Some ancient crocodiles, like Simosuchus, were doing things vastly different to surviving species, such as eating plants. Credit: Smokeybjb/Wikimedia Commons
Phys.org has a story about the history of crocodiles. There are 28 species of living crocodiles, but this represents a small fraction of the the many types that have lived in the past. The ancestors of modern crocodilians likely appeared in North America up to 145 million years ago during the late Jurassic Period. Two recent papers touch on the history of crocodiles. A paper in the journal Royal Society Open Science looks at the ability for crocodiles to tolerate saltwater. The researchers were looking into how crocodiles were able to migrate to other parts of 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 at the Natural History Museum who worked on both papers.
"It looks like the ability to cross saltwater bodies has allowed crocodiles to become much more widely dispersed than alligators: crocodiles are found all over the world, including in tropical oceans, whereas alligators are confined to freshwater and unable to reach some areas. Different crocodile subgroups seem to have prospered and originated in different regions."
The second paper was published in the journal Current Biology. It compared at the physiology of crocodiles and birds. Crocodiles and birds are each other's closest living evolutionary relatives, but their physiological strategies have been radically different for over 220 million years.
Turn back the clock to the Triassic Period and the ancient crocodilians alive back then were far from lumbering, lethargic animals. The fossils of these creatures reveal that they were in fact fast-growing, active animals.
So when did crocodiles make the switch to taking things more slowly? It had been suggested that this occurred with the movement into water, that their growth slowed with the adoption of semi-aquatic, lurking habits.
"The first question was: is the slowdown in growth because of the crocodiles' aquatic habits, or does it predate this?" asks Paul. "And secondly, at what point in the evolution of crocodiles do they switch off their ancestrally high metabolism and re-evolve what looks like a reversion to a more primitive slow-growing condition?"
