Erpeton was considered an early divergence from the homalopsid stem by Gyi (1970), and indeed as noted in the introduction Dowling et al. (1983) presented evidence that the Erpeton lineage diverged 45.2 MYA. Voris et al. (2002) analyzed mtDNA from 16 homalopsids including Erpeton and suggested Erpeton was in a clade with Enhydris bocourti, Cerberus, and Homalopsis.