Najash

Najash is an extinct genus of snakes from Late Cretaceous Argentina. Its fossils preserve a pelvis and functional hind limbs, showing that early snakes retained legs.

Snake: Snakes are elongated, limbless reptiles in the group Serpentes. Najash belongs to the snake lineage despite retaining hind limbs.
Snake locomotion: Snake locomotion is movement produced through coordinated body bending, scale contact, and, in some species, limb remnants. Najash’s hind limbs complicate accounts that treat early snake movement as entirely limbless.
Cenomanian: The Cenomanian is the earliest age of the Late Cretaceous, spanning roughly 100 to 94 million years ago. Najash fossils are known from Cenomanian deposits in Patagonia.
Snake terrestrial origin hypothesis: The terrestrial-origin hypothesis proposes that snakes evolved from land-dwelling ancestors rather than aquatic ones. Najash’s robust pelvis and hind limbs support interpretations emphasizing terrestrial early snakes.
Snake evolution: Snake evolution is the lineage’s transformation from ancestral reptiles into modern snakes. Najash is a fossil anchor for early stages of this transformation.
Axial elongation: Axial elongation is the evolutionary increase in the number or length of vertebral regions along an animal’s body. Snake body elongation occurred alongside limb reduction in the lineage Najash helps illuminate.
Candeleros Formation: The Candeleros Formation is a geological unit in Argentina containing Late Cretaceous terrestrial fossils. It is the formation that yielded the original Najash remains.
Snake aquatic origin hypothesis: The aquatic-origin hypothesis proposes that snakes evolved from marine or otherwise aquatic ancestors. Najash’s limb-bearing anatomy is weighed against proposals based on aquatic fossil relatives.
Snake pelvis: A snake pelvis is the remnant or retained pelvic structure associated with the hind-limb region. Najash preserves a substantial pelvis unlike the reduced structures of most living snakes.
Limb reduction: Limb reduction is the evolutionary loss or diminution of limbs and their associated skeletal structures. Najash documents a stage in which hind limbs persisted during this process.

Linked from 1 page