Bonini et al.—New toxodont from Jujuy Province, Argentina
late Miocene), Entre Ríos Province, northeast Argentina (Brunetto et al., 2013).
Other species.—Besides the type species, X. doellojuradoi, X. prominens, X. cristatus, X. major, and X. ambrosettii (see Fig. 1.1). See comments above on the taxonomic validity of X. smaltatus.
Generic diagnosis.—(after Pascual et al., 1966): Toxodontid with skull high and compressed, narrow palate and quite exca- vated. Highly compressed premolars, arranged in closed series; P1 crescent-shaped, with labial convexity, with a layer of labial and lingual enamel; P2 with a convex labial face. Upper molars with the anteroposterior diameter very oblique with respect to the direction of the jugal series; postero-lingual lobe shorter than Hemixotodon; M3 without lingual groove, and enamel almost reaching the postero-labial side. Lower molars with lingual enamel extended anteriorly and the anterolingual column short and prominent.
Xotodon maimarensis new species Figures 3.1–3.3, 4.1–4.3, Tables 1, 2
Holotype.—JUY-P 49: incomplete mandible with right hor- izontal ramus with all teeth, symphysis with all incisors, and a small fragment of the left ramus without teeth. Maimará Formation (late Miocene–early Pliocene), Jujuy Province, northwestern Argentina.
Diagnosis.—Lower incisors more procumbent than in X. cristatus, X. major, and X. prominens; symphysis long and narrow with slight divergence of its lateral borders; chin angle lower than in Xotodon major, X. cristatus, and Calchaquither- ium mixtum, rather different from Mixotoxodon larensis and Toxodon sp.; chin bulging at the level of p2–3, which continues anteriorly in a short labial keel more marked than in X. major; the bulge limits strong lateral concavities.
Occurrence.—Maimará Formation (late Miocene–early Pliocene), outcropping at the west of National Route 9 and Maimará town (23°37'27''S, 65°24'48''W), Quebrada de Mai- mará, Jujuy Province, Argentina. Note that the most fossilifer- ous levels at Quebrada de Maimará, where we recently collected the first vertebrates with precise stratigraphic provenance for this formation (Pujos et al., 2012; Candela et al., 2013; Abello et al., 2015), are located between the most basal tuffs of the section that outcrops west of Maimará town.
Description.—The mandible is high, with short diastemata anterior and posterior to the canine and p1. In lateral view (Figs. 3.1, 4.1) the incisors appear procumbent. The horizontal ramus is higher at the level of p4–m1 than posteriorly (Table 1), and its ventral margin is straight, without a ventral projection. The alveolar margin is slightly divergent with respect to the ventral margin from m3 to p2–3. At p3–4 level, the horizontal ramus is narrow and projects ventrolaterally in a little expanded edge. In occlusal view (Figs. 3.2, 4.2), the symphysis is completely fused, narrow and long, forming a well-developed
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U-shaped channel, barely widening forward; the posterior end of the symphysis reaches the level of p3–4. In ventral view (Figs. 3.3, 4.3), both hemimandibles
converge at the level of the ventrolateral expansion, forming a bulging chin that continues ahead into a centered short keel (Fig. 3.3), which would correspond to the “keeled chin” sensu Madden (1990, 1997). From this level, the symphysis widens and becomes labially flattened. Concerning preserved dentition (Figs. 3, 4; Table 2), the
incisors are heteromorphic, as in the most advanced Toxodonti- dae (Bond et al., 2006). The i1 and i2 are small and triangular in cross section, labio-lingually compressed, with an enamel band covering the mesial and labial sides and a narrow lingual enamel band near the mesial corner. The i3 are tusk-like and deeply implanted. They are subtriangular, mesially wide and with distally directed apices, with a round vertex (Fig. 3.2). The lingual enamel band is larger than the labial one, covering approximately three quarters of the lingual side; the mesial side lacks enamel. The canine and the premolars are broken. The canine is
separated from i3 and p1 by a short diastema; it is oval in cross section and bears a narrow enamel band on its labial side. The p1 is laterally compressed and approximately similar in size to p2 and p3 (Table 2). The p2 is separated from p1 by a short diastema; the posterior portion of p2 is broken, and is flattened transversally. Enamel covers the labial and lingual sides, both of which are smoothly concave. The p3 is similar to p2, but it is not possible to ascertain whether it has an enamel band. The p4 is the largest of the premolar series (Table 2). It is antero- posteriorly elongated, with lingual and labial enamel, and bears a smooth fold on the labial side. The molars are euhypsodont (sensu Mones, 1982). Their
crowns, typical of advanced toxodontids (Bond et al., 2006), are long and narrow, with a wide and labially convex trigonid and a long talonid that constitutes more than half of the molar (Figs. 3.2–4.2). These teeth present some characteristics indicated by Pascual et al. (1966) for Xotodon, such as the lingual enamel extended anteriorly, the paraconid extended laterally and anteroposteriorly short, and m1–2 with a slight lingual convexity. In addition, they present four columns and two lingual sulci as in Dinotoxodon Mercerat, 1895 or Toxodon, but they differ from these genera in depth of the sulci, outline of the columns, and contact between them. The labial side is completely covered by enamel in m1–3 and exhibits a deep and wide fold, posterior to the level of the anterior lingual fold. In the m1–2 the meta-entoconid fold is deeper, closer, and
directed more obliquely forward than the ento-hypoconid fold. The lingual enamel starts at the level of the anterior fold and reaches the posterior end of the hypoconulid, which is slightly extended lingually. The postero-labial angle of these teeth is well marked. In m3, the talonid is longer than in m1–2, and the ectoloph
bears a smooth concavity opposite to the ento-hypoconid fold. The postero-labial angle is more open than in m1–2, as a regular convexity.
Etymology.—Named after Maimará, a small town located in Tilcara Department, Jujuy Province, Argentina; the name is an Omaguaca (native language) word meaning “falling star.”
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