Untangling the taxonomic validity of Asterostemma Ameghino (Xenarthra, Cingulata, Glyptodontidae)

Abstract

Ameghino described the glyptodont Asterostemma, including originally three species (A. depressa, A. granata, and A. laevata) all based on osteoderms of the carapace from “Barrancas del Río Chico”, Santa Cruz Province, Argentina (Santa Cruz Formation, Early Miocene). Currently, Asterostemma is represented by two valid species: A. depressa, the type species, and A. barrealense. According to that, the objective of this contribution is to analyze the validity of both of them, and perform a revision of the assigned specimens. Asterostemma depressa was described by Ameghino in 1889 from at least two fragments of carapace. The osteoderms have a typical “rosette” pattern, with the central figure posteriorly displaced and well-marked sulci. The type material is currently lost (but described and figured by Ameghino) in the Museo Argentino de Ciencias Naturales “Bernardino Rivadavia” (MACN-A, Colección Nacional Ameghino) in Buenos Aires Province, and the description and illustrations of Ameghino do not offer diagnostic characters (e.g., a central figure surrounded by peripheral figures = rosette pattern) that allow to allocate or differentiate it from previously described glyptodonts from the Early Miocene (e.g., other Propalaehoplophoridae species). Asterostemma barrealense was described by Rusconi in 1946 from one fragment of carapace. The osteoderms have a typical “rosette” pattern, with the central figure posteriorly displaced and poorly marked sulci. The type material is located in the Museo de Ciencias Naturales y Antropológicas “Juan Cornelio Moyano” (MCNAM PV 154, type), in Mendoza Province. Of the two species, only A. depressa has specimens assigned to it, including a carapace fragment (MACN-A 1041), four osteoderms (MACN-A 4747–50), a portion of the cranium with molariforms, two osteoderms, a fragment of caudal armor, a fragment of carapace (MACN-A 7663–66), a fragment of the palate and a fragment of the caudal armor (MACN-A 7667), a fragment of the carapace (MACN-A S/N), and a caudal armor located in the Peabody Museum of Natural History, Yale University, U.S.A. (YMP VPPU 16001), but none of the assignations were justified. In summary, we found no diagnostic characters in the description and illustration of the type specimens of A. depressa or in the type specimen of A. barrealense that clearly justifies the recognition of two different species of Propalaehoplophoridae glyptodonts.