Say hello to an old relative of yours: Euchambersia mirabilis. An ancient cousin of the mammals, it may not seem too unusual from the outside – about half a metre (1.5 feet) long with a mouth full of sharp teeth. But new research into the adaptations inside its jaws hints at something very special indeed: one of the oldest venomous bites in the fossil record.
Mammals (including you and me) are the only living members of an ancient group called the synapsids. In the distant past, even before the dinosaurs showed up, non-mammal synapsids like Euchambersia dominated their ecosystems. They were quite similar to living mammals, but with unusual features such as reptile-like jaws and a habit of laying eggs instead of giving birth to live young.
Euchambersia lived during the Permian Period in what is now South Africa, around 260 million years ago. It shared its habitat with other early mammal cousins such as the saber-toothed carnivorous gorgonopsids, as well as large reptiles like the armoured plant-eating pareiasaurs.
Venom and the glands that contain it don't typically preserve in fossils, but ever since Euchambersia was first discovered on a South African farm in the early 1930s, palaeontologists have wondered about odd features on its jaws that may have been part of a special venom-delivery system.
"The 'venomous Euchambersia' hypothesis is not a new idea," says Christian Kammerer of the Museum für Naturkunde in Berlin, who was not involved in the new study. "It was first proposed by the nobleman scientist Baron Franz Nopcsa in 1933 and has been generally accepted ever since."
But a few scientists have expressed doubts about the venom hypothesis, and Julien Benoit of the University of the Witwatersrand in Johannesburg is one of them. And since the field of palaeontology is experiencing a bit of a technological revolution these days, Benoit decided to re-address the question with a high-tech approach.
By putting Euchambersia under a micro-CT scanner, Benoit and his team were able to get a super-detailed look at its upper jaws, digitally reconstruct its cranium, and even see some features no one had noticed before. "[W]e discovered previously undescribed teeth hidden in the vicinity of the bones and rock," Benoit says.
It is the teeth of Euchambersia that provide the first sign of a venomous bite. Some of them have shallow ridges along their edges – they're not deep grooves like some venomous snakes have in their fangs, but the ridges would have provided enough of a channel to direct venom down along the teeth and into the bite wound of a victim. North America's Gila monster lizards envenomate their prey in a similar fashion.
And there's more. In each upper jaw, Euchambersia has a bowl-shaped depression – prime real estate for a fluid-secreting gland. Two holes in this bowl lead to a small tunnel called the maxillary canal. In many animals, this canal provides passage for nerves and blood vessels; in Euchambersia, it may have had the extra job of shuttling a toxic cocktail from the venom sac to the teeth, where it could slide down along those ridges. All it would have taken is for the animal to bite down on something and squeeze those glands.
Any one of these features by itself wouldn't be too convincing, but all of them together make a compelling case. "A venomous animal must possess ... at least one venom gland, a mechanism to deliver the venom, and an apparatus with which to inflict a wound," the researchers note in their study. With a gland to produce venom, the canal to deliver it to the mouth, and those sharp, ridged teeth, Euchambersia meets the criteria.
"If this is true, Euchambersia represents the earliest known venomous terrestrial vertebrate," Benoit says. "[It] would have used its venom for either protection or hunting. Most venomous species today use their venom for hunting, so this is a much more probable option."
This research can give scientists a better idea of how to recognise venom in ancient animals, as well as shining a light on the life of this particular creature.
"The main thing that its bizarre morphology emphasises is the incredible diversity of pre-mammalian synapsids," Kammerer adds. "[They included] burrowers, tree-climbers, sabre-toothed predators, and yes, probably venomous forms."
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