Megachirella

Megachirella wachtleri is a small reptile from the Middle Triassic of the Italian Dolomites. Its fossil was known for years before a 2018 study used high-resolution micro-CT data and a broad phylogenetic analysis to identify it as the oldest known stem squamate in that analysis. The result shifted the documented fossil record roughly 75 million years earlier than the previously recognised oldest squamates. It does not date the exact origin of lizards and snakes, but it makes Megachirella an important entry in the ancient lizard and snake catalogue.

Quick facts

Discovery in the Dolomites

Michael Wachtler discovered the fossil in the Italian Alps. Silvio Renesto and Renato Posenato described it in 2003, naming the species Megachirella wachtleri in recognition of the finder. The holotype, PZO 628, is a small articulated reptile preserved on a slab from the Dont Formation near Kühwiesenkopf in the Dolomites. Its association of skull, trunk and limb bones made it more useful than an isolated tooth, even though the fine anatomy was not yet fully understood.

The specimen is around 240 million years old, from the Middle Triassic. It was found in deposits that also preserve plants and other vertebrates. Its burial in a sedimentary setting does not show that it lived in water: the skeleton lacks evidence of a specialised aquatic body plan. The rocks document where it was preserved, while limb anatomy and overall proportions are the evidence relevant to how it moved.

Why researchers returned to the fossil

In 2018, Simões and colleagues rescanned the holotype with high-resolution microfocus X-ray computed tomography. Digital slices exposed features in the skull, wrist and shoulder that were difficult to assess on the original slab. The team combined those observations with a large phylogenetic dataset including fossil anatomy and molecular information from living reptiles.

The authors recovered Megachirella as a stem squamate. Squamata is the branch that includes living lizards, snakes and amphisbaenians. A stem member lies outside the living crown group but closer to it than to its nearest non-squamate relatives. This placement differs from earlier interpretations that treated the animal more generally as a lepidosaur of uncertain position.

A fossil date is not an origin date

Before the 2018 redescription, the oldest widely recognised squamate fossils were Middle Jurassic. Megachirella is roughly 75 million years older, so it extended the known fossil occurrence into the Middle Triassic. This is a minimum age for the presence of the lineage, not proof that squamates originated exactly when this individual lived. The actual divergence could predate the oldest fossil yet found.

The study also changed interpretations of early branching among living squamates, finding a result consistent with geckos diverging early. Such a conclusion emerges from a phylogenetic model and a particular sample of characters and taxa. New fossil discoveries or changes in analytical assumptions can alter the branching order without changing the bones visible in PZO 628.

What the skeleton can and cannot establish

The fossil preserves a small skull, an elongate neck and a four-limbed body. Tomography revealed details that support a squamate relationship, but Megachirella is not a miniature modern gecko. The traits of early stem forms were assembled in different combinations, and no living species reproduces its full anatomy.

Published length estimates are approximate because the body is small and some parts are incomplete or difficult to measure in the slab. The specimen does not reveal exact mass, colour, skin texture, prey or reproductive behaviour. A small terrestrial predator or insect-eater is plausible, but no stomach contents establish a particular diet. These limits distinguish observations on the skeleton from ecological reconstructions.

Place in the wider reptile story

Megachirella is substantially older than the Middle Jurassic Bellairsia, which preserves a different mixture of squamate traits in a far more complete skeleton. The comparison is useful precisely because neither animal is a simple rung in a ladder. Each preserves a branch of early lepidosaur history at a different time and with different anatomical detail.

The Triassic discovery shows that the evolutionary history of squamates extends beyond the first known Jurassic body fossils. It does not identify the first lizard, establish a direct ancestor of snakes, or settle every conflict between molecular clocks and morphology. The strongest conclusion is that a stem squamate already existed in the Italian Alps about 240 million years ago.