Researchers have discovered a pelvis and partial pelvic from a 375 million-year-old Tiktaalik roseae fossil.

Tiktaalik roseae is believed to be a transitional species between fish and the first legged animals, according to a press release issued by the University of Chicago Medical Center.

The discovery changes the current theory that large "mobile hind appendages" began as enhanced hind fins and that back legs only formed once these creatures started transitioning into land species.

The creature is believed to have looked like a mix between a shark and crocodile and was approximately nine feet long.

"Previous theories, based on the best available data, propose that a shift occurred from 'front-wheel drive' locomotion in fish to more of a 'four-wheel drive' in tetrapods," Neil Shubin, PhD, Robert R. Bensley Distinguished Service Professor of Anatomy at the University of Chicago and co-author of the study, said, according to the press release. "But it looks like this shift actually began to happen in fish, not in limbed animals."

The pelvis is what really made the creature stand out according to the press release. The pelvic girdle was approximately the same size as the shoulder girdle, and it contained a ball-in-socket joint that could have connected a femur.

Also noted by the researchers was crests on its hips, which could mean it had strong muscles, according to the university.

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