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Wednesday, 5 December 2012

Out with the old, in with the, er... old

There are busy, exciting times afoot. Not only did my book proofs arrive this morning, but my PR image of the oldest known dinosaur, which accompanies the hot-off-the-press paper by Sterling Nesbitt and colleagues, has been making waves on Internet press sites. There's lots of cool things to say about the paper and the image, but time is a little short today, so I'll have to keep my discussion brief.

Starring front and centre in the image Nyasasaurus parringtoni, the 2-3 m long possible dinosaur (or extremely dinosaur-like dinosauriform) from the Middle Triassic Manda Formation of Tanzania. As anyone with an ear to the ground for palaeontology news will know, Nesbitt et al. (2012) have rescued Nyasasaurus from the nomina nuda bin and made a compelling case for it to represent the oldest dinosaur remains yet known, or at least a dinosauriform species that was only a evolutionary stones throw from Dinosauria proper (see Nesbitt et al. 2012 for full details, or one of the many write ups populating the Internet). Unfortunately, Nyasasaurus is known from only a handful of scrappy bones including a few vertebrae and a partial humerus, which doesn't give much to work from for an artist. Paul Barrett and Sterling Nesbitt, the brains behind this image, suggested that another ancient dinosaur, Eoraptor, should be the primary reference, but with a some influence from early sauropodomorphs. The result is an admittedly slightly speculative animal, but one that hopefully captures the generalised anatomy that may have been common to the first dinosaurs and their immediate ancestors. The question of integument, a crucial consideration for any modern image of a Mesozoic dinosaur, was addressed fairly quickly: "...definitely no feathers!" It's funny to think that palaeontologists now have to defend the choice not to cover their dinosaurs in feathers or other fancy integuments, but I don't disagree with the decision here. Feathers are spreading down towards the base of Dinosauria at a rapid rate, but direct evidence is still some distance from the root of the tree. Of course, the occurrence of fuzz in pterosaurs, which some authors have already controversially interpreted as representing early types of feather, does create the potential for fuzzy integuments in all ornithodirans, but we're still waiting for smoking gun evidence of this. Elaborate restorations of prehistoric animals are definitely in fashion at the moment, but we do need to keep perspective on what the fossil record tells us. In the absence of fuzz, I chose the wrinkly, dappled scales of a perente monitor as the inspiration for the Nyasasaurus skin.


At least part of the rationale behind the dabbled, camouflaged tones of the centre animal came from its likely place in its Middle Triassic ecosystem. Nyasasaurus and other dinosauriforms were minor faunal components of a world dominated by other types of reptile (Nesbitt et al. 2012), so they may have done well to remain largely remain inconspicuous for much of the time. The rhynchosaur Stenaulorhynchus (see image detail above, showing the rhynchosaurs in all their inelegant glory) seems to have been a particularly common animal in the Manda Formation, with dozens of individuals being found compared to the one occurrence of Nyasasaurus. We wanted to feature this ecological relationship in the image, showing a lonely early dinosaur in a landscape controlled by other animals. Rather than simply including a bunch of Stenaulorhynchus in the distance however, we thought it would be cool to have the Nyasasaurus following a trail of destructive rhynchosaur foraging. Rhynchosaurs are noted for their adaptations for scratch digging with their hindlimbs, which may have been used to unearth roots, tubers or other food (Benton 1983, 1990) . In this image, several shallow excavations have been made by a troop of Stenaulorhynchus in their quest for food, which the Nyasasaurus is picking over to nab exhumed invertebrates and nutritious plant matter left behind. I must admit that the charisma of Stenaulorhynchus almost stole the show for me when drawing the image: I didn't realise how cool digging, buck-toothed reptopigs were, and I think the depiction of them digging is a first for palaeoart generally.

Finally, a quick word on the environment. Say 'Triassic climate' to most folks and their thoughts will travel to arid, barren landscapes, but this is only true for the latter half of the Triassic. The Early and Middle Triassic (which account for only the first 40 % of Triassic time) were rather wetter and, presumably, lusher than we usually imagine them (e.g. Benton 1983). In keeping with this trend, the Manda Formation palaeoenvironment was a fairly mesic, temperate setting that was likely a lot greener than the Triassic scenes we're used to. And that will have to do for now. So much for a 'brief' post. Again.

References

  • Benton, M. J. 1983. Dinosaur Success in the Triassic: A Noncompetitive Ecological Model. The Quarterly Review of Biology, 58, 29-55.
  • Benton, M. J. 1990. The species of Rhynchosaurus, a rhynchosaur (Reptilia, Diapsida) from the Middle Triassic of England. Philosophical Transactions of the Royal Society of London. Series B, Biological Sciences, 328, 213-306.
  • Nesbitt, S. J., Barrett, P. M., Werning, S., Sidor C. A. and Charig, A. J. 2012. The oldest dinosaur? A Middle Triassic dinosauriform from Tanzania. Biology Letters, 9. doi. 10.1098/rsbl.2012.0949

7 comments:

  1. This is gorgeous. I was thrilled to see it attached to Switek's article.

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  2. Thanks David. You may well see some more scenes of lower Triassic fauna from me over time, as there's a huge vacuum in palaeoart coverage for this interval. I certainly have one more foray into lower Triassic weirdness on the go, but I don't think it'll be published until well into next year.

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  3. Great to see you blogging. Regarding feathers though, doesn't Tianyulong complicate things? One of the three most parsimonious trees places Nyasasaurus as the basalmost ornithischian, after all. And if Butler is right and heterodontosaurids are the most basal ornithischians besides Pisanosaurus, that puts Nyasasaurus only two nodes away from confirmed feathers. The alternative is convergently developed feathers in Tianyulong.

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  4. Can't argue with that, Mickey, though I must admit to being unaware that the integument of Tianyulong had been confirmed as genuine feathers. If this is the case, then the conservative depiction taken here is probably a less parsimonious way of portraying early dinosaurs. I'll save face for the time being by hiding behind the (seemingly lessening) murk over heterodontosaurid relationships and any remaining questions over integument homology, but point taken. FYI, the hypothetical pterosauromorphs in my book are fuzzy (I've reworked Wild's 1980s protopterosaur idea), which is also inconsistent with the Nyasasaurus depicted here.

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    1. Well, the structures in Tianyulong and pterosaurs are both filamentous and hollow, so are as "confirmed" as Sinosauropteryx I'd say. So morphologically they fit, and homology really depends on phylogeny and character state optimization. I feel it's more likely Dinosauria was basally feathered, with large taxa losing them, though your mileage will vary.

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    2. Thanks for sharing this nice picture. It's a little funny to thinks that basal state for dinosaur could be fuzzy (but it would be consistent with an early homeothermy). But if fuzzy was the basal state how could it revert to scale; indeed unfeathered part of bird like the ostrich neck are naked, not scaly.

      I've an unrelated question about pterosaurs. Recently I was on Google scholar for article about pterosaur and I found these one: "Enigmatic Giant Pterosaur Tracks and Associated Ichnofauna from the Cretaceous of Korea: Implication for the Bipedal Locomotion of Pterosaurs”
      I've tried to know more but it's under paywall. I would like to have your opinion about this article and the implications for pterosaur locomotion. Thanks for any answer

      Alexandre

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  5. I fully support Benton and his approach that The Early and Middle Triassic were rather wetter and, presumably, lusher than we usually imagine them. Thank you a lot for this objective approach for the review of this time.

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