Comparative anatomy of the ossified braincase of legless anguine lizard Pseudopus apodus (Pallas, 1775) (Squamata, Anguimorpha).

The braincase and inner ear of the largest species of legless anguine lizards, Pseudopus apodus, are described in detail based on high-resolution x-ray microcomputed tomography. Here, the ontogeny of its braincase is briefly described. The detailed anatomy of the individual braincase bones of P. apodus is presented and compared with those of the modern anguine species Anguis fragilis and species of Ophisaurus, Dopasia, and Hyalosaurus. Because only the extant species of Anguinae are studied and discussed here, the generic names of modern taxa defined genetically-Ophisaurus (North America), Dopasia (Southeast Asia), and Hyalosaurus (North Africa)-are used here. The shape of the supraoccipital in juveniles was similar for all species found in all three geographic territories. During growth, the shape of the supraoccipital changes significantly in Pseudopus, Dopasia, and Ophisaurus, and its shape is very similar to that in adults of the anguine taxon Ophisauriscus quadrupes from the Middle Eocene of Germany. Instead, the shape of the supraoccipital in the adults of Hyalosaurus and Anguis is very similar to that in the juveniles of Pseudopus, Dopasia, and Ophisaurus. This suggests that paedomorphosis probably played a role in the shape formation of the supraoccipital in Hyalosaurus and Anguis. The morphological and proportional changes in several other braincase structures during ontogeny are also described.