Abstract:

The inference of Mesozoic avialan bird diets previously relied on traditional methods such as morphological comparisons among taxa and direct evidence such as identifiable stomach contents. However, the application of these approaches has been limited because of uncommon preservation of relevant fossil evidence. We searched for additional informative characteristics to help develop new methods to assess the diet of fossil birds. In particular, the morphology of the avialan neck is highly modularized and plays roles in multiple functions including food acquisition. The structure of and variation among the cervical vertebrae likely reflects the demands of feeding ecology in fossil and extant birds because the avialan neck evolved to, at least in part, replace the forelimbs by assisting with activities such as cranioinertial feeding and other ecological functions. Here, we utilize morphometric and statistical analyses to establish an initial quantitative relationship between cervical morphology and dietary modes in both extant and extinct birds. This morphometric framework derived from the cervical morphology of living birds is used as a basis to estimate the diet categories of five taxa of Mesozoic birds. The results indicate that there is a quantitative correlation between cervical morphology differentiation and their interrelated feeding modes. The enantiornithine taxa examined exhibit cervical morphologies similar to extant insectivorous or carnivorous birds. The ornithurine species show cervical morphologies that are more aligned with generalist or herbivorous birds, and exhibit preliminary morphological features tied to aquatic adaptions. These findings are consistent in part with other direct fossil evidence, as well as hypotheses developed from other skeletal comparisons. Therefore, the cervical vertebral series, as a skeletal system closely linked to food acquisition, can serve as one of the valuable metrics to provide information for inferring the diet of long extinct Mesozoic birds.

Key words: Mesozoic birds, cervical morphology, diet, ecological variation

摘要：

中生代鸟类的食性推断往往依赖于传统的形态对比和直接的化石证据，但不完整的化石记录和特异埋藏的稀缺性使得我们需要寻找更多有用特征和方法来对化石鸟类进行食性评估。鸟类颈部结构是一个高度模块化、形态和功能密切关联的系统；在恐龙向鸟类演化的过程中，前肢由于飞行适应独立出来，使得颈部需要更多地帮助鸟类实现捕食及其他生态功能。因此，颈部有可能成为鸟类食性推断的显著特征之一。利用形态测定和统计分析，建立起现生鸟类和中生代灭绝鸟类的颈椎形态和食性模式之间的量化关系。基于现生鸟类构建了形态-功能框架，评估了早白垩世热河生物群中发现的5种鸟类的食性模式。结果表明，颈椎形态分异与鸟类取食多样性量化相关，3种反鸟表现出了食虫或食肉鸟类的颈椎形态特征，两种今鸟型类则表现出杂食性或植食性，以及原始的水生适应形态特征。新的分析结果与之前发现的化石直接证据以及其他相关的形态研究基本一致，因此，颈椎作为与取食功能密切相关的骨骼系统，可以为中生代鸟类取食生态的推断提供一定信息。

关键词: 中生代鸟类, 颈椎形态, 食性, 生态分异