Floating Islands: A Mode of Long-Distance Dispersal for Small and Medium- Sized Terrestrial Vertebrates

This paper evaluates whether the floating island model is a plausible transoceanic mode of dispersal among small to medium-sized land vertebrates. The actual Atlantic Ocean served as a model of winds and currents velocity, and data were sampled from modern marine pilot charts in two areas of the ocean. The main objective was to quantify the number of days required for a floating island to cross three Paleogene water barriers, 50, 40 and 30 Mya, namely the Atlantic Ocean, the Caribbean Sea as well as the Southeast Indian Ocean between Sundaland and the northern Australian Plate. Paleodistances and ancient circulation patterns of winds and currents are known in each region. It is proposed that paleowinds (not paleocurrents), and its effect on floating objects, were the key accelerating force of floating islands' velocity. In the most conservative scenario, the Paleogene Atlantic oceanic barrier could have been crossed westerly by a floating island in 7.7 days at 50 Mya, 10.8 days at 40 Mya and 14.7 days at 30 Mya; the Paleogene Caribbean Sea from South to North America could have been surmounted northerly in 18.2 days at 50 Mya, 16.6 days at 40 Mya and 15.1 days at 30 Mya; finally, the Southeast Indian Ocean from Australia to Sundaland could have been crossed northerly in 25.6 days at 50 Mya, 19.5 days at 40 Mya and 12.2 days at 30 Mya. There are many physical, physiological and behavioral constraints to transoceanic migrations. Such migrations can be considered as potentially successful however if it is shown that the journey did not exceed the survival limit of a given genetically viable group of animals. Metabolic studies involving survival limits to water deprivation suggest that proposed scenarios are plausible for small to medium size mammals and most land reptiles. These studies also suggest that migrating groups were probably preadapted in their original habitats (before the oceanic journey) to some degree of temporary dehydration and therefore to strong or moderate seasonal variations in water and food availability in order to survive the transoceanic event. Considering for example, the origin of the South American platyrrhine monkeys and caviomorph rodents, respective ancestors of these mammal groups probably lived in habitats with definite dry and rainy seasons. This conclusion implies that the survival limit of both platyrrhines and rodents ancestors ranged between 10 and 15 days, an assumption related to the transoceanic scenarios presented here