A new fairy armadillo (Cingulata, Chlamyphoridae) from the Late Miocene of Argentine Pampas : first fossil record of the most enigmatic Xenarthra

Abstract

Recent reassessments of the systematic schemes of Cingulata, mainly based on molecular analyses, point out that its evolutionary history could be more complex than previously believed. An ancient divergence, ca. 45 Ma, was proposed for armadillos, recognizing two large monophyletic groups, Dasypodidae (including Dasypodinae) and Chlamyphoridae (including Euphractinae, Tolypeutinae, and Chlamyphorinae). Extant species included within Chlamyphorinae (fairy armadillos), Chlamyphorus truncatus Harlan, 1825, and Calyptophractus retusus Burmeister, 1863, are among the most bizarre, elusive and unknown mammals of the world, probably due to their strict fossorial behavior. Molecular data suggested the divergence of both species at ca. 17 Ma, coinciding with a marine ingression that could have stimulated cladogenesis. Here we report the first accurate fossil record of this enigmatic subfamily, coming from the Late Miocene (Arroyo Chasicó Formation; ~9 Ma) of the Argentine Pampas (southern Buenos Aires province), which represents a new genus and species. Materials (MMH-CH-87-7-100) include fixed and mobile osteoderms of the dorsal carapace, part of the rump plate, left hemimandible with complete dental series and other postcranial remains. The presence of a rump plate, ornamentation pattern and dental features allow including the fossil specimen within Chlamyphorinae. The size (~40% bigger than the extant species), larger thickness of the osteoderms and morphology of the rump plate, point towards a new taxon. The phylogenetic analysis carried out reflects the monophyly of the three known chlamyphorines, well supported by several unambiguous synapomorphies, and, in addition, includes the new fossil taxon as a sister group of the two extant species.