Brocklehurst Neil, Field Daniel J
Department of Earth Sciences, University of Oxford, South Parks Road, Oxford, UK.
Department of Earth Sciences, University of Cambridge, Downing Street, Cambridge, UK.
iScience. 2021 Mar 1;24(3):102243. doi: 10.1016/j.isci.2021.102243. eCollection 2021 Mar 19.
Several potential drivers of avian tooth loss have been proposed, although consensus remains elusive as fully toothless jaws arose independently numerous times among Mesozoic avialans and dinosaurs more broadly. The origin of crown bird edentulism has been discussed in terms of a broad-scale selective pressure or trend toward toothlessness, although this has never been quantitatively tested. Here, we find no evidence for models whereby iterative acquisitions of toothlessness among Mesozoic Avialae were driven by an overarching selective trend. Instead, our results support modularity among jaw regions underlying heterogeneous tooth loss patterns and indicate a substantially later transition to complete crown bird edentulism than previously hypothesized (∼90 mya). We show that patterns of avialan tooth loss adhere to Dollo's law and suggest that the exclusive survival of toothless birds to the present represents lineage-specific selective pressures, irreversibility of tooth loss, and the filter of the Cretaceous-Paleogene (K-Pg) mass extinction.
虽然在中生代鸟类乃至更广泛的恐龙中，完全无牙的颌骨曾多次独立出现，但关于鸟类牙齿脱落的潜在驱动因素仍未达成共识。冠鸟类无牙现象的起源已从广泛的选择压力或无牙趋势方面进行了讨论，不过这从未经过定量检验。在这里，我们没有发现中生代鸟类中反复出现的无牙现象是由总体选择趋势驱动的模型的证据。相反，我们的结果支持颌骨区域之间的模块化，这种模块化是牙齿脱落模式异质性的基础，并表明向完全冠鸟类无牙现象的转变比之前假设的要晚得多（约9000万年前）。我们表明，鸟类牙齿脱落模式符合多洛法则，并认为无牙鸟类独存至今代表了谱系特异性选择压力、牙齿脱落的不可逆性以及白垩纪-古近纪（K-Pg）大灭绝的筛选作用。
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