Evolution of the patellar sesamoid bone in mammals
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Abstract
The patella is a sesamoid bone located in the major extensor tendon of the knee joint, in the hindlimb of many tetrapods. Although numerous aspects of knee morphology are ancient and conserved among most tetrapods, the evolutionary occurrence of the patella is highly variable. Among extant (crown clade) groups it is found in most birds, most lizards, the monotreme mammals and almost all placental mammals, but it is absent in most marsupial mammals as well as many reptiles. Here we integrate data from the literature and first-hand studies of fossil and recent skeletal remains to reconstruct the evolution of the mammalian patella. We infer that patellae most likely evolved between four to six times in crown group Mammalia: in monotremes, in the extinct multituberculates, in one or more stem-mammal genera outside of therian or eutherian mammals, and up to three times in therian mammals. Furthermore, a patella was lost several times in mammals, not including those with absent hindlimbs: once or more in marsupials (with some re-acquisition), and at least once in bats. Our inferences about patellar evolution in mammals are reciprocally informed by the existence of several human genetic conditions in which the patella is either absent or severely reduced. Clearly, development of the patella is under close genomic control, although its responsiveness to its mechanical environment is also important (and perhaps variable among taxa). Where a patella is present it plays an important role in hindlimb function; especially in resisting gravity by providing an enhanced lever system for the knee joint. Yet the evolutionary origins, persistence and modifications of a patella in diverse groups with widely varying habits and habitats -- from digging to running to aquatic, small or large body sizes, bipeds or quadrupeds -- remain complex and perplexing, impeding a conclusive synthesis of form, function, development and genetics across mammalian evolution. This meta-analysis takes an initial step toward such a synthesis by collating available data and elucidating areas of promising future inquiry.
Cite this as
2017. Evolution of the patellar sesamoid bone in mammals. PeerJ Preprints 5:e2594v2 https://doi.org/10.7287/peerj.preprints.2594v2note This preprint is not peer-reviewed. You may wish to reference the subsequent peer-reviewed version of this article.
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Revised post-review at PeerJ; under consideration.
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Supplemental Information
Supplementary Information
Supplementary Tables S1,S2; Supplementary Figures S1-S6; and Supplementary References.
Additional Information
Competing Interests
John R Hutchinson is an Academic Editor for PeerJ.
Author Contributions
Mark E Samuels conceived and designed the experiments, performed the experiments, analyzed the data, contributed reagents/materials/analysis tools, wrote the paper, prepared figures and/or tables, reviewed drafts of the paper.
Sophie Regnault conceived and designed the experiments, performed the experiments, analyzed the data, contributed reagents/materials/analysis tools, wrote the paper, prepared figures and/or tables, reviewed drafts of the paper.
John R Hutchinson conceived and designed the experiments, performed the experiments, contributed reagents/materials/analysis tools, wrote the paper, prepared figures and/or tables, reviewed drafts of the paper.
Data Deposition
The following information was supplied regarding data availability:
The raw data has been supplied as a supplementary file.
Funding
MES was supported by the Centre de Recherche du CHU Ste-Justine. JRH was supported by a Senior Research Fellowship from the Royal Society and Leverhulme Trust in 2012, and grant number RPG-2013-108 from the Leverhulme Trust. SR was supported by a PhD studentship from the Royal Veterinary College. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
