Maga A Murat, Beck Robin M D
Division of Craniofacial Medicine, Department of Pediatrics, University of Washington, Seattle, Washington, United States of America.
Department of Anthropology, University of Washington, Seattle, Washington, United States of America.
PLoS One. 2017 Aug 16;12(8):e0181712. doi: 10.1371/journal.pone.0181712. eCollection 2017.
We describe a near-complete, three-dimensionally preserved skeleton of a metatherian (relative of modern marsupials) from the middle Eocene (Lutetian: 44-43 million years ago) Lülük member of the Uzunçarşıdere Formation, central Turkey. With an estimated body mass of 3-4 kg, about the size of a domestic cat (Felis catus) or spotted quoll (Dasyurus maculatus), it is an order of magnitude larger than the largest fossil metatherians previously known from the Cenozoic of the northern hemisphere. This new taxon is characterised by large, broad third premolars that probably represent adaptations for hard object feeding (durophagy), and its craniodental morphology suggests the capacity to generate high bite forces. Qualitative and quantitative functional analyses of its postcranial skeleton indicate that it was probably scansorial and relatively agile, perhaps broadly similar in locomotor mode to the spotted quoll, but with a greater capacity for climbing and grasping. Bayesian phylogenetic analysis of a total evidence dataset comprising 259 morphological characters and 9kb of DNA sequence data from five nuclear protein-coding genes, using both undated and "tip-and-node dating" approaches, place the new taxon outside the marsupial crown-clade, but within the clade Marsupialiformes. It demonstrates that at least one metatherian lineage evolved to occupy the small-medium, meso- or hypo-carnivore niche in the northern hemisphere during the early Cenozoic, at a time when there were numerous eutherians (placentals and their fossil relatives) filling similar niches. However, the known mammal fauna from Uzunçarşıdere Formation appears highly endemic, and geological evidence suggests that this region of Turkey was an island for at least part of the early Cenozoic, and so the new taxon may have evolved in isolation from potential eutherian competitors. Nevertheless, the new taxon reveals previously unsuspected ecomorphological disparity among northern hemisphere metatherians during the first half of the Cenozoic.
我们描述了一具近乎完整、三维保存的中始新世（路特阶：4400 - 4300万年前）土耳其中部乌尊恰尔希代雷组吕吕克段的有袋类（现代有袋动物的近亲）骨架。其估计体重为3 - 4千克，与家猫（Felis catus）或斑袋鼬（Dasyurus maculatus）大小相近，比此前已知的北半球新生代最大的有袋类化石大一个数量级。这个新分类单元的特征是具有大而宽的第三前磨牙，这可能代表了对硬食物摄食（食硬）的适应，其颅齿形态表明它有产生高咬合力的能力。对其后肢骨骼的定性和定量功能分析表明，它可能是树栖性的且相对敏捷，运动模式可能与斑袋鼬大致相似，但攀爬和抓握能力更强。使用未标定时间和“枝端-节点标定”方法，对包含259个形态特征和来自五个核蛋白编码基因的9kb DNA序列数据的全证据数据集进行贝叶斯系统发育分析，将这个新分类单元置于有袋类冠群之外，但在有袋形目分支内。这表明在新生代早期，至少有一个有袋类谱系在北半球进化，占据中小型、中或低食肉动物生态位，而此时有大量真兽类（胎盘类及其化石近亲）占据类似生态位。然而，来自乌尊恰尔希代雷组的已知哺乳动物群似乎高度特有，地质证据表明土耳其的这个地区在新生代早期至少部分时间是一个岛屿，因此这个新分类单元可能是在与潜在的真兽类竞争者隔离的情况下进化而来的。尽管如此，这个新分类单元揭示了北半球新生代上半叶有袋类动物此前未被怀疑的生态形态差异。
