Quiñones Sofía I, Luna Carlos A, Miño-Boilini Ángel R, Candela Adriana M, Zurita Alfredo E
Laboratorio de Evolución de Vertebrados y Ambientes Cenozoicos, Centro de Ecología Aplicada del Litoral (CECOAL-CONICET) and Universidad Nacional del Nordeste, Corrientes, Argentina.
División Paleontología Vertebrados, Museo de La Plata, CONICET, Facultad de Ciencias Naturales y Museo, Universidad Nacional de La Plata, La Plata, Argentina.
J Anat. 2025 Feb;246(2):171-189. doi: 10.1111/joa.14152. Epub 2024 Oct 15.
Within Xenarthra (Eocene-Recent), Folivora developed (late Eocene-Recent) a remarkable diversity with respect to ecology and taxonomy over its evolutionary history. Knowledge of the diversity achieved by members of this clade in high-altitude areas of South America (i.e., Altiplano and Puna regions of Peru, Bolivia, and northwestern Argentina) has been improved in recent decades. A particular example involves the late Neogene Mylodontidae Simomylodon uccasamamensis, known mostly from multiple specimens recovered from the Bolivian Altiplano. Although several anatomical descriptions of this ground sloth have been published, almost nothing is known about its ontogenetic development and the associated morphological changes. Here we describe and compare new specimens of S. uccasamamensis from the upper level of the Tafna Formation (Pliocene) in the eastern Puna (ca. 3800 masl), Argentina, representing the southernmost record of this species. The new material is represented by specimens showing different ontogenetic stages, from infant to adult. One subadult specimen reached an estimated body mass of ca. 232 kg. The comparative study of external and internal morphology (the latter obtained from CT scans and radiography) shows remarkable changes in the mandible and molariforms associated with ontogeny; in addition, evidence suggests that the mfs2-3 are the first functional teeth, followed by mf1 and cf1. Based on our body mass estimates (ca. 232 kg.), we inferred an average lifespan of 14 years, 9-month gestation time, and sexual maturation at 4.1 years, quite similar to the values we obtained based on estimated body masses of adult specimens from Bolivia published by previous authors. Along its latitudinal distribution (ca. 14° S-21° S) S. uccasamamensis co-occurred with other ground sloths (e.g., Megatheriinae, Thalassocninae, and Scelidotheriinae), suggesting niche partitioning. The presence of this medium-sized ground sloth is consistent with the similarity between the faunas of eastern Puna and the Bolivian Altiplano during the Pliocene, which is also concordant with what was observed in other clades, such as Rodentia and Notoungulata.
在异关节总目（始新世至今）中，树懒亚目（晚始新世至今）在其进化历史中，在生态和分类学方面呈现出显著的多样性。近几十年来，人们对该类群成员在南美洲高海拔地区（即秘鲁、玻利维亚以及阿根廷西北部的阿尔蒂普拉诺高原和普纳地区）所实现的多样性有了更多了解。一个具体例子是新近纪晚期的磨齿兽科动物乌卡萨马米西蒙地懒，主要依据从玻利维亚阿尔蒂普拉诺高原采集到的多个标本得知。尽管已经发表了关于这种地懒的一些解剖学描述，但对于其个体发育过程以及相关的形态变化却几乎一无所知。在此，我们描述并比较了来自阿根廷普纳东部塔夫纳组上部层位（上新世，海拔约3800米）的乌卡萨马米西蒙地懒新标本，这代表了该物种最南端的记录。新材料包括显示从幼年到成年不同个体发育阶段的标本。一个亚成年标本的估计体重约为232千克。对外部和内部形态的比较研究（后者通过CT扫描和X光摄影获得）表明，下颌骨和臼齿状牙齿与个体发育相关的显著变化；此外，有证据表明mfs2 - 3是最早发挥功能的牙齿，随后是mf1和cf1。根据我们的体重估计（约232千克），我们推断其平均寿命为14年，妊娠期为9个月，性成熟年龄为4.1岁，这与我们根据先前作者发表的玻利维亚成年标本估计体重得出的值非常相似。沿着其纬度分布（约南纬14° - 21°），乌卡萨马米西蒙地懒与其他地懒（如大地懒亚科、海懒亚科和雕齿兽亚科）共生，这表明存在生态位划分。这种中型地懒的存在与上新世普纳东部和玻利维亚阿尔蒂普拉诺高原动物群之间的相似性相符，这也与在其他类群（如啮齿目和南方有蹄目）中观察到的情况一致。
