The evolution of the tetrapod humerus: morphometrics, disparity, and evolutionary rates

Ruta, Marcello and Krieger, Jonathan and Angieczyk, Kenneth D. and Wiils, Matthew A. (2019) The evolution of the tetrapod humerus: morphometrics, disparity, and evolutionary rates. Earth and Environmental Science Transactions of the Royal Society of Edinburgh . ISSN TRE-2018-0013.R1

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The evolution of the tetrapod humerus: morphometrics, disparity, and evolutionary rates
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Abstract

The present study explores the macroevolutionary dynamics of shape changes in the humeri of all major grades and clades of early tetrapods and their fish-like forerunners. Coordinate Point Eigenshape analysis applied to humeral outlines in extensor view reveals that fish humeri are more disparate than those of most early tetrapod groups and significantly separate from the latter. Our findings indicate sustained changes in humeral shape in the deepest portions of the tetrapod stem-group and certain portions of the crown. In the first half of sampled tetrapod history, subclades show larger than expected humeral disparity, suggesting rapid diffusion into morphospace. Later in tetrapod evolution, subclades occupy smaller and non-overlapping morphospace regions. This pattern may reflect in part increasing specializations in later tetrapod lineages. Bayesian shifts in rates of evolutionary change are distributed discontinuously across the phylogeny, and most of them occur within rather than between major groups. Most shifts with the highest Bayesian posterior probabilities are observed in lepospondyls. Similarly, maximum likelihood analyses of shifts support marked rate accelerations in lepospondyls and in various subclades within that group. In other tetrapod groups, rates either tend to slow down or experience only small increases. Somewhat surprisingly, no shifts are concurrent with structural, functional, or ecological innovations in tetrapod evolution, including the origin of digits, the water-land transition, and increasing terrestrialization. Although counter-intuitive, these results are consistent with a model of continual phenotypic innovation that, although decoupled from key evolutionary changes, is possibly triggered by niche segregation in divergent clades and grades of early tetrapods.

Additional Information:The final published version of this article can be accessed online at https://www.cambridge.org/core/journals/earth-and-environmental-science-transactions-of-royal-society-of-edinburgh/article/evolution-of-the-tetrapod-humerus-morphometrics-disparity-and-evolutionary-rates/AFF645D718E5C460486A0755B403F14D
Keywords:amniotes, eigenshape analysis, evolutionary rate shifts, humeral morphology, lepospondyls, lissamphibians
Subjects:C Biological Sciences > C182 Evolution
F Physical Sciences > F641 Palaeontology
C Biological Sciences > C300 Zoology
Divisions:College of Science > School of Life Sciences
ID Code:33227
Deposited On:22 Oct 2018 14:47

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