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How do living caecilians differ from the Jurassic fossil caecilian?

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Zoom in on the serpentine locomotion of the limbless, amphibious caecilian over soil — Gymnophiona Caecilian moving over soil.

The primary difference between living caecilians and the known Jurassic fossil caecilian is the presence of limbs. While the Jurassic fossil caecilian possessed small limbs, all living species of caecilians are entirely limbless.1

Living caecilians are characterized by a specialized, wormlike morphology adapted for their largely subterranean existence. Their bodies are long and cylindrical, featuring a compact, bony skull where fused ossification centers create a strong, spadelike braincase. Unlike the fossil form, modern caecilians have evolved to move through soil using concertina locomotion, supported by a unique axial musculoskeletal system where the skin is attached to the muscles to form a tough, protective sheath. Additionally, living caecilians exhibit various derived traits, such as degenerate eyes and the presence of a specialized tentacle for chemoreception, which assist them in their specific environments.23