Diversity and disparity of sparassodonts (Metatheria) reveal non-analogue nature of ancient South American mammalian carnivore guilds.

Darin A Croft,Tatiana Dolgushina,Russell K Engelman,Gina Wesley

doi:10.1098/rspb.2017.2012

Abstract

This study investigates whether terrestrial mammalian carnivore guilds of ancient South America, which developed in relative isolation, were similar to those of other continents. We do so through analyses of clade diversification, ecomorphology and guild structure in the Sparassodonta, metatherians that were the predominant mammalian carnivores of pre-Pleistocene South America. Body mass and 16 characters of the dentition are used to quantify morphological diversity (disparity) in sparassodonts and to compare them to extant marsupial and placental carnivores and extinct North American carnivoramorphans. We also compare trophic diversity of the Early Miocene terrestrial carnivore guild of Santa Cruz, Argentina to that of 14 modern and fossil guilds from other continents. We find that sparassodonts had comparatively low ecomorphological disparity throughout their history and that South American carnivore palaeoguilds, as represented by that of Santa Cruz, Argentina, were unlike modern or fossil carnivore guilds of other continents in their lack of mesocarnivores and hypocarnivores. Our results add to a growing body of evidence highlighting non-analogue aspects of extinct South American mammals and illustrate the dramatic effects that historical contingency can have on the evolution of mammalian palaeocommunities.

Highlights

The evolution of mammals during South America’s protracted Cenozoic geographical isolation is well documented [1,2,3]
We quantify and analyse the taxonomic diversity and morphological disparity of sparassodont metatherians, the predominant carnivorous land mammals of ancient South America, in order to characterize their evolutionary history and examine dietary resource partitioning among members of the terrestrial carnivore guild
Sparassodonts are organized into five family-level groups: Borhyaenidae, Proborhyaenidae, Thylacosmilidae, Hathliacynidae and the monotypic Hondadelphidae, the first three of which comprise Borhyaenoidea [5 –7]. They ranged in size from less than 1 kg to approximately 150 kg, and their fossil record extends from the early Cenozoic to the Pliocene

Summary

Introduction

The evolution of mammals during South America’s protracted Cenozoic geographical isolation is well documented [1,2,3]. We coded nine additional carnivorous metatherian genera for comparative purposes: three extant Australian dasyuromorphians and six extinct South American didelphimorphians (electronic supplementary material, table S1). The former may be the closest extant ecomorphological analogues for sparassodonts, whereas the latter coexisted with sparassodonts during the late Neogene and have been suggested to have occupied similar niches and/or competitively replaced some species [10,21]. All OTUs (sparassodonts, dasyuromorphians, didelphimorphians, North American Cenozoic carnivoramorphans and modern carnivorans) were included in a single analysis to obtain individual scores that were subsequently used to determine occupied morphospace. Other statistical analyses and data visualization were conducted in JMP PROw 13.0 for Mac [31]

Results

Miocene

Findings

Discussion