South American Cenozoic Mammalian ichnology: towards a global research program

KRAPOVICKAS, V.; VIZCAÍNO, S

Simposio; III Simposio Latinoamericano de Icnología; 2015

Reviews of Cenozoic vertebrate ichnology are scarce, albeit they may serve as starting point to deeper ichnologic analyses, compiling bibliography and evaluating the biological, ethological, and ecological information provided by footprints in the framework of the evolutionary history of their producers. Identifying the problems and promises of the mammalian paleoichnological record of each continent will help to develop a research program that will permit global comparisons. The long-term isolation of the South American continent for the greater part of the Cenozoic produced a highly peculiar terrestrial biota, of which one of the best-known components is its endemic mammalian fauna, with no living counterparts in most of the cases. Presently there are more than 20 known localities that record footprints of South American mammals. The ichnologic assemblages are principally distinguished in (1) those in which the producers belong to lineages that underwent diversification and ecological specialization in isolation from other continents, and (2) other assemblages including also representatives of North American lineages. The Eocene and Oligocene ichnologic assemblages mostly represent forms of uncertain affinity up to now, including: small caviomorph rodents or typothere notoungulates, large undetermined notoungulates, medium-size undetermined tetradactyl mammals, Macrauchenichnus isp. assigned to small toxodontid notoungulates or macraucheniid litopterns. Among the Miocene assemblages there are footprints assigned to ground sloths (e.g. Venatoripes riojanus, cf. Venatoripes riojanus, kidney-like footprints), macraucheniiids (e.g. Macrauchenichnus rector) and proterotheriid litopterns, rodent-like caviomorph rodents or typothere notoungulates, hegetotheriid notoungulates, and toxodontid notoungulates or macraucheniid litopterns (e.g. Macrauchenichnus isp.), and Tacheria troyana assigned to a large dinomyid caviomorph rodent. The Late Miocene-Pliocene and Late Pleistocene assemblages include footprints of both native South American mammals and North American taxa arrived during the Great American Biotic Interchange. The native South American lineages consist of a variety of ground sloths (e.g. Megatherichnum oportoi, Falsatorichnum calceocannabius) including megatheriids (e.g. Iribarnichnum megamericanum, Neomegatherichnum pehuencoensis) and mylodontids (e.g. Acunaichnus dorregoensis, Milodontichnum rosalensis), glyptodonts, macraucheniid (e.g. Macrauchenichnus rector, Eumacrauchenichnus patachonicus) and proterotheriid litopterns, hydrochoerid caviomorph rodents (e.g. Porcellusignum consulcator), undetermined ungulates, and carnivorous marsupials. The North American examples are equids (e.g. Caballichnus impersonalis, Ichnhippus cotaposi, Hippipeda isp.), gomphotheriids (e.g. Stegomastodonichnum australis), camelids (e.g. Lamaichnum guanicoe, Megalamaichnum tulipensis), cervids (e.g. Odocoileinichnum commune), and several carnivoran lineages as felids and mustelids (e.g. Pumaeichnum biancoi, Pehuencoichnus gracilis, Mustelidichnum enigmaticum).One of the most relevant ichnological records correspond to the Early Eocene rodent-like footprints of Paruro. If future careful analysis confirms the caviomorph affinity of the Paruro footprints, they could reinforce the recent hypothesis about the southward expansion of the earliest caviomorphs during the late Middle Eocene?Early Oligocene period. Moreover, the footprints would expand the early record of rodents in South America to the Early Eocene. In terms of trackmaker function, there is scarce information about the range of functional capabilities revealed in South American mammal trackways; it is necessary to conduct deep analysis of the locomotory modes expressed in trackways and analyze how this range compares to that of living mammals. However, the discussion about the locomotion capacity of megatheres based on the record of their trackways has provided valuable information to the understanding of megatheres paleobiology. The cluster analysis of the mammalian taxa represented by the fossil footprint record of South America compared with the faunal evolutionary phases proposed by Goin and coauthors (2012), shows two major clusters that roughly separate the faunas corresponding to the Early and Late South American evolutionary phases from the Interamerican phase. Environmentally, footprints are uniquely preserved on floodplain facies during the Eocene, Oligocene and Pleistocene. The record of mammalian fossil footprints on deserts of South America occur in a variety of sub-environments (dunes, wet interdunes, and salt flats), involving semi-arid and arid climates, during the Miocene and Pliocene.