Lobo et al.—Dental features of Xenorhinotherium
calculated only for third lower molars that do not exhibit excessive dental wear. Therefore, the HI in X. bahiense is based on five specimens (MCL 3558, 3772, 3776, 3795, 3839), which are classified in stages 1 and 2. All the measurements are in millimeters (mm).
Results
Eruption sequence.—The dental remains of MCL 2643 (Xenorhinotherium bahiense paratype) are composed of two fragmented upper jaws with cheek teeth and 17 isolated teeth, adding up to 26 teeth belonging to this juvenile individual (Fig. 3). The right dentition contains dP3–M3 in a fragmentary upper jaw, and dI3–dC, dP2, I1–I3, and P2 isolated; also, the alveolar crypt of P3 and P4 is preserved. The left dentition contains dP4–M3 implanted in a fragmentary upper jaw, and dP1–dP3, I1–I2, and P2–P4 isolated, and the alveolar crypt of P4. The two sides of the paratype dentition exhibit the same dental features (Table 1). The two deciduous teeth exhibit distinct degrees of wear, with dP3 more worn than dP4. This makes it possible to determine that dP3 erupted before dP4. For the incisors, I1 and I2 exhibit roots in the same stage of devel- opment as the root of M2, which indicates that the I1 and I2 erupted before M3. All other premolars exhibited the same parameters examined, suggesting that all premolars erupted in a short period. Although there is a lack of information on permanent premolar eruption sequence, we obtained some information on the permanent eruption sequence through an analysis of deciduous premolars. The occlusal surfaces of the dP1–dP3 are completely worn, and even the dP4 is considerably worn, with occlusal structures still present and outlined by enamel (fossettes mesiolingual, median, and distolingual). This indicates that dP1–dP3 lost their function, whereas dP4 was still functional, therefore P1–P3 should have erupted before P4. Due to the absence of both C, their positions in the replacement sequence cannot be assessed. Therefore, we assumed that the sequence of replacement of permanent dentition in this juvenile specimen was M1>M2>I1>I2>M3>I3>P1>P2>P3>P4. The dentition of MCL 2644 (right and left) in the skull of
Figure 1. Structures of the cheek teeth of Xenorhinotherium bahiense. Abbreviations for upper cheek teeth (1): dc, distal cingulum; dif, distolingual fossette; el, ectoloph; hy, hypocone; maf, mesiolabial fossette; mast, metastyle; mc, mesial cingulum; me, metacone; mef, median fossette; mif, mesiolingual fossette; mst, mesostyle; pa, paracone; phc, protocone-hypocone crest; pro, protocone; pst, parastyle. Abbreviations for lower cheek teeth (2): co, cristid oblique; ecfd, ectoflexid; edfd, endoflexid; etd, entoconid; etfd, entoflexid; hyd, hypoconid; hyld, hypoconulid; hyphld, hypolophulid; med, metaconid; meld, metalophid; mefd, metaflexid; pald, paralophid; prod, protoconid; tal, talonid basin; tri, trigonid.
the holotype has the right I1–M3 and left P1–M3 (Fig. 4.1). The only incongruence within the eruption sequence is that the P4 exhibit the same wear stage of M1. The sequence I1–C exhibits the same level of wear, with the paracone worn but still keeping its shape. Other upper dentitions of adult individuals, MCL 3546 and MCL 3549, were also examined (Fig. 4.2, 4.3). As observed for MCL 2644, the P4 were more worn than M3 in all adult specimens. MCL 3546, a specimen with teeth less worn
1085
Figure 2. Wear degrees of Xenorhinotherium bahiense in upper (above) and lower (below) teeth. With wear progression, the enamel (highlighted in white) is worn and the dentine (highlighted in gray) is progressively exposed, whereas upper teeth fossettes (represented in black) become apparently smaller due to their conical shape until they disappear (see Figure 1 for structures identification).
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