Megafauna: Giant Beasts of Pleistocene South America

8 General Paleoecology

275 8 General Paleoecology We have already seen how the Pleistocene mammals got to South America, with some having ancestors already established there since the dawn of the Tertiary, notably marsupials, xenarthrans and the native ungulates, others having arrived in Tertiary times by crossing the Atlantic from Africa against overwhelming odds (primates and caviomorph rodents), and still others venturing into southern lands once (or just before) the Panamanian land bridge was formed: sigmodontine cricetids among Rodentia, procyonids, mustelids, canids, ursids, and felids among Carnivora, cervids, tayassuids, and camelids among Cetartiodactyla, equids and tapirs among Perissodactyla , and gomphotheriids among Proboscidea. Many aspects of their proposed habits have been dealt with in previous chapters, so we are now ready to consider how this whole fauna worked together. Paleoecology deals with reconstructing ecosystems of the past by using data from the fossil record and from its geologic context. It includes the study of the habits of past organisms and their interactions and natural environment. It works on the basis of actualistic, often statistical, models to figure out the habitats of those organisms that we find today as fossils. When dealing with fossils and ancient environments, however, postmortem factors such as temperature and mineral supplies can bias our interpretations, adding another layer of complexity to this discipline when compared with modern ecology. A usual way of dividing the conceptual realm of this subject matter is to consider paleoautecology, which treats the environment from the organism’s perspective, and paleosynecology, which studies the large-scale interactions at higher levels, such as communities and ecosystems. In the following pages, we will summarize the findings and approaches related to the paleoecology of this splendid fauna. Because we have already considered studies on the life habits of particular species, we will focus especially on synecological efforts. Until recently, the quality of information on this fauna was essentially what could be derived from common knowledge. To get a sense of the perception paleontologists had (and conveyed to other people) of this assemblage, it is easier to consider visual reconstructions of Pleistocene landscapes as opposed to the typical scientific publications, which are cumbersome to track and cite. For instance, the splendid illustration depicted in Fig. 8.1, which adorns one of the entrances of the División Paleontología de Vertebrados of the Museo de La Plata, is enormously significant for several reasons. To begin with, it was conceived at the end of the nineteenth century, just after the city of La Plata had been founded, as an artist’s rendition of a plan to embellish the gardens between the museum and the neighboring zoo. This space was envisioned as a place where the Definition, scope, and background Megafauna 276 extinct beasts, whose bones resided in the museum, were brought back to life in the form of life-sized sculptures (and hence why there are pedestrian pathways also depicted). Regrettably, this wondrously grand scheme was never realized, though the reasons why have been lost with time. However, the plan admirably depicts the way those megamammals and their habits were then viewed. For example, Megatherium, in the center background, is represented as furry and walking on all fours along a prairie similar to the pampas that the Ameghinos were familiar with (i.e., before fertilizers). Apart from the general portrayal of a rather luxuriously vegetated plain, it draws attention to the locomotory habits of this giant sloth, considered alternatively as a quadruped or as a biped. It is interesting to note that Cuvier saw it as a quadruped, while Owen (1838) drew it as a biped leaning against a trunk and reaching for leaves, despite Darwin’s observations. In the left foreground, two glyptodonts, likely Panochthus and Doedicurus , seem cordial in their close proximity; the former seems to be engaged in excavating, an activity based certainly on the habits of its closest living relatives. Although glyptodont anatomy does not, at least in principle, preclude digging behavior, it is unlikely that they practiced such behavior (as discussed further in Chapters 6 and 7). In the center foreground, a mastodon ambles majestically, and two smaller glyptodonts, Neosclerocalyptus, seem attentive to the danger of being trampled by the proboscidean. A similar contemplative attitude is depicted for Glyptodon, just to the right of its smaller relatives. Across the pedestrian pathway, one Macrauchenia watches warily while another drinks from a shallow pond. Meanwhile, in the background and from left to right, a ground sloth, probably Glossotherium, seems to be leaving the scene, exiting stage left, and...