Nonplantigrade Foot Posture: A Constraint on Dinosaur Body Size.

Tai Kubo,Mugino O Kubo,Andrew A Farke

doi:10.1371/journal.pone.0145716

Abstract

Dinosaurs had functionally digitigrade or sub-unguligrade foot postures. With their immediate ancestors, dinosaurs were the only terrestrial nonplantigrades during the Mesozoic. Extant terrestrial mammals have different optimal body sizes according to their foot posture (plantigrade, digitigrade, and unguligrade), yet the relationship of nonplantigrade foot posture with dinosaur body size has never been investigated, even though the body size of dinosaurs has been studied intensively. According to a large dataset presented in this study, the body sizes of all nonplantigrades (including nonvolant dinosaurs, nonvolant terrestrial birds, extant mammals, and extinct Nearctic mammals) are above 500 g, except for macroscelid mammals (i.e., elephant shrew), a few alvarezsauroid dinosaurs, and nondinosaur ornithodirans (i.e., the immediate ancestors of dinosaurs). When nonplantigrade tetrapods evolved from plantigrade ancestors, lineages with nonplantigrade foot posture exhibited a steady increase in body size following Cope’s rule. In contrast, contemporaneous plantigrade lineages exhibited no trend in body size evolution and were largely constrained to small body sizes. This evolutionary pattern of body size specific to foot posture occurred repeatedly during both the Mesozoic and the Cenozoic eras. Although disturbed by the end-Cretaceous extinction, species of mid to large body size have predominantly been nonplantigrade animals from the Jurassic until the present; conversely, species with small body size have been exclusively composed of plantigrades in the nonvolant terrestrial tetrapod fauna.

Highlights

Body size affects many aspects of biological phenomena in organisms; the evolution of body size is one of the central issues in evolutionary biology [1]
When the number of species is plotted against log body mass, dinosaurs exhibit a distribution that is skewed toward a large body size; the distributions of other major vertebrate groups are typically skewed toward a small body size [14]
The body size data considered in the present study indicate that a lower size limit existed for terrestrial nonplantigrades, regardless of age and taxon

Summary

Introduction

Body size affects many aspects of biological phenomena in organisms; the evolution of body size is one of the central issues in evolutionary biology [1]. Nonplantigrade Foot Posture of Dinosaurs sizes among dinosaur species have been analyzed using large datasets [3,4,13,14] Compared with those of other major terrestrial vertebrate groups, the body size distribution of dinosaur species exhibits three distinct features. The smallest species of dinosaurs was heavier than those of other major terrestrial vertebrate groups, such as mammals, birds and fossil mammals of the Mesozoic and the Cenozoic, by more than two orders of magnitude [14,16,17,18]

Methods

Results

Conclusion