snake, in zoology: Locomotion and Limblessness
Locomotion and Limblessness
A snake moves by means of muscular contraction, which can produce several types of locomotion, the commonest types being undulation and straight-line movement. Straight-line movement is aided by the ventral plates, elongated scales on the abdomen that overlap with their open ends pointing toward the tail. These plates can be moved forward by means of muscles attached to the ribs.
It is believed that snakes are descended from lizards, but how and why they evolved toward limblessness is uncertain. Some paleontologists have held that limblessness was an evolutionary advantage in the dense vegetation that formed the early environment of snakes, or that it developed to facilitate burrowing habits, but others believe that the earliest snakes evolved in an aquatic environment and are descended from marine reptiles related to mosasaurs. The fossil evidence for a land or marine origin is inconclusive; the earliest known snakelike reptiles date to some 167 million years ago.
Sections in this article:
- Types of Snakes
- Locomotion and Limblessness
The Columbia Electronic Encyclopedia, 6th ed. Copyright © 2024, Columbia University Press. All rights reserved.
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