Bonini et al.—New toxodont from Jujuy Province, Argentina
Xotodon major (MACN PV 8570, ~45º). Xotodon cristatus has a more upraised symphysis, ~60º, similar to Calchaquitherium mixtum Nasif, Musalem, and Cerdeño, 2000 (~58º), which also is greater than in JUY-P 49. Toxodon Owen, 1837 and Mixotoxodon larensis Van Frank, 1957 present a very small angle (~20°) and protruding symphysis, and clearly differ from JUY-P 49 by the convex ventral profile of the horizontal ramus. Regarding the mandibular features, JUY-P 49 shows a
labial keel located at a basal position of the symphysis similar to, but less marked than, that observed in the other species of Xotodon. It differs from Calchaquitherium mixtum, in which the keel is thinner and more proximally placed. In addition, the symphysis of JUY-P 49 has a flattened surface anterior to the keel, as in C. mixtum, Posnanskytherium desaguaderoi Liendo Lazarte, 1943, X. major, X. cristatus, and X. prominens. The presence of a completely fused, U-shaped symphysis
constitutes a similar feature to that observed in X. cristatus, X. major, and C. mixtum, but in these species the symphysis is shallower and more elevated. In addition, the posterior border of the symphysis reaches the level of p3–4 similar to X. cristatus, X. prominens, and X. ambrosettii. The greatest height of the horizontal ramus of JUY-P 49
occurs at the same level as in C. mixtum. The lack of a ventral projection differentiates JUY-P 49 from Dinotoxodon paranensis (Laurillard in d’Orbigny, 1842), Pericotoxodon platignathus Madden, 1997, Gyrinodon quassus Hopwood, 1928, and Hoffstetterius imperator Saint-André, 1993. The morphology of i1 is similar to that observed in
X. prominens, whereas it differs from X. major by the absence of a lingual concavity and lesser labiolingual compression. The i2 differs from those of X. major, X. prominens, and X. cristatus because in these species it is crescent-shaped and presents a lingual concavity. The enamel bands of i1 and i2 show a similar arrangement to that in the species of Xotodon, as well as in
Table 1. Mandibular measurements (mm) of Xotodon maimarensis n. sp. (JUY-P 49, holotype).
Maximum length of the horizontal ramus (from p2 level backward) 310 Maximum length of the vertical ramus Symphyseal labial length
Maximum height of the horizontal ramus (p4–m1 level) Maximum height of the vertical ramus Width of the horizontal ramus at p2 level Width of the horizontal ramus at m3 level
55 70 75 85
26.4 28.1
571
Mixotoxodon larensis, Calchaquitherium mixtum, and Perico- toxodon platignathus. The i3 of JUY-P 49 is more rounded mesially and less compressed bucco-lingually than in X. major and X. prominens. Moreover, the lingual enamel band is broader than the labial one, as it occurs in X. cristatus, X. major, Pericotoxodon platignathus, Palyeidodon obtusum Roth, 1899, Hoffstetterius imperator, and Calchaquitherium mixtum. The presence of a diastema between i3 and p1 occurs in the
species of Xotodon as well as in Pericotoxodon platignathus, Toxodon platensis Owen, 1837, Hoffstetterius imperator, Trigodon gaudryi, and Hyperoxotodon speciosus (Ameghino, 1887). Although the species of Posnanskytherium present a lingually extended short paraconid that lacks enamel, they differ from JUY-P 49 in lacking an ento-hypoconid fold. The p1 is oval in cross section (Figs. 4, 5) as in Xotodon
cristatus, X. major, and C. mixtum, differing from X. prominens, in which this tooth is transversely compressed. The p2–3 of JUY-P 49 are transversely compressed as in other
species of Xotodon, and differ from Calchaquitherium mixtum,in whichthe p1 is oval in crosssectionand similarinsizetop2–3. The p4 is proportionally similar to that of species of
Xotodon and to C. mixtum, while its labial sulcus is less marked than in C. mixtum and X. ambrosettii, and similar to the condition in X. major and X. cristatus. The lower molars exhibit an anterior fold, which is placed
anterior to the level of the labial groove, as in Xotodon, Toxodon, and other toxodontids. The metaconid of the m1 (Figs. 4, 5) is slightly more
concave than in X. doellojuradoi, X. ambrosettii, X. cristatus, and X. major. The meta-entoconid fold is more developed than the posterior ento-hypoconid, as in most of species of Xotodon, except X. prominens, in which both folds are barely marked. The entoconid is more developed than in X. prominens and X. major. The hypoconulid does not protrude lingually with respect to the metaconid as in X. doellojuradoi. The posterior labial edge is more angular than in the other species of Xotodon, and is particularly different from those of X. cristatus and X. prominens. The posterior margin of the tooth is labio- lingually orientated, differing from the other species of the genus. The labial concavity opposite to the ento-hypoconid fold is less marked than in X. major and X. ambrosettii. The hypoconulid of m2 is more compressed anteroposter- iorly than in the other species of Xotodon, and is somewhat
Table 2. Lower cheek teeth dimensions (mm) of Xotodon maimarensis n. sp. (JUY-P 49, holotype) and other species of Xotodon.L = Length, W = width, * = approximately.
Taxa
Xotodon maimarensis n. sp. (JUY-P 49, holotype) Xotodon major
Xotodon foricurvatus (MLP M-200)
Xotodon ambrosettii Xotodon cristatus c
(MACN PV 8578, holotype) W 5.4 Xotodon doellojuradoi
L
(MACN 7965, holotype) W Xotodon prominens (MACN 7708)
L 8.12 W 5.05 L 9.1
p1
(MLP 52-X-6-21, holotype) W —— — L —— — W —— — — —
L —— —
7.16* 5.2* 7.7 5.5
L 7 W 5
(MLP 12-1672, holotype) W 4.1 L 8.7
10 5
7.54 4.67
10.8* 4.3*
19 11
p2 —
5.9*
14.7/14 6.8/6.5
p3
8.1* 6.3*
17.4/18.5 8.5/8 — — — —
16.59 7.68
12.6 6.2
15.58 9.37
16 7.5
13.8 7.9
p4
15.6* 9.4*
20.3/20.4 9/8.8 — — — —
16.64 9.79 — —
20 10.5 m1 25.7 10.35
32.4/31.7 10/9.2 26.65 7.6 — —
24.64 12.15 24.9 10.5 30.3 9.4
m2
24.6* 8.4*
31.7/32.2 9.9/10 26.77 8.9
27.28 9.98
24.69 11.27 25.4 11.4 28* 10.3
m3
35.86 10.7
42.5/43.2 8.4/9.2 33.61 6
— —
32.38 10.16 34.3 10.6 35.9 10.5
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