No body fossils of uncontested mammals from the Late Triassic-Early Jurassic of South America have yet been found. The South American record for this period consists of tracks and trackways, some of uncertain age and some of debatable affinities. We have drawn from the remarkably complete, meticulous monograph of Leonardi (1994) in summarizing the possible mammalian ichnofossils from the Late Triassic-Early Jurassic of South America (figure 2.7).
Stipanichnus bonetti is based on tracks said to belong to either a therapsid or mammal from an unnamed Upper Triassic (Norian-Rhaetian) unit at Los Menucos, Río Negro Province, Argentina. Ameghinichnus patagonicus, from the "Lias de Piedra Pintada," is from Neuquén Province, Argentina. Leonardi (1994) referred the tracks to the Jurassic; Rainforth and Lockley (1996) ascribed them to the La Matilde Formation, which they indicated to be Middle Jurassic. Assignment of these tracks to Mammalia has not been contested. Casamiquela (1964) ascribed the tracks to a "pantothere"; on the basis of an inferred galloping gait, Kielan-Jaworowska and Gambaryan (1994) suggested that the tracks might have been made by a multituberculate. Whatever the case, they provide evidence of alternating gaits and hopping in an early mammal (Rainforth and Lockley, 1996). Much larger tracks from the Newark Supergroup, eastern North America, have been ascribed to Ameghinichnus (see Olsen, 1980). To our knowledge, these have not yet been fully described and compared with the tracks from Argentina.
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