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Dino-Era Fossil Reveals Two-Footed Croc Relative

Brian Handwerk
for National Geographic News
January 25, 2006
 
After languishing for decades in the bowels of a New York museum, a dinosaur- era crocodile relative is seeing the light—and shedding secrets.

New studies of the forgotten fossil reveal that the species walked on two feet and looked much like a so-called ostrich dinosaur, though the two are barely related, paleontologists report.

The 2-yard-long (1.8-meter-long) reptile fossil could add to our understanding of ancient crocodile-like reptiles and how they evolved (interactive map: "World of the Crocodilians").

The species, called Effigia okeeffeae, was "more closely related to living crocodiles than to the ostrich dinosaurs," said Mark A. Norell. A curator in the Division of Paleontology at New York's American Museum of Natural History, Norell is a coauthor of a paper describing the species.

Despite the reptile's resemblance to an ostrich dinosaur, or ornithomimid, Effigia is actually some 80 million years older.

Effigia roamed North America in the Triassic period some 210 million years ago.

"This is totally unexpected and reminds us that crocodilian relatives were more diverse in the past than they are today," said paleontologist James Clark, chair of the Department of Biological Sciences at the George Washington University in Washington, D.C.

"Ornithomimids are one of the most specialized of the dinosaurs, and for crocodilians to have come up with that kind of specialization—a duck-like skull—before the dinosaurs did is pretty impressive."

Effigia's recent rediscovery is reported in the current issue of the journal Proceedings of the Royal Society: B.

Croc and Dino Evolution Converges?

The fossil was discovered nearly 60 years ago at the Ghost Ranch quarry.

The ranch is in the region of New Mexico that was frequented by the painter Georgia O'Keeffe, for whom the animal's species classification is named.

Encased in a plaster jacket, the bones had remained hidden in the American Museum of Natural History for decades. Recently, though, Norell and study coauthor Sterling Nesbitt, a graduate student, reexamined the long-warehoused fossils.

The pair soon spotted the distinctive "crocodile" ankle that first alerted them to the fossil's potential importance.

Ankle aside, Effigia had large eyes, a long tail, and a toothless beak—not unlike the ostrich dinosaurs.

Effigia also walked on two feet, unlike modern crocs.

These physical similarities suggest that Effigia and the ornithomimid dinosaurs evolved similarly during two different eras, the scientists say.

The fossil record shows that many different features have been reinvented time and again in different species. But the Effigia example is a bit surprising.

"We expect things like feeding adaptations to be convergent—things that we can assign a specific functionality to, like a duck bill," Norell said.

"But when a pelvis looks pretty much the same in two very different groups, that opens up a set of very fascinating questions."

The theory of convergence in evolution suggests that Effigia lived in a similar habitat to that occupied by the ornithomimid dinosaurs some 80 million years later.

The two also likely shared many of the same pressures.

Both Effigia and the ostrich dinosaurs would have evolved from a common ancestor that lived long before, the study says.

Croc Decline Key to Dino Rise?

Modern crocodiles are but one remnant of what was once a far more diverse croc family.

"Today we think of crocodiles as looking basically the same," said Nesbitt, of the American Museum of Natural History and Columbia University's Lamont-Doherty Earth Observatory. "But in their history they took on a wide variety of different body plans."

"Some looked like reptilian armadillos or cats, and others looked like little dinosaurs," Nesbitt said.

The crocodilian family may have been at its peak during the Triassic period.

"Toward the end of the Triassic period you have this crazy diversification of these crocodile relatives, including this animal," Nesbitt said.

"It was really the heyday of the crocodile-like animals, but the only lineage to really make it out of the Triassic was the lineage that led to modern crocodiles."

Nesbitt explains that dinosaur evolution was likely in its infancy during this period.

"We're not 100 percent sure what the story is," he cautioned.

"Now it seems that dinosaurs were there with these animals, they were part of the fauna. But they remained pretty small and not very diverse.

"We don't see the typical museum type dinosaurs until the Jurassic. Nothing is really happening [in dinosaur evolution] until after these crocodile relatives are gone," Nesbitt added.

It may be that Effigia-like animals were widespread but dinosaurs were comparatively rare during this era, Norell, the museum curator, explained.

If so, dinosaur evolution might have blossomed only after most crocodile-like animals became extinct. Those extinctions might have left an attractive environmental niche for the dinosaurs.

The theory seems to be backed by the abundance of Effigia-like animals found from North America's late Triassic period.

Many fossils once thought to be dinosaurs turn out, on closer inspection, to be crocodile-like animals that, like Effigia, only look like dinosaurs.

Many of these croc-like animals "are difficult to identify without nearly complete specimens, especially skulls," Nesbitt said. "If you just have a vertebra, for example, you can't tell them apart."

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