If the dinosaurs could wait, I guess I can too…

19 07 2007

Tomorrow a new paper in Science well help to explain the pattern of the origin and radiation of dinosaurs, revealing a much more gradual process than has previously been assumed. Although I’ll save most of my comments until after I get to read the paper (while everyone else is lining up to get their copies of Harry Potter), it could do a lot of good in helping to dispel myths about evolution. The “classic” dinosaur story is that their ancestors were adapted to have their limbs under their bodies, allowing for a much more efficient gait that also freed their hands and allowed them more speed. This adaptation allowed them to quickly overtake all other amniotes of the time, dominating the world for well over a hundred million years, other organisms only becoming large or becoming more specialized after dinosaurs disappeared. Darren at Tetrapod Zoology has done a lot to help dispel the idea that dinosaurs were the be all and end all of Mesozoic critters, and the recently (re)discovered Effigia okeeffeae has shown that dinosaurs were not the only group to develop an advanced bipedal posture.

The LiveScience article announcing the paper doesn’t provide much detail other than the potential shake-up involved for thoughts on evolutionary turnover in the Triassic (as well as the announcement of a “dinosauromorph” named Dromomeron romeri, after the famous paleontologist A.S. Romer). I’m sure more capable bloggers will be able to give some more in-depth insights than I can, but the fact that dinosauromorphs persisted for so long, even coexisting with dinosaurs, requires a bit of re-thinking when it comes to how dinosaurs evolved and became the dominant large animals on the earth. I certainly look forward to learning more tomorrow.

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5 responses

19 07 2007
Zach Miller

Brother, this is one paper you’ve GOT to email to me. Basal Dinosauriformes fascinate me because they’re basically indistinguishable from basal Saurischia, yet their survival rate after the Late Jurassic was zilch. Greg Paul argues that these little buggers WERE dinosaurs, and he very well may be right. As we discover more primitive forms like Saturnalia, Lesothosaurus, Eoraptor, and Herrerasaurus, many of the supposedly uniquely dinosaurian features (three sacrals, tridactyl pes, open acetabelum) are beginning to erode away.

Not surprisingly, the line between lagosuchid (my paraphyletic term for these “near-dinosaurs”) and dinosaur is becoming increasingly blurred, just like the maniraptor/bird transition. I think the best example of this blurring has come from Silesaurus, an herbivorous “near-dinosaur” with a predentary bone. A predentary! If they’d only found the thing’s skull, they’d call it the most primitive known ornithischian! But the skeleton is actually reasonably complete, and a few of the axial features make a dinosaurian identification iffy.

Personally, I think that a predentary, in addition to the host of other traditionally “dinosaurian” features that Silesaurus exhibits cement it as a basal ornithischian. I find it hard to believe that an animal SO CLOSE to the base of the Dinosauria would evolve a predentary independantly of actual ornithischians. That’s just not parsimonious.

So clearly they are a fascinating group. If you are able to email that paper to me when you get it, I’d really appreciate it, sir.

19 07 2007
laelaps

Even that comment was more impressive than what I’m likely to write Zach; I will certainly pass the paper along as soon as I’m able to get it. I’ve long been meaning to catch up on Triassic dinosaurs and their closest relatives, but I’ll have a rather steep learning curve if I try to get it all out tomorrow (and the likes of you and Darren will likely be much more competent discussing it). Regardless, I can’t wait to see it, and I hope it gets the attention it deserves.

19 07 2007
Julia

It’s been summarised on the BBC news website too – Dinosaurs’ slow rise to dominance, including some nice soundbites from my pal Richard. Looks like an interesting one.

19 07 2007
Will Baird

I did just put up a post that I may be forced to retract on the subject. You guys are far more informed than I. It will be interesting to see what you write about wrt this.

7 10 2011
Hillary Coverton

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