[1] Distinct ridges cover the prefrontal and postfrontal bones of the skull, distinguishing Philydrosaurus from related genera.

The lower temporal fenestra, usually present as a hole in the back of the skull of choristoderes, is closed by bone in Philydrosaurus.

Philydrosaurus is considered more basal than these choristoderes because its eyes are not as closely spaced and face laterally rather than dorsally.

The shortness of the skull and the laterally facing eye sockets likely represent the ancestral condition for choristoderes, but the closed lower temporal fenestra links the genus with more advanced forms.

[2] A skeleton of Philydrosaurus has been found with associated post-hatchling stage juveniles, suggesting that they engaged in post-hatching parental care.