Ancient feeding ecology inferred from stable isotopic evidence from fossil horses in South America over the past 3 Ma

Abstract

BackgroundStable isotope ratios (13C/12C and 18O/16O) in fossil teeth and bone provide key archives for understanding the ecology of extinct horses during the Plio-Pleistocene in South America; however, what happened in areas of sympatry between Equus (Amerhippus) and Hippidion is less understood.ResultsHere, we use stable carbon and oxygen isotopes preserved in 67 fossil tooth and bone samples for seven species of horses from 25 different localities to document the magnitude of the dietary shifts of horses and ancient floral change during the Plio-Pleistocene. Dietary reconstructions inferred from stable isotopes of both genera of horses present in South America document dietary separation and environmental changes in ancient ecosystems, including C3/C4 transitions. Stable isotope data demonstrate changes in C4 grass consumption, inter-species dietary partitioning and variation in isotopic niche breadth of mixed feeders with latitudinal gradient.ConclusionsThe data for Hippidion indicate a preference varying from C3 plants to mixed C3-C4 plants in their diet. Equus (Amerhippus) shows three different patterns of dietary partitioning Equus (A.) neogeus from the province of Buenos Aires indicate a preference for C3 plants in the diet. Equus (A.) andium from Ecuador and Equus (A.) insulatus from Bolivia show a preference for to a diet of mixed C3-C4 plants, while Equus (A.) santaeelenae from La Carolina (sea level of Ecuador) and Brazil are mostly C4 feeders. These results confirm that ancient feeding ecology cannot always be inferred from dental morphology. While the carbon isotope composition of horses skeletal material decreased as latitude increased, we found evidence of boundary between a mixed C3/C4 diet signal and a pure C4 signal around 32° S and a change from a mixed diet signal to an exclusively C3 signal around 35°S.We found that the horses living at high altitudes and at low to middle latitude still have a C4 component in their diet, except the specimens from 4000 m, which have a pure C3 diet. The change in altitudinal vegetation gradients during the Pleistocene is one of several possibilities to explain the C4 dietary component in horses living at high altitudes. Other alternative explanations imply that the horses fed partially at lower altitudes.

Contrasts in the large herbivore faunas of the southern continents in the late Pleistocene and the ecological implications for human origins

“…Among the South American species classified as grazers, the gomphotheres Cuvieronius hyodon and Stegomastodon waringi , various equids and both toxodontid species all showed quite variable C 4 /C 3 plant proportions in different regions of their distribution ranges, indicating some dietary flexibility (Sánchez et al ., ; MacFadden, ; Prado et al ., ). Although C. hyodon exhibited relatively low‐crowned dentition, carbon isotope analysis indicated that its diet in Bolivia was drawn largely from C 4 grasses (MacFadden & Shockey, ).…”

“…The even larger S. waringi likewise showed variable C 3 /C 4 plant proportions, despite exhibiting the extreme hypsodonty typical of a grazer (Sánchez et al ., ). Equids in the genus Hippidion showed higher C 3 plant proportions in their diets than Equus spp., but nevertheless had equally high‐crowned dentition, indicating latitudinal or elevational differences in where they grazed (Prado et al ., ).…”

“…Among the South American species classified as grazers, the gomphotheres Cuvieronius hyodon and Stegomastodon waringi, various equids and both toxodontid species all showed quite variable C 4 /C 3 plant proportions in different regions of their distribution ranges, indicating some dietary flexibility (S anchez et al, 2004;MacFadden, 2005;Prado et al, 2011). Although C. hyodon exhibited relatively lowcrowned dentition, carbon isotope analysis indicated that its Figure 1 Contrasting patterns in the large mammalian herbivore faunas among continents: (a) comparison of body mass distribution among the three southern continents, (b) comparison of the relative proportions of grazers versus browsers in different body mass classes for the three southern continents, and (c) comparison of the body mass distribution for South America with that for the Palaearctic (North America plus Eurasia combined) and tropical Asia.…”

Global evolution of Equidae and Gomphotheriidae from South America

“…; Prado et al . ). In this paper, we revise the latest information about the systematics, biogeography and ecology of these groups during the late Cenozoic in South America.…”

Extinción de Equidae y Proboscidea en América del Sur. Un test usando datos de isótopos de carbono

“…En contraste, las especies de gonfoterios de finales del Pleistoceno parecen tener una dieta menos especializada con una combinación de plantas C 3 y C 4 , que está en consonancia con los supuestos de la hipótesis del mosaico de nutrientes, pero no admite los supuestos de la hipótesis de desequilibrio Co-evolutivo. saldiasi) utilized the Andes corridor, whereas the large forms of these groups (Stegomastodon waringi, Stegomastodon platensis, Equus neogeus and Hippidion principale) utilized the Eastern route and some coastal areas. The route of each form seems to reflect an adaptive shift in their ecology (Alberdi & Prado, 1992;Sánchez et al, 2004;Prado et al, 2011).…”