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

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.

本文记述了产自阿根廷西北部胡胡伊省迈马腊组（晚中新世—早上新世）的后弓兽目（Notoungulata）弓齿兽科（Toxodontidae）一新种——迈马腊始弓兽（Xotodon maimarensis n. sp.）。这是东科迪勒拉山脉地区首次发现弓齿兽科物种。该标本馆藏于胡胡伊国立大学地质与矿物研究所地质、矿物与古生物学博物馆。标本为一件不完整下颌骨，保存有带部分齿列的右下颌支、保留全部门齿的部分下颌联合，以及无牙的左下颌支小片段。以下特征可将其确立为新分类单元：下颌联合狭长，侧缘轻微外展；下门齿强烈前倾，第三门齿（i3）植入深厚；下颌角低于X. major与X. cristatus；且具隆起的唇侧龙骨突，限定出显著的侧凹。基于最新修订的新近纪弓齿兽科类群开展的比较分析显示，迈马腊标本与始弓兽属（Xotodon）及混弓兽属（Mixotoxodon）共享下颌骨与牙齿特征，但相较于混弓兽属，其下颌联合位置更为上提。迈马腊始弓兽（Xotodon maimarensis n. sp.）的系统发育位置支持将该研究标本归入始弓兽属（Xotodon）新种的分类学判定。这一弓齿兽科新物种的发现，提升了我们对阿根廷西北部该类后弓兽类群多样性与辐射演化的认知。