Introduction to Adalatherium hui (Gondwanatheria, Mammalia) from the Late Cretaceous of Madagascar

Abstract

Adalatherium hui is a latest Cretaceous (Maastrichtian) gondwanatherian mammal based on only a single specimen, a virtually complete, articulated, and well-preserved skull and postcranial skeleton. The specimen is the most complete and best preserved of any mammaliaform from the Mesozoic of the southern supercontinent Gondwana. It was discovered in the Anembalemba Member of the Maevarano Formation in the Mahajanga Basin of northwestern Madagascar. The holotype specimen includes the only complete lower jaw and the only postcranial remains known for Gondwanatheria, which, other than the cranium of Vintana sertichi (also from the latest Cretaceous of Madagascar), are represented only by isolated teeth and fragmentary dentaries. Despite being represented by an immature individual, A. hui is third only to V. sertichi and Coloniatherium cilinskii as the largest Mesozoic mammaliaform (based on body fossils) from Gondwana. Here, we (1) review the paucity of mammaliamorph skull and postcranial skeletal material from the Mesozoic of Gondwana relative to the record from Laurasia; (2) review the systematic paleontology of A. hui; (3) provide an overview of the history of discovery of the holotype specimen; (4) detail the preservation of the holotype, its preparation history, and the imaging techniques used to study it; (5) provide an overview of the geological context of A. hui, which indicates that the species lived close to the end-Cretaceous extinction event in a highly seasonal, semiarid climate; and (6) estimate the body mass of A. hui in the context of other Mesozoic mammaliaforms.

A new pelomedusoid turtle,Sahonachelys mailakavava, from the Late Cretaceous of Madagascar provides evidence for convergent evolution of specialized suction feeding among pleurodires

“…The Maevarano Formation was deposited at a time when northwestern Madagascar had a highly seasonal ( pronounced dry and wet seasons), semi-arid climate and was positioned at approximately 30°S latitude (15°farther south than today), in the subtropical desert belt [24,25]. Madagascar was isolated in the Indian Ocean, having been separated from the African mainland before 165 Ma, from Antarctica-Australia at approximately 124 Ma, and the Indian subcontinent at approximately 88 Ma, approximately 20 Myr earlier than when the Maevarano Formation was deposited [25].…”

“…The Maevarano Formation is of Maastrichtian (latest Cretaceous) age (see summary of geochronological data in [24]). The vertebrate assemblage from the formation includes dipnoan fishes (1 sp.…”