Eocene metatherians from Anatolia illuminate the assembly of an island fauna during Deep Time

Abstract

Island biotas have disproportionately influenced the history and development of evolutionary biology, but understanding their genesis and evolution across geological timescales has been hindered by a poor fossil record. Here we augment the insular Eocene (~43 Ma) mammalian fauna known from the Pontide terrane of central Anatolia by describing two new metatherian taxa (stem marsupials) from the Lülük Member of the Uzunçarşıdere Formation in the Orhaniye Basin. Geological and paleontological data indicate that the Pontide terrane was an island on the northern margin of Neotethys during the middle Eocene. Reflecting its geodynamic context in a region of active tectonic convergence, the Eocene Pontide terrane hosted a unique combination of Laurasian and Gondwanan mammals, including an anachronistic radiation of pleuraspidotheriids (archaic ungulates) that went extinct on the European mainland ~13 Ma earlier. Most of the mammalian clades occupying the Pontide terrane colonized it by dispersal across marine barriers rather than being stranded there through vicariance. Endemic radiations of pleuraspidotheriid ungulates and polydolopimorphian metatherians on the Pontide terrane reveal that in situ diversification was an important factor contributing to faunal assembly and evolution. The insular fauna that arose on the Pontide terrane is highly analogous to that of modern Sulawesi, which evolved under strikingly similar geological conditions. Illustrating the ephemeral nature of insular biotas across macroevolutionary timescales, the demise of the Pontide fauna coincided with paleogeographic changes enabling more cosmopolitan taxa to reach it for the first time. The high level of endemism shown by the mammalian fauna of the Uzunçarşıdere Formation eliminates the Pontide terrane as a potential early Eocene dispersal corridor between western Europe and India.

Phylogenetic tree of Litopterna and Perissodactyla indicates a complex early history of hoofed mammals

“…This is sustained by a large number of taxa shared between Africa and South America, but also with other landmasses and especially India, including hystricognath rodents, anthropoid monkeys, afrotherian mammals, pipid frogs, freshwater fishes (cichlids and aplocheiloids), birds (parrots, hoatzins, phororhacoids), and lizards (geckos), and Malpighiaceae, Asteraceae, and Bromeliaceae among plants 52,[54][55][56][57][58][59] . Further support for this interchange includes the finding of several lineages of metatherians, anthropoid monkeys and hystricognath rodents in South America, indicating multiple dispersals between South America and Africa and vice-versa during the Paleogene [60][61][62][63][64] . As enumerated above, the evidence indicating a fluid interchange between South America and other Southern Hemisphere landmasses and India has been greatly increasing during the last years (see below).…”

Late Paleogene herpetofaunas from the crossroads between two continents – new amphibian and reptile remains from the Oligocene of southern Balkans and Anatolia

“…Such a dispersal, at least from the Balkans to central Europe seems to have taken place slightly later than the above discussed northern route (i.e., around 31 Ma versus around 33 Ma; see Mennecart et al 2018b). Interestingly, it has also been recently demonstrated, again on the basis of mammal finds, that during the Eocene, the area of central Anatolia was an island environment (the "Pontide terrane") possessing a remarkable diversity of peculiar and endemic forms, all of which became ultimately extinct during the Oligocene when the loss of the insular status of the area permitted the arrival of several other mammal lineages from both Europe and Asia (see Métais et al 2018). Nevertheless, given the absence of adequate Oligocene amphibian and reptile remains from the area of Anatolia and the southern Balkans, such southern dispersal route for the herpetofauna as well and any relevant biogeographic patterns have remained obscure.…”

Taxonomy and Affinities of African Cenozoic Metatherians

“…A Paleocene dispersal of metatherians from South America to Africa could not only account for the inferred affinities of Kasserinotherium but also for the presence of anatoliadelphyid polydolopimorphians (Anatoliadelphys, Orhaniyeia) in the middle Eocene of Central Anatolia (Turkey). Interestingly, Métais et al (2018) found phylogenetic affinities between anatoliadelphyids and South American and Australian bunodont polydolopimorphian metatherians such as Palangania, Chulpasia and Thylacotinga. "We hypothesize that basal polydolopimorphians were actually present in Africa during the early and/ or middle Eocene, whence they rafted northward across Neotethys to colonize the Pontide terrane."…”