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Atoposaurid crocodyliforms represent an important faunal component of Late Jurassic to Early Cretaceous Laurasian semi-aquatic to terrestrial ecosystems, with numerous spatiotemporally contemporaneous atoposaurids known from western Europe. In particular, the Late Jurassic of France and Germany records evidence for high diversity and possible sympatric atoposaurid species belonging to  Alligatorellus ,  Alligatorium  and  Atoposaurus . However, atoposaurid taxonomy has received little attention, and many species are in need of revision. As such, this potentially high European diversity within a narrow spatiotemporal range might be a taxonomic artefact. Here we provide a taxonomic and anatomical revision of the Late Jurassic atoposaurid  Alligatorellus . Initially described as  A .  beaumonti  from the Kimmeridgian of Cerin, eastern France, additional material from the Tithonian of Solnhofen, south-eastern Germany, was subsequently referred to this species, with the two occurrences differentiated as  A. beaumonti beaumonti  and  A. beaumonti bavaricus , respectively. We provide a revised diagnosis for the genus  Alligatorellus , and note a number of anatomical differences between the French and German specimens, including osteoderm morphology and the configuration and pattern of sculpting of cranial elements. Consequently, we restrict the name  Alligatorellus beaumonti  to include only the French remains, and raise the rank of the German material to a distinct species:  Alligatorellus bavaricus . A new diagnosis is provided for both species, and we suggest that a recently referred specimen from a coeval German locality cannot be conclusively referred to  Alligatorellus . Although it has previously been suggested that  Alligatorellus ,  Alligatorium  and  Atoposaurus  might represent a single growth series of one species, we find no conclusive evidence to support this proposal, and provide a number of morphological differences to distinguish these three taxa that appear to be independent of ontogeny. Consequently, we interpret high atoposaurid diversity in the Late Jurassic island archipelago of western Europe as a genuine biological signal, with closely related species of  Alligatorellus ,  Alligatorium  and  Atoposaurus  in both French and German basins providing evidence for allopatric speciation, potentially driven by fluctuating highstand sea levels.

peerj

Revision of the Late Jurassic crocodyliform<i>Alligatorellus</i>, and evidence for allopatric speciation driving high diversity in western European atoposaurids

Revision of the Late Jurassic crocodyliformAlligatorellus, and evidence for allopatric speciation driving high diversity in western European atoposaurids