A re-examination of the original type series of Prangner (1845) and Hofmann (1887a) of the primitive alligatoroids from the middle Miocene of Styria, led to a reappraisal of the taxonomy of the following species of Diplocynodon: D. steineri and D. styriacus. Of unsettled affinities, Enneodon ungeri was also re-examined. It is here demonstrated that it belongs to the same taxon of the specimens described by Hofmann (1887a). These taxa are in fact junior synonyms of the previously erected Enneodon ungeri. Moreover, comparison with other European alligatoroids reveals that the Austrian specimens described by Prangner (1845) and Hofmann (1887a) belong to the same genus: Diplocynodon Pomel, 1847. According to the rules of the International Commission on Zoological Nomenclature (ICZN), Diplocynodon has priority over Enneodon. Under the principle of priority, it is therefore proposed to rename all the Miocene remains of alligatoroids from Styria as Diplocynodon ungeri Prangner, 1845. Comparison of almost complete skulls from various Miocene contemporaneous localities reveals that there is no reason to erect another taxon for the French specimens of D. "styriacus" described in Ginsburg & Bulot (1997). However, these specimens need to be redefined as D. ungeri as well. D. ungeri was coded and included in a character matrix to cladistically test its affinities with other alligatoroids. A total of six species of Diplocynodon were analysed including: D. ratelii, D. hantoniensis, D. tormis, D. muelleri, D. darwini and D. ungeri. The results are consistent with previous studies and favour a monophyletic diplocynodontid clade. D. ungeri is the first species of the genus to be recognized from distant coeval European deposits, namely the Paris and the Pannonian Basins.