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bioRxiv · 10.64898/2026.06.24.734298

Constrained body mass evolution and decoupled morphological rates in plesiosaurs

Zhao, R. J.·Zhang, C.
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Abstract

Body size, through its links to various physiological traits, has often been hypothesized to influence evolutionary rates. Negative body size-rate correlations have been reported in the morpho-logical or molecular evolution of several extant vertebrate groups, including mammals, birds, reptiles, and teleost fishes. In this study, we estimated body masses for 89 species of plesiosaurs, a clade of Mesozoic aquatic reptiles, and found that their body size evolution conforms to a three-regime Ornstein-Uhlenbeck process, indicative of constrained evolution. Rates of morphological evolution, inferred using the skyline fossilized birth-death process and the variable-rates model, show minimal support for a correlation with body size in this clade. Our results thus serve as a counterexample, suggesting that the negative body size-rate relationship is not a universal vertebrate pattern, but rather a trend restricted to certain lineages.

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Zhao, R. J., Zhang, C.. 2026-06-29. Constrained body mass evolution and decoupled morphological rates in plesiosaurs. https://doi.org/10.64898/2026.06.24.734298

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