Najash

Najash rionegrina was a snake from Cenomanian deposits of northern Patagonia, yet it retained a sacrum, a pelvis attached to the spine and small hind limbs. Its anatomy documents a stage in which the body was already unmistakably snake-like while the rear appendages had not vanished. Continental rocks at La Buitrera also showed that a legged Cretaceous snake did not have to live in the sea. Later skulls and skeletons have strengthened the species diagnosis and made Najash central to debates about early snake evolution. It is one of the snake profiles in the ancient lizard and snake catalogue.

Quick facts

A snake from La Buitrera

Sebastián Apesteguía and Hussam Zaher named Najash rionegrina in 2006 from fossils in the Candeleros Formation of Río Negro Province, Argentina. The name refers to a biblical serpent, while the species epithet honours the province. The holotype includes a section of vertebral column and the pelvic region with hind-limb bones. Additional material accumulated from the La Buitrera Palaeontological Area, a rich Cretaceous locality in northern Patagonia.

In 2019, a skull with closely associated vertebrae helped address a longstanding concern: some bones included in the original species concept had not been found articulated with the type. The newly described specimen shared vertebral features with the holotype and matched the partial skull previously attributed to Najash. A larger 2019 study then used micro-CT data from several skulls and skeletons to examine how the snake head was assembled.

A pelvis unlike that of living snakes

Modern snakes lack a sacrum and a functional pelvic girdle, although some boas and pythons retain tiny external spurs. Najash preserves sacral vertebrae that articulate with the pelvis, plus a femur, tibia, fibula and elements of the foot. The limbs were small relative to the elongated trunk, but they were far more complete than the spurs of living boas.

The anatomy demonstrates that limb reduction was a sequence, not a single switch. A snake body plan could develop while parts of the ancestral pelvis and hind limbs remained. It does not show that Najash walked on its legs like a lizard: the long trunk and small appendages make that an unlikely description of normal locomotion. Their precise roles, perhaps in mating or body support, are not directly preserved.

What its skull adds

The newer cranial material preserves bones that were missing or difficult to interpret in the first fossils. CT imaging can separate overlapping structures without mechanically splitting a delicate specimen. The scans show a skull with recognisably snake-like characters alongside retained features found in more primitive squamates, including a jugal bone that is absent in living snakes.

The skull is not the fully specialised, wide-gape apparatus of many living snakes. Its anatomy helps place Najash among early snakes and track the development of cranial mobility, but the exact order of changes depends on how different fossil taxa are related. A modern feeding mechanism should not be projected wholesale onto this animal.

Why the habitat matters

Some famous snakes with hind limbs, including Pachyrhachis, are known from marine rocks of the Middle East. Najash came from continental deposits in Patagonia, associated with a terrestrial ecosystem of floodplains and river channels. This is direct evidence that the early history of snakes included land-dwelling forms. It does not settle whether the deeper ancestors of snakes were terrestrial, aquatic or adapted to another setting.

The fossil record contains no preserved meal for Najash. Its teeth and jaw support a predatory interpretation, but the exact prey is unknown. Calling it a specialist burrower or a constrictor of large animals would go beyond the evidence.

A branch, not a missing link with a predetermined destination

Phylogenetic studies recover Najash as a basal snake outside the crown group of living snakes, often among madtsoiid relatives. That makes it valuable for reconstructing early ophidian anatomy. It is not known to be the direct ancestor of any later snake, and it does not turn evolution into a ladder from “lizard” to “snake.” The older Triassic Megachirella belongs much farther back in squamate history; it is not a demonstrated ancestor of Najash.

The strongest conclusions are anatomical and geological: an early snake had a sacrum, an attached pelvis and external hind limbs, and it lived in a continental Cretaceous environment. Function, exact diet and the complete sequence of snake origins remain open questions.