Croc extinction led to dinosaur domination

 

Pseudosuchians such as Longosuchus meani had features like sturdy body armour and strong tails for whacking enemies (Source: Nobu Tamura/Wikimedia Commons)

Jennifer Viegas
Discovery News

A mass extinction that occurred over 200 million years ago, killed off a slew of huge predators, including hefty beasts that looked like crocodiles and enormous armadillos, according to new research.

Some of the prehistoric predators - animals known collectively as the early pseudosuchians - likely preyed on certain dinosaurs, which later evolved some of impressive characteristics of the ancient pseudosuchians. Those included features like sturdy body armour and strong tails for whacking enemies.

"It is likely, therefore, that dinosaurs prospered to some extent as a result of the extinction of most pseudosuchians and many other groups at the end of the Triassic," says co-author Richard Butler, a palaeontologist at Ludwig-Maximilians-Universität.

He adds that some evidence suggests dinosaurs "had better locomotor and breathing systems than pseudosuchians," so they thrived in the Jurassic after the mass extinction.

As for what caused that die-off, researchers suspect an enormous burst of volcanic activity, as part of the Atlantic Ocean's formation, led to dramatic increases in atmospheric carbon dioxide and rapid global warming.

For the latest study, published in Biology Letters , Butler and colleague Olja Toljagić assessed changes in pseudosuchians that occurred during the critical Late Triassic and Early Jurassic periods.
The study shows that during the extinction event 201 million years ago, these animals declined rapidly, with only one lineage surviving into the Jurassic. Some of the animals evolved into ancestors of today's alligators and crocodiles. Another lineage, referred to as the "bird-line archosaurs", consisted of the non-avian dinosaurs and their species that later evolved into modern birds.

Luck, in part, helps to explain why some animals died, while others survived.

"Selectivity of mass extinction events is sometimes linked with body size, ecological constraints and competition, while other times it could be related to just pure luck of the survivors," explains Toljagić.

Rise of new archosaurs

Stephen Brusatte, a palaeontologist at the University of Edinburgh, previously studied how crocodile-line archosaurs changed during the Triassic and across the Triassic-Jurassic boundary.

Brusatte says that the recent study by Butler and Toljagić is important "because we really need to understand what happens at mass extinction events in order to better understand how our own world may change in the face of warming temperatures."

"Many early relatives of crocodiles flourished during the Triassic, but many of them were killed off at or near the Triassic," he says."After they were killed, whole different groups of crocodile-line archosaurs had a chance to rise in their place, and it was this dramatic moment that was the root of the diversification of the lineages leading to living crocodiles."

More than anything, he says, this study shows what can happen during and after mass extinction events.

"Extinctions often reset the evolutionary clock," he concludes.

Non-avian dinosaurs appear to have benefited, at least in part, from one extinction event, but they bit the dust during another. Mammals then seem to have benefited when the dinosaurs died out.

It remains to be seen which mammals - including humans - will survive the next big extinction event. The current biodiversity crisis has already resulted in drastic population drops for some species and the extinction of others.