1084


Journal of Paleontology 91(5):1083–1090 Tooth eruption sequence is a topic of important concern for


the study of ungulates, extant and extinct, due to its use in phylogenetic reconstructions and description of life history (Smith, 2000). In fact, this topic brought to light a discussion of SANU’s relationship with the high-level extant clades, in which Agnolin and Chimento (2011) claimed the close relationship of two SANU orders, Notoungulata and Astra- potheria, with Afrotheria. This hypothesis was based on their interpretation of three morphological characters: thoracolumbar vertebrae, late replacement of deciduous cheek teeth, and the presence of a fossa on astragalus. However, Billet and Martin (2011) and Kramarz and Bond (2014) examined material of three among the five SANU orders (Notoungulata, Astra- potheria, and Pyrotheria), and found no evidence to support an afrotherian-like delayed dental eruption in notoungulates, astrapotheres, and pyrotheres, contrary to the statement by Agnolin and Chimento (2011). Moreover, proteomic studies using collagen proteins to perform phylogenetic analysis suggested that SANU is within Laurasiatheria and closely related to Perissodactyla (Welker et al., 2015). Regarding the dental sequence of replacement for litopterns, the only data were provided by Bergqvist (2010), but they are restricted to the succession of the third and fourth premolars, and from Paleocene litopterns from Brazil. The pattern of dental replacement may indicate whether the


species lived and died on a fast or a slow time scale (Smith, 2000). However, the mammalian dentition also should provide other information by the classification of a tooth crown. This classification, at the hypsodonty level, could be determined by an index, expressing the ratio of tooth dimension (Janis, 1988). Nevertheless, the index of hypsodonty brings informa- tion about crown height, and, consequently, relates to mode of feeding. Its information has to be aligned with other aspects, such as habitat type and other morphological features, to provide insight about species diet (Damuth and Janis, 2011). Most characterizations of crown height in Macraucheniidae refer to Macrauchenia patachonica Owen, 1838, and, in a subjective way, are characterized as more hypsodont macrau- cheniid (Cifelli, 1985) or are just cited as hypsodont cheek teeth (Paula-Couto, 1979). Aside from these instances, there are no rigorous classifications for the tooth crowns of Pleistocene macracheniids (Paula-Couto, 1979; Cifelli, 1985). Consequently, the family needs a classification for phylogeny or morphological comparison, as is available for Protherotheriidae (Bond et al., 2001). In the present study, we describe the eruption sequence of


permanent upper dentition of the Pleistocene macraucheniid Xenorhinotherium bahiense using the juvenile paratype to evaluate if this species, a Late Pleistocene SANU, shows a delay on dental eruption. In addition, we determine the hypsodonty status of X. bahiense in order to clarify its ecological classifi- cation in the RIB biome, so providing information of this taxon to test hypotheses of relationship within the family.


Materials and methods


All the specimens analyzed came from Toca dos Ossos limestone cave, located at the municipally Ourolândia


(UTM 24K 275224, 8790872), Bahia State, Brazil. Cartelle and Lessa (1988) stated that the fossils were deposited at the cave during the Late Pleistocene to early Holocene.


Anatomical abbreviations.—C = upper canine; d = deciduous; HI = hypsodonty index; I = upper incisive; P, p = upper and lower premolars, respectively; M,m = upper and lower molars, respectively.


Repository and institutional abbreviation.—The material is housed in the MCL (Museu de Ciências Naturais da Pontifícia Universidade Católica de Minas Gerais, Belo Horizonte).


Description of eruption sequence.—The documentation of the dental ontogeny of X. bahiense is based on the juvenile paratype (MCL 2643), which has an upper jaw with nine deciduous teeth and 17 permanent teeth. We also analyzed eight jaws, three uppers (MCL 2644/01, 3546, 3549) and five lowers (MCL 3559, 3560, 3577, 3658, 3769), of adult specimens, observing the wear stages of fully erupted permanent teeth in order to compare the sequence of replacement in the juvenile specimen. Qualitative macroscopic analysis was performed in all teeth


to describe their ontogeny, evaluating three features: eruption stage, development of tooth’s root, and degree of wear. For the eruption stage, we assigned four stages: “not erupted” (with germ in its dental crypt); “erupting” (below alveolar margin); “erupting above alveolar margin”; and “fully erupted.” For the development of the tooth root, we assigned three stages: “root fully opened” (with neck that may be delimited); “root start closing” (neck and roots are well delimited); and “root closed” (all roots fully formed and closed). For the degree of wear, we assigned five wear stages for each dentition that had been delimited by a combination of occlusal structure features, seen in upper (Fig. 1.1), and lower (Fig. 1.2) dentition. For upper teeth, the stages range from “no wear” (stage 1) to “extremely worn” (stage 5); when cusps are completely worn, they have straight mesial and distal margins, and mesiolabial fossette is vestigial or absent (Fig. 2). The three intermediate stages are: “little wear” (stage 2), when mesial and median structures are little worn but distal structures (metacone, metastyle) not are worn; “inter- mediate wear” (stage 3), when all cups and styles are worn and the mesial and distal cingulum are still present; “heavyworn” (stage 4), when the mesiolabial fossette is shallow, the mesial cingulum is absent, and the distal cingulum is vestigial or absent. For lower teeth, the stages range from “no wear” (stage 1) to “cuspids extremely worn out” (stage 5), when all structures are completely worn and forming a continuous flat surface (Fig. 2). The three intermediate stages are: “little wear” (stage 2), when the paralophid, protoconid, and metalophid (labial trigonid structures) are more worn than metaconid and all talonid structures; “intermediate wear” (stage 3), when trigonid structures show the same level of wear, the talonid structures are less worn than trigonid, and the metaconid and cristid oblique still are indepen- dent; “heavy wear” (stage 4), when the trigonid and talonid are deeply worn and join the metaconid and cristid obliquely.


Hypsodonty index.—For the classification of X. bahiense,we used the hypsodonty index (HI; Janis 1988), which is the ratio between height and width of tooth crown. This index is


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