The Structure of the Mammalian Predator Guild in the Santa Cruz Formation (Late Early Miocene)

Abstract

The Santa Cruz Formation (late early Miocene, Santacrucian age) registers 11 species of mammalian predators (Metatheria, Sparassodonta). Together with large carnivorous flightless birds, they comprised the terrestrial predator guild. The Santacrucian sparassodonts were diverse in body size, had different locomotory habits, and were primarily hypercarnivores. The objective of this work is to analyze the guild structure of the sparassodonts of the Santa Cruz Formation, using the variables of body mass, diet, and locomotion as proxies. Furthermore, we analyze the interaction with other predators and potential prey. The univariated test V of Poole and Rathcke and the multivariated test of Clark-Evans were used to construct the models. In the multivariate test, we made a Principal Component Analysis to resume and standardize the variables. With body mass and locomotion we obtained an evenly spaced pattern of segregation for the sparassodont species, being non-significant and significant, respectively. The pattern was aggregated and significant only with diet. The analysis of all variables together resulted in an evenly spaced and significant pattern, which is consistent with character displacements (segregation of species throughout the morphospace) that would help to diminish interspecific competition during the Santacrucian age and would allow selection of prey species of different sizes and substrate specializations. When the body size pattern of predator birds and sparassodonts were plotted together, the pattern is evenly spaced and nonsignificant. Other factors, including locomotion, would differentiate these species and their ecological niches.

Mandible morphology and diet of the South American extinct metatherian predators (Mammalia, Metatheria, Sparassodonta)

“…Our results also showed differences with the diets inferred using the RGA index (relative molar grinding area), which assigned all the studied sparassodonts to the hypercarnivore class. Alternatively, mandible shape could be related to relative prey size, and species with shorter and robust mandibles could have preyed on larger prey (similar or larger than their own body size) and taxa with long and slender mandibles could have hunted only small prey, as was recently proposed for the Santacrucian fauna (Ercoli et al 2014).…”

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

“…Although the dietary classification of sparassodontans has been controversial (Croft ; Ercoli et al . ; Prevosti et al . ; Zimicz ), our study has focused on the ecological interactions that might have been contributing factors in their extinction.…”

“…Data were also obtained for newly described species and new records representing range extensions from the literature (Beck ; Ercoli et al . ; Prevosti et al . ; Engelman & Croft ; Woodburne et al .…”

“…The probability of competition between sparassodontans and terror birds, which survived until at least 1.8 Ma, has been argued, although it has also been noted that phorusrhacid diversity may have been too low to account for declines in sparassodontans, particularly during the Pliocene, when sparassodontan extinction occurred (Ercoli et al . ; Prevosti et al . ).…”

“…As a result of these issues, the sparassodontan fossil record is clearly far from complete, either spatially or temporally (Ercoli et al . ; Prevosti et al . ; Forasiepi et al .…”