Abstract

Background: Studies 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 Findings: A 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 sabertoothed
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/Significance: Ancestors 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.