Cryptic complexity in felid vertebral evolution: shape differentiation and allometry of the axial skeleton

Marcela Randau,Andrew R Cuff,Stephanie E Pierce,Anjali Goswami,John R Hutchinson

doi:10.1111/zoj.12403

Abstract

Members of the mammalian family Felidae (extant and extinct cats) are grossly phenotypically similar, but display a 300-fold range in body size, from less than 1 kg to more than 300 kg. In addition to differences in body mass, felid species show dietary and locomotory specializations that correlate to skull and limb osteological measurements, such as shape or cross-sectional area. However, ecological correlates to the axial skeleton are yet untested. Here, we build on previous studies of the biomechanical and morphological evolution of the felid appendicular skeleton by conducting a quantitative analysis of morphology and allometry in the presacral vertebral column across extant cats. Our results demonstrate that vertebral columns of arboreal, scansorial and terrestrial felids significantly differ in morphology, specifically in the lumbar region, while no distinction based on dietary specialization was found. Body size significantly influences vertebral morphology, with clear regionalization of allometry along the vertebral column, suggesting that anterior (cervicals and thoracics) and posterior (lumbar) vertebrae may be independently subjected to distinct selection pressures.

Highlights

The carnivoran family Felidae (Mammalia, Placentalia) includes ca. 37 living species of grossly morphologically similar animals (Ewer, 1973; Johnson et al, 2006; MacDonald et al, 2010; Sunquist & Sunquist, 2002; Turner & Antón, 1996)
Our results demonstrate that vertebral columns of arboreal, scansorial, and terrestrial felids significantly differ in morphology, and more so in the lumbar region, while no distinction based on dietary specialisation was found
Regressions of all significant PC scores from the ‘all vertebrae’ Principal Component Analyses (PCA) on log10 total vertebral column length, before and after phylogenetic correction and between locomotory groups, demonstrated that shape variables were statistically uncorrelated with size (r2 > 0.05) and that the effects of size variation were removed prior to PCA

Summary

Introduction

The carnivoran family Felidae (Mammalia, Placentalia) includes ca. 37 living species of grossly morphologically similar animals (Ewer, 1973; Johnson et al, 2006; MacDonald et al, 2010; Sunquist & Sunquist, 2002; Turner & Antón, 1996). With the exception of fur patterning, body size is the greatest gross anatomical difference observed between species, with the Felidae displaying a considerable body mass range from 1kg in the rusty-spotted cat (Prionailurus rubiginosus) to over 300kg in the tiger (Panthera tigris). In addition to their overall phenotypic similarity, felids are an exception to the general mammalian biomechanical trend of size-correlated limb posture. It has been hypothesized that the lack of correlation between body size and limb posture in felids may reflect a large-bodied ancestral condition for the clade (Day & Jayne, 2007; Johnson et al, 2006; Mattern & McLennan, 2000; but see Cuff et al, 2015)

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Conclusion