Early Lizard Evolution Uncovered: Insights from Tiny Triassic Reptiles

Today, lepidosaurs, which include lizards, snakes, and the New Zealand tuatara, stand as some of the most diverse vertebrates on Earth. However, their early evolutionary history remains a mystery. A newly discovered jaw fossil in southern Brazil is aiding paleontologists in unraveling the history of human anatomy and evolution. This fossil belongs to Karguninia Enigmatica, a small lepidosaur relative that roamed the Earth during the late Triassic period alongside some of the earliest dinosaurs.

Living approximately 225 million years ago during the early Norian period of the late Triassic, Karguninia Enigmatica inhabited a world shared with early dinosaurs, mammal relatives, primitive crocodilians, and early tuatara relatives.

Discovered in 2010, Karguninia Enigmatica was initially identified from a single lower jaw fragment. It belongs to a lineage called Lepidosauromorpha, which eventually led to modern lepidosaurids.

However, paleontologists have long debated where exactly Karguninia Enigmatica fits into the lepidosaur family tree.

“Lepidosauria is now richly diverse, represented by squamates and rhinocephalans,” noted Dr. Lissy Vitoria Soares Damke from the Federal University of Santa Maria and colleagues. “Its origins trace back to the end of the Permian, when the stem lineages Lepidosauromorpha and Arcosauromorpha diverged.”

“Several species within the lepidosauromorph stem lineage have uncertain phylogenetic placements,” they added. “Karguninia Enigmatica is a rare taxon from Brazilian strata, known from a single specimen, specifically a fragmentary left dentary tooth.”

Initially interpreted as a non-rhinocephalic lepidosaur based on its teeth, approximately 0.4-0.5 mm wide, researchers noted similar dental features to Calgunia and Ikarosaurus, a cueneosaur from the Late Triassic of the United States. However, they contended that this evidence alone doesn’t sufficiently categorize this taxon within Ikarosaurus or its close relatives.

A new specimen of Karguninia Enigmatica was uncovered at the Linha San Luis site in Facinal do Soturno, Rio Grande do Sul, Brazil. This fossil, though incomplete, includes a left lower jaw fragment less than 9 mm long with 12 preserved teeth, suggesting the animal may have had up to 18 teeth.

Paleontologists employed micro-CT scans to analyze the internal structures of the specimen, allowing them to trace the trigeminal nerve responsible for facial and jaw sensation and motor control. It was found that the neural branching patterns of Karguninia Enigmatica closely resemble those of modern lepidosaurs.

Researchers concluded that Karguninia Enigmatica likely perceived its environment similarly to its living relatives concerning trigeminal sensory input.

Computational phylogenetic analysis consistently positioned Karguninia Enigmatica as a non-lepidosaur lepidosaur, reinforcing the idea that it is an early branch that diverged before true lepidosaurs emerged.

“This is the first time its phylogenetic position has been computationally investigated, confirming previous assumptions,” the authors stated.

The findings will be published in an upcoming issue of Anatomical Records.

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Lissie Vitoria Soares Damke et al. New fossil reveals unusual lepidosaur tooth anatomy of Karguninia Enigmatica from the late Triassic period in southern Brazil. Anatomical Records published online on July 4, 2026. doi: 10.1002/ar.70268