This Mammalian Ancestor Was Also Earth's Earliest Venomous Vertebrate

An artist's rendering of what the reptilian Euchambersia, the size of a small dog, could have looked like. Wits University
An artist's rendering of what the reptilian Euchambersia, the size of a small dog, could have looked like. Wits University

The word "venomous" conjures up a mental image of a coiled king cobra ready to strike, or perhaps of a young Elizabeth Taylor portraying an Egyptian queen committing suicide-by-snake in the 1963 film "Cleopatra." But you may be surprised to learn that the earliest known venomous vertebrate lived 93 million years before snakes show up in the fossil record, and that it was an ancestor not of snakes, but of mammals.

The creature in question is Euchambersia mirabilis, a reptilian ancestor of mammals that lived 260 million years ago during the Permian period, near what is now central South Africa. The earliest snakes don't show up in the fossil record until about 167 million years ago, and the first dinosaurs not until about 230 million years; Euchambersia predates them both.

As detailed in a newly published study in the journal PLoS ONE, researchers used CT scans to study a pair of Euchambersia fossils — one found in 1931 and the other in 1966 — and found evidence to support earlier scientists' suspicion that Euchambersia had the right anatomical equipment to deliver a poisonous bite.

"This is the first evidence of the oldest venomous vertebrate ever found, and what is even more surprising is that it is not in a species that we expected it to be," said Julien Benoit, a researcher at the Bernard Price Institute for Palaeontological Research at the University of the Witwatersrand, and one of the study's authors, in a press release.

Euchambersia was just about 20 inches (50 centimeters) long, the size of a small dog. It had a blunt head with a wide, deep circular space in its upper jaw that scientists believe accommodated a venom gland, which was connected to its teeth and mouth by a fine network of bony grooves and canals. The scans Benoit and his colleagues created revealed a key, previously undiscovered detail: two incisors and a pair of large canines that all had a sharp ridge.

"Such a ridged dentition would have helped the injection of venom inside a prey," Benoit said.

The skull of the Euchambersia fossil shows a large space for the venom glands, in the top jaw, directly behind the front teeth. (The teeth are pictured on the right side of the photo, to the left of Dr. Julien Benoit's index finger.)
The skull of the Euchambersia fossil shows a large space for the venom glands, in the top jaw, directly behind the front teeth. (The teeth are pictured on the right side of the photo, to the left of Dr. Julien Benoit's index finger.)
Wits University

Unlike snakes, which actively inject venom through fangs, Euchambersia let its venom flow into its mouth and into the ridges on its teeth, so that it had to bite a victim to poison it. The researchers think the creature could have used its venom for hunting or as a self-defense weapon.