Najash rionegrina was an extinct, primitive snake from the Late Cretaceous period, approximately 90 to 100 million years ago. This ancient reptile is notable for possessing well-developed hind limbs. Its discovery provided insights into the early evolutionary history of snakes.
The Fossil Discovery
Fossils of Najash rionegrina were unearthed in the Candeleros Formation of northern Patagonia, in the Río Negro Province of Argentina. Initial descriptions of this species were based on a 2003 fossil, with more complete specimens, including a preserved skull, found in 2013 at the La Buitrera Paleontological Area. These fossils were preserved in three dimensions, an unusual preservation that allowed for detailed anatomical study.
The name Najash rionegrina has meaning related to its origin. “Najash” is derived from the biblical Hebrew word for “snake” (Nahash), referencing a legged serpent in ancient texts. The second part of its name, “rionegrina,” refers to the Río Negro Province in Argentina, where the fossils were found.
Defining Physical Features
Najash rionegrina had physical features that set it apart from modern snakes. Its most notable feature was two well-developed hind legs, which extended outside its rib cage. Unlike many other fossil snakes that retained vestigial limbs, Najash’s legs were robust and functional, suggesting they were actively used.
A sacrum, a pelvic bone of fused vertebrae, was a significant anatomical detail of Najash. This sacrum connected its spine to a pelvic girdle, a feature absent in modern snakes and most other fossil snakes. The presence of a sacrum indicates a more lizard-like body plan and supports its terrestrial nature.
Evolutionary Significance
The discovery of Najash rionegrina influenced the scientific debate regarding the origins of snakes. For many years, paleontologists discussed whether snakes evolved from marine ancestors, such as mosasaurs, or from terrestrial, burrowing lizards. Earlier reports of fossil marine snakes with hind limbs, like Haasiophis, Pachyrhachis, and Eupodophis, initially supported the marine origin theory.
Najash emerged as evidence supporting the terrestrial origin hypothesis. Its fossils were found in terrestrial deposits, indicating a desert environment, not an aquatic one. The robust, functional hind limbs and the presence of a sacrum, which connects the pelvis to the spine, suggest a terrestrial, burrowing lifestyle. This combination of features positions Najash rionegrina as a primitive snake, providing a clearer picture of how ancestral snakes transitioned from lizards to limbless forms.