PNAS:美国科学家发现三角龙进化的形态学证据

摘要 : 美国落基山博物馆的一项研究说，来自美国蒙大拿的三角龙颅骨让人们可以一瞥白垩纪晚期恐龙物种正在进行的形态与进化过程。这些结果强调了地层学证据在澄清进化历史、物种关系以及恐龙的物种多样性方面的作用。相关文章发表于2014年6月30日的《PNAS》杂志上。

科研人员对TrICEratops horridus 和Triceratops prorsus这两种三角龙的形态区别是否代表了种内变异、性二形性或两个不同的物种的特点存在争论。

John B. Scannella及其同事研究了蒙大拿Hell Creek地层的50多个三角龙的颅骨的布局。这个90米厚的白垩纪Hell Creek地层包含了一大批植物和动物物种，三角龙构成了最丰富的恐龙属。拥有长的鼻角和短的眶后角的T. prorsus标本占据了这个地层的上面1/3，而在该地层的下地层发现了T. horridus的标本。

在这两个变种之间发现了过渡形态。这些结果提示，在100万到200万年的时间里，三角龙属可能经历了累变，即从一个物种到另一个物种的转换变化，而不是通过系枝发生分成两个现有的物种。这组作者说，这些结果强调了地层学证据在澄清进化历史、物种关系以及恐龙的物种多样性方面的作用。

原文摘要：

Evolutionary trends in Triceratops from the Hell Creek Formation, Montana

John B. Scannella, Denver W. Fowler, Mark B. Goodwin and John R. Horner

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 ofTriceratops 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.

作者：物种多样性

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