Ancient Snake Fossil Reveals Hind Legs and Lost Cheekbone

A well-preserved fossil from Argentina is clarifying the evolution of snakes. The specimen, *Najash rionegrina*, is an ancient snake with hind limbs that lived nearly 100 million years ago. Its skull shows that these early snakes possessed a jugal bone, or cheekbone. This feature has almost entirely disappeared in modern snake species.

The 2019 study, published in *Science Advances*, added new information to the sparse fossil record of early snake evolution. The findings challenge previous ideas that snakes originated as small burrowing creatures. Instead, evidence from *Najash* suggests that ancestors of modern snakes were larger animals with wide mouths.

Early snakes retained their hind limbs for an extended period. Modern snakes are mostly limbless. Researchers used micro-computed tomography (micro-CT) scanning to study the fossil without causing damage. This allowed them to reconstruct the skull in detail, including nerve and blood vessel paths.

This detailed view helped resolve a long-standing anatomical debate about the jugal bone in snakes. The *Najash* fossils provided direct evidence to correct previous misunderstandings. The study's authors state that these new skulls and skeletons clarify the sequence of bone loss that led to the specialized skulls of modern snakes.

Subsequent research has added further complexity to the snake origin story. A 2020 study described *Boipeba tayasuensis*, a large blind snake from the Late Cretaceous period in Brazil. A 2023 study suggested that the ancestor of crown snakes may have been adapted for burrowing while also exhibiting opportunistic behavior. A 2025 study described a Middle Jurassic squamate from Scotland with both lizard-like and snake-like characteristics.

Despite these later discoveries, *Najash* remains important for understanding a crucial stage of snake evolution. It represents a transitional form, showing snakes with hind limbs and a more lizard-like skull. This combination provides valuable insight into how the snake body plan developed.