Ancient relatives

By | Science & Technology
A computer generated reconstruction of the crocodile ancestor Carnufex carolinensis. Credit@JorgeGonzales

Palaeontologists have uncovered fossils in the United States of a giant, prehistoric crocodile that hunted on its hind legs. It lived about 231 million years ago, standing at the top of the food chain just before the first dinosaurs appeared. In a study published in the open access journal Scientific Reports last week, they call it Carnufex carolinensis, or the ‘Caroline butcher’ after its menacing features.

North Carolina State University palaeontologist Lindsay Zanno, who led the research, told The Positive, “Carnufex is one of the most primitive crocodylomorphs yet discovered. Its anatomy is quite bizarre, having a mosaic of features otherwise known in crocs and their closest relatives, a now-extinct group of predators known as rauisuchids.” Unlike modern crocodiles, Carnufex appeared to live on land and lurked around on two legs in the wet, warm equatorial region that North Carolina was at the time. “Carnufex was different from living crocodiles. It was an agile, terrestrial predator that hunted on land,” Zanno said. “Carnufex predates the group that living crocodiles belong to.”

Part of the creature’s skull, ribs, vertebrae and a forelimb were unearthed in what is now Chatham County, North Carolina. The fossil was cut out of the surrounding rock in an active quarry. Teams periodically search these sites for clues of animals that may have been alive during the Triassic period.

Photo of the cheek bone of Carnufex. Credit@LindsayZanno

Photo of the cheek bone of Carnufex. Credit@LindsayZanno

The butcher also has a bizarrely ornamented skull decorated with pits and grooves. “We were quite surprised by the large body size of Carnufex, as most well known early crocs are quite small. Carnufex was so large it likely occupied a top predator niche in equatorial Pangaea,” Zanno also told The Positive. The current data suggests that dinosaurs crossed into North America after the time of Carnufex, meaning it may have been able to hold on to its predator role for some time. Typical predators roaming the supercontinent Pangaea included the large-bodied cousins of ancient crocodiles who also became extinct in the Triassic.

The 3D reconstruction of the skull was achieved through a combination of actual bones and scans of Carnufex‘s closest relatives in the crocodylomorph family tree to hypothesise the absent components. It serves as an expert guess for now, but researchers may be able to tell how accurate the model is once more complete remains are uncovered. Susan Drymala, a graduate student at NC State and co-author of the paper said to The Positive, “In the case of Carnufex, the bones of the skull were extremely thin and fragile, so we wanted to handle the actual bones as little as possible, even though it appeared as though they should all fit together quite nicely.”

The reconstructed skull - the 3D surface models of skull bones are shown in white, and the gray areas are missing elements reconstructed from close relatives. Credit@LindsayZanno

The reconstructed skull – the 3D surface models of skull bones are shown in white, and the gray areas are missing elements reconstructed from close relatives. Credit@LindsayZanno

Fossils from the Late Triassic period are important to researchers because they hold information about the earliest crocodylomorphs and theropod dinosaurs. These ancient groups initially evolved in the Triassic periods, yet managed to survive to today in the form of crocodiles and birds. The discovery of Carnufex is equally significant in understanding early crocodylomorph evolution. Until now, the only crocodylomorphs researchers knew of were small, slender animals with all evidence pointing toward a large, robust ancestor. Carnufex is a sort of transitional fossil, filling the gap between modern crocodiles and their ancient ancestors before they evolved a smaller body size.

As the Triassic period drew to a close, roughly 201 million years ago, a mass extinction event ended Carnufex’s reign as top predator. The event left behind surviving smaller crocodylomorphs and theropods dinosaurs. “Theropods were ready understudies for vacant top predator niches when large-bodied crocs and their relatives bowed out,” Zanno adds. “Predatory dinosaurs went on to fill these roles exclusively for the next 135 million years.” During this time period, the ancestors of modern crocodiles became progressively smaller and took on the types of roles a modern fox might do today. They developed small, sleek bodies and long limbs. Drymala explained, “If you want to picture these animals, just think of a modern day fox, but with alligator skin instead of fur.”

How might today’s four-legged crocodiles be better adapted to their environment than Carnufex was during the Late Triassic?


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