Utaherpeton franklini (Carroll et al. 1991) Mississippian/Pennsylvanian ~320 mya, at ~6 cm in length was much smaller than its predecessors and successors. Carroll, Bybee and Tidwell (1991) considered tiny Utaherpeton to be the oldest microsaur. Here Utaherpeton was derived from a sister to Tuditanus and Anthracodromeus. Since Utaherpeton is morphologically derived, it is likely that the majority of microsaur divergence preceded it and the various other microsaurs are rather late examples. Even so, Utaherpeton bears a strong resemblance to several early reptiles, including Westlothiana and Cephalerpeton.
Distinct from Tuditanus the skull of Utaherpeton had a straight jawline. The maxilla was deeper but the teeth were smaller. The prefrontal extended to the premaxilla. The ventral mandible was straighter. The cervical ribs were smaller. The pelvis was more gracile. The tibia and femur were shorter. The medial pedal metatarsals and digits were much smaller than the lateral ones, but digit 5 was much smaller (if complete). |
