The family tree of the ancient crocodiles reveals unexpected twists


The family tree of the ancient crocodiles reveals unexpected twists

Artist’s impression of Macrospondylus- an extinct fossil group of teleosauriodes. Credit: Nikolay Zverkov

Scientists investigating the dark past of a group of prehistoric crocodiles have discovered a timeless truth: study anyone’s family tree long enough and something surprising will emerge.

Despite 300 years of research and a recent resurgence in the study of their biological composition, the mysterious and marauding teleosauroids have remained forever elusive.

Scientific understanding of this distant cousin of the modern-day long-nosed gharials has been hampered by poor understanding of their evolutionary journey, until now.

Researchers at the University of Edinburgh have identified a previously unknown teleosauroid species and seven of its close relatives, part of a group that dominated the Jurassic shores from 190 to 120 million years ago.

Their analysis offers tantalizing glimpses of how teleosauroids adapted to the momentous changes that occurred during the Jurassic period, as Earth’s seas underwent many changes in temperature.

“Our study has only scratched the surface of teleosauroid evolution,” says Dr Michela M. Johnson, of the University’s School of GeoSciences. “But the results are impressive and raise interesting questions about their behavior and adaptability.

“These creatures represented some of the most successful prehistoric crocodiles during the Jurassic period and there is a lot more to learn about them.”

The study reveals that not all teleosauroids were engaged in cut-and-pushed lifestyles, catching other reptiles and fish from seas and swamps near the coast.

Instead, they were a complex and diverse group capable of exploiting different habitats and searching for a variety of food sources. Their physical structure is also more diverse than previously thought, scientists say.

Previous research had provided insights into the origins and evolution of the metacolids of the whale-like relatives of this fossilized crocodile, but less was known about teleosauroids.

To solve this problem, the expert team of paleontologists examined more than 500 fossils from more than 25 institutions around the world.

State-of-the-art computer software allowed the team to collect revealing data on their anatomical similarities and differences, examining the entire skeleton, teeth and bone armor, which indicated whether the species were closely related or not.

This information allowed the team to create an updated family tree of the teleosauroid group from which two new large groups emerged, whose anatomy, abundance, habitat, geography and feeding styles differ significantly from each other.

The first group, the teleosaurids, were more flexible in terms of habitat and feeding. The second group known as machimosaurids – which included the fearsome turtle crushers, Lemmysuchus and Machimosaurus – were more abundant and widespread.

The team’s names given to seven fossils just described, found in both teleosaurids and machimosaurids, reflect a curious range of anatomical features, including Proexochokefalos, meaning “large head with large tuberosities” and Plagiophthalmosuchus, the “side-eyed crocodile. “.

There are even hints of their different behavioral characteristics and unique places: Charitomenosuchus, which means “graceful crocodile” and Andrianavoay, the “noble crocodile” of Madagascar.

The researchers named the recently discovered species, Indosinosuchus kalasinensis, after the Kalasin province in Thailand, where the fossil, now housed at Maha Sarakham University, was found.

Recognition of I. kalasinensis shows that at least two species lived in similar freshwater habitats during the late Jurassic – an impressive feat as teleosauroids, with the exception of Machimosaurus, were becoming rare during this period.

Dr. Steve Brusatte, Reader in Vertebrate Palaentology, at the School of Geosciences, University of Edinburgh, said, “In the same way that the family trees of our ancestors and cousins ​​tell us our story, this huge new family tree of teleosauroids clarifies their evolution. They were some of the most diverse and important animals in the Jurassic oceans and would have been familiar places along the coasts for tens of millions of years. “

The study, published in the scientific journal PeerJ.

Warm-blooded crocodiles thrived in the Jurassic cold snap

More information:
Michela M. Johnson et al. The phylogenetics of Teleosauroidea (Crocodylomorpha, Thalattosuchia) and the implications for their ecology and evolution, PeerJ (2020). DOI: 10.7717 / peerj.9808

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