568
Journal of Paleontology 91(3):566–576
established the relationships of the Xotodon clade. These trees are discussed in the corresponding section and compared with previous results (Forasiepi et al., 2015). In the case of the analysis of radiation of the genus
Xotodon, the incompleteness of the fossil record means that minimum divergence times must be established through the calculation of ghost lineages (Norell, 1996), which extend the temporal range of a lineage (a species) prior to its appearance in the fossil record based on information from its sister lineage. Calibrated phylogenetic trees were obtained using a script that takes into account the chronostratigraphic information for fossil taxa in TNT (it calculates MSM*, GER, and provides a calibrated topology in nexus format). We identified “ghost lineages” following the methodology proposed by previous authors (Pol and Norell, 2001), considering the age of the first appearance of each terminal taxon in the fossil record as the only relevant temporal information (Pol et al., 2004).
Basin area (modified from Abello et al., 2015), showing Maimará and Tilcara formations and 206Pb/238U zircon ages obtained from several volcanic ashes in Humahuaca Basin volcanic rocks (Pingel et al., 2013). (2) Stratigraphic section at Quebrada de Maimará (modified from Abello et al., 2015) showing the most basal tuffs of the section, modified from Pujos et al. (2012).
Figure 2. (1) Simplified Cenozoic chronostratigraphy of the Humahuaca
We added a third state to character 26 because some taxa exhibit a smooth posterolingual groove in P3–P4 (262). The data matrix (see Supplementary Data) comprises 31
terminal taxa and 59 morphological (cranial and dental) characters, treated as non-additive. We conducted a heuristic search with Tree Bisection Reconnection (TBR) using 100 random addition sequences and saving 20 trees per round. Subsequently, we performed a new TBR search, saving the new trees. With this methodology, we obtained 27 most parsimo- nious trees of 192 steps with a consistency index (CI) of 0.43 and a retention index (RI) of 0.67. Then, we carried out searches under implied weights (k3–k100) and from k6 the program provided two most parsimonious topologies, which better
Repositories and institutional abbreviations.—The specimen JUY-P 49 is represented by an incomplete right mandibular ramus with poorly preserved dentition, part of the symphysis with the incisors (i3 broken) and canines, and a small fragment of the left ramus without teeth. This specimen is housed in the Museo de Geología Mineralogía y Paleontología (MGMyP), Instituto de Geología y Minería, Universidad Nacional de Jujuy, Argentina. JUY-P 49 was found by Dr. R. Loss on January 5, 1950, in the outcrops of Maimará Formation, in the Quebrada de Maimará west of Maimará town (Fig. 1.2). Morphometric and taxonomic studies included direct comparisons with material assigned to several species of Neogene toxodontids deposited in various national institutions, and bibliographical research focused on SouthAmerican Toxodontidae (e.g., Madden, 1990, 1997; Saint-André, 1993; Nasif et al., 2000; Bond et al., 2006, and Forasiepi et al., 2015). FMNH-P, Field Museum of Natural History, Vertebrate Paleontological Collections, Chicago, USA; JUY-P, Museo de Geología, Mineralogía y Paleontología, Instituto de Geología y Minería, Universidad Nacional de Jujuy, San Salvador de Jujuy, Argentina;MACN, Museo Argentino de Ciencias Naturales “Bernardino Rivadavia”, Buenos Aires, Argentina; MLP, Museo de La Plata, La Plata, Argentina; MMP, Museo Municipal de Ciencias Naturales “Lorenzo Scaglia”, Mar del Plata, Argentina; PVL, Facultad de Ciencias Naturales e Instituto Miguel Lillo, Sección de Paleovertebrados Lillo, San Miguel de Tucumán, Argentina.
Systematic paleontology
Anatomical abbreviations.—c, canine; i, incisor; m, molar; p, premolar.
Class Mammalia Linnaeus, 1758 Order Notoungulata Roth, 1903
Suborder Toxodontia Owen, 1853 Family Toxodontidae Gervais, 1847
Subfamily Toxodontinae Trouessart, 1898 Genus Xotodon Ameghino, 1887
Type species.—Xotodon foricurvatus (Ameghino, 1885), “Mesopotamiense” (lower member of the Ituzaingó Formation,
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