Yet another Bipedal Crocodile! (via Carl Zimmer)
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.
At a glance, it would be tempting to call Poposaurus gracilis a dinosaur. This 225-million-year-old reptile stood on two legs, had small forelimbs, and sported a long, tapering tail that allowed it to balance while walking and running about the Late Triassic landscape. But Poposaurus wasn’t a dinosaur at all. It was much more closely related to the forerunners of crocodiles, and, according to a new study, its curious mode of walking challenges a leading hypothesis about why dinosaurs were so successful.
First described over a century ago, Poposaurus is a “rauisuchian,” part of an extinct lineage of reptiles whose diverse array of members included the precursors of crocodiles and their closest relatives. Rauisuchians differed from crocodiles as we know them today in holding their limbs upright beneath their bodies rather than out to the side. This arrangement made them more efficient at walking and running on land, and, until recently, all rauisuchians were thought to have walked on all fours.
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