Knapp A, Knell R J, Hone D W E
Department of Earth Sciences, The Natural History Museum, London, UK.
Department of Organismal Biology, Queen Mary University of London, London, UK.
Proc Biol Sci. 2021 Feb 10;288(1944):20202938. doi: 10.1098/rspb.2020.2938. Epub 2021 Feb 3.
Socio-sexual selection is predicted to be an important driver of evolution, influencing speciation, extinction and adaptation. The fossil record provides a means of testing these predictions, but detecting its signature from morphological data alone is difficult. There are, nonetheless, some specific patterns of growth and variation which are expected of traits under socio-sexual selection. The distinctive parietal-squamosal frill of ceratopsian dinosaurs has previously been suggested as a socio-sexual display trait, but evidence for this has been limited. Here, we perform a whole-skull shape analysis of an unprecedentedly large sample of specimens of using a high-density landmark-based geometric morphometric approach to test four predictions regarding a potential socio-sexual signalling role for the frill. Three predictions-low integration with the rest of the skull, significantly higher rate of change in size and shape during ontogeny, and higher morphological variance than other skull regions-are supported. One prediction, sexual dimorphism in shape, is not supported, suggesting that sexual differences in are likely to be small. Together, these findings are consistent with mutual mate choice or selection for signalling quality in more general social interactions, and support the hypothesis that the frill functioned as a socio-sexual signal in ceratopsian dinosaurs.
社会性别选择被认为是进化的一个重要驱动力，影响着物种形成、灭绝和适应。化石记录提供了检验这些预测的一种方法，但仅从形态学数据中检测其特征是困难的。然而，在社会性别选择下的性状，会有一些特定的生长和变异模式。之前有人提出，角龙类恐龙独特的顶骨-鳞状骨褶边是一种社会性别展示性状，但对此的证据一直有限。在这里，我们使用基于高密度地标点的几何形态测量方法，对大量前所未有的三角龙头骨标本进行了全颅骨形状分析，以检验关于褶边潜在社会性别信号作用的四个预测。其中三个预测得到了支持，即与颅骨其他部分的整合度低、个体发育过程中大小和形状的变化率显著更高，以及比其他颅骨区域具有更高的形态变异性。一个预测，即形状上的两性异形，未得到支持，这表明三角龙在形状上的性别差异可能很小。总的来说，这些发现与在更一般的社会互动中相互择偶或对信号质量的选择相一致，并支持了褶边在角龙类恐龙中作为社会性别信号发挥作用的假设。
