Huge Croc Extinction Led to Dinosaur Domination

A mass extinction of supersized crocs at the end of the Triassic paved the way for dinosaurs to take over.

Approximately 201 million years ago, the Triassic-Jurassic mass extinction killed off a slew of huge predators, including hefty beasts that looked like crocodiles and enormous armadillos, according to new research that also suggests dinosaurs benefitted from the losses.

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 armor 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," co-author Richard Butler, a paleontologist at Ludwig-Maximilians-Universität, told Discovery News.

He added 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," Toljagić explained.

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

Brusatte told Discovery News 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 said. "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 said, this study shows what can happen during and after mass extinction events.

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He concluded, "Extinctions often reset the evolutionary clock."

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.

As paleontologists increasingly unearth evidence of feathers in prehistoric fossils, our conceptions of what dinosaurs looked like when they roamed the earth has gradually evolved.

Instead of the reptilian appearance we all recognize from childhood toys and films like Jurassic Park, many dinosaurs in fact more closely resembled birds, kind of like this recently discovered little guy, Eosinopteryx brevipenna, a flightless theropod dinosaur that roamed China during the Middle/Late Jurassic period.

Archaeopteryx, also known as Urvogel, the German word for "original bird" or "first bird," was first discovered in 1860 and later fossils of this species presented some of the earliest evidence of flight in these prehistoric animals.

An intermediate creature that was not quite dinosaur but not exactly a bird either when it lived 150 million years ago, Archaeopteryx had teeth, a long tail, and wings capable of flight with claws at the end for grabbing prey.

A century after the discovery of Archaeopteryx, paleobiologists increasingly found anatomical connections between birds and dinosaurs. In the 1970s, artists began to portray dinosaurs with feathers based on accumulating evidence.

Megapnosaurus, shown here, was another species with whom researchers began early to identify with feathers. A lightweight animal that could reach up to 10 feet in length and roamed Jurassic Zimbabwe, Megapnosaurus, also known as Syntarsus, traveled in packs and preyed on small reptiles and fish.

Many of the fossils unearthed that provided evidence of feathers had deteriotated over the eons they remained buried. It wasn't until 2010 that researchers identified color pigments in feathers from dinosaurs and early birds.

Sinosauropteryx, illustrated here, was a theropod dinosaur that had "simple bristles -- precursors of feathers -- in alternate orange and white rings down its tail," according to a description of the study's findings.

Given that so many feathered dinosaurs were in fact flightless, the purpose of the feathers has been a subject of debate. Some dinosaurs may have evolved feathers for social signaling; others had plumage to provide insulation.

In the cases of some dinosaurs, such as the two oviraptors, herbivores related to T. rex that lived during the Cretaceous period, researchers believe the feathers were used for mating displays, similar to modern-day peacocks and turkeys.

You might be fooled into thinking the animals in this illustration are something between a murder of crows and a band of blue jays. In fact they are Microraptors that lives more than 130 million years ago.

These four-winged, plumed dinosaurs were no larger than modern-day pigeons and sported iridescent tail feathers.

Researchers believe the shimmering plumage was likely used in mating and other social interactions.

Like the diversity among birds today, not all feathered dinosaurs were lightweight, agile animals. A massive tyrannosaur that lived in China until about 65 million years ago, Yutyrannus huali, meaning "beautiful feathered tyrant," grew up to 30 feet long and could weigh more than 3,000 pounds.

This titanic tyrannosaur, as it was described, significantly increases the size range for feathered dinosaurs.

In a stunning find published in the journal Science in 2011, paleontologists uncovered dinosaur feather preserved in amber that dated back some 79 million years ago.

This discovery provided scientists a new window into the evolution of feathers in terms of structure in the evolutionary timeline from dinosaurs to birds. Even shades of color remained well preserved in the amber.