CONICET-Departamento de Biodiversidad y Biología Experimental, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Pabellón II Ciudad Universitaria, Buenos Aires, Argentina.
CONICET-Departamento de Ecología, Genética y Evolución, Instituto de Ecología, Genética y Evolución (IEGEBA-CONICET), Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Pabellón II Ciudad Universitaria, Buenos Aires, Argentina.
J Morphol. 2024 Aug;285(8):e21752. doi: 10.1002/jmor.21752.
Detailed osteological descriptions of the craniomandibular complex of passerine birds are lacking for most species, limiting our understanding of their diversity and evolution. Cowbirds (genus Molothrus) are a small but widespread group of New World nine-primaried songbirds, well-known for their unique brooding parasitic behavior. However, detailed osteological data for cowbirds and other Icteridae are currently scarce and several features of their skulls remain undescribed or poorly known. To address this issue, a detailed comparative osteology of cowbird skulls is presented here for the first time based on data from x-ray microcomputed tomography, dry skeletal data, and multivariate analyses of linear morphometric data. Cowbird skulls offer some functional insights, with many finch-like features probably related to a seed-rich diet that distinguishes them from most other icterids. In addition, features previously overlooked in earlier studies might provide valuable phylogenetic information at different levels of passerine phylogeny (Passerida, Emberizoidea, Icteridae, and Agelaiinae), including some of the otic region and nasal septum. Comparisons among cowbirds show that there is substantial cranial variation within the genus, with M. oryzivorus being the most divergent cowbird species. Within the genus, distantly related species share similar overall skull morphology and proportions, but detailed osteological data allow species identification even in cases of strong convergence. Further efforts are warranted to furnish baseline data for future studies of this iconic group of Neotropical birds and to fully integrate it into phylogenetic comparative frameworks.
对大多数雀形目鸟类的颅颌复合体的详细骨骼描述都缺乏，这限制了我们对其多样性和进化的理解。牛鹂（Molothrus 属）是一小群广泛分布于新大陆的九枚初级鸣禽，以其独特的孵育寄生行为而闻名。然而，目前有关牛鹂和其他拟鹂科鸟类的详细骨骼数据仍然很少，它们的许多头骨特征仍未被描述或知之甚少。为了解决这个问题，本文首次基于 X 射线微计算机断层扫描、干骨骼数据和线性形态计量数据的多元分析，提供了牛鹂头骨的详细比较骨骼学。牛鹂的头骨提供了一些功能上的见解，具有许多雀形目鸟类的特征，可能与富含种子的饮食有关，这使它们与大多数其他拟鹂科鸟类区分开来。此外，在早期研究中被忽视的特征可能在不同水平的雀形目系统发育（雀形目、燕雀目、拟鹂科和 Agelaiinae）中提供有价值的系统发育信息，包括一些耳区和鼻中隔。牛鹂之间的比较表明，该属内存在大量的颅骨变异，其中 M. oryzivorus 是最具变异的牛鹂物种。在属内，亲缘关系较远的物种具有相似的整体头骨形态和比例，但详细的骨骼数据甚至可以在强烈趋同的情况下识别物种。有必要进一步努力为这个标志性的新热带鸟类群体的未来研究提供基线数据，并将其完全整合到系统发育比较框架中。
