Ancient crocodile relatives became vegetarians at least 3 different times


No doubt about it, the crocodile is a masterful carnivore, but the 200-million-year history of these amazing reptiles tells a fascinating story. We’ve seen crocs hanging around on riverbanks, their huge toothy jaws wide-open and we’ve also seen them snag large prey like it was nothing, but some crocodilian ancestors preferred a different sort of food: Plants.

 

Pakasuchus was a small crocodile
Pakasuchus hunting in an ancient forest. Image by Smokeybjb, license CC SA 3.0 via Wikimedia Commons

These ancient crocs took diversity to a whole new level, National Geographic reports. Many were land-dwelling, fleet-footed creatures, unlike their modern relatives that have claimed the water.

 

Analysis of 146 fossil teeth, belonging to 16 extinct crocodile relatives reveal that relatives of today’s modern crocodiles feasted on a plant-based diet at least three times in their evolutionary road trip. Teeth in modern crocs are pointedly identical (pun intended). However, even in the case of crocodiles, there’s room for variation, notes Keegan Melstrom, a paleontologist from the University of Utah.

“But that is nothing compared to the staggering diversity in the teeth of extinct crocodile-like reptiles, or Crocodyliformes,” he told National Geographic. “Some of those extinct crocs had really weird teeth.”

But those weird teeth worked remarkably well for their owners.

 

Crocodile diversity shows they were sometimes herbivorous or omnivorous
An amazing array of extinct crocs. Artwork by Jorge Gonzalez, NewScientist.

“This shows this was a successful dietary strategy,” said Melstrom, whose research team published the results last week in the journal, Current Biology.  “And I think that as we find more teeth in the future, we are likely to find, we are likely to find even more groups that independently became carnivores.”

In order to better understand this, Melstrom and his University of Utah colleague and co-author Randall Irmis, used a method that’s specially designed for comparing diverse teeth and studied work previously done by paleontologists who were studying ancient mammals.

“What it comes down to is that we count how many separate surface areas there are on every tooth,” Melstrom says. “We consider them to be separate if they are tilted in a different direction.”

By taking a page from the mammal and reptile notebooks, scientists understand that carnivores have teeth that are, overall, pretty basic, with few separate surfaces. Today’s Komodo dragon, a fearsome predator in its own right, has teeth that resemble steak knives. Thin, sharp and un-serrated, they get the job done.

 

The Komodo dragon (Varanus komodoensis) resting quietly on Komodo Island, NTT, Indonesia. Photo by Jeffrey Manzini, license CC 2.0 via Flickr

But at the other end are creatures with teeth full of crevices, fissures, nooks, and crannies that increase the surface area. This, in turn, creates more space and handy tools for grinding and crunching tough plants.

“These teeth almost invariably belong to animals that feed on plants, the leafs, branches, and stems of which often require a lot of chewing before they can be digested,” Melstrom notes.

The tooth models below provide a good idea what some of these ancient teeth looked like.

 

The owner of this tooth was a plant-eating crocodile
These 3-D printed models from two extinct crocodile cousins show they were likely herbivores. Photo by Mark Johnston, NHMU, National Geographic
Tooth of another plant-eating crocodile
Photo by Mark Johnston, NHMU, National Geographic.

While the teeth of modern crocs are simple, some extinct species had teeth with up to 20 separate surfaces. Which means they very likely engaged in some heavy-duty chomping or found other ways to use these teeth to dig into woody vegetation.

 

For Melstrom, one small croc ancestor comes to mind: Simosuchus, an oddly short-tailed, short-snouted crocodilian from the Cretaceous of Madagascar.

 

Simosuchus was a dog-sized crocodile
Simosuchus prowled Madagascar in the late Cretaceous. It was likely herbivorous. Illustration by Smokeybjb, license CC SA 3.0 via Wikimedia Commons.

“One of the most complex teeth in the set we’ve studied are those of Simosuchus, a small crocodyliform with an almost rectangular snout, as if someone hit a crocodile in the head with a shovel,” Melstrom says.

Simosuchus’s teeth resemble those of modern-day marine iguanas. These aquatic residents of the Galapagos Islands crop algae from underwater rocks.

“Simosuchus wasn’t aquatic but probably did live near the water, so one might imagine it did something similar,” he said.

But perhaps the most fascinating aspect of this research is that it shows this herbivory didn’t show up only once on the crocodylian family tree, New Scientist reports. Indeed, this trait showed up in several branches of this amazing tree. Herbivory, Melstrom adds, evolved “anywhere from three to six times.” And even for today’s modern crocodiles, fruit is still on the menu. In fact, for half of all crocodile and alligator species supplement their high-protein diets with fruit.

 

Paleontologists, however, are scratching their heads over why herbivorous crocodiles (and in fact all terrestrial crocodiles) disappeared along with nearly three-quarters of all life on Earth 66 million years ago. They haven’t evolved this time around, perhaps because mammals have filled the ecological niche they left behind.

“There’s a lot of things that have changed 66 million years,” Melstrom says.

Currently, there are two dozen species of crocodiles living today, mostly inhabiting lakes, rivers, and seashores, living nearly unchanged from their amazing ancestors. They are reminders of a lost world, a world that once was.

 

And just for fun, I just can’t resist adding this video showing one truly formidable croc which terrorized dinosaurs in the early Cretaceous of Africa and South America.

 


Featured illustration by Jorge Gonzalez for National Geographic

 


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