Origin of Madagascar's extant fauna: A perspective from amphibians, reptiles and other non‐flying vertebrates

Abstract

The origins of the highly endemic and partly very diverse fauna and flora of Madagascar were longtime unsolved and are still strongly disputed, although dispersalists are recently prevailing over advocates of Gondwanan vicariance. Madagascar has been separated from other continents and continental fragments since the Mesozoic, and the assumption of vicariance origins requires very old ages of the lineages involved. Herein I review the recent progress of knowledge on the molecular phylogenetic relationships of the amphibians, reptiles, and other non-flying vertebrates of Madagascar. Of 17 Malagasy clades for which relationships seem to be resolved with sufficient and unanimous support, the largest proportion have their sister-group in Africa, and very few show a general area cladogram consistent with the succession of events in the fragmentation of the supercontinent Gondwana. A survey of pairwise sequence divergences between 25 Malagasy lineages and their non-Malagasy relatives in the 16S and 12S rRNA genes resulted in values that in most cases were distinctly below the saturation plateaus of these genes. Multiple calibrations based on 34 largely independent data points indicate that such saturation would be strongly expected in the case of ages corresponding to the geographical isolation of Madagascar in the Jurassic and Cretaceous. A Cenozoic age for most Malagasy lineages is therefore most likely. Analysis of phylogenetic patterns of some taxa provides indications for a scenario in which the ancestors of the Malagasy clades first arrived by transmarine dispersal from Africa at the Malagasy west coast, and in a second step a subset of them underwent species-rich radiations into the rainforests.

A giant frog with South American affinities from the Late Cretaceous of Madagascar

“…However, as the Late Cretaceous fauna of the Maevarano Fm (1, 4), including its ceratophryine anuran, bears little resemblance to that of modern Madagascar, major biotic changes clearly occurred on the island in the intervening period. When and how the ancestors of the endemic mantellid and microhylid anurans arrived on Madagascar remains controversial (5,6,8,12,18,19), but there is general agreement that these frogs did not diversify significantly until the Paleogene (5,6,12,18,19). Their radiation has been linked, at least in part, to the expansion of rainforests, but may also have been facilitated by the extinction of archaic faunal elements (5), including ceratophryines.…”

“…Ultimately, the Indian subcontinent continued north to contact Eurasia, and Madagascar was left 430 km from Africa, isolated by the deep Mozambique Channel (4). The remarkable diversity and endemicity of the Malagasy biota has prompted intense debate as to the role of vicariance and, more recently, of dispersal in its history (5)(6)(7). The frogs of Madagascar are important to this discussion because amphibians are generally considered to be poorly suited to transoceanic dispersal (7), although exceptions are known (8,9).…”

“…In recent years, molecular phylogenetic analyses have clarified the relationships of key groups [e.g., the monophyly of Malagasy mantellids (10-13)]. Of Ͼ200 documented species, only two, the ranids Ptychadena mascareniensis and Hoplobatrachus tigerinus, are nonendemic, the latter a recent human introduction (5). The endemics are all either microhylids or mantellids, with the single exception of the hyperoliid Heterixalus (10).…”

“…Molecular analyses have offered persuasive evidence that Heterixalus (14), and also Ptychadena mascareniensis (15), arrived from Africa in the Neogene. For these taxa, transoceanic dispersal offers the most parsimonious explanation, but the history of the endemic Malagasy mantellids and microhylids is equivocal, and both vicariant-based (7,12,(16)(17)(18) and dispersal-based (5,6,19) hypotheses have been formulated. A good fossil record would aid the debate, but apart from the Triassic proanuran Triadobatrachus (20) and some preliminarily identified Late Cretaceous finds (21), this record has been lacking.…”

Biogeography of worm lizards (Amphisbaenia) driven by end-Cretaceous mass extinction

“…Among the more striking examples is the Fijian iguana Brachylophus; its close relationship to New World species [7,59] implies trans-Pacific dispersal from the Americas to the South Pacific. Similarly, the existence of iguanas in Madagascar implies oceanic dispersal [60].…”