Durophagous adaptations in a new crocodyliform from the Santonian of Hungary and a systematic reassessment of European Cretaceous atoposaurids

Atoposauridae comprises a group of diminutive, semiterrestrial, brevirostrine neosuchian crocodyliforms that represents a characteristic component of European Jurassic-Cretaceous tetrapod faunas. Although frequently evaluated within the context of crown-group Crocodylia origins, their highly contested phylogenetic relationships continue to obscure their precise role in crocodylomorph evolutionary history. Particular ambiguity surrounds the monophyly of the genus Theriosuchus - with some hypotheses inferring long-term persistence of the lineage in Mesozoic Europe, whereas others interpreting select Cretaceous species as representatives of separate, even non-atoposaurid clades (e.g. Sabresuchus spp). We describe a new, stratigraphically intermediate taxon from the Santonian of Hungary based on isolated cranial elements, consistently placed as the sister taxon of Sabresuchus (Theriosuchus) sympiestodon from the Maastrichtian of Romania by our comprehensive set of phylogenetic analyses using three separate datasets. Sabresuchus tribodon sp. nov. is either recovered within Atoposauridae (global datasets) or Paralligatoridae (ingroup analysis) and can be distinguished from all other representatives of these groups by a specialized morphology consisting of massive, thick-enameled bulbous posterior maxillary teeth ornamented with apicobasal ridges, an extremely short rostrum with a reduced number of maxillary and dentary teeth, and the significantly upturned dorsal margin of the posterior dentary and surangular. Comparable anatomical adaptations are present in ecomorphologically convergent extinct crocodyliforms whose inferred feeding ecology included durophagy. However, this complete suite of characters has not been previously documented in either atoposaurids or paralligatorids. Our systematic reassessment results in an up-to-date taxonomy of Cretaceous European atoposaurids and tentatively confirms the polyphyly of Theriosuchus, though more definitive conclusions require combining individual, differently focused datasets. We reinterpret Aprosuchus ghirai from the Maastrichtian of Romania as a junior synonym of Sabresuchus sympiestodon and the putative European notosuchian Ogresuchus furatus from the Maastrichtian of Spain as an indeterminate atoposaurid.