Gephyrostegus specimen 1 (CGH IIIB 21 c. 587) and counterpart (MP451), specimen 1 of Brough and Brough (1967) is a very small Gephyrostegus that Carroll (1970) considered not congeneric. Here it nests as a more primitive sister to Gephyrostegus bohemicus and G. watsoni, derived from a sister to Silvanerpeton.
Distinct from Silvanerpeton, specimen 1 was overall much smaller in size. This may not have been due to immaturity, since pre-reptiles developed as tadpoles. But at some point described hypothetically by Carroll (1970) the tadpole stage took place completely within the egg and the hatchling emerged as a miniature of the adult, as is the custom with reptiles.
The skull was narrower. The rostral profile was straighter. The naris was smaller. The nasal was wider. The lacrimal was relatively deeper with a taller orbit contact. The jugal was not so deep beneath the orbit, but taller posterior to the orbit, wrapping around the posterior postorbital. The prefrontal was longer and did not descend so far. The otic notch was reduced with a longer skull roof that produced a vertical rim to the posterior squamosal, a key trait of reptiles. The coronoid process was taller.
The neural spines were lower.
The scapula/coracoid and clavicle were smaller. The cleithrum was larger. The humerus was hourglass-shaped, longer and narrower. The radius and ulna were longer.
The pelvis was smaller with a proportionately smaller ventral pelvis. |
