Archaeovenator hamiltonensis (Reisz and Dilkes 2003) Upper Carboniferous ~306 mya, was originally considered the oldest varanopid and the sister to all other varanopseids, such as Varanops. Here, Archaeovenator does indeed nest outside of the Varanopidae, but at the base of the Protodiapsida. Derived from a sister to Heleosaurus, Archaeovenator phylogenetically preceded Mesenosaurus and Spinoaequalis.
Distinct from Heleosaurus, the skull of Archaeovenator was relatively smaller. The naris was not displaced posteriorly. The maxilla + jugal were slightly deeper. The mandible was shallower. There is no trace of a large canine as all the teeth are tiny here.
Next to the smaller skull, the cervical series was relatively more robust and now no smaller than the dorsals. The dorsal ribs were shorter.
The scapulocoracoid was smaller and the humerus was more gracile.
The pelvis was smaller. The pubis and ischium were fused. The femur was more gracile. Long tendril-like toes suggest an arboreal lifestyle. The rest of the body also converged on monitor lizards.