Bird clades with less complex appendicular skeletons tend to have higher species richness

Andrew Brinkworth, Emily Green, Yimeng Li, Jack Oyston, Marcello Ruta, Matthew Wills

Research output: Contribution to journalArticlepeer-review


Species richness is strikingly uneven across taxonomic groups at all hierarchical levels, but the reasons for this heterogeneity are poorly understood. It is well established that morphological diversity (disparity) is decoupled from taxonomic diversity, both between clades and across geological time. Morphological complexity has been much less studied, but there is theory linking complexity with differential diversity across groups. Here we devise an index of complexity from the differentiation of the fore and hind limb pairs for a sample of 983 species of extant birds. We test the null hypothesis that this index of morphological complexity is uncorrelated with clade diversity, revealing a significant and negative correlation between the species richness of clades and the mean morphological complexity of those clades. Further, we find that more complex clades tend to occupy a smaller number of dietary and habitat niches, and that this proxy for greater ecological specialisation correlates with lower species richness. Greater morphological complexity in the appendicular skeleton therefore appears to hinder the generation and maintenance of species diversity. This may result from entrenchment into morphologies and ecologies that are less capable of yielding further diversity.
Original languageEnglish
Article number5817
Number of pages13
JournalNature Communications
Issue number1
Early online date19 Sept 2023
Publication statusPublished - 31 Dec 2023

Bibliographical note

Funding: This work was supported by funding from the John Templeton Foundation (Grant 61408) to MAW and MR, and from a NERC GW4 + DTP Studentship 2481350 to AB and MAW. MAW’s work was also supported by BBSRC grants BB/K015702/1 and BB/K006754/1. We thank Roger Benson for enormously helpful feedback, enabling us to substantially improve this paper. We also thank Daniel J. Field and Matthew Lowe for granting access to collections at the University Museum of Zoology (UMZC, Cambridge, UK).

Data availability:
The morphological, ecological, phylogenetic, and species richness data used in this study have been deposited in Figshare (10.6084/m9.figshare.23941488). All data necessary for replication of the analyses and figures in this work are provided in the files available from this repository.


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