![]() ![]() It has been further suggested that Pleistocene ecosystems could not have supported the plant biomass demands of all the presumed large herbivores, which implies that secondary consumers disguised as herbivores must exist in the fossil record but have not been recognized as such 4. Allometric functions relating population densities to body mass indicate that Pleistocene SA mammalian communities were ecologically imbalanced because the herbivore biomass markedly surpassed the energetic requirements of carnivores 4. Lack of placental mammalian carnivores is particularly puzzling for the Pleistocene because all large marsupials (e.g., borhyaenoids) and non-mammalian predators such as terrestrial crocodiles (i.e., sebecids) and large flightless “terror birds” (i.e., phorusrhacids), which likely maintained terrestrial food web energy transfer balances in the Tertiary, were already extinct by this epoch. Another aspect of this perceived uniqueness is the depauperate abundance and diversity of mammalian carnivores throughout the Cenozoic. Characterizing the paleoecology of South American (SA) fossil mammals is particularly challenging, because those communities bear little resemblance to modern or fossil guilds from other continents due to marked taxonomic and phylogenetic disparities and unusually large numbers of entirely extinct clades 3. Little is known, however, about the ecological structure of mammalian communities before the megafaunal extinctions of the last Pleistocene ice age, when more than 80% of mammals above 40 kg became extinct 2. Home to more than half of Earth’s land biota, South America contains the highest diversity of extant terrestrial mammals of any continent 1.
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