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Leap Forward, High Over It

By Michael AbramsJanuary 1, 1996 6:00 AM


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From a Navajo reservation in Arizona came word this past year of a 190-million-year-old frog--the oldest yet discovered--that was already a decent jumper. Prosalirus bitis, unearthed by biologists Neil Shubin of the University of Pennsylvania and Farish Jenkins of Harvard, is 15 million years older than the previous record holder, and unlike that fossil it has hind legs and a well-preserved pelvis. Those legs were long enough to give the frog a powerful forward spring, says Shubin (Prosalirus means to leap forward in Latin), while the pelvis was flexible enough to transmit the force of the jump efficiently and lift the frog’s whole body (bitis means high over it in Navajo). The pelvis was also steadied during a jump by muscles that had been converted from tail duty--Prosalirus had lost the tail of its amphibian ancestors. But judging from the marks those muscles left at their attachment points on the pelvis, they weren’t as prominent as they are in modern frogs, which suggests that Prosalirus wouldn’t have won any contests in Calaveras County. Nevertheless, as Shubin points out, the body plan that arose at least 190 million years ago is extremely successful. With it, frogs survived several major extinction events, and there are now over 4,000 modern species.

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