What's so special about dinosaurs?

By Carl Zimmer | May 11, 2011 4:11 pm

Effigia%20medium.jpgLong, long ago–actually, in 2006–I wrote an article for the New York Times about a very strange relative of today’s alligators and crocodiles. Effigia, which lived 210 million years ago, did not slouch around inTriassic swamps. Instead, it stood on two big hind legs, holding its front legs–arms, really–aloft. It looked an awful lot like a bipedal dinosaur, despite the fact that the ancestors of dinosaurs and crocodiles split off 250 million years ago.

As just one species standing upright, Effigia might have been an evolutionary fluke. But today at Science Now, Brian Switek writes that a contemporary relative of Effigia was a biped, too. So now it appears that there was a lineage of crocodile relatives running around upright at the same time as some dinosaurs were too. The dinosaurs went on to fame and glory–or, at any rate, a continued upright existence. The crocodile lineage ended up on all fours, where they remain today.

[Reconstruction by Carl Buell]

CATEGORIZED UNDER: Evolution

Comments (5)

  1. MarekB

    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?

  2. Jim

    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.

  3. 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.

  4. MarekB

    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!

  5. Matt B.

    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?

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The Loom

A blog about life, past and future. Written by DISCOVER contributing editor and columnist Carl Zimmer.

About Carl Zimmer

Carl Zimmer writes about science regularly for The New York Times and magazines such as DISCOVER, which also hosts his blog, The LoomHe is the author of 12 books, the most recent of which is Science Ink: Tattoos of the Science Obsessed.

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