Centre for Evolutionary Biology, School of Animal Biology, University of Western Australia, Crawley, Western Australia 6009, Australia.
Am Nat. 2010 Aug;176(2):141-8. doi: 10.1086/653001.
The function of the exaggerated structures that adorn many fossil vertebrates remains largely unresolved. One recurrent hypothesis is that these elaborated traits had a role in thermoregulation. This orthodoxy persists despite the observation that traits exaggerated to the point of impracticality in extant organisms are almost invariably sexually selected. We use allometric scaling to investigate the role of sexual selection and thermoregulation in the evolution of exaggerated traits of the crested pterosaur Pteranodon longiceps and the sail-backed eupelycosaurs Dimetrodon and Edaphosaurus. The extraordinarily steep positive allometry of the head crest of Pteranodon rules out all of the current hypotheses for this trait's main function other than sexual signaling. We also find interspecific patterns of allometry and sexual dimorphism in the sails of Dimetrodon and patterns of elaboration in Edaphosaurus consistent with a sexually selected function. Furthermore, small ancestral, sail-backed pelycosaurs would have been too small to need adaptations to thermoregulation. Our results question the popular view that the elaborated structures of these fossil species evolved as thermoregulatory organs and provide evidence in support of the hypothesis that Pteranodon crests and eupelycosaur sails are among the earliest and most extreme examples of elaborate sexual signals in the evolution of terrestrial vertebrates.
许多化石脊椎动物华丽结构的功能在很大程度上仍未得到解决。一个反复出现的假设是，这些精致的特征在体温调节中起作用。尽管观察到在现存生物中，夸张到不切实际程度的特征几乎总是与性选择有关，但这种正统观念仍然存在。我们使用异速生长比例关系来研究性选择和体温调节在华丽的有羽恐龙冠饰栉龙、帆背合弓龙类恐龙（包括异齿龙和基龙）和地蜥鳄的进化中的作用。冠饰栉龙的头部冠饰具有非常陡峭的正异速生长比例关系，这排除了该特征主要功能的所有当前假设，除了性信号以外。我们还发现异齿龙和基龙的帆具有种间异速生长比例关系和性二态性模式，以及地蜥鳄的精致模式，这些都与性选择功能一致。此外，小的祖先帆背合弓龙类恐龙太小，不需要适应体温调节。我们的研究结果对这些化石物种的华丽结构是作为体温调节器官进化的流行观点提出了质疑，并为栉龙冠饰和帆背合弓龙类恐龙的帆是陆地脊椎动物进化中最早和最极端的复杂性信号之一的假说提供了证据。
