Neither a rodent nor a platypus : a reexamination of Necrolestes patagonensis Ameghino ; American Museum novitates, no. 3546

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New York, NY : American Museum of Natural History
We present new descriptions, figures, and interpretations of well-preserved cranioskeletal elements of the early Miocene, fossorial mammal Necrolestes patagonensis from Argentina. As previously noted, this animal is highly apomorphic and its phylogenetic affinities are difficult to interpret. Its derived features include hypsodont upper cheek teeth, a partially fused cervical spine, an unfused atlas consisting of separate right and left massae, and a distally ossified flexor tendon of the forearm. Characters that support its status as a therian mammal include a coiled cochlear housing of the inner ear. Consistent with its status as a metatherian is the presence of five upper incisors, transverse canal foramina, and a broad proximal fibula. However, we cannot confirm other characters claimed by previous researchers as evidence for affinity with marsupial or nonplacental mammals, such as the presence of an inflected mandibular angle and epipubic bones. Furthermore, Necrolestes shows similarities to eutherian mammals, such as small incisive foramina and possibly three molars. On biogeographic and some anatomical grounds, identification of Necrolestes as a metatherian remains a compelling option. However, pending a combined-data phylogenetic analysis encompassing Theria and accounting for the anatomical diversity of Necrolestes, possible membership in Eutheria should not be ruled out.
40 p. : ill. ; 26 cm.
Includes bibliographical references (p. 37-40).