Venomous history: New Late Triassic venomous reptile discovered in Arizona

A new study published in PeerJ Life & Environment describes a new species of small, venomous reptile from the Late Triassic Chinle Formation in northeastern Arizona. Microzemiotes sonselaensis has helped to shed light on the evolution of venomous feeding strategies within reptiles and ancient ecosystems during this time in the United States.

The fossil is of a partial left dentary with grooved teeth, and the researchers believe it represents a new species that would have used venom to hunt its prey. The discovery is the third venomous reptile from the Late Triassic and the earliest reptile with venom-conducting teeth preserved within the specimen's jaw. Before this evidence for the use of venom by reptiles from the Late Triassic was limited to teeth from Uatchitodon.

Microzemiotes sonselaensis has two deep grooves on each of its teeth, from the base of the tooth to the crown, which is similar to venom-conducting grooves of modern venomous beaded lizards and rear-fanged snakes. The grooves would have been for delivering venom, meaning that the new species would have relied on a venomous feeding strategy. Microzemiotes sonselaensis’ teeth are around 10 times smaller than Uatchitodon, suggesting that venom use could have evolved independently within multiple groups of reptiles with different body sizes -Microzemiotes sonselaensis was very small measuring around 30 cm in length.

Venom use in ancient reptiles

Helen Burch, a PhD student at Virginia Tech and the paper’s lead author said that the discovery adds more evidence for venom use in Mesozoic reptiles. “We know very little about the origins of reptile venom systems outside of living snakes and lizards, so Microzemiotes sonselaensis is a very exciting addition to a small handful of Mesozoic envenomaters,” said Burch.

The study also sheds light on the evolutionary diversity of venom-delivery systems in reptiles. The exact phylogenetic placement of Microzemiotes sonselaensis is still uncertain, but it would fall outside the clade Toxicofera, which includes living venomous lizards and snake groups such as Monitor lizards, iguanas and Gila Monsters, representing an independent evolution of a venom system.

The findings help expand the known diversity of Triassic reptiles and also help to provide valuable information regarding venom evolution. The implications extend beyond palaeontology, as it offers insights into ancient ecosystems and how feeding methods have varied within reptiles.

Source of the news:

Burch, H.E., Eddins, H.-M.S., Stocker, M.R., Kligman, B.T., Marsh, A.D., Parker, W.G. and Nesbitt, S.J. (2024). A small venomous reptile from the Late Triassic (Norian) of the southwestern United States. PeerJ, [online] 12, pp.e18279–e18279. DOI: https://doi.org/10.7717/peerj.18279