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

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.

Strangers in a strange land: Ecological dissimilarity to metatherian carnivores may partly explain early colonization of South America by Cyonasua-group procyonids

“…Chapalmalania was far larger than both Cyonasua and Stylocynus, with a body mass estimated at 120-180 kg (Prevosti and Forasiepi 2018), but this taxon is first recorded approximately 2 million years after the last record of Stylocynus (Prevosti et al 2013), suggesting that these taxa may not have overlapped in time. The new evidence presented here reinforces conclusions of previous studies that competitive exclusion was not a significant factor in the extinction of the Sparassodonta (e.g., Marshall 1977;Forasiepi et al 2007;Prevosti et al 2013;Engelman and Croft 2014;Zimicz 2014;López-Aguirre et al 2017;Croft et al 2018;Prevosti and Forasiepi 2018).…”

“…1), in agreement with most previous studies. Although the degree to which sparassodonts were omnivorous has been debated (Marshall 1977;Prevosti et al 2013;Croft et al 2018), virtually all authors agree that no South American metatherian (sparassodont or didelphimorphian), with the possible exception of Stylocynus, was as omnivorous as extant procyonids or ursids. However, even Stylocynus plots outside the hypocarnivore morphospace occupied by Ailurus, procyonids, and ursids (as well as Cyonasua-group procyonids), closer to mesocarnivorous or even hypercarnivorous taxa such as Canis lupus, Chrysocyon brachyurus, and Spilogale spp.…”

“…This resulted in a data set of 18 characters (listed in Supplementary Table 1) and 365 taxa. Additional modifications to the data set of Croft et al (2018) are described in Supplementary Table 2, and specimens examined for comparative purposes and used to add new codings and taxa are detailed in Supplementary Table 3. The complete data set used for this study is presented in Supplementary Table 4.…”

“…For most of the Cenozoic, terrestrial carnivorans were not present in South America. Instead, the terrestrial carnivore guild was primarily composed of a wide variety of non-placental and nonmammalian carnivores, including several groups of metatherians (including sparassodonts; see Croft et al 2018 and references therein; Prevosti and Forasiepi 2018 and references therein), cariamiform birds (Alvarenga et al 2011;Degrange et al 2012;Tambussi and Degrange 2013), and terrestrial sebecid crocodyliformes (Pol et al 2012). It is not until the late Miocene that fossils of terrestrial carnivoransspecifically procyonids-are found in South America.…”

Chlorocyon phantasma, a Late Eocene Borhyaenoid (Mammalia: Metatheria: Sparassodonta) from the Los Helados Locality, Andean Main Range, Central Chile

“…Chlorocyon further dif¬ fers from these taxa in having diastemata among the lower premolars, and is distinct from Pharsophorus lacerans in having pi-3 that increase gradually in size, rather than pi being significantly smaller than p2-3 (the condition is unknown in Plesiofelis and Pharsophorus tenax). Chlorocyon is comparable in size to the late Eocene Procladosictis anomala (see Croft et al, 2018), but the latter taxon is known only from a highly unusual upper dentition, thereby precluding direct comparison of dental morphology. Nonetheless, P. anomala is considered a hathliacynid or basal sparassodont rather than a borhyaenoid (Marshall, 1981;Forasiepi, 2009), thus distinguishing it from Chlorocyon, which is most likely a borhyaenoid.…”