Boyer Doug M, Prasad Guntupalli V R, Krause David W, Godinot Marc, Goswami Anjali, Verma Omkar, Flynn John J
Department of Ecology and Evolution, Stony Brook University, Stony Brook, NY 11794-5425, USA.
Naturwissenschaften. 2010 Apr;97(4):365-77. doi: 10.1007/s00114-010-0648-0. Epub 2010 Feb 4.
Extant species of the supraordinal mammal clade Euarchonta belong to the orders Primates, Scandentia, or Dermoptera. The fossil record of euarchontans suggests that they underwent their initial radiation during the Paleocene (65-55 million years ago) in North America, Eurasia, and Africa. The time and place of origin is poorly resolved due to lack of definitive fossils of euarchontan stem taxa. We describe a fragmentary humerus and two fragmentary ulnae from the latest Cretaceous of India that bear significantly on this issue. The fossils are tentatively referred to Deccanolestes cf. hislopi due to their small size and the fact that Deccanolestes is the only eutherian dental taxon to have been recovered from the same locality. The new fossils are used to evaluate the existing behavioral hypothesis that Deccanolestes was arboreal, and the competing phylogenetic hypotheses that Deccanolestes is a stem eutherian versus a stem euarchontan. The humerus resembles those of euarchontans in possessing a laterally keeled ulnar trochlea, a distinct zona conoidea, and a spherical capitulum. These features also suggest an arboreal lifestyle. The ulnar morphology is consistent with that of the humerus in reflecting an arboreal/scansorial animal. Detailed quantitative comparisons indicate that, despite morphological correlates to euarchontan-like arboreality, the humerus of Deccanolestes is morphologically intermediate between those of Cretaceous "condylarthran" mammals and definitive Cenozoic euarchontans. Additionally, humeri attributed to adapisoriculids are morphologically intermediate between those of Deccanolestes and definitive euarchontans. If adapisoriculids are euarchontans, as recently proposed, our results suggest that Deccanolestes is more basal. The tentative identification of Deccanolestes as a basal stem euarchontan suggests that (1) Placentalia began to diversify and Euarchonta originated before the Cretaceous-Tertiary boundary and (2) the Indian subcontinent, Eurasia, and Africa are more likely places of origin for Euarchonta than is North America.
真灵长总目哺乳动物分支的现存物种属于灵长目、树鼩目或皮翼目。真灵长类动物的化石记录表明，它们在古新世（6500万至5500万年前）于北美、欧亚大陆和非洲经历了最初的辐射演化。由于缺乏真灵长类干群分类单元的确切化石，其起源的时间和地点仍难以确定。我们描述了来自印度晚白垩世的一块肱骨碎片和两块尺骨碎片，这些化石对这个问题有重要影响。由于它们的尺寸较小，且德干兽是唯一从同一地点发现的真兽类牙齿分类单元，这些化石暂被归入德干兽属（Deccanolestes cf. hislopi）。这些新化石被用于评估现有的行为假说，即德干兽是树栖动物，以及相互竞争的系统发育假说，即德干兽是真兽类干群还是真灵长类干群。该肱骨与真灵长类动物的肱骨相似，具有外侧有嵴的尺骨滑车、明显的圆锥区和球形肱骨头。这些特征也表明其具有树栖生活方式。尺骨形态与肱骨一致，反映出一种树栖/攀缘动物。详细的定量比较表明，尽管德干兽的肱骨在形态上与类似真灵长类的树栖性有关，但它在形态上介于白垩纪“有蹄类”哺乳动物和确定的新生代真灵长类动物之间。此外，归属于阿氏猬兽类的肱骨在形态上介于德干兽和确定的真灵长类动物之间。如果如最近所提出的，阿氏猬兽类是真灵长类动物，我们的结果表明德干兽更为原始。将德干兽初步鉴定为真灵长类干群基部物种表明：（1）胎盘类开始多样化，且真灵长总目在白垩纪 - 第三纪边界之前就已起源；（2）印度次大陆、欧亚大陆和非洲比北美更有可能是真灵长总目的起源地。
