Rare fossil of bone-crushing crocodile cousin found in Brazil

The prehistoric reptile likely played a surprising but vital role in its Triassic ecosystem.Thursday, 6 February 2020

Rodrigo Müller was working a block of rock and dirt at the base of Agudo Hill, an hour from Porto Alegre, when he first saw an unusual set of osteoderms, bony deposits that form plates on the skin of a reptile or amphibian.

“It was a surprise, because we had never seen anything like this in Brazil before,” Müller, a palaeontologist at the Federal University of Santa Maria, says of what was otherwise an ordinary visit to the Janner dig site, once home to some of the earliest dinosaurs to roam Earth.

As he continued his delicate work, he brushed dirt from an intact cranium and several other fossilised bones. Together, the collection formed a well-preserved and almost complete skeleton of a rare Ornithosuchidae reptile, a family considered cousins to today’s crocodiles and alligators that had been previously recorded only in Argentina and Scotland.

Dated to 230 million years ago, Dynamosuchus collisensis—newly named for its powerful bite and the location of the find—was described January 31 in the journal Acta Palaeontologica Polonica by a team that includes Müller’s colleagues at Argentina’s Museo de La Plata and Virginia Tech in the United States. Only three other species of Ornithosuchid have been discovered in the world, the last of which was found in Argentina and described 50 years ago.

While its bite could crush bones and its blade-like teeth tore through meat, Müller and company believe Dynamosuchus collisensis was a slow scavenger, or necrophagous, similar to the vultures and hyenas of today. It fed mostly off animal carcasses and easy-to-catch prey, meaning it filled a crucial part of the food chain that palaeontologists hadn’t known existed in this region of Brazil until now.

“It helps us understand better how that ecosystem worked,” Müller says.

Without scavengers like the Dynamosuchus collisensis, carcasses and other organic waste would pile up rather than breaking down. This decay allows plants to absorb essential nutrients. Those plants then feed herbivores and omnivores, allowing the cycle to continue.

Bone bonanza

This Triassic reptile was quite large compared to other animals that lived during the period, measuring roughly seven feet in length. Unlike its modern relatives, Dynamosuchus collisensis was terrestrial. Its four limbs swung underneath its body and not at its sides, while its osteoderms ran in two protective rows down its back.

It stalked around forested areas surrounded by rivers, alongside some of the oldest known dinosaurs in the world, mammal ancestors called cynodonts and other reptiles like rhynchosaurs.

The newly revealed fossils connect the evolution and interactions between the land masses where Ornithosuchidae lived, which at the time, were all part of the supercontinent Pangaea. The animal discovered in Brazil is more closely related to one of the specimens found in Argentina than the two specimens in Argentina are to each other. This finding indicates the fauna exchanged members over long distances and didn’t evolve in an isolated fashion, Müller says.

“The fact that you have organisms that are very close in terms of kinship in Brazil and Argentina during the same time period indicates a similarity in environment and ecologies, although each region had differences that promoted speciation,” says Marco Aurélio Gallo de França, a palaeontologist from the Federal University of the Valley of San Francisco who did not take part in the discovery.

Thanks to the intactness of the Dynamosuchus collisensis fossil, Müller and the other researchers can run further tests on the strength of the reptile’s bite, using CT scans to create 3D digital models.

“It’s really well preserved. There’s practically no deformation in any of the bones, and there’s a good part of the cranium and the postcranial skeleton, so it’s very complete for this type of animal,” Müller says of the fossil. “There’s so much information in those bones.”

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