A team of researchers has discovered that the ancestors of mammals were the first animals to gain the ability to produce venom. After analyzing the fossils of an ancient mammal-like reptile, Euchambersia mirabilis, the team determined that the creature had evolved venom glands long before snakes and other true reptiles. The findings were just published in the journal PLOS ONE.
The word “venom” refers to any toxin that is injected by one animal into another. This is in contrast to poisonous animals that must be touched or eaten; poisonous animals don’t actively inject their toxins. Modern day examples of venomous animals include rattlesnakes, jellyfish, scorpions, and Komodo dragons. Venom is rare in mammals and most people associate the term with reptiles, especially snakes. Venom glands don’t fossilize properly so it has been difficult for scientists to track the evolution of venomous animals. Some researchers had suggested that a mammal-like reptile called Euchambersia mirabilis may have been venomous. Euchambersia was a small, short creature that lived in South Africa 255 million years ago, during the Late Permian period. It was one of the earliest ancestors of mammals and lived on the planet millions of years before snakes. If Euchambersia did have venom glands, it would have been the first known venomous animal in the fossil record.
Researchers from the University of the Witwatersrand used advanced computerized tomography (CT) scanning techniques to analyze the anatomy of Euchambersia, focusing on its skull and canine teeth. The team used this information to create a 3D rendering of the animal’s skull. After extensive research, the team determined that Euchambersia had characteristics of venomous animals as well as anatomical features that would have allowed for the development venom glands. They found teeth with ridges that had been previously undescribed. These teeth would have helped the animal inject venom into prey or would-be predators.
The team’s results are exciting because scientists had generally assumed that early reptiles, such as snakes, would have been the first to evolve venom. Instead, Euchambersia, an early ancestor of mammals, had evolved venom glands at least 255 million years ago. Euchambersia was small and otherwise defenseless so it would have made sense for it to evolve venom to compensate. Although venomous mammals are rare today, the research team’s findings show that early mammals were the first to gain the ability.
Benoit et al. Reappraisal of the envenoming capacity of Euchambersia mirabilis (Therapsida, Therocephalia) using μCT-scanning techniques. PLOS ONE (2017).