A new Eocene Toxodontia (Mammalia, Notoungulata) from northwestern Argentina

A new species of Toxodontia (Mammalia, Notoungulata), <i>Pampahippus secundus</i> sp. nov., is described based on remains recovered from outcrops of the Lumbrera Formation exposed in Salta Province, northwest Argentina. The material studied consists of mandibular, maxillary, and premaxillary fragments with complete and incomplete teeth representing at least three individuals. It differs from the type species <i>P. arenalesi</i> by its smaller size and the presence of several dental features: I2 smaller than the I1 and I3, paraconule absent on the P3, upper molars wider than long and subquadrangular, with a single crista projecting from the ectoloph, strong mesiolingual cingulum surrounding the protocone on the M1, conspicuous metacone fold on the ectoloph of M1 and M2, and absence of labial cingulids on lower molars. In order to determine the phylogenetic position of <i>P. secundus</i> as well as different Paleogene notoungulates of northwestern Argentina, we performed a cladistic analysis. This analysis supports the paraphyly of Notohippidae proposed by previous authors and validates the monophyly of the genus <i>Pampahippus</i>, which ranks as a relatively basal taxon within Toxodontia. This contribution illustrates the significant and yet poorly known diversity of Paleogene toxodontians from northwestern Argentina and the importance of their study in the reconstruction of the evolutionary history of Notoungulata. http://zoobank.org/urn:lsid:zoobank.org:pub:EF8DACB3-3F71-4515-B99B-157ABBBFE092 SUPPLEMENTAL DATA—Supplemental materials are available for this article for free at www.tandfonline.com/UJVP Citation for this article: Deraco, V., and D. A. García-López. 2015. A new Eocene Toxodontia (Mammalia, Notoungulata) from northwestern Argentina. Journal of Vertebrate Paleontology. DOI: 10.1080/02724634.2015.1037884.

基于阿根廷西北部萨尔塔省出露的伦布赖拉组（Lumbrera Formation）地层中采集的化石标本，本文记述了弓齿兽目（Toxodontia，哺乳纲、南方有蹄目Notoungulata）一新种——次潘帕斯马（Pampahippus secundus）sp. nov.（新种）。
本次研究的标本包含下颌骨、上颌骨及前上颌骨碎片，附带完整与不完整的牙齿，代表至少3个个体。
该新种与模式种P. arenalesi的区别在于体型更小，且具备多项牙齿鉴别特征：上门齿2（I2）小于上门齿1（I1）与上门齿3（I3）；P3无小前尖（paraconule）；上臼齿宽大于长，呈近四边形，外脊（ectoloph）仅具1条脊状突起；M1的原尖（protocone）被发达的舌侧近中齿带环绕；M1与M2的外脊具显著的后尖褶（metacone fold）；下臼齿无唇侧齿带（labial cingulids）。
为确定次潘帕斯马（Pampahippus secundus）以及阿根廷西北部不同古近纪（Paleogene）南方有蹄类的系统发育位置，本文开展了支序分类学分析。
本次支序分析支持前人提出的马型有蹄科（Notohippidae）并系性观点，同时验证了潘帕斯马属（Pampahippus）的单系性，该属在弓齿兽目（Toxodontia）中属于较为基干的类群。
本研究揭示了阿根廷西北部古近纪弓齿兽类丰富但仍鲜为人知的多样性，以及此类群研究对于复原南方有蹄目（Notoungulata）演化历史的重要意义。
http://zoobank.org/urn:lsid:zoobank.org:pub:EF8DACB3-3F71-4515-B99B-157ABBBFE092
补充数据——本文补充材料可通过www.tandfonline.com/UJVP免费获取。
本文著录格式：Deraco, V. 与 D. A. García-López，2015年。来自阿根廷西北部的始新世弓齿兽目新类群（哺乳纲、南方有蹄目）。《Journal of Vertebrate Paleontology》（脊椎动物古生物学杂志）。DOI: 10.1080/02724634.2015.1037884。