Evolution: crocodiles ancient evolution (Evolution)

by David Turell , Monday, November 20, 2023, 18:17 (158 days ago) @ David Turell

Related to birds:

https://phys.org/news/2023-11-unraveling-complex-history-crocodiles.html

There are about 28 living species of crocodilians found throughout the tropical and sub-tropical regions of the world.

But this is just a tiny fraction of the number of crocodile species that used to exist.

"A pair of new papers has been delving into this rich evolutionary history, tracking where this group originated and how it spread around the world, as well as exploring the origin of their typical slow growth. Researchers found that the larger, modern group of crocodilians likely first appeared in Europe up to 145 million years ago.

"Following on from this, the ancestors of crocodiles and alligators then split from each other in North America, with the ability for crocodiles to tolerate saltwater meaning that they were then able to spread much further around the world.

"'It seems most likely that the ancestors of today's alligators and crocodiles evolved in North America, and then subsequent to that alligatorids [which includes alligators and caimans] stay more or less within the Americas while crocodiles get everywhere else," explains Professor Paul Barrett, a paleontologist

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"'Some of these animals were large predators that preyed on dinosaurs," explains Paul. "But others were very small, fleet-footed animals that were probably preying on things like insects. There were even herbivorous crocodilians of various types, with very complicated—almost mammal-like—teeth, that might have been chewing plants before swallowing."

"This included animals such as Simosuchus, which looked a bit like a short-snouted modern-day armadillo but was likely feeding on fruits, tubers and ferns. There were also purely marine predatory crocodilians like the thalattosuchians that had flippers instead of feet and some small, lightly-built runners like Terrestrisuchus that looked a bit like reptilian whippets.

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"The fossils of an ancient crocodile-like relative dating to 220 million years ago seem to rule out the aquatic lifestyle theory. Despite being the earliest known crocodilian to show a slowed growth rate, this new animal lived way before crocodiles started exploring the water. But why this land-living animal evolved a slower metabolism is still up for debate.

"'It might be to do with the resources available at the time—they were living in reasonably resource-poor environments," explains Paul. "But interestingly, they are also living directly alongside the other big branch of archosaur evolution: the dinosaurs."

"'Dinosaurs were doing something completely different, which was to grow fast. So while today we have slow-growing crocs and fast-growing birds, that difference has existed between these two big groups since at least the Late Triassic. But the reasons why they adopted those different strategies is still guesswork."

"Paul and his colleagues were also able to trace back the origin of Crocodylomorpha. They showed that this group first appeared in what would become modern Europe, before the ancestors of crocodiles and alligators split somewhere in what is now North America. From here, the salt-adapted crocodiles were better able to spread across the world and colonize Africa, Asia and Oceania, while alligators and their relatives were typically limited to the Americas."

Comment: dinosaurs gave us crocs and birds. The diversification of both shows how life evolves to make more and more forms of each original type. That is why 99.9% of all forms are now extinct.