Ancient Crocodile Diversity
September 11, 2013

Ancient Croc Relatives Were Exceptionally Diverse

[ Watch the Video: Crocodiles Thrived During Prehistoric Times ]

Brett Smith for - Your Universe Online

Ancient relatives of crocodiles had a wide range of habitats and ecosystems, with some species built like domestic dogs and others built for swimming through the open seas.

Using a combination of morphological and biomechanical metrics to analyze these ancient crocodilians, a new study from researchers at the University of Bristol in the UK identified distinct trends that allowed these creatures to flourish among the dinosaurs, according to their report in the journal Proceedings of the Royal Society B.

"The ancestors of today's crocodiles have a fascinating history that is relatively unknown compared to their dinosaur counterparts,” said lead researcher Tom Stubbs, a Mesozoic reptile expert at the University of Bristol. “They were very different creatures to the ones we are familiar with today, much more diverse and, as this research shows, their ability to adapt was quite remarkable.”

"Their evolution and anatomical variation during the Mesozoic Era was exceptional,” Stubbs added. “They evolved lifestyles and feeding ecologies unlike anything seen today."

To determine the differences among the various species, the scientists used a unique combination of numerical methods to look at distinctions in the shape and function of the lower jaw remains of over 100 ancient crocodiles.

"We were curious how extinction events and adaptations to extreme environments during the Mesozoic - a period covering over 170 million years - impacted the feeding systems of ancient crocodiles and to do this we focused our efforts on the main food processing bone, the lower jaw,” explained Stephanie Pierce, an evolutionary biomechanics expert from The Royal Veterinary College.

The lower jaw of these ancient predators provided Bristol researchers with unique insights into how crocodilians’ feeding systems evolved and subsequently responded to the altered distribution of ecological resources after the devastating extinction event at the end of the Triassic.

The Bristol team was able to show, for the first time, that ancient crocodiles invaded the newly reorganized Jurassic seas and developed jaws with the hydrodynamic efficiency to capture fish and other nimble prey. However, only a small array of lower jaw shapes was actually suitable in the Jurassic seas.

The researchers also found that jaw shape variation peaked again in the Cretaceous, between 145 and 66 million years ago. During this time, ancient crocodiles developed a large variety of lower jaw shapes, as they evolved to take advantage of a wide range of food and terrestrial ecosystems, while in competition with the dinosaurs.

Surprisingly, the lower jaws of these later crocodiles did not show a large amount of biomechanical variation, researchers said. Instead, the fossils indicate novel adaptations in other areas of their anatomy, including an armadillo-like body armor.

"Our results show that the ability to exploit a variety of different food resources and habitats, by evolving many different jaw shapes, was crucial to recovering from the end-Triassic extinction and most likely contributed to the success of Mesozoic crocodiles living in the shadow of the dinosaurs,” Pierce said.

The Bristol team noted the ancient crocodiles’ exceptional anatomical variation, which has never before been explored numerically for such a large range of crocodiles over such a long period of evolutionary time.