An early Campanian (late cretaceous) mammalian fauna from the lower shale member of the Aguja formation in the Big Bend region of Texas

The Lowerverse Local Fauna is a diverse early Campanian (c. 80-82 Ma) microvertebrate assemblage known from a single site in the lower shale member of the Aguja Formation near Big Bend National Park, Texas. The fauna includes chondrichthyan and osteichthyan fishes, amphibians, lizards, dinosaurs, birds, and mammals. Mammals are represented by more than 325 teeth and tooth fragments forming a diverse assemblage, including the spalacotheriid Symmetrodontoides, and at least ten species of multituberculates including ?Janumys, Paracimexomys, Cedaromys, Dakotamys, Cimolodon, and Meniscoessus. Seven species of marsupials are also present, including new species of Eoalphadon and ?Turgidodon, as well as representatives of ?Albertatherium, Varalphadon, several species of Alphadon, and the pediomyid Aquiladelphis, which is exemplified by the first reported deciduous premolars attributed to that genus. Eutherians are represented by new species of Paranyctoides and Gallolestes. A single unusual tooth fragment is attributed to the enigmatic South American taxa, ?Ferugliotheriidae.
Unique aspects of the Lowerverse mammalian assemblage may reflect its southern paleolatitude, but it also differs significantly from the younger Terlingua Local Fauna, known from the upper shale member of the Aguja Formation. The Lowerverse fauna has many genera in common with the Terlingua assemblage, but the presence of primitive taxa, particularly the plagiaulacid multituberculate ?Janumys and the spalacotheriid Symmetrodontoides, distinguish it from the Terlingua fauna. The two faunas are similar, however, in having several endemic taxa. Just as the Terlingua fauna is characterized by genera and species not reported elsewhere in the Western Interior (e.g. Alphadon perexiguus, Paleomolops langstoni), the Lowerverse fauna has a number of endemic species, for instance, the new species of Gallolestes and Paranyctoides. The enigmatic taxon ?Ferugliotheriidae has not previously been reported in North America. Although North American late Santonian (Aquilan) and middle Campanian (Judithian) mammalian faunas are well known, only two localities have thus far yielded probable early Campanian mammals (lower Wahweap Formation of Utah, and Menefee Formation of New Mexico). The Lowerverse fauna represents a third assemblage from this intermediate time frame, and may be useful in refining criteria used to define the boundary between Aquilan and Judithian North American Land Mammal Ages.

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