Journal of Paleontology, 91(5), 2017, p. 1083–1090 Copyright © 2017, The Paleontological Society 0022-3360/17/0088-0906 doi: 10.1017/jpa.2017.54
Dental eruption sequence and hypsodonty index of a Pleistocene macraucheniid from the Brazilian Intertropical Region
Leonardo Souza Lobo,1,2 Gisele Lessa,3 Cástor Cartelle,4 and Pedro S. R. Romano3
1Programa de Pós-Graduação em Biologia Animal, Universidade Federal de Viçosa. Avenida Peter Henry Rolfs, 36570-900, Viçosa, MG, Brazil ⟨
leoloboo@gmail.com⟩ 2Current address: Laboratório de Processamento de Imagem Digital, Museu Nacional, Universidade Federal do Rio de Janeiro. Quinta da Boa
Vista, São Cristóvão, 20940-040, Rio de Janeiro, RJ, Brazil 3Departamento de Biologia Animal, Universidade Federal de Viçosa. Avenida Peter Henry Rolfs, 36570-900, Viçosa, MG, Brazil
⟨
gislessa@yahoo.com.br⟩; ⟨
psrromano@gmail.com⟩ 4Pontifícia Universidade Católica de Minas Gerais (PUC Minas). Avenida Dom José Gaspar, 290 Coração Eucarístico, 30535-610, Belo Horizonte, Minas Gerais, Brazil ⟨
cartelle@pucminas.br⟩
Abstract.—Litopterna is represented in the Pleistocene of the Brazilian Intertropical Region by a monospecificgenus of Macraucheniidae, Xenorhinotherium. Although most of the knowledge about this family is derived from the denti- tion, some dental features still remain unknown. This study describes the eruption sequence of permanent dentition and classifies the hypsodonty status of X. bahiense. The specimens studied are from Toca dos Ossos, a limestone cave loca- ted in Bahia State. We perform qualitative macroscopic analysis to describe the eruption dental sequence. Additionally, we perform quantitative analysis to determine the hypsodonty index. The dental eruption sequence of the juvenile speci- men is M1, M2, I1, I2, M3, I3, P1, P2, P3, and P4. In addition, the analysis of tooth wear in adult specimens provides similar results. The hypsodonty index assigns a mesodont tooth crown for X. bahiense. The dental eruption sequence is most similar to a rapid-growth extant mammal. Moreover, our results do not support afrotherian-like delayed dental eruption to Litopterna. The hypsodonty index can be related to data on vegetation of the Brazilian Intertropical Region and the shape of the premaxilla of X. bahiense, both of which suggest a browsing diet for this macraucheniid.
Introduction
With 15 genera,Macraucheniidae Gervais, 1855 is one of the two more diverse and representative families of the order Litopterna, which is recorded fromthe late Eocene to Late Pleistocene–Early Holocene (Bond et al., 1999; Schmidt and Ferrero, 2014). This order is part of the group called SouthAmerican native ungulates (SANU) (Cifelli, 1985; Bond, 1999). Macraucheniidae includes middle- to large-sized herbivores and is considered a familymore conservative in dental and postcranial aspects than Proterother- iidae because of its complete dentition without diastema and the presence of three digits (Paula-Couto, 1979; Bond, 1999). Moreover, the lineage ofmacraucheniids is characterized mainly by gradual retraction of the nasals and the backward shift of the nostrils, which reaches the maximum in Pleistocene taxa (Bond, 1999; Cartelle, 1999). Records of macraucheniids in the Pleis- tocene are widely distributed throughout South America. In the Pleistocene, three monospecific genera are currently valid: Macrauchenia Owen, 1838; Macraucheniopsis Paula-Couto, 1945; and Xenorhinotherium Cartelle and Lessa, 1988 (Bond, 1999; Schmidt and Ferrero, 2014). The genus Xenorhinotherium, the focus of this study, occurred in Late Pleistocene–early Holocene. Its record is mainly in the Brazilian Intertropical Region (BIR), and it has also been recorded inMatoGrosso State and Venezuela, but these two occurrences of X. bahiense need to
be revised (Cartelle and Lessa, 1988; Cartelle, 1999; Salles et al., 2006; Socorro, 2006). Moreover, we do not agree with the nomenclatural action by Guérin and Faure (2004), which assigned X. bahiense Cartelle and Lessa, 1988 as a junior syno- nym of Macrauchenia patachonica Owen, 1838. First, Guérin and Faure (2004) did not compare their sample from caves in Piauí State with the type material of X. bahiense. Second, Guérin and Faure (2004) did not contest any diagnostic features of X. bahiense as originally assigned by Cartelle and Lessa (1988). Instead, Guérin and Faure (2004) deemed the observed variation between X. bahiense and M. patachonica species-level variation without properly testing such an assumption. Indeed, other stu- dies (e.g., Scherer et al., 2009) do not follow the taxonomic arrangement of Guérin and Faure (2004), and further phyloge- netic studies of Schmidt and Ferrero (2014) and Forasiepi et al. (2016) refuted the idea by revealing consistent morphological features that differ between the two monospecific genera. Initially, the BIR paleogeographic region of X. bahiense
occurrence was defined as characterized by dry forests, Cerrado and Caatinga ecosystems (sensu Cartelle, 1999). However, with input of new information from palynological and carbon isotope data, the definition of BIR was refined as a mixed environment of Atlantic and dry tropical forest, with a latitudinal difference that influenced the vegetation structure (Werneck et al., 2011; Dantas et al., 2013).
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