The origin of platyrrhines: An evaluation of the Antarctic scenario and the floating island model

Abstract

This paper evaluates whether 1) protoplatyrrhines could have migrated to South America via Antarctica, and 2) the floating island model is a plausible transoceanic mode of dispersal for land vertebrates like protoplatyrrhines. Results show that Eocene Antarctica and Australia supported large and dense forests, and that the Antarctic fauna was comprised of many species of vertebrates, including placental and marsupial land mammals. However, no primate remains have ever been reported from these continents. Antarctica and South America were connected until the Middle Eocene (i.e., after the oldest Asian anthropoids), but two major water barriers existed between Antarctica and Asia since the Early Eocene. The Eocene and Oligocene water gap separating Africa and Antarctica was excessively large. Thus, all scenarios involving an Antarctic route have been rejected. The African scenario is difficult to falsify because only one water barrier existed, both paleowinds and paleocurrents were favorable, and Paleogene African anthropoids show phylogenetic affinities to platyrrhines. I tested whether a journey on a hypothetical floating island over the Paleogene Atlantic Ocean exceeds the survival limit of a genetically viable group of animals such as protoplatyrrhines. Studies of water deprivation suggest that they could have been able, with a body weight averaging 1 kg, to survive without water for at least 13 days. I have used the present Atlantic Ocean as a model for the velocity of Paleogene paleowinds and paleocurrents. Considering winds as the key accelerating force of floating islands, the Paleogene Atlantic water barrier could have been crossed, in the most conservative scenario, in 8 days at 50 Mya, 11 days at 40 Mya, and 15 days at 30 Mya. In order to survive a transoceanic journey, however, protoplatyrrhines had to be preadapted to strong seasonal variations in water availability in their original (African) environment. Once on the sea, their brains would have physiologically interpreted the rarity of water as the beginning of the dry season, and the group would have switched its diet to alternative foods, i.e., everything available on the floating island.

Origin of tropical American burrowing reptiles by transatlantic rafting

“…The distance separating the two continents at that time, between 3500 and 6000 km, would have precluded the survival of these small vertebrates floating or swimming directly in the water. However, survival would have been possible if they rafted on a floating island of vegetation (flotsam), which would have been aided by favourable marine currents (North Equatorial Current) and palaeowinds (Guppy 1917;Pitman et al 1993;Houle 1999).…”

Primate chromosome evolution: Ancestral karyotypes, marker order and neocentromeres

“…It now appears that the division between two major branches of primates (Strepsirrhini and Haplorrhini) occurred over 70 Mya and probably closer to 77 Mya (Yoder et al 1996, Poux & Douzery 2004 Chromosome painting has shown that strepsirrhines have highly derived karyotypes, both in diploid number and in apomorphic syntenic associations (Muller et al 1997, 1999, Stanyon et al 2002, Warter et al 2005, Nie et al 2006) and that they are highly variable (Horvath & Willard 2007). Many human chromosome homologues are found fragmented in these species and numerous translocations have resulted in chromosomal syntenies, or hybridization associations, which differ from those found in humans.…”

Two New Taxa (Caviomorpha, Rodentia) from the Early Oligocene Tinguiririca Fauna (Chile)

“…The group's presence in the high latitudes thus almost certainly postdates the Mustersan given the dense sampling of this and earlier SALMAs in the region (vucetich et al, 1999;Madden et al, 2010), even for small-bodied taxa. Caviomorphs are widely inferred to have reached South America from Africa (Lavocat, 1974(Lavocat, , 1976Jaeger, 1989;Martin, 1994Martin, , 2005Marivaux et al, 2004;Coster et al, 2010;Sallam et al, 2011), via one or more crossings of a ~1000-1500 km wide South Atlantic (Houle, 1999) during the Paleogene. An earlier alternative scenario, invoking dispersal from North America via the proto-Antilles (Wood and Patterson, 1959;Wood, 1968;1972;, was predicated on the now discredited (Hoffstetter and Lavocat, 1970;Bugge, 1985;Meng, 1990;Martin, 1994) notion of a close relationship between North American franimorphs and Caviomorpha.…”

“…An Asian origin for caviomorphs has been proposed on molecular and morphological grounds (Hussain et al, 1978;Flynn et al, 1986;Jaeger, 1989;Huchon and Douzery, 2001). Nevertheless, dispersal between Asia and South America via North America or Australia-Antarctica is contradicted by the lack of early Cenozoic hystricognaths in any of these locations (Hartenberger, 1985;Wood, 1985;Houle, 1999;Marivaux et al, 2002). South America's isolation during most of the Cenozoic produced highly endemic land mammal faunas.…”