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The Squamozoic actually happened (kind of): giant herbivorous lizards in the Paleogene

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


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A (hypothetical) scene from the (hypothetical) Squamozoic. Image by Darren Naish, colouring by Tim Morris.

In the hypothetical alternative geological epoch known as the Squamozoic, giant iguanian lizards known as uromastyxians dominate big-bodied herbivore niches across Africa, the Middle East and Asia. Short-headed, stout-limbed and often decorated with long, branched tail spikes, the uromastyxians evolved from the (real world) Uromastyx species, variously known as spiny-tailed lizards, mastigures or dabbs (and highly popular in the pet trade). If you haven’t heard of the Squamozoic before and don’t know what it is, go here. It’s a frivolous exercise in speculative zoology. Anyway, it’s curious and sometimes gratifying when speculation is mirrored by fact, and today we get to see just such an event in action. For you see, those big, Squamozoic uromastyxians are real: they really did evolve, but in our own world, not in an imaginary parallel timeline…

As revealed today in Proceedings of the Royal Society B, Jason Head of the University of Nebraska-Lincoln and a team of his colleagues have discovered the fossils of a remarkable new iguanian lizard that they’ve named Barbaturex morrisoni. Good news: the paper is open access! Acrodont teeth (= teeth that are fused to the underlying jaw bones) and other features demonstrate without doubt that Barbaturex is a member of the iguanian clade Acrodonta.

Egyptian spiny-tailed lizard (Uromastyx aegyptius) in captivity; photo by Adrian Pingstone, in the public domain.

More specifically, Head et al. (2013) find Barbaturex to be most closely related to the spiny-tailed Uromastyx species, with Leiolepis being the next closest relative. Their favoured cladogram shows this (Leiolepis + (Barbaturex + Uromastyx)) clade as the sister-group to the more diverse iguanian assemblage that includes chameleons, sailfin lizards, the Australasian dragons, and the agamas and their kin (Head et al. 2013).

Based on its dentition (it has tightly occluding, triangular teeth that would have performed a shearing bite in life), we can be confident that Barbaturex was herbivorous (though the possibility of opportunistic animalivory can’t be ruled out). This is consistent both with its large size (herbivory is more efficient at large body size) and its phylogenetic relationships, since it’s surrounded in the phylogeny by herbivorous and omnivorous taxa (Head et al. 2013).

Life restoration of Barbaturex morrisoni, by Angie Fox, University of Nebraska-Lincoln.

Incidentally, the name is pretty neat. Barbaturex means ‘bearded king’, with the ‘bearded’ bit referring to the presence of a series of sagittally aligned knobs that are spaced along the ventral surface of the mandible (in life, did these anchor some sort of fleshy display structure or structures?). The species name honours Jim Morrison, “vocalist and lizard king” (Head et al. 2013, p. 2 of preprint). Awesome.

Why Barbaturex is remarkable

Barbaturex is from the middle Eocene Pondaung Formation of Myanmar, a geological unit well known for its early primates and numerous other placental mammals (e.g., Ducrocq et al. 2000, Holroyd & Ciochon 2000, Marivaux et al. 2003, 2005, Jaeger et al. 2004, Remy et al. 2005, Holroyd et al. 2006, Métais et al. 2007). Important fossil turtles, snakes and members of other groups are known from the Pondaung Formation as well.

What makes Barbaturex remarkable is its size. Though the fossils are fragmentary (virtually all are incomplete jaw segments), they show that this lizard was about 1 m long in SVL (= snout to vent length). We don’t have a complete skeleton, nor indeed any part of the tail, so a complete length can only be guessed at. Seeing as some of the related iguanians are comparatively short-tailed, Barbaturex might ‘only’ have been 1.4 m long or less, but it was more likely rather longer (1.8-2 m long or so in total).

Barbaturex (in green) compared with Pondaung Formation mammals (ungulates in black, predators in grey) in ranked body mass. Note that the lizard is in the 'middle' of the size range. From Head et al. (2013).

And what makes Barbaturex doubly remarkable is that it lived alongside a diverse assemblage of herbivorous, omnivorous and carnivorous mammals where – get this – it was one of the largest members of the fauna. Head et al. (2013) estimate that Barbaturex had a mean body mass of 26.7 kg (the estimated range is from 18.9 to 36.9 kg), in which case it was larger than the smaller Pondaung perissodactyls and artiodactyls, and somewhere in the middle of the known size range for all Pondaung ungulates. It was also larger than, or similar in size to, most of the predatory mammals from the assemblage (Head et al. 2013).

Convention would have it that big, terrestrial reptilian herbivores can’t exist alongside ungulates and other large mammals since predation and competition essentially prevents their evolution. Yet here we see a big-bodied herbivorous lizard living alongside a diverse array of contemporaneous ungulates and carnivorous mammals. This pattern is fundamentally unlike that seen in modern ecosystems where even the largest herbivorous lizards are substantially smaller than even the smallest ungulates (Head et al. 2013).

Why so big?

Awesome lifesized Titanoboa model, photographed when on display in New York (humans for scale). Image by jinkinpark.

How and why did iguanians get to be so large in a place and time that supposedly ‘belonged’ to mammals? Head et al. (2013) favour the idea that the elevated global temperatures of the middle Eocene facilitated the evolution of Barbaturex, both by making it easier for a poikilothermic terrestrial tetrapod to grow and operate at optimal physiological capability, and by encouraging high productivity of the sort of vegetation it would have relied on as a food source. Fans of fossil squamates will of course know that Head and colleagues previously argued that the exceptionally high global temperature of the Paleogene similarly facilitated the evolution of the stupendous boid snake Titanoboa from Colombia (Head et al. 2009) [adjacent photo by jinkinpark].

This all sounds logical, and it’s pretty well supported by what we know about climatic conditions and reptile diversity across the Cenozoic. However, it’s also worth taking seriously the possibility that animals like boas and iguanians simply do have the potential to evolve large size, and to potentially compete against similar-sized mammals and other animals, when opportunity allows (and those ‘opportunities’ might be reduced predation, optimal foraging time or a habitat that promotes the evolution of gigantism).

Either way, the very existence of this intriguing giant iguanian is fascinating and let’s hope that more complete remains are discovered in future.

Iguanians of several lineages have been discussed on Tet Zoo before. See…

Refs – -

Ducrocq, S., Soe, A. N., Auung, A. K., Benammi, M., Bo, B., Chaimanee, Y., Tun, T., Thein, T. & Jaeger, J.-J. 2000. A new anthracotheriid artiodactyl from Myanmar, and the relative ages of the Eocene anthropoid primate-bearing localities of Thailand (Krabi) and Myanmar (Pondaung). Journal of Vertebrate Paleontology 20, 755-760.

Head, J. J., Bloch, J. I., Hastings, A. K., Bourque, J. R., Cadena, E. A., Herrera, F. A., Polly, P. D. & Jaramillo, C. A. 2009. Giant boid snake from the Palaeocene neotropics reveals hotter past equatorial temperatures Nature 457, 715-717.

- ., Gunnell, G. F., Holroyd, P. A., Hutchinson, J. H. & Ciochon, R. L. 2013. Giant lizards occupied herbivorous mammalian ecospace during the paleogene greenhouse in SouthEast Asia. Proceedings of the Royal Society B 20130665 http://dx.doi.org/10.1098/rspb.2013.0665

Holroyd, P. A. & Ciochon, R. L. 2000. Bunobrontops savagei: a new genus and species of brontotheriid perissodactyl from the Eocene Pondaung fauna of Myanmar. Journal of Vertebrate Paleontology 20, 408-410.

- ., Tsubamoto, T., Egi, N., Ciochon, R. L., Takai, M., Tun, S. T., Sein, C. & Gunnell, G. F. 2006. A rhinocerotoid perissodactyl from the late middle Eocene Pondaung Formation, Myanmar. Journal of Vertebrate Paleontology 26, 491-494.

Jaeger, J.-J., Chaimanee, Y., Tafforeau, P., Ducrocq, S., Soe, A. N., Marivaux, L., Sudre, J., Tun, S. T., Htoon, W. & Marandat, B. 2004. Systematics and paleobiology of the anthropoid primate Pondaungia from the late Middle Eocene of Myanmar. C. R. Palevol 3, 243-255.

Marivaux, L., Chaimanee, Y., Ducrocq, S., Marandat, B., Sudre, J., Naing Soe, A., Thura Tan, S., Htoon, W. & Jaeger, J.-J. 2003. The anthropoid status of a primate from the late middle Eocene Pondaung Formation (Central Myanmar): tarsal evidence. Proceedings of the National Academy of Science 100, 13173-13178.

- ., Ducrocq, S., Jaeger, J.-J., Marandat, B., Sudre, J., Chaimanee, Y., Thura Tan, S., Htoon, W. & Naing Soe, A. 2005. New remains of Pondaungimys anomaluropsis (Rodentia, Anomaluroidae) from the latest middle Eocene Pondaung Formation of Central Myanmar. Journal of Vertebrate Paleontology 25, 214-227.

Métais, G., Soe, A. N., Marivaux, L. & Beard, K. C. 2007. Artiodactyls from the Pondaung Formation (Myanmar): new data and reevaluation of the South Asian Faunal Province during the Middle Eocene. Naturwissenschaften 94, 759-768.

Remy, J. A., Jaeger, J.-J., Chaimanee, Y., Soe, U A. N., Mairvaux, L., Sudre, J., Tun, S. T., Marandat, B. & Dewaele, E. 2005. A new chalicothere from the Pondaung Formation (late Middle Eocene of Myanmar). C. R. Palevol 4, 341-349.

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. Halbred 7:59 pm 06/4/2013

    I’m assuming that this article was written long before those croc skulls were posted because it would be downright EVIL of you to post a lengthy new blog post instead of a short one identifying those crocs (which would have taken five minutes). :-P

    Link to this
  2. 2. Jerzy v. 3.0. 8:38 pm 06/4/2013

    Cool, although lizards belong to the biggest herbivores in Galapagos and some Caribbean islands.

    BTW – any info on how wildlife might look like if Earth was much warmer than today? I am toying with an post-climate change Earth where average temperatures are 40-70oC plus usually wet climate (think rainforest not desert). Insights from Eocene thermal optimum etc welcome.

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  3. 3. Yodelling Cyclist 8:39 pm 06/4/2013

    Could gut fermentation be relevant here? Could a poikilothermic animal evolve (in a benign environment) to a point where heat released from plant digestion was sufficient to keep it permanently warm and active, while competing mammals struggled to dump heat as they scaled up?

    Such an environment would, I guess have to be warm enough to make mammals struggle, and wet enough to have lush vegetation. Which leaves the question: why not in the modern Amazon? Also, in this scenario, one route to being a big mammal is something like a hippo: using the water to stay cool. Does this describe the larger mammal herbivores from this fauna?

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  4. 4. Yodelling Cyclist 9:03 pm 06/4/2013

    #2: That’s kind of the point: herbivorous poikilotherms don’t compete well with mammals. Without the mammals (i.e. on islands), poikiloterms can dominate. Hence giant tortoises, for example.

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  5. 5. David Marjanović 9:19 pm 06/4/2013

    Whoa. I really didn’t expect that kind of animal to exist.

    Barbaturex means ‘bearded king’

    It would, if it were Barbatorex. *sigh* I guess the sighing over Cristatusaurus wasn’t loud enough!

    where average temperatures are 40-70 [°C]

    Whoa, whoa. 70?!? When the global climate warms, the tropics stay almost as they are, and the poles heat up. The rainforest zone simply expands (unless you reach Cenomanian temperatures).

    Could gut fermentation be relevant here?

    Not for the babies.

    using the water to stay cool. Does this describe the larger mammal herbivores from this fauna?

    Good question.

    Link to this
  6. 6. CS Shelton 12:21 am 06/5/2013

    >>”Could gut fermentation be relevant here?”
    –>>”Not for the babies.”

    Would you mind elaborating on that? By the way, do you know if there are any extant non-mammalian gut fermenters we could compare to?

    Link to this
  7. 7. ectodysplasin 1:08 am 06/5/2013

    Most juvenile herbivorous lizards take animal protein until they reach subadulthood, at which point they start switching over to a diet richer in plants (but still generally omnivorous). This is the case for herbivorous varanids, herbivorous agamids, herbivorous teiids, and most herbivorous iguanids. A few species of iguanid buck that trend, but they still often specialize in higher protein plant foods early in ontogeny and then switch to a more folivorous diet later as they approach adulthood.

    Link to this
  8. 8. ectodysplasin 1:12 am 06/5/2013

    @YC:

    Could gut fermentation be relevant here?

    Uromastyx employs hindgut fermentation, so that’s not unlikely.

    Link to this
  9. 9. Heteromeles 1:18 am 06/5/2013

    It’s worth while looking at the braincases of Eocene and (especially) Paleocene mammals. They’re tiny compared to modern species. The only things comparable are the tree kangaroo skulls in Flannery’s Mammals of New Guinea (if you have that in your library, and not a fossil cranium to hand).

    While mammals are endothermic, a small-brained mammal in a hothouse has lost two potential mammalian advantages over a reptile. It’s therefore less surprising that there would be giant reptiles in such an environment.

    The other interesting point is that, if we go truly nuts with this little mass extinction and global warming thing, we’ll have something that resembles the paleogene rather more than I’m comfortable with. Yes, the surviving rats and raccoons will be big-brained, but the Florida pythons have gotten pretty good at hunting them regardless. Happy fun times.

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  10. 10. vdinets 1:53 am 06/5/2013

    It seems to me that the mystery we should explain is just the opposite: How can mammals compete with large herbivorous reptiles? Plant matter has low nutritional value, so it doesn’t make good fuel for calories-intensive endotermic animals. Reptiles should be much better at surviving on this diet, just as they are better at being high-patience ambush hunters.

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  11. 11. John Scanlon FCD 3:47 am 06/5/2013

    I was going to say what David M said about the barbaric construction of the name – and after I gave Jason a ticking off for ‘Varanus prisca’!

    Interesting that Australian lizards have not gone in for the large-herbivore thing; our varanids are all carnivores as far as I know, while extant bluetongues and the large agamids are all at least partly so. Maybe if we had fossils from the Eocene of north Queensland, it might have been warm enough for something at least as big as Lapitiguana. And we don’t know what Aethesia frangens or Tiliqua laticephala were eating (or even if they were parts of the same animal).

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  12. 12. ectodysplasin 3:48 am 06/5/2013

    @vdinets

    It seems to me that the mystery we should explain is just the opposite: How can mammals compete with large herbivorous reptiles? Plant matter has low nutritional value, so it doesn’t make good fuel for calories-intensive endotermic animals.

    Yes, but juvenile herbivorous mammals don’t eat plants. They eat milk.

    Link to this
  13. 13. John Scanlon FCD 4:22 am 06/5/2013

    The paper is on the Proceedings B site now, here.

    Link to this
  14. 14. naishd 6:21 am 06/5/2013

    Thanks for comments. With reference to comment # 1… sorry, I honestly have not had time to deal with that, I’ll try and do it soon.

    The embargo for the new paper broke at midnight (BST) last night (June 5th), but the paper wasn’t released online for a few hours. Evidently, it’s out there now, so I’ve now added its citation to the article above. Great that it’s open access: well done, Jason and colleagues.

    Oh — John (comment # 11), re: Varanus prisca, it should be priscus, right?

    Darren

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  15. 15. WKatz 6:24 am 06/5/2013

    “It would, if it were Barbatorex. *sigh* I guess the sighing over Cristatusaurus wasn’t loud enough!”

    And Sciurumimus, and Bellubrunnus, etc., etc. There’s an ms name for a new ceratopsian out there called “Nasutuceratops titusi”, I just pray it gets fixed before publication.

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  16. 16. vdinets 10:57 am 06/5/2013

    Halbred (#1): Darren never said he knew anything about those skulls. Perhaps he doesn’t.

    ectodysplasin (#12): that doesn’t explain much. Adult voles of some species are smaller than juvenile iguanas are at the time when they switch to herbivory. So it is easily possible to grow to sufficient size on insect diet, then switch to herbivory. (And countless insects are herbivorous from hatching, when they are less than 1 mm long).

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  17. 17. Gigantala 11:13 am 06/5/2013

    I think we’re overlooking one VERY important fact: giant ectothermic herbivores did exist in the Cenozoic.

    They’re called “tortoises” or “testudinoids”.

    In the late Cenozoic, giant turtles dominated tropical and subtropical climates of the world over, even reaching giant sizes like Colossochelys. Only with the anthropogenic extinctions did giant ectothermic herbivores disappear.

    So, the question might be less to do with competing with mammals and more competition with turtles. The Galapagos are an exception, but then again the Caribbean had both giant iguanas and rodents and sloths, so islands are probably unique exceptions.

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  18. 18. Yodelling Cyclist 1:50 pm 06/5/2013

    With regards my gut fermentation suggestion: I was actually thinking that this is what causes the lizard to be so high in the mass rankings by preventing the mammals from getting large, rather than encouraging the lizard to get big (although living in a hot house presumably helped at that end, too).

    Colossochelys is a very good point, but maybe a slightly misleading one: it belonged to a fairly chunky fauna, so it would not be as high up in the relative mass rankings. One could imagine that as the average mass of herbivores trends upwards in a fauna, the heaviest representatives of all orders get larger – I am only speculating. Also testudinoids do have the interesting shell, which must help in terms of protection and permitting species to grow large in the face of mammal predation, so one freak turtle may well be just an exception – a poikilotherm that is so well armoured it can weather the mammals, and maybe able to out compete mammalian herbivores in the event of drought.

    I know very little (that statement stands alone quite well…) about turtles in the Miocene – but “dominated”? Really?

    Just googling all the herbivores from the paper that were larger than Barbaturex: only the top three Indricotheres are seem to be non-aquatic. Don’t know how good those remains are though. Maybe they also liked a swim. Bet they needed a lot of water though.

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  19. 19. ectodysplasin 1:54 pm 06/5/2013

    @vdinets;

    ectodysplasin (#12): that doesn’t explain much. Adult voles of some species are smaller than juvenile iguanas are at the time when they switch to herbivory. So it is easily possible to grow to sufficient size on insect diet, then switch to herbivory. (And countless insects are herbivorous from hatching, when they are less than 1 mm long).

    Just because an animal is an herbivore does not mean that it needs to necessarily be large, but for an animal to be large AND be an herbivore is really quite difficult. The reason why is that growth is difficult for herbivores. Someone mentioned tortoises, but it’s worth pointing out that tortoises take decades to reach adult size, and mass-wise they’re far smaller than many herbivorous mammals. Cattle are large enough to slaughter within 2 years.

    Evolutionarily, an animal that takes decades to reach a size at which it can attain reproductive maturity is not going to be able to outcompete animals that are able to reach that same size within a year or two….or it’s going to simply reach reproductive maturity at a small size and never bother to grow particularly large. Iguanas, for example, reach reproductive maturity at around a year and a half, but they’re still relatively small at that age (SVL ~ 30 cm, mass ~ 1-2 kg), and they never reach a size comparable to Barbaturex.

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  20. 20. Crown House 3:46 pm 06/5/2013

    love this blog, but *cough* mr. naish, sir, *cough* http://www.youtube.com/watch?v=x01ZVRPxAhM

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  21. 21. Gigantala 3:57 pm 06/5/2013

    @Yodelling Cyclist: From the Miocene onwards Africa, North America, South America and Eurasia had several taxa of giant tortoises, in an otherwise mammal-dominated fauna, their disappearence coinciding with hominid expansion and development.

    In the Pliocene of Africa, for instance, there is “Geochelone” laetoliensis and Stigmochelys brachygularis, in the midst of felines, bovids, elephants, primates, et cetera.

    Link to this
  22. 22. vdinets 6:43 pm 06/5/2013

    Ectodysplasin: didn’t sauropods grow like bamboo shoots? There were some crazy estimates floating around.

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  23. 23. Yodelling Cyclist 7:52 pm 06/5/2013

    @Gigantala: fascinating. Thank you for the information.

    I’m wondering about few things: how do the chelonians stack up in terms of their relative mass rankings (are they amongst the largest animals in the environment, or are there many larger mammals, or are these amongst the largest herbivores as for Barbaturex), is this something unique to chelonians (is it the shell that is permitting this), and are these dry habitats where the aridity is pushing the mammals out (I’m assuming that none of these giant tortoises colonised temperate ecosystems)?

    Really amazed by the giant continental tortoises…

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  24. 24. Yodelling Cyclist 8:26 pm 06/5/2013

    @vdinets: Sauropods may as well be aliens. They’re just too weird. I’m not sure if we can really use them for a comparison with, well, anything else, due to the fact that there are too many fundamental known unknowns about their biology.

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  25. 25. Gigantala 8:37 pm 06/5/2013

    @Yodelling Cyclist: Based on the general bosy mass tendencies, I’d say “medium sized”, with Colossochelys and a few others being on the same ranks as the largest modern mammals, though obviously still smaller than the largest contemporary mammals.

    I’m not sure if any studies have been determined about the preffered ranges of continental giant tortoises, but most seem to have been flexible habitat wise. The aforementioned african species co-existed with miombo fauna, while Colossochelys’ range extended well into dense tropical rainforests and possibly temperate woodlands.

    Link to this
  26. 26. Yodelling Cyclist 9:32 pm 06/5/2013

    Wow.

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  27. 27. ectodysplasin 9:45 pm 06/5/2013

    @vdinets:

    Ectodysplasin: didn’t sauropods grow like bamboo shoots? There were some crazy estimates floating around.

    Yes. Yes they did.

    Periodically it’s hypothesized in the literature that sauropods may have produced crop milk of some sort or another. This sounds ridiculous at first glance, but there’s a wide assortment of reasons why this might be less crazy than it sounds.

    But yes, how herbivorous dinosaurs got so big is an underrecognized problem (in comparison with the more general “how did dinosaurs get so big” question) and one that unfortunately requires reference to behavior and visceral soft tissue, and is thus probably out of the reach of paleontology to answer.

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  28. 28. LeeB 1 11:31 pm 06/5/2013

    Large tortoises were common on the mainland in tropical regions until the Pliocene, then disappear when hominids evolved.
    But even in the Pleistocene you could find large Hesperotestudo in North America; Chelonoidis in the Caribbean, South America and Galapagos; Aldabrachelys on Madagascar and the Seychelles; Cylindraspis on the Mascarene Islands; Ninjemys and Meiolania in Australia, and Meiolania or related forms on New Caledonia, Lord Howe Island, Vanuatu and Fiji.
    Some of the South American Chelonoidis apparently were about twice the size of a living Galapagos tortoise.
    Because these different tortoises were not closely related they had evolved gigantism many times so it must have been a favourable ecological niche for them.
    Incidentally some of the tortoises in Africa can still reach quite large sizes occasionally, probably hunting pressure by humans is all that stops them doing so more often.
    If people were to stop hunting them they would probably re-evolve giant forms again.

    LeeB.

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  29. 29. Jurassosaurus 11:37 pm 06/5/2013

    Convention would have it that big, terrestrial reptilian herbivores can’t exist alongside ungulates and other large mammals since predation and competition essentially prevents their evolution.

    Convention brought about by (placental) mammal chauvinism and brought into paleo by Bakker in the 70′s. It’s always been a just-so story with no real empirical backing (kinda like the placentals vs. marsupials hypothesis). It’s great to see Barbaturex morrisoni helping challenge the party line. It gets to share the spotlight with meiolaniids, Colossochelys (if it’s still called that), and a whole swath of other giant tortoises that routinely got large (or at least stayed large) in the face of mammalian competition / predation. Heck, extant Geochelone sulcata and Stygmochelys pardalis are still some of the largest fauna in their respective habitats.

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  30. 30. vdinets 7:37 am 06/6/2013

    ectodysplasin: OK, let’s test the theory that attaining competitive growth rate is a major problem for herbivores. Is there a substantial difference in growth rate between, say, herbivorous iguanas and carnivorous tejids? The theory predicts that there should be such a difference.

    Link to this
  31. 31. vdinets 7:38 am 06/6/2013

    of course, the data should be for wild animals. captive carnivores probably grow a lot faster than wild ones.

    Link to this
  32. 32. Jurassosaurus 9:43 am 06/6/2013

    Growth rate data on reptiles is extremely poor, especially wild growth rate. Herpetologists seem overly reliant on measuring SVL so what little growth charts that are out there tend to show only length per year. The best data on growth rate would probably be from the herpetoculture community. It has the caveat that it is coming from captive animals, but that’s not necessarily bad. If herbivory imparts an actual limit on growth rate then it should appear here just as readily as in the wild.

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  33. 33. vdinets 10:05 am 06/6/2013

    Jurassosaurus: yes, but the difference between growth rates in captivity and in the wild should be much more pronounced for carnivores, because they are the ones saving more energy and escaping food shortages in captivity. So among captive animals, carnivores probably appear faster-growing than herbivores, but this cannot be extrapolated to wild animals.

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  34. 34. ectodysplasin 10:12 am 06/6/2013

    Either way, you’re going to need to control for phylogeny, which means a LOT of data collection.

    There’s a paper in there somewhere I’m sure, but this is pretty far afield from my research interests.

    Link to this
  35. 35. ectodysplasin 10:16 am 06/6/2013

    This is, by the way, not something that’s only of interest for dinosaurs. It’s also relevant to questions like “why are no amphibians besides tadpoles herbivorous” and “why do we see anomalous gain and loss of rapid fibrolamellar bone deposition within the stem lineages of both archosaurs and mammals”

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  36. 36. ectodysplasin 10:27 am 06/6/2013

    There are, however, some very suggestive experimental manipulations such as this one:

    Bouchard, S. S., & Bjorndal, K. A. (2006). Ontogenetic diet shifts and digestive constraints in the omnivorous freshwater turtle Trachemys scripta. Physiological and Biochemical Zoology, 79(1), 150-158.

    Link to this
  37. 37. vdinets 10:36 am 06/6/2013

    ectodysplasin: wasn’t there something on TetZoo about herbivorous frogs? Sirens are herbivorous hindgut fermenters, although they also eat fish (see Pryor, G. S., German, D. P. & Bjorndal, K. A. 2006. Gastrointestinal fermentation in greater sirens (Siren lacertina). Journal of Herpetology 40, 112-117). Accidentally, sirens are among the largest extant amphibians.

    Link to this
  38. 38. Heteromeles 10:37 am 06/6/2013

    @34: Actually, you might be able to apply Leibig’s Law of the Minimum in here somewhere (although it is a simplification).

    Don’t know that one? It’s that growth is limited by the element in shortest supply. If you have a diet that’s abundant in calories and protein but deficient in iron, growth will be limited by the amount of iron available.

    In other words, you don’t necessarily have to compare growth rates of carnivorous and herbivorous reptiles if you can do a good dietary analysis on what people are feeding them for healthy growth. Since a lot of those data are available, that might be an easier approach than trying to get growth data and getting in a fight over phylogenetic corrections.

    So far as I can tell, the reason herbivores would grow more slowly is are limits on nutrient intake, particularly proteins and protein precursors. From the plant side, nitrogen tends to be expensive (in energetic terms) to acquire, and plants tend to have a lot of mechanisms for holding on to it. This is also true to a lesser extent for phosphorus. Herbivores have to do the hard work of getting those elements out of plants, while carnivores get to do the more dangerous job of getting it out of herbivores. Growth depends to a large part on which is easier, hard herbivory or dangerous carnivory.

    Link to this
  39. 39. naishd 10:42 am 06/6/2013

    Here’s a link to a particularly neat study I like (Meshaka et al. 2007): a population of introduced green iguanas in Florida grew extremely rapidly when predatory raccoons were removed (‘growth’ here meaning in terms of demography), and the growth rates of the iguanas were pretty impressive too (sexual maturity in just over two years)… of course, ‘impressive’ is relative and the growth curve here is likely far less steep than that for fast-growing birds, mammals and so on. There is some crazy data indicating incredibly rapid growth in leatherback turtles.

    Herbivorous frogs: yes, the treefrog Xenohyla eats fruit and deliberate eating of algae and leaves is known for the Indian ranid Euphlyctis hexadactylus (stomach contents include as much as 80% plant material). Fruit-eating has been reported in a few other species as well.

    Darren

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  40. 40. David Marjanović 1:22 pm 06/6/2013

    Fermentation requires a certain gut retention time, and (for any given metabolic rate) that’s only possible above a certain size, which is 10 times higher for mammals than for squamates.

    Smaller herbivores don’t rely on fermentation. Often they are primarily seed-eaters and/or are actually omnivores; or, in the cases of insects and mites, they hardly eat any cellulose at all and concentrate on the cell contents instead.

    re: Varanus prisca, it should be priscus, right?

    Not “it should be”. It is. Gender agreement is automatic.

    Periodically it’s hypothesized in the literature that sauropods may have produced crop milk of some sort or another. This sounds ridiculous at first glance, but there’s a wide assortment of reasons why this might be less crazy than it sounds.

    It’s not crazy at all. I just don’t know how to test it. Isotopes, somehow?

    Leibig’s Law of the Minimum

    Liebig.

    There is some crazy data indicating incredibly rapid growth in leatherback turtles.

    That’s interesting, because don’t they have an unusually high basic metabolic rate?

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  41. 41. Jurassosaurus 1:44 pm 06/6/2013

    That’s interesting, because don’t they have an unusually high basic metabolic rate?

    That shouldn’t matter. Metabolic rate by itself means very little. Biomass production is what really matters (i.e., how much ingested food is actually going towards growth rather than maintenance). Birds and mammals tend to grow fast likely because their young don’t have to devote ingested energy to keeping warm or looking for food. They have parents that do that for them.

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  42. 42. ectodysplasin 2:01 pm 06/6/2013

    @heteromeles

    So far as I can tell, the reason herbivores would grow more slowly is are limits on nutrient intake, particularly proteins and protein precursors.

    Correct.

    @darren:

    Herbivorous frogs: yes, the treefrog Xenohyla eats fruit and deliberate eating of algae and leaves is known for the Indian ranid Euphlyctis hexadactylus (stomach contents include as much as 80% plant material). Fruit-eating has been reported in a few other species as well.

    Perhaps I should be more careful about specifying folivory, then. Fruits and seeds are very high-energy and easily digested food sources and do not require as much specialized digestion as leaves do.

    It’s not crazy at all. I just don’t know how to test it. Isotopes, somehow?

    Isotope fractionation seems to occur during lactation in mammals, but it’s not clear whether this also occurs during cropmilk secretion in birds. If you could demonstrate changes in isotopes between, say, prenatal, neonatal, and adult pigeon bone, then maybe you’d have some isotopic basis for comparison with sauropod bones.

    @jurassosaurus:

    That shouldn’t matter. Metabolic rate by itself means very little. Biomass production is what really matters

    Bingo.

    Link to this
  43. 43. ectodysplasin 2:02 pm 06/6/2013

    forgot to note that the comment in the third post that I was responding to was @David Marjanovic.

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  44. 44. Yodelling Cyclist 8:16 pm 06/6/2013

    @David Marjanović: “Isotopes somehow?” (how does one get italics again?)

    I’m not a biologist – I’m a physical chemist, so I maybe missing crucial points – but couldn’t we just sample though bone sections to examine the isotopic ratios at different points in ontogeny? My understanding is that the heavier isotopes drop away with each step in the food chain – the KIE means that heavier isotopes are incorporated into tissue more slowly than the lighter ones, so each level up in the food chain there should be fewer of the heavier isotopes. Crop milk – or some other form of parental nutrition – is an additional step in the food chain to my mind, so in the scenario with milk the value of N14 abundance/N15 abundance should decrease as the animal ages and switches to a herbivorous diet. But can we distinguish this from carnivorous infant sauropods (weird though it would be)?

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  45. 45. Jurassosaurus 10:04 pm 06/6/2013

    It would depend on whether there was any young enough bone left. Bone gets resorbed and reworked throughout life. This tends to happen from the inside out, so the bone that would be most informative for this isotope experiment could very likely be gone by the time we have an animal old enough to measure. One could attempt this with a growth series though. There seems to be no shortage of those nowadays. :) At the very least it could support the hypothesis that the young ate stuff very different from the adults.

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  46. 46. SRPlant 12:53 am 06/7/2013

    @ YC
    The following is a copy of Dartian’s explanation;
    “Here, on the Sci Am blogs incarnation of Tet Zoo, the HTML tag for italics is: the less-than sign + the letter ‘i’ + the greater-than sign on the one side of what you want to italicize, and the less-than sign + the slash sign + the letter ‘i’ + the greater-than sign on the other side of it.
    If you want to have bold text you do the same but you replace the letter ‘i’ with the letter ‘b’. You can also use them both at the same time (but keep the tags separate!) and then you get bold italics.”

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  47. 47. ectodysplasin 1:54 am 06/7/2013

    text in italics

    text in bold

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  48. 48. ectodysplasin 1:55 am 06/7/2013

    bah, tried to put spaces but didn’t work

    Basically text in italics

    just delete the periods.

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  49. 49. David Marjanović 9:29 am 06/7/2013

    HTML: <i>italics</i>, <b>bold</b>. (To write this, I had to spell out the HTML entities for < and >; they are &lt; and &gt;, and to write that, I needed the HTML entity for &, which is &amp;. :-) )

    These work not just here; they’re basic HTML tags that work all over the Internet. The exceptions are sites that filter all tags out when you submit a comment, like SciAm articles (stupidly enough), and maybe forums that use simplifications of HTML like BBCode; but in principle, when you find a blog, these work. <blockquote> also works usually, but not here or on Blogspot blogs.

    Metabolic rate by itself means very little. Biomass production is what really matters

    Anabolism is part of metabolism, though.

    forgot to note that the comment in the third post that I was responding to was @David Marjanovic.

    :-) I read everything anyway, and the comment you were responding to wasn’t “at” me.

    couldn’t we just sample though bone sections to examine the isotopic ratios at different points in ontogeny?

    Sure, always hoping there hasn’t been too much diagenesis.

    Crop milk – or some other form of parental nutrition – is an additional step in the food chain to my mind

    Very good point.

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  50. 50. ectodysplasin 11:15 am 06/7/2013

    @David;

    I read everything anyway, and the comment you were responding to wasn’t “at” me.

    I tend to respond to very short snippets, so sometimes it makes sense (to me at least) to note who made the original comment. That’s all.

    This ain’t twitter or anything I guess.

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  51. 51. Yodelling Cyclist 12:01 pm 06/7/2013

    @David Marjanović: Ah, well, diagenesis: I had no idea about that. That’s why I love this blog, I’m always learning, and it’s never anything useful for my “real life” :-) .

    I guess a really crude approach might then be to establish an “average” nitrogen ratio for Mesozoic herbivores, and then examine any juvenile sauropods that might be available.

    If carnivorous plants were a large source of nutrition, this would also be a problem.

    Link to this
  52. 52. David Marjanović 7:49 am 06/8/2013

    It would be, but it’s really not likely! :-)

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  53. 53. ChasCPeterson 6:32 pm 06/8/2013

    Anabolism is part of metabolism, though.

    But it’s not part of basal or standard metabolic rates, by definition.

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  54. 54. David Marjanović 9:06 am 06/9/2013

    …That’s a strange definition, then. Let me guess: it was made for animals with determinate growth?

    Even stranger is that nothing I’ve read so far has told me this. The metabolic rates of non-neornithean dinosaurs have been an active topic for about 40 years now!

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  55. 55. Heteromeles 3:39 pm 06/9/2013

    @51 YC: I’d suggest looking at phosphorus cycling rather than nitrogen cycling. Obviously, mesozoic fossil bones are missing most of the elements we really want them to contain, but I don’t think much nitrogen at all gets into fossilized bones. Still, phosphorus can be limiting, and we can probably get some order-of-magnitude cycling numbers by looking at what the dinosaurs had to deposit in their bones. Possibly there are also some isotopic things that might be useful, although I don’t know of anyone who studies phosphorus isotopes in ecosystems.

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  56. 56. Yodelling Cyclist 4:18 pm 06/9/2013

    Trouble is phosphorus has only one naturally occurring isotope – P31.

    Link to this
  57. 57. Jurassosaurus 7:42 pm 06/9/2013

    That’s a strange definition, then. Let me guess: it was made for animals with determinate growth?

    It’s not that strange. This is the original definition for SMR/BMR (e.g., see McNab 1997, which cites this definition all the way back to 1938). SMR/BMR is the rate in the zone of thermoneutrality of an adult, postabsorptive and nonreproductive animal measured during its inactive (sleeping) state.

    Things like growth, absorption of food, reproduction and even healing wounds all interfere with measurements of SMR/BMR. The postabsorptive problem was responsible for the oft-held notion that metabolic rate scaled to the .75 power (Kleiber and others measured ruminants that were not postabsorptive). Given that the point of SMR/BMR is to determine the bare minimum of energy expenditure needed to sustain life, excluding all these other things makes sense.

    All that said, I agree that one hardly sees this mentioned in the paleo literature. It’s a problem that extends beyond paleo and into many current physiological studies. This is frustrating since it means many cases of BMR/SMR in the literature are really just examples of resting metabolic rate, which limits their usefulness for comparison studies.

    Ref: McNab, B.K. 1997. On the Utility of Uniformity in the Definition of Basal Rate of Metabolism. Phys. Zool. Vol. 70(6): 718-720

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  58. 58. David Marjanović 9:59 am 06/10/2013

    I don’t think much nitrogen at all gets into fossilized bones

    That’s easy to underestimate, though. People used not to look for it, because they assumed all organic material is replaced in fossils. Apparently fossilization often just means that minerals fill the empty spaces; such things as plant cuticles or cell walls in silicified wood have long been known to remain, and now Schweitzer et al. have found sequenceable fragments of collagen and osteocalcin (two proteins) in Late Cretaceous bone… even fragments too small to sequence would still contain original nitrogen.

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  59. 59. Heteromeles 12:30 pm 06/10/2013

    @58: Whatever works, David. I wasn’t aware of that.

    Incidentally, a book that’s useful for these kind of elemental analyses is Sterner, Elser, and Vitousek’s Ecological Stoichiometry. It’s old (2002), and I think anything more recent has replaced it, which is a pity. It’s an unusual way to analyze ecosystems, but potentially a useful one.

    Link to this

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