Crocodiles have had great success through rapid evolution

In a new study from the University of Bristol, researchers have discovered that crocodiles once thrived on land and in the water as a result of rapid evolution.

Modern crocodiles are predators that live in rivers, lakes and wetlands. They use their powerful jaws to snatch up their prey, including fish, reptiles, birds, and mammals.

The latest research shows that ancient crocodiles were much more diverse. During the time that dinosaurs lived, some types of crocodiles were fast-moving plant eaters, while others had features that were similar to dolphins.

The experts analyzed more than 200 skulls and jaws, including fossils from the entire 230-million-year history of crocodiles and their extinct relatives. The team examined shape variations among the specimens to identify differences between species and to investigate how quickly certain groups changed over time.

The study revealed that some extinct crocodile groups, including the dolphin-like thalattosuchia, evolved very fast over many millions of years. The skulls and jaws of these ancient crocodiles transformed as they expanded into niches that are occupied by other animal groups today.

The experts also determined that crocodiles, alligators, and gharials – the only living crocodilians – are more conservative than these extinct fossil groups. They have evolved steadily,  but more slowly, for the last 80 million years.

“Crocodiles and their ancestors are an incredible group for understanding the rise and fall of biodiversity,” said study lead author Dr. Tom Stubbs.

“There are only 26 crocodile species around today, most of which look very similar. However, there are hundreds of fossil species with spectacular variation, particularly in their feeding apparatus.”

Experts have long assumed that dramatic shifts in habitat and diet can trigger rapid evolution, but these patterns are usually documented in groups with a large amount of diversity like birds, mammals, and fish. This is the first time the pattern has been established in crocodiles.

“Ancient crocodiles came in a dizzyingly array of forms. They were adapted to running on land, swimming in the water, snapping fish, and even chewing plants,” said Dr. Stephanie Pierce.

“Our study shows that these very different ways of living evolved incredibly fast, allowing extinct crocodiles to rapidly thrive and dominate novel ecological niches over many millions of years.”

“It’s not clear why modern crocodiles are so limited in their adaptations,” noted Professor Michael Benton. “If we only had the living species, we might argue they are limited in their modes of life by being cold-blooded or because of their anatomy.”

“However, the fossil record shows their amazing capabilities, including large numbers of species in the oceans and on land. Perhaps they only did well when world climates were warmer than today.”

The study is published in the journal Proceedings of the Royal Society B: Biological Sciences.

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By Chrissy Sexton, Earth.com Staff Writer