A new oxytomid bivalve from the Upper Jurassic – Lower Cretaceous of Antarctica
Praeaucellina umbonoradiata gen. et sp. nov. is a small pteriomorph bivalve from the Upper Jurassic-Lower Cretaceous of Antarctica which can be referred to the family Oxytomidae, within the superfamily Monotoidea. Sub-rounded to strongly obliquely elongated in outline, it is markedly inequivalve. The left valve is somewhat narrower than the right, and the latter possesses a clearly defined, but tiny, anterodorsal ear. This feature takes the form of a rounded blade which is strongly inclined with respect to the plane of commissure. This is a typical oxytomid feature, as is the presence of a pseudoctenolium. Indeed, there is now a considerable volume of morphological and stratigraphical evidence to suggest close phylogenetic ties with Late Jurassic-Early Cretaceous genera such as Aucellina and Oxytoma. Other austral oxytomids, such as Arctotis and Maccoyella, comprise a distinct morphological subgroup characterized by much thicker hinges. Whilst elucidation of the features of Praeaucellina helps to consolidate the taxonomic differences between the Oxytomidae and Buchiidae, it highlights further possible similarities between the former of these categories and the Monotidae. Resolution of phylogenetic relations within the Monotoidea will greatly assist studies of the evolution of Mesozoic high-latitude bivalve faunas.