Madagascar: Heads It’s a Continent, Tails It’s an Island

Abstract

▪ Abstract Neither geologists nor biologists have a definition that is capable of classifying Madagascar unambiguously as an island or a continent; nor can they incorporate Malagasy natural history into a single model rooted in Africa or Asia. Madagascar is a microcosm of the larger continents, with a rock record that spans more than 3000 million years (Ma), during which it has been united episodically with, and divorced from, Asian and African connections. This is reflected in its Precambrian history of deep crustal tectonics and a Phanerozoic history of biodiversity that fluctuated between cosmopolitanism and parochialism. Both vicariance and dispersal events over the past 90 Ma have blended a unique endemism on Madagascar, now in decline following rapid extinctions that started about 2000 years ago.

Reconciling the Origins of Africa, India and Madagascar with Vertebrate Dispersal Scenarios

“…• The split between Africa and Madagascar was part of the earliest major rifting event in Gondwana, 170-155 million years ago, when western and eastern Gondwana separated, forming distinct basins between them [Reeves and de Wit, 2000;de Wit, 2003;Jokat et al, 2003Jokat et al, , 2005Ali and Aitchison, 2005]. Africa and South America comprised the western portion, while the eastern portion was made up chiefly of Indo-Madagascar, Antarctica, and Australia.…”

Diversification and the adaptive radiation of the vangas of Madagascar

“…Relatively few colonization events have been hypothesized to have occurred into Madagascar, with most endemic lineages proposed to be colonizers of African origin from across the Mozambique channel [15,16]. Hypotheses of modes of colonization of most terrestrial groups include rafting across the Mozambique Channel [15,[17][18][19][20] or via landbridges that no longer exist [21,22], with the former receiving more support. Its proximity to Africa makes it reasonable to assume that much of the modern biota of Madagascar is derived from there, although an Asian component has been detected in some lineages [15,[23][24][25][26].…”

Malagasy Primate Origins: Phylogenies, Fossils, and Biogeographic Reconstructions

“…Coffin and Rabinowitz, 1987;Storey, 1995;Hay et al, 1999;de Wit, 2003]. For example, some Malagasy taxa appear to share taxonomic affinities with continental African fauna, suggesting dispersal across the Mozambique Channel [Leroy, 1996;Yoder et al, 2003;Vences et al, 2004], whereas other taxa may be more closely related to Asian forms [Eger and Mitchell, 1996;Rage, 1996; but see Thewissen and McKenna, 1992;McKenna, 1995].…”

“…Inferences regarding habitat vicariance are strengthened by common speciation patterns in unrelated groups [Myers and Giller, 1988]. For example, hypotheses abound as to the sequence and timing of the breakup of Gondwanan landmasses during the Cretaceous [Coffin and Rabinowitz, 1987;Storey, 1995;McCall, 1997;Hay et al, 1999;de Wit, 2003]. Congruent phylogenetic patterns in different vertebrate clades have been used to test ideas regarding the persistence of connections between certain landmasses or habitats to the exclusion of others [Raxworthy and Nussbaum, 1996a;Krause et al, 1997;Sampson et al, 1998].…”

“…Dispersal scenarios can be greatly strengthened by refinements of geophysical evidence documenting barriers, land bridges or stepping stones that may have influenced the movements of animals in the past [e.g. de Wit, 2003;Masters et al, this vol., pp. 399-418].…”