How does a caecilian’s compact skull help it tunnel through soil?

A caecilian’s skull is highly specialized for its subterranean lifestyle. The skull is bony and compact, featuring fused centers of ossification that create a strong, spadelike braincase. This robust, reinforced structure provides the necessary durability and rigidity to tunnel effectively through soil.12

Because the skull is so compact, there is limited space for internal jaw muscles. To compensate for this, caecilians have evolved a unique arrangement where the lower jaw attaches to the primary adductor muscle via a retroarticular process located outside the cranium. This adaptation allows the animal to maintain a powerful, streamlined head shape suitable for burrowing while still retaining functional jaw mechanics.21