Comments on: What’s so special about dinosaurs?

By: Matt B.

Matt B. — Fri, 20 May 2011 17:23:23 +0000

Those pictures of Effigia look unbalanced, like it’s going to fall on its face at any moment. I would expect it to keep its thighs almost horizontal so its center of mass is over its feet, and this would also help it reach things on the ground with its short arms.

So was the title supposed to be a sarcastic rhetorical question?

By: MarekB

MarekB — Thu, 12 May 2011 16:33:36 +0000

Thanks for the tree. After checking out some images of various taxa from the cladogram, I understand that the sprawling posture of modern crocodiles and alligators is derived, rather than primitive, with respect to the earlier quadruped but still rather erect posture of their ancestors. Very cool!

By: Thomas R. Holtz, Jr.

Thomas R. Holtz, Jr. — Thu, 12 May 2011 13:45:13 +0000

The bipedal guys are off on a side branch (in Poposauroidea). If you take a look at a recent phylogenetic analysis of the archosaurs (http://archosaurmusings.files.wordpress.com/2011/05/nphylo-1.jpg) you can see that the poposauroids are off an a side branch relative to modern crocs (represented here by Alligator).

Some of the individual groups on side closer to crocs than to poposauroids may have been at least partly bipedal, but the basic line was essentially quadrupedal.

(I say “essentially”) because it is quite likely that many of these croc-lineage animals, archosaurs in general, and their lizard cousins (lepidosaurs) all got up on their hindlegs in an all-out run, at least at small body size. Most living small bodied lizards do this.

By: Jim

Jim — Thu, 12 May 2011 13:07:38 +0000

And here I was hoping that this would be an attempt to explain why all young children (most especially boys) are so easily enraptured by dinosaurs. This is very cool, though and my son will love hearing about it.

By: MarekB

MarekB — Thu, 12 May 2011 00:41:13 +0000

So… Does that imply modern crocodile posture is secondary through a bipedal stage? Or are those Effigia and Poposaurus guys are a bipedal, specialized offshoot of otherwise crawling rauisuchians? Or, maybe we don’t have enough fossil record to know that?