The last horned armadillos: phylogeny and decline of Peltephilidae (Xenarthra, Cingulata) by DANIEL BARASOAIN 1, * , DARIN A. CROFT 2 , ALFREDO E. ZURITA 1 , VICTOR H. CONTRERAS 3 and RODRIGO L. TOMASSINI 4 1 Laboratorio de Evolucion de Vertebrados y Ambientes Cenozoicos, Centro de Ecolog ıa Aplicada del Litoral (UNNE-CONICET) y Catedra de Paleontolog ıa de Vertebrados, Facultad de Ciencias Exactas, Naturales y Agrimensura, Universidad Nacional del Nordeste, Corrientes RP5 3400, Argentina; danielbarasoain@gmail.com; aezurita74@yahoo.com.ar 2 Department of Anatomy, Case Western Reserve University School of Medicine, 10900 Euclid Ave, Cleveland 44106-4930 OH, USA; dcroft@case.edu 3 Facultad de Ciencias Exactas, F ısicas y Naturales, Instituto de Geolog ıa Dr Emiliano P. Aparicio, Departamentos Geolog ıa y Biolog ıa, Universidad Nacional de San Juan, Avenida Ignacio de La Rosa y Calle Meglioli, Rivadavia, San Juan 5400, Argentina; vcontre@unsj-cuim.edu.ar 4 INGEOSUR, Departamento de Geolog ıa, Universidad Nacional del Sur (UNS-CONICET), Avenida Alem 1253, Bah ıa Blanca 8000, Argentina; rodrigo.tomassini@yahoo.com.ar *Corresponding author Typescript received 6 September 2022; accepted in revised form 18 April 2023 Abstract: Peltephilidae (Xenarthra, Cingulata) is an ancient lineage of medium–large-sized ‘armadillos’ from South America, characterized by chisel-shaped molariforms, a U-shaped dental arcade, and cephalic osteoderms modified into hornlike structures. Although the biochron of the group extends from the early Eocene to the Late Miocene, the most abundant and complete records come from the Early Mio- cene of Patagonia. Remains from the Late Miocene are very scarce, and the last records of the group are from the Chas- icoan Stage (Tortonian). The only taxon known from this interval is Epipeltephilus kanti from the Arroyo Chasico For- mation (9.23 0.09 Ma; Buenos Aires Province, Argentina), a species previously represented only by a few isolated osteo- derms. Here we report new remains assigned to E. kanti from the Late Miocene of Loma de Las Tapias Formation (c. 9.0–7.8 Ma; San Juan Province, Argentina), including a hemimandible and several fixed and mobile osteoderms. These new specimens constitute the youngest record of Pel- tephilidae. The inclusion of E. kanti within Epipeltephilus and the monophyly of the genera Peltephilus and Epipeltephi- lus are corroborated for the first time through a cladistic analysis. The decline and eventual disappearance of this ‘armadillo’ group in the Late Miocene is chronologically coincident with the replacement of subtropical/tropical envi- ronments by more open and arid ones and with the prolifer- ation of other large armadillos such as Vetelia, Macrochorobates, and Macroeuphractus. Key words: Cenozoic, Epipeltephilus, evolutionary history, Miocene, Peltephilus, Xenarthra. X ENARTHRA is a major clade of placental mammals endemic to the Americas that is known for having an ancient origin and unusual evolutionary history due to the isolation of South America during most of the Cenozoic (O’Leary et al. 2013; Gaudin & Croft 2015; Foley et al. 2016). Within Xenarthra, two orders are recognized: Pilosa, which groups sloths (Folivora) and anteaters (Vermilingua); and Cingulata, which includes a large series of taxa with dermal armour (e.g. glyptodonts and armadillos; McKenna & Bell 1997; Delsuc et al. 2012; Gaudin & Croft 2015). In Cingulata, representatives of Peltephilidae constitute a very peculiar lineage, with a series of singular anatomi- cal features that enable them to be easily differentiated from other members of this order: (1) the presence of osteoderms of the cephalic shield at the level of the nasals modified into hornlike structures; (2) skull and dentary with robust structure; and (3) a very unusual dental series that includes chisel-shaped molariforms, a U-shaped den- tal arcade, and the absence of the anterior dental diastema that characterizes most cingulates (Ameghino 1891, 1894; Scott 1903–1904; Vizca ıno & Fari~ na 1997; Gonzalez-Ruiz et al. 2012; Montoya-Sanhueza et al. 2017). The anatomy of the armour of peltephilids is still not well known. Previous studies have described a cephalic shield and a dorsal carapace including at least several mobile bands and a pelvic shield (Gonzalez-Ruiz 2010; Gonzalez-Ruiz et al. 2012, 2013a, 2013b). Peltephilid osteoderms have several unique characteristics, such as a very rough dorsal surface, large dorsal foramina, and a reduced articular portion (in mobile osteoderms). More- over, in contrast to most other cingulates, peltephilids do not have osteoderms with an ornamentation pattern com- posed of differentiated figures, making it necessary to use © 2023 The Palaeontological Association. doi: 10.1002/spp2.1514 1 [Papers in Palaeontology, 2023, e1514]