Bonini et al.—New toxodont from Jujuy Province, Argentina
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genus, such as the lingual enamel extended anteriorly, the paraconid extended laterally and anteroposteriorly short, and m1–2 with a slight lingual convexity. However, JUY P–49 also has some characteristics that distinguish it as a new species: symphysis long and narrow with the slight divergence of its lateral borders; strong procumbence of lower incisors and dee- ply implanted i3; chin angle lower than in X. major and X. cristatus, and bulging labial keel limiting strong lateral con- cavities. The phylogenetic analysis provided two topologies that support the taxonomic interpretation of the specimen JUY P–49 as pertaining to the genus Xotodon. Our results indicate that the major diversification of Xotodon predated the Miocene/Pliocene boundary (5.3 Ma). The new species increases knowledge of the diversity and radiation of this group of notoungulates in northwest Argentina.
Acknowledgments
Figure 7. Chronostratigraphic calibration of the phylogenetic analysis. Abbreviations: Huayq., Huayquerian; Ma, mega annum; Marpl., Marplatan; Mh., Montehermosan; Piacen., Piacenzian; S. Am., South American.
as the sister group of X. maimarensis n. sp., which represents the sister group of the clade (X. prominens, X. major, X. cristatus). This relationship varies, however, in the second topology (Fig. 6.2) because X. maimarensis n. sp. results in the sister group of the clade formed by X. ambrosettii, X. prominens, X. major,and X. cristatus in node 21, although the relationships among these four species are not resolved. In both cases, the phylogenetic position of X. maimarensis n. sp. supports the taxonomic interpretation of JUY-P 49 as a new species of the genus Xotodon.
Radiation of the genus Xotodon.—Xotodon was widely dis- tributed during the Neogene in Argentina, and it was the most diversified Neogene Toxodontidae. The new species of Xotodon increases the knowledge on the radiation of Toxodontinae in northwest Argentina. The oldest known records of Xotodon come from late Miocene beds in northeast Argentina (Entre Ríos Province). The two species recorded from these beds, X. for- icurvatus and X. doellojuradoi, are only known by mandibular fragments and isolated teeth. The relatively limited Huayquerian fossil record does not indicate by itself the occurrence of a radiation during this time. However, when the obtained phylo- genetic hypotheses are calibrated against the geological age of fossil taxa, a basal radiation of Xotodon is revealed by the pre- sence of three ghost lineages that must have originated during the late Miocene (in addition to the two species recorded for this age; Fig. 7). These ghost lineages provide a minimum estimate for the age of the major diversification of Xotodon that predated the Miocene/Pliocene boundary (5.3 Ma).
Conclusions
The complete study of the toxodontid specimen JUY P–49 from the Maimará Formation (late Miocene–early Pliocene), Jujuy Province, northwestern Argentina, indicates that it should be identified as a new species of the genus Xotodon. Xotodon maimarensis n. sp. exhibits some general characters of the
Wethank the anonymous reviewers and Editor of the Journal for their critical and valuable comments that improved the quality and clarity of this paper. Thanks to B. Coira and C. Galli for their support during fieldwork at Quebrada de Humahuaca. We particularly thank A. Rivero for her valuable assistance during our work at the Museo de Geología, Mineralogía y Paleontolo- gía (Instituto de Geología y Minería, Universidad Nacional de Jujuy) and S.H. del Pino for his help during the calibration of Xotodon clades. We also thank D. Voglino and G. González for illustrations.
Accessibility of supplemental data
Data available from the Dryad Digital Repository: http://doi. org/10.5061/dryad.3111m
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