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

Abstract

It was once thought that the endemic carnivorous mammals of South America, the metatherian sparassodonts, were driven extinct by North American carnivorans through competitive exclusion. However, sparassodonts went extinct before most groups of carnivorans entered South America; only the endemic Cyonasua-group procyonids (Cyonasua and Chapalmalania), which immigrated to South America nearly 4 million years earlier than other carnivorans, significantly overlapped with sparassodonts in time. In this study, we examine the functional morphology of the dentition of Cyonasua and Chapalmalania through quantitative analysis to determine the dietary habits of these taxa and the degree to which they may have ecologically overlapped sparassodonts and large predatory Neogene didelphimorphians. We find Cyonasua and Chapalmalania to be more carnivorous than extant procyonids, other than Bassariscus, in agreement with previous studies, but more omnivorous than most other carnivorans and all meat-eating South American metatherians, including sparassodonts. The extreme ecological dissimilarity between Cyonasua-group procyonids and members of the endemic South American predator guild may explain why procyonids were able to successfully establish themselves in South America several million years earlier than most other northern mammals (including all other carnivorans): they moved into a previously unoccupied ecological niche (large omnivore) and avoided direct competition with incumbent native species, a situation similar to that documented in historical cases of biological invasion. The omnivorous diets and climbing/swimming abilities of procyonids may have increased their chances for a successful over-water dispersal relative to other carnivorans, further favoring their successful establishment in South America.

The multicausal twilight of South American native mammalian predators (Metatheria, Sparassodonta)

“…However, he suggested competitive exclusion in some cases. Our results support the hypothesis that the diversity of Carnivora did not affect the speciation and extinction rates of Sparassodonta, as suggested by previous authors 7 , 8 , 37 , 38 , 41 , 43 . This is evidenced by the lack of significant correlations between the diversity of carnivorans and the rate of speciation and extinction of sparassodonts (Fig.…”

“…1). As a matter of fact, the carnivores that entered South America at this time, that is procyonids, were omnivorous and thus occupied a different ecological niche from the mesocarnivorous to hypercarnivorous coeval sparassodonts 5,7,8,38,43 . By contrast, later carnivorans that would have competed with sparassodonts (mustelids, canids, and felids) only entered South America after the extinction of Sparassodonta 5,7,8,24,38,43,55,86,87 , and hence occupied ecological roles that had been left empty by the already extinct sparassodonts.…”

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

“…Placental carnivores attainted higher diversity in South America than sparassodonts did in the past ( 31 ). This may be related to a higher morphological variation (disparity) and ecological diversity of placental carnivores that allowed them to occupy diverse niches across South America ( 35 ). Sparassodonts had lower diversity ( 36 ) and dental disparity ( 37 ) than placental carnivores, a pattern that is general to placental vs. nonplacental mammals ( 38 ).…”

On the Supposed Presence of Miocene Tayassuidae and Dromomerycinae (Mammalia, Cetartiodactyla) in South America

“…The last of the three phases described above is known as the Great American Biotic Interchange (GABI), and is considered one of the most significant biogeographic events of the Cenozoic (Webb, 1976(Webb, , 1991Cione et al, 2015). During the GABI, it is generally agreed that initial and limited exchange occurred during the late Miocene and early Pliocene; procyonid carnivorans and sigmodontine rodents were the first northern immigrants in South America, and two types of ground sloths were the first southern immigrants to Mexico and the southern United States (Woodburne, 2010;Cione et al, 2015;Barbiére et al, 2019;Engelman and Croft, 2019). Procyonid carnivorans, such as Cyonasua and Chapalmalania, are known from the Huayquerian South American Land-Mammal "Age" (SALMA) of Argentina and Uruguay (late Miocene, 9.0-6.8 Ma) (Reguero and Candela, 2011;Prevosti and Soibelzon, 2012;Prevosti et al, 2013;Engelman and Croft, 2019;Soibelzon et al, 2019).…”

“…During the GABI, it is generally agreed that initial and limited exchange occurred during the late Miocene and early Pliocene; procyonid carnivorans and sigmodontine rodents were the first northern immigrants in South America, and two types of ground sloths were the first southern immigrants to Mexico and the southern United States (Woodburne, 2010;Cione et al, 2015;Barbiére et al, 2019;Engelman and Croft, 2019). Procyonid carnivorans, such as Cyonasua and Chapalmalania, are known from the Huayquerian South American Land-Mammal "Age" (SALMA) of Argentina and Uruguay (late Miocene, 9.0-6.8 Ma) (Reguero and Candela, 2011;Prevosti and Soibelzon, 2012;Prevosti et al, 2013;Engelman and Croft, 2019;Soibelzon et al, 2019). Mustelids have also been reported from the Huayquerian SALMA (Verzi and Montalvo, 2008), but this has been refuted by Prevosti and Pardiñas (2009).…”