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Behold, Carnufex: The Two-Legged Croc of the Triassic

All hail the Carolina Butcher.
March 19, 2015, 10:00am
​Carnufex carolinensis: Nightmare fuel. Credit: Jorge Gonzales

The Triassic world was packed to the brim with spectacular predators, but few are as intimidating as a newly discovered species called Carnufex carolinensis. Even the animal's name sounds badass, as does the nickname it has already earned for itself—the "Carolina Butcher." I've barely even started describing this crocodile ancestor and it's already clear it deserves its own biopic.

Naturally, it gets even better. Unlike its modern relatives, Carnufex walked upright on two legs, likely feeding on armored reptiles and early mammal-like animals. Measuring nine feet from head to tail, it roamed the planet 231 million years ago in what is now North Carolina. Only one fragmentary set of fossils from this species has been recovered, described in a study published this morning in Scientific Reports.

Carnufex in all its glory. Credit: Jorge Gonzales

"The fossils of Carnufex were discovered around a decade ago and were stored unprepared in the [North Museum of Natural Sciences] collections until we started working on the specimen in 2012," lead author Lindsay Zanno, director of the Zanno Lab, told me. "This is the only known specimen of this new animal."

The holotype includes partial skull, spine, and limb fragments, which were recovered from North Carolina's Pekin Formation in Chatham County. Zanno and her team digitally reconstructed the animal's skull by creating three dimensional models of each of the cranial fossils with a high-resolution surface scanner. The researchers further filled in the blanks by comparing Carnufex's skull to those of its close relatives.

While it may be difficult to imagine such a unique predator even having comparable relatives, Zanno said bipedal crocodilians were far from a one-off during this era.

"It may seem bizarre, but that is largely because the dominant animals of the Triassic are not as famous as dinosaurs, which reigned later in time," she told me. "There are many different Triassic critters that likely walked on two legs, both within the crocodile lineage and within the dinosaur-bird lineage."

The reconstructed skull of Carnufex carolinensis. 3D surface models of skull bones are shown in white. Grey areas are missing elements reconstructed from close relatives of Carnufex. Credit: Lindsay Zanno

"Carnufex is one of the earliest and most primitive crocodylomorphs we've yet discovered so it shares a lot of features with both crocodylomorphs and their closest cousins, a group known as rauisuchids," she continued. "Some rauisuchids were capable of walking on two legs and on four legs and Carnufex likely inherited that way of life from them."

The wide variety of carnivorous body plans during this period reflects an unusual boom in predator diversity during the late Triassic. Indeed, though the subperiod that Carnufex lived in, called the Carnian stage, is named for the Carnic Alps, it may as well be a reference to how ecologically overwhelmed this era was with carnivores competing for apex status.

"We don't know exactly why there were so many different kinds of predators in the Triassic," Zanno said. "It's abnormal compared to what we see today and what we've seen for most of the past 200 million years. The planet was recovering from the largest mass extinction in its history, so it may be that animal communities hadn't yet settled into the kind of trophic structure we are used to today."

When I asked her what kind of the ecological effects of this abundance of predators might have had, Zanno said, "in a nutshell, predators become prey."

The upshot seems to be that the world Carnufex inhabited was an unrelenting bloodbath between upstart dinosaur species and incumbent mainstays like crocodylomorphs. It must have been a violent era to live through, but the rich medley of meat-eaters that it produced paints a fascinating portrait of a hunter-heavy ecosystem.