Gabriela I. Schmidt

An almost complete skeleton of a new Mesotheriidae (Notoungulata) from the Late Miocene of Casira, Bolivia

A partial mesotheriine skeleton (Notoungulata, Mesotheriidae) from the Late Miocene Casira locality, southern Bolivia, is fully described and reinterpreted taxonomically. This specimen (MNHN-Bol-V-003724) was partially described previously without a taxonomic discussion, as it was considered to be Plesiotypotherium sp. After comparison with other Bolivian, Argentinean and Chilean mesotheres, we recognize a new species of the genus Plesiotypotherium Villarroel, P. casirense sp. nov., characterized by: nasals slightly enlarged posteriorly; zygomatic arch with strong antero-distal angle; zygomatic plate starting at the level of P4 and reaching the level of the anterior part of M3; lacrimal bony process; large infraorbital foramen; posterior border of the mandible very convex; P4 without lingual groove and with narrow and projected parastyle; M3 with simple third lobe; larger and more robust skeleton than other Plesiotypotherium species. Most postcranial elements are described in detail for the first time for Plesiotypotherium. The incomplete skull GB-KKL 740 from the same locality is also referred to the new taxon. P. casirense is the sister group of P. achirense Villarroel in the phylogenetic analysis, but the genus Plesiotypotherium appears as paraphyletic. The revised partial skull GB-ACH 100 from Achiri, Bolivia, which was labelled as Plesiotypotherium sp., does not belong to this genus, and it appears phylogenetically closer to Pseudotypotherium and Mesotherium. Plesiotypotherium casirense sp. nov. increases the known diversity of the Mesotheriidae in both the Miocene of Bolivia and the South American faunal context.

Exceptional Skull of Huayqueriana (Mammalia, Litopterna, Macraucheniidae) From the Late Miocene of Argentina: Anatomy, Systematics, and Paleobiological Implications

ABSTRACT The Huayquerías Formation (Late Miocene, Huayquerian SALMA) is broadly exposed in west-central Argentina (Mendoza). The target of several major paleontological expeditions in the first half of the 20th century, the Mendozan Huayquerías (“badlands”) have recently yielded a significant number of new fossil finds. In this contribution we describe a complete skull (IANIGLA-PV 29) and place it systematically as Huayqueriana cf. H. cristata (Rovereto, 1914) (Litopterna, Macraucheniidae). The specimen shares some nonexclusive features with H. cristata (similar size, rostral border of the orbit almost level with distal border of M3, convergence of maxillary bones at the level of the P3/P4 embrasure, flat snout, very protruding orbits, round outline of premaxillary area in palatal view, and small diastemata between I3/C and C/P1). Other differences (e.g., lack of sagittal crest) may or may not represent intraspecific variation. In addition to other features described here, endocast reconstruction utilizing computer tomography (CT) revealed the presence of a derived position of the orbitotemporal canal running below the rhinal fissure along the lateroventral aspect of the piriform lobe. CT scanning also established that the maxillary nerve (CN V2) leaves the skull through the sphenoorbital fissure, as in all other litopterns, a point previously contested for macraucheniids. The angle between the lateral semicircular canal and the plane of the base of the skull is about 26°, indicating that in life the head was oriented much as in modern horses. Depending on the variables used, estimates of the body mass of IANIGLA-PV 29 produced somewhat conflicting results. Our preferred body mass estimate is 250 kg, based on the centroid size of 36 3D cranial landmarks and accompanying low prediction error. The advanced degree of tooth wear in IANIGLA-PV 29 implies that the individual died well into old age. However, a count of cementum lines on the sectioned left M2 is consistent with an age at death of 10 or 11 years, younger than expected given its body mass. This suggests that the animal had a very abrasive diet. Phylogenetic analysis failed to resolve the position of IANIGLA-PV 29 satisfactorily, a result possibly influenced by intraspecific variation. There is no decisive evidence for the proposition that Huayqueriana, or any other litoptern, were foregut fermenters.

Taxonomic reinterpretation of Theosodon hystatus Cabrera and Kraglievich, 1931 (Litopterna, Macraucheniidae ) and phylogenetic relationships of the family

ABSTRACT Associated fragments of a maxilla and mandible of Theosodon hystatus Cabrera and Kraglievich (Macraucheniidae, Litopterna) from the late Miocene Arroyo Chasicó locality (Buenos Aires Province, Argentina) are described and taxonomically reinterpreted. The systematic arrangement is supported by the first phylogenetic analysis of the family. The holotype (MLP 29-IX-1-75) of T. hystatus was originally poorly described and its generic assignation was not fully justified. The comparison of MLP 29-IX-1-75 with Paranauchenia denticulata Ameghino from the ‘Mesopotamiense’ (lower member of the Ituzaingó Formation, Entre Ríos Province; late Miocene) shows significant morphological similarities that lead us to propose that T. hystatus belongs to the genus Paranauchenia Ameghino, resulting in the new combination Paranauchenia hystata. The phylogenetic analysis of Macraucheniidae supports this proposal because both taxa form a monophyletic clade, sharing one synapomorphy: metaconid of m2 lingually placed. This new taxonomic interpretation implies the geographic extension of Paranauchenia to Buenos Aires Province. The obtained phylogeny also corroborates the monophyly of Macraucheniidae, but not that of the currently considered subfamilies, because Cramaucheniinae is paraphyetic.

First record of Toxodontidae (Mammalia, Notoungulata) from the late Miocene–early Pliocene of the southern central Andes, NW Argentina

Abstract. A new species of toxodontid notoungulate, Xotodon maimarensis n. sp., is described from the Maimará Formation (late Miocene—early Pliocene), Jujuy Province, northwestern Argentina. This is the first record of a toxodontid from the Eastern Cordillera. The specimen is housed at the Museo de Geología, Mineralogía y Paleontología, Instituto de Geología y Minería de la Universidad Nacional de Jujuy. It consists of an incomplete mandible preserving the right mandibular ramus with part of the dental series, partially preserved symphysis with all the incisors, and a small portion of the left ramus without teeth. The following characters distinguish it as a new taxon: symphysis long and narrow with slight divergence of its lateral borders; strong procumbence of lower incisors and deeply implanted i3; chin angle lower than in X. major and X. cristatus and bulging labial keel limiting strong lateral concavities. Comparative analysis in the context of the recently revised Neogene Toxodontidae indicates that the Maimará specimen shares mandibular features and dental characters with Xotodon and Mixotoxodon, differing from the latter by the more upraised symphysis. The phylogenetic position of Xotodon maimarensis n. sp. supports the taxonomic interpretation of the studied specimen as a new species of Xotodon. This new Toxodontidae increases the knowledge of the diversity and radiation of this group of notoungulates in northwest Argentina.