Cacops aspidephorus (Williston 1910) Early Permian ~40 cm in length was derived from a sister to Amphibamus and represented the last of this lineage, other than perhaps Platyhystrix and kin, which are not listed here.
Larger overal and distinct from Amphibamus, the skull of Cacops was deeply pitted, taller and narrower. It was a third of the entire length. The orbit was raised and the otic notch was completely encircled. The central palatal bones were raised to the level of mid-orbit. The posterior mandible was deeper. The sutures between the skull bones could not be distinguished by Williston (1910) but Reisz et al. (2009) succeeded. Between the prefrontal and jugal the lateral palatine made an appearance unknown in other tetrapods. The maxilla and quadratojugal were taller. The nasal was longer than the frontal. The postorbital was smaller.
Only 22 presacral vertebrae were present, down by a third. The dorsal ribs in the dorsal areas were longer and those in the lumbar area were much shorter. The tail was no longer than the pelvis.
The pectoral girdle was grealy enlarged. The cleithrum topped the scapula, which leaned posteriorly. The humerus was more robust. The hand was relatively shorter.
The pelvis was much more robust. The foot was considerably smaller and not larger than the hand.
Dermal scutes lined the dorsal neural spines. Reisz et al. (2009) considered Cacops the earliest tetrapod with evidence for a tympanic membrane (eardrum). They also considered Cacops a top terrestrial predator, using its stiffened backbone to support the torso.