A new bizarre armadillo (Mammalia, Xenarthra, Dasypodidae) from the late Miocene of Ecuador

Abstract

The Dasypodidae (Astegotheriinae, Stegotheriinae and Dasypodinae), constitute the sister group of the remaining diversity of "armadillos" (Chlamyphoridae), and the most ancient group within Xenarthra, with a divergence estimated in ca. 40 Ma. Among Dasypodidae, only Dasypodinae has living representatives, including over 8 species of Dasypus. Dasypodinae armadillos have their oldest records coming from the middle Miocene of La Venta (Colombia), and become relatively abundant at lower latitudes in South America during the Miocene. Recognized taxa for this lapse include Plesiodasypus colombianus (La Victoria Formation, ca. 13 Ma) and Anadasypus hondanus (Villavieja Formation, ca. 12 Ma) for the middle Miocene of La Venta, Colombia, and Anadasypus aequatorianus (Letrero Formation, ca. 11.2-9 Ma) for the late Miocene of Nabón, Ecuador. Here, we report a new and bizarre armadillo exhumed from the Letrero Formation levels outcropping at Nabón basin, southern Ecuador. Materials (EPNPv-6381) are housed in the Colección de Paleontología, Escuela Politécnica Nacional (Quito, Ecuador), and include several fixed and mobile osteoderms of the dorsal carapace belonging to a single individual, which was found partially articulated in the field. The presence of enlarged mobile osteoderms with a very developed articular portion and a clear dasypodine-like ornamentation pattern (shared by all dasypodine armadillos) on their exposed surface allow to include it within Dasypodidae Dasypodinae. In turn, the presence of fixed osteoderms with a rectangular outline, and an ornamentation pattern composed of an elongated and keeled central figure surrounded by minor peripheral figures allow its inclusion within Plesiodasypus. This new taxon is supported by some unusual features that represent solid autapomorphic characters, being the most relevant: 1) denticulated lateral edges in fixed osteoderms and the articular portions of mobile osteoderms, and 2) very large foramina along the main sulcus that delimitates the central figure of mobile osteoderms, tentatively interpreted as a complex glandular system restricted to mobile osteoderms, though a certain degree of associated pilosity cannot be discarded. A morphological cladistic analysis including several extinct and extant Chlamyphoridae and Dasypodidae armadillos corroborates its inclusion within Plesiodasypus, as well as the early divergent position of this genus within Dasypodinae. This taxon represents the second armadillo recorded for the Letrero Formation (the other being A. aequatorianus), increasing the Dasypodidae diversity at low latitudes during the late Miocene. Additionally, the unusual morphology of this taxon is concordant with the associated endemic paleofauna previously recorded at Nabón basin, which suggests some kind of isolation. R2