’s (2008) character set to see how much of the signal is just superficial convergence.

    Reanalyse? Ha. Just throw another hundred characters at that matrix. For the huge number of taxa that it has, it has way too few characters. Below 3 times as many characters as taxa I wouldn’t even publish an original morphological matrix.

    …I do think Conrad didn’t order any characters, though. (Too lazy to look it up at this time of the night.) If so, that’s bad.

    Link to this
  36. 36. Jurassosaurus 4:07 pm 05/10/2012

    I had a chance to talk with Jacques Gauthier a couple of weeks back and he suggested keeping an eye on the next Bulletin of the Yale Peabody Museum. It took six years, but it looks like Townsend et al’s ass-backward matrix on squamate phylogeny is finally going to get the morphological smackdown it had coming. The bulletin was supposed to be out by now, so keep your eyes peeled.

    Link to this
  37. 37. David Marjanović 4:53 am 05/11/2012

    Will be interesting to see how they do a morphological smackdown of a molecular matrix…

    Link to this
  38. 38. Michał 12:17 pm 05/23/2012

    That study does seem to be out:

    http://www.bioone.org/doi/abs/10.3374/014.053.0101

    Link to this
  39. 39. naishd 12:20 pm 05/23/2012

    Wow – 308 pages. I look forward to seeing and reading it, thanks for the heads-up.

    Darren

    Link to this
  40. 40. David Marjanović 11:40 am 01/20/2014

    Belatedly: the Asian gastornithid Zhongyuanornis should be mentioned.

    Link to this

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

More from Scientific American

Scientific American Back To School

Back to School Sale!

12 Digital Issues + 4 Years of Archive Access just $19.99

Order Now >

X

Email this Article

X