Archaeovenator hamiltonensis (Reisz and Dilkes 2003) Upper Carboniferous ~306 mya, was originally considered the oldest varanopseid 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 Ellitosmithias, Archaeovenator phylogenetically preceded Mesenosaurus and Orovenator.
Distinct from Heleosaurus, the skull of Archaeovenator was relatively smaller. The naris was greatly elongated and relatively large. 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. This is yet another appearance of an antorbital fenestra without a fossa. The mandible may also have a fenestra.
The cervical series was relatively more robust and 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 with monitor lizards.