Gephyrostegus bohemicus (Jaeckel 1902) Upper Carboniferous (~310 mya)~22 cm snout-vent length, was a lizard-like reptilomorph from Nyran in the Czech Republic. Derived from a sister to Silvanerpeton, Gephyrostregus phylogenetically preceded the basal reptiles, Casineria and Cephalerpeton.
Distinct from Silvanerpeton, the skull of Gephyrostegus descended posteriorly. The lacrimal and quadratojugal were shorter. The otic notch was reduced.
The presacral vertebral count was reduced to 24.
The humerus was more gracile. An olecranon process (elbow) developed on the ulna. Manual digits IV and V were shorter.
The pelvis was shorter. The dorsal process of the ilium was shorter. Certain anklebones fused together to create a larger bone, the astragalus, otherwise found only on reptiles.
While most early tetrapods lived their lives in water, Gephyrostegus was among the few that preferred land (= moss covered coal forest logs). Smaller than other basal tetrapods and slightly smaller than its more primitive sister, Silvanerpeton, a sister to Gephyrostegus preceded even smaller basal reptiles (see below).
Juveniles had a relatively larger head and orbit (eye socket). Eggs would have been laid in or near water to prevent dessication because, presumeably, no amniotic membrane or shell surrounded the embryo. Tiny circular scales covered the body except beneath where large V-shaped scales were present.
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