Extinction of South American sparassodontans (Metatheria): environmental fluctuations or complex ecological processes?

Abstract

Sparassodontans are a diverse but now extinct group of metatherians that were apex predators in South America during most of the Cenozoic. Studying their decline has been controversial mainly due to the scarcity of the fossil record, and different methodological approaches have led to contradictory hypotheses. In an effort to explore questions about their extinction, we developed a novel multi‐model statistical approach to analyse all of the currently available data at a continental scale. Using multiple regression analysis and new advances in beta diversity analysis, we used all currently available fossil data at a continental scale to test four competing hypotheses to account for the decline of sparassodontans: competition with placental carnivorans, competition with avian phorusrhacids, non‐competitive ecological interactions, and environmental fluctuations. Our results show that the sparassodontan extinction was a gradual process with species disappearing throughout the Cenozoic. Multiple regression analysis supported non‐competitive ecological interactions as the best extinction model. Native South American ungulates, African migrants (caviomorph rodents and platyrrhine primates) and didelphimorphians were the groups with the highest statistical significance. Sparassodontan beta diversity increased between South American Land Mammal Ages after the Paleocene–Eocene boundary. Our results demonstrate that ecological modelling techniques illuminate aspects of extinction processes whilst mitigating the limitations of the fossil record. Our study suggests that non‐competitive ecological interactions could have been the main driver for sparassodontan extinction rather than, as commonly assumed, a result of competition and/or abiotic fluctuations.

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).…”

“…Occupation of an ecological niche distinct from those occupied by incumbent South American mammals may have been the most important factor, but several other aspects of procyonid ecology may have favored over-water dispersal. We find no evidence for significant competition between Cyonasua -group procyonids and endemic South American carnivorous mammals such as sparassodonts, in support of other studies that have suggested that the extinction of sparassodonts was due to other factors (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). The successful establishment of procyonids in South America was undoubtedly partly due to luck but perhaps principally due to the simple fact that these animals were entering a previously unoccupied ecological niche.…”

Disproportionate extinction of South American mammals drove the asymmetry of the Great American Biotic Interchange

“…Sparassodonts went extinct in the early Pliocene (4.5 to 3.3 Ma) ( 31 ) and it has been proposed that they were outcompeted by placental carnivores that arrived from North America ( 3 , 32 ). However, analyses based on the diversity trends, temporal and ecological overlap between sparassodonts and placental carnivores do not support the competition hypothesis ( 33 , 34 ). The extinction of sparassodonts left an empty ecological space which was occupied by placental carnivores ( 34 ).…”

New radiometric 40Ar–39Ar dates and faunistic analyses refine evolutionary dynamics of Neogene vertebrate assemblages in southern South America

“…The Red Queen hypothesis focuses on the effects of competition between native lineages (Simpson’s strata 1 and 2) and immigrants (stratum 3) during the GABI, as in the classic example of native metatherian predators vs. immigrant placental carnivorans 73 , 77 . However, recent reviews have not supported the idea that these new arrivals directly caused the extinction of autochthonous predator lineages, or that competitive displacement occurred among different metatherian clades 5 , 27 , 78 (Fig. 2 ).…”