古生物学：ジュラ紀の骨格化石から爬虫類の進化に関する手掛かり

The near-complete skeleton of an early reptile from the Middle Jurassic period of Scotland is presented in a paper published in Nature. The fossil may improve our understanding of the anatomical transformations that led to the establishment of the body plan of reptiles such as modern lizards and snakes.

Squamates are a group of reptiles that includes more than 10,000 living species descended from a shared common ancestor that lived approximately 240 million years ago. Our understanding of the origin and evolution of the body plan of squamates is limited by gaps in the early fossil record and ongoing debates over molecular and morphological hypotheses.

Mateusz Tałanda, Roger Benson and colleagues describe the well-preserved, mostly complete skeleton of Bellairsia gracilis, a primitive squamate from the Isle of Skye, Scotland that dates back to the Middle Jurassic period, approximately 167 million years ago. The authors analysed the skeleton of B. gracilis using high-resolution X-ray imaging. B. gracilis is revealed to have had both ancestral traits (those inherited from the shared common ancestor of squamates) and derived traits (those that have originated through evolutionary divergence), revealing new insights into the evolution of the body plan of squamates. Its ancestral traits are observed in the roof of the mouth and the spine, whilst its derived traits are identified in the head and shoulders

The authors conclude that predicted similarities between B. gracilis and other fossil squamate species indicate that advanced, early species of squamates may have lived amongst land groups until at least the mid-Cretaceous period (around 120 million years ago).