Convergence and divergence in the evolution of cat skulls: temporal and spatial patterns of morphological diversity.

Manabu Sakamoto,Marcello Ruta

doi:10.1371/journal.pone.0039752

Abstract

BackgroundStudies of biological shape evolution are greatly enhanced when framed in a phylogenetic perspective. Inclusion of fossils amplifies the scope of macroevolutionary research, offers a deep-time perspective on tempo and mode of radiations, and elucidates life-trait changes. We explore the evolution of skull shape in felids (cats) through morphometric analyses of linear variables, phylogenetic comparative methods, and a new cladistic study of saber-toothed cats.Methodology/Principal FindingsA new phylogenetic analysis supports the monophyly of saber-toothed cats (Machairodontinae) exclusive of Felinae and some basal felids, but does not support the monophyly of various saber-toothed tribes and genera. We quantified skull shape variation in 34 extant and 18 extinct species using size-adjusted linear variables. These distinguish taxonomic group membership with high accuracy. Patterns of morphospace occupation are consistent with previous analyses, for example, in showing a size gradient along the primary axis of shape variation and a separation between large and small-medium cats. By combining the new phylogeny with a molecular tree of extant Felinae, we built a chronophylomorphospace (a phylogeny superimposed onto a two-dimensional morphospace through time). The evolutionary history of cats was characterized by two major episodes of morphological divergence, one marking the separation between saber-toothed and modern cats, the other marking the split between large and small-medium cats.Conclusions/SignificanceAncestors of large cats in the ‘Panthera’ lineage tend to occupy, at a much later stage, morphospace regions previously occupied by saber-toothed cats. The latter radiated out into new morphospace regions peripheral to those of extant large cats. The separation between large and small-medium cats was marked by considerable morphologically divergent trajectories early in feline evolution. A chronophylomorphospace has wider applications in reconstructing temporal transitions across two-dimensional trait spaces, can be used in ecophenotypical and functional diversity studies, and may reveal novel patterns of morphospace occupation.

Highlights

Patterns of convergence and divergence of biological shape – both in time and throughout the range of theoretical or realized morphotypes – are key to understanding the dynamics of clade evolution
The evolution of skull form and function in fossil and living cats has been subjected to considerable scrutiny [6,7,8,9,10,11,12,13,14], and phylogenetic thinking has informed the interpretation of major patterns of shape change
With reference to the most parsimonious tree, moderate support is assigned to the node subtending all saber-toothed cats more apical than AMNH 105446 (70%)

Summary

Introduction

Patterns of convergence and divergence of biological shape – both in time and throughout the range of theoretical or realized morphotypes – are key to understanding the dynamics of clade evolution. Cats (Carnivora; Felidae) are excellent model organisms for macroevolutionary analyses of morphological shape diversification Their relatively recent origin (,10 million years ago [Ma] for extant Felinae [1] and ,28.5–35 Ma for Felidae [2]) allows us to investigate patterns of constraint, convergence, and divergence in a successful group of predatory mammals. We explore the evolution of skull shape in felids (cats) through morphometric analyses of linear variables, phylogenetic comparative methods, and a new cladistic study of saber-toothed cats

Methods

Results

Conclusion