A transitional form between lizards & modern-day snakes found

Published in The Hindu on July 26, 2012

Lizard
Coniophis (middle), a transitional fossil between snakes and other lizards compared with a modern lizard (gila monster, top) and snake (bottom).— photo: Nick Longrich

A transitional snake — an intermediate form between lizards and the highly evolved snakes seen today — has been finally identified.

This is a major step in answering many contentious questions such as whether snakes had their origin in a marine or terrestrial environment, how their unique feeding mechanism evolved, and the size and kind of their prey.

More importantly, the identification of a transitional snake further strengthens the robustness of the theory of evolution. The interesting and important find is described today (July 26) in a paper published in Nature.

The authors studied the previously ignored Coniophis precedens fossil of the Late Cretaceous period (approximately 70 million years ago). They firmly state that the fossil is not an anilioid snake (burrowing snakes with vestigial pelvis and hind legs).

The transitional snake has a “snake-like body and a lizard-like head.” The shape of the skull is also intermediate between that of the lizards and snakes seen today.

Origin

Some earliest forms of snakes have an elongate body with reduced limbs. So was this body shape with reduced limbs used for burrowing or for swimming? The answer to this question would indicate whether snakes are of terrestrial or marine origin.

Dispelling the notion that the basal snake fossil will exhibit its marine origin, the authors found that Coniophis lacked the vital adaptations required for marine life. Instead it had several anatomical features that supported a burrowing nature. The 70-cm long body is ideal for a burrowing animal. The fossil was recovered from continental floodplain deposits.

Based on these parameters, the authors state that the transitional fossil had a terrestrial origin and was fossorial (one that is adapted to digging and life underground). “ Coniophis therefore supports the hypothesis that the elongate body and reduced limbs of snakes evolved as burrowing adaptations,” they write. “The small size and reduced neural spines indicate fossorial habits, suggesting that snakes evolved from burrowing lizards.”

Coniophis thus represents a functional chimera, combining a snake-like body with a lizard-like head. It is a small, fossorial carnivore that preyed upon small vertebrates,” they write.

Jaw and teeth

The upper jaw of the transitional snake fossil is firmly fixed to the skull. This would have limited its ability to prey on bigger animals. They found that the jaw has a combination of characteristics that is both lizard-like and snake-like. The teeth are very much snake-like in being “tall, pointed and cylindrical.” Even the shape of the teeth and their implantation are snake-like.

The snake has an intramandibular joint — where the front half of the lower jaw rotates to a few degrees relative to the posterior half. Based on the teeth features and the intramandibular joint, the authors suggest that the snake preyed on small vertebrates.

According to the authors, the tall and pointed teeth allowed the snake to pierce and hold soft-bodied prey.

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