An Introduction to Cingulate Evolution and Their Evolutionary History during the Great American Biotic Interchange: Biogeographical Clues from Venezuela

Abstract

As we have discussed, the latest finds from northern Venezuela, along with a reanalysis of the remains from Colombia, have brought about a new interpretation of the evolutionary and biogeographical history of oneof the major groups of glyptodonts, the Glyptodontinae (glyptodontines).This can be summarized in the following points: 1 The morphological evidence suggests that the glyptodonts from the Middle Miocene–Pliocene (ca. 12–5 Ma) of northernmost South America (Colombia and Venezuela) do not belong to the subfamily Propalaehoplophorinae, but actually represent the first stages in the cladogenesis and later dispersion of the Glyptodontinae. 2 As a consequence of this, the Propalaehoplophorinae are restricted to southernmost South America (Argentine Patagonia). Likewise, the oldest records of Glyptodontinae are those from the Miocene–Pliocene of the current territories of Colombia and Venezuela 3 The oldest records of Glyptodontinae in southernmost South America, from the latest Miocene and Pliocene of Argentine provinces Catamarca and Tucumán, partly coincide with the peak of the “Age of Southern Plains.” This great latitudinal extension of open savanna environments could have stimulated the southward dispersal of these glyptodonts, by way of “biogeographical corridors,” as proposed for other mammals. 4 At some point during the Pliocene, the glyptodontines (probably together with the glyptatelines) passed onto Central and North America, along with many other mammalian orders. At present, Glyptotherium is the only genus recorded in those areas. 5 The presence of Glyptotherium (cf. G. cylindricum) in the latest Pleistocene (ca. 14 ka) of Venezuela (Falcón state) suggests an entry of these glyptodontines into South America at some point during the Late Pleistocene, probably associated with “biogeographical corridors” that could have formed during the glacial periods, as proposed for other Cingulata (e.g., Pampatheriidae). 6 During the GABI, the pampatheriids (like the glyptodontines) migrated into Central and North America. The genus Holmesina, with the species H. septentrionalis, would have evolved in these regions. 7 Later, this genus reentered South America, following two routes: one “para-Andean” and another parallel to the eastern coast. The cyclical climatic-environmental fluctuations that occurred during the Pleistocene would have triggered speciation processes that gave rise to endemic South American species. 8 Finally, and possibly during the Early Pleistocene–Middle Pleistocene lapse, another genus (Pampatherium) would have migrated towardNorth America, originating the species Pampatherium mexicanum. 10 Later, this genus reentered South America, following two routes: one “para-Andean” and another parallel to the eastern coast. The cyclical climatic-environmental fluctuations that occurred during the Pleistocene would have triggered speciation processes that gave rise to endemic South American species. 11 Finally, and possibly during the Early Pleistocene–Middle Pleistocene lapse, another genus (Pampatherium) would have migrated toward North America, originating the species Pampatherium mexicanum