Heleosaurus scholtzi (Broom 1907) Middle Permian ~270 mya, ~30 cm snout to vent length, was considered an indeterminate diapsid by Broom (1907) and Carroll (1976), but Reisz and Modesto (2007) determined it was a varanopid synapsid, a week after I had coincidentally nested it there having never seen the fossil. Here, with the benefit of new data on the skull (Botha, Brink and Modesto 2009) Heleosaurus nested just outside of Varanodon+Varanops+Synapsida at the base of previously unrecognized clade, the Protodiapsida. Derived from a sister to Varanodon, Heleosaurus phylogenetically preceded Archaeovenator and Mesenosaurus. Overall Heleosaurus was lower and smaller than the varanopseids.
Distinct from Varanops, the skull of Heleosaurus has a low angled rostrum. The squamosal formed a right angle at the back of the skull, rather than angling forward. The naris was displaced away from the snout tip. The maxilla created an ascending process behind the naris, blocking the lacrimal from contact. The tooth row included a single large canine, twice as long as the other teeth. The prefrontals were enlarged and lowered. The mandible was shallow.
The cervicals were elongated, but slightly smaller than the dorsals. The vertebral spines were lower. The dorsal ribs were shor, creating a shallow torso. The posterior dorsal ribs were extremely short, creating a large lumbar region.
The scapulocoracoid was lower in synch with the shallower torso. The ulna and radius were straighter and more closely appressed, creating a narrower forearm. The forelimbs were much smaller than the hindlimbs.
Numerous osteoderms covered the neck.
A recent find (Botha Brink and Modesto 2009) of four small individuals huddled with a large one likely indicates communal nesting of a family unit. None adequately document the manus or pes, but the skull can now be reconstructed.