Mitchell Jonathan S, Makovicky Peter J
Committee on Evolutionary Biology, The University of Chicago, Chicago, IL 60637, USA Department of Science and Education, The Field Museum of Natural History, Chicago, IL 60615, USA
Department of Science and Education, The Field Museum of Natural History, Chicago, IL 60615, USA.
Proc Biol Sci. 2014 Jul 22;281(1787). doi: 10.1098/rspb.2014.0608.
Ecological divergence is thought to be coupled with evolutionary radiations, yet the strength of this coupling is unclear. When birds diversified ecologically has received much less attention than their hotly debated crown divergence time. Here, we quantify how accurately skeletal morphology can predict ecology in living and extinct birds, and show that the earliest known assemblage of birds (=pygostylians) from the Jehol Biota (≈125 Ma) was substantially impoverished ecologically. The Jehol avifauna has few representatives of highly preservable ecomorphs (e.g. aquatic forms) and a notable lack of ecomorphological overlap with the pterosaur assemblage (e.g. no large or aerially foraging pygostylians). Comparisons of the Jehol functional diversity with modern and subfossil avian assemblages show that taphonomic bias alone cannot explain the ecomorphological impoverishment. However, evolutionary simulations suggest that the constrained ecological diversity of the Early Cretaceous pygostylians is consistent with what is expected from a relatively young radiation. Regardless of the proximate biological explanation, the anomalously low functional diversity of the Jehol birds is evidence both for ecological vacancies in Cretaceous ecosystems, which were subsequently filled by the radiation of crown Aves, and for discordance between taxonomic richness and ecological diversity in the best-known Mesozoic ecosystem.
生态分化被认为与进化辐射相关联，然而这种关联的强度尚不清楚。鸟类在生态上的分化时间受到的关注远少于其备受争议的冠群分化时间。在这里，我们量化了骨骼形态能多准确地预测现存和已灭绝鸟类的生态，并表明来自热河生物群（约1.25亿年前）的已知最早鸟类组合（=尾综骨鸟类）在生态上显著匮乏。热河鸟类群中高度可保存的生态形态（如水生形态）的代表很少，并且与翼龙组合在生态形态上明显缺乏重叠（例如没有大型或空中觅食的尾综骨鸟类）。将热河生物群的功能多样性与现代和亚化石鸟类组合进行比较表明，仅保存偏差无法解释生态形态的匮乏。然而，进化模拟表明，早白垩世尾综骨鸟类受限制的生态多样性与相对年轻的辐射所预期的情况一致。无论直接的生物学解释如何，热河鸟类异常低的功能多样性既证明了白垩纪生态系统中存在生态空缺，随后这些空缺被冠群鸟类的辐射所填补，也证明了在最著名的中生代生态系统中分类丰富度与生态多样性之间的不一致。
