New insights into Europe’s most diverse Late Cretaceous anuran assemblage from the Maastrichtian of western Romania

Abstract

Uppermost Cretaceous (Maastrichtian) continental deposits in the Transylvanian region of western Romania contain a diverse and important assemblage of fossil vertebrates, including lissamphibians. Bones of anurans (frogs) and albanerpetontids are abundantly represented at multiple vertebrate microfossil localities in the region, but there continues to be no evidence for urodeles (salamanders) at any locality. Using previously reported and new collections of isolated bones, here we provide an up-to-date and comprehensive account of the anuran component of the Romanian assemblage, with particular emphasis on new specimens exhibiting features that are informative for differentiating species and resolving their higher level affinities. We recognise at least five species belonging to two or three families of moderately primitive (i.e. non-neobatrachian), crown-clade anurans: the alytids Paralatonia transylvanica, cf. Bakonybatrachus sp. and cf. Eodiscoglossus sp.; the bombinatorid Hatzegobatrachus grigorescui; and an indeterminate, possible pelobatid. Ilia previously reported as cf. Paradiscoglossus (a monotypic alytid genus reliably known only from the Maastrichtian of western North America) are here referred to Paralatonia. Also present are indeterminate alytids and at least two potentially distinctive, but indeterminate, taxa of uncertain family affinities. New specimens allow Hatzegobatrachus, formerly regarded as incertae sedis, to be assigned to Bombinatoridae as the geologically oldest member of that family. The Romanian Maastrichtian anuran assemblage is the most diverse yet documented for the European Late Cretaceous. It contains a mix of endemic taxa (Paralatonia and Hatzegobatrachus), a relict taxon (cf. Eodiscoglossus sp.), and one taxon (cf. Bakonybatrachus) possibly resulting from a pre-Maastrichtian dispersal from present-day Hungary. Compared to contemporaneous and older (Santonian–Campanian) anuran assemblages elsewhere in Europe, the Romanian assemblage is similar in containing alytids and a pelobatid-like taxon, but differs in having more alytid taxa (n = 3) and a bombinatorid, and in lacking the palaeobatrachids seen in the Campanian–Maastrichtian of Western Europe and the probable ranoid Hungarobatrachus reported from the Santonian of Hungary.