Museum of the Rockies andDepartment of Earth Sciences, Montana State University, Bozeman, MT 59717; and
Museum of the Rockies andDepartment of Earth Sciences, Montana State University, Bozeman, MT 59717; and.
Proc Natl Acad Sci U S A. 2014 Jul 15;111(28):10245-50. doi: 10.1073/pnas.1313334111. Epub 2014 Jun 30.
The placement of over 50 skulls of the well-known horned dinosaur Triceratops within a stratigraphic framework for the Upper Cretaceous Hell Creek Formation (HCF) of Montana reveals the evolutionary transformation of this genus. Specimens referable to the two recognized morphospecies of Triceratops, T. horridus and T. prorsus, are stratigraphically separated within the HCF with the T. prorsus morphology recovered in the upper third of the formation and T. horridus found lower in the formation. Hypotheses that these morphospecies represent sexual or ontogenetic variation within a single species are thus untenable. Stratigraphic placement of specimens appears to reveal ancestor-descendant relationships. Transitional morphologies are found in the middle unit of the formation, a finding that is consistent with the evolution of Triceratops being characterized by anagenesis, the transformation of a lineage over time. Variation among specimens from this critical stratigraphic zone may indicate a branching event in the Triceratops lineage. Purely cladogenetic interpretations of the HCF dataset imply greater diversity within the formation. These findings underscore the critical role of stratigraphic data in deciphering evolutionary patterns in the Dinosauria.
将 50 多个著名角龙三角龙的头骨放置在蒙大拿州上白垩统地狱溪组（HCF）的地层框架内，揭示了该属的进化转变。可归为三角龙的两个公认形态种，T. horridus 和 T. prorsus 的标本在 HCF 中是地层上分离的，T. prorsus 形态在该组的上三分之一中回收，而 T. horridus 在该组的下部发现。因此，这些形态种代表单一物种内的性或个体发生变异的假说是站不住脚的。标本的地层位置似乎揭示了祖先-后代的关系。过渡形态在该组的中部单元中发现，这一发现与三角龙的进化特征是重演进化相一致，即一个谱系随时间的推移而发生变化。来自这个关键地层区域的标本之间的变异可能表明三角龙谱系发生了分支事件。对 HCF 数据集的纯粹分支发生解释意味着该地层内的多样性更大。这些发现强调了地层数据在解读恐龙进化模式中的关键作用。
