ASSEMBLY OF AN ENDEMIC ISLAND BIOTA ON THE EOCENE PONTIDE TERRANE (NORTHERN ANATOLIA): PALEOGEOGRAPHIC AND PALEOCLIMATIC IMPLICATIONS

The discovery of Paleogene vertebrates from island contexts is quite rare, limiting the capacity of the fossil record to inform us about the genesis of island faunas during Deep Time. The mammalian fauna of the Uzunçarşıdere Formation (UCF) in the Orhaniye Basin (northern Anatolia) provides detailed insights into the assembly of the endemic island biota inhabiting the Pontide terrane during the middle Eocene. Taxa currently known from the UCF include four or five species of the pleuraspidotheriid “condylarth” Hilalia, one or two embrithopods including Hypsamasia seni, a bat, an omomyid primate, and two or more metatherians (including a herpetotheriid and a polydolopimorph). Notably absent from the UCF fauna are mammalian taxa that are otherwise ubiquitous across Eurasia by the middle Eocene, including Rodentia, Carnivora, Perissodactyla and Artiodactyla. The low diversity and unbalanced character of the UCF fauna are both consistent with its inferred island context.

Aside from Hilalia, pleuraspidotheriids are restricted to the Paleocene of western Europe, where they were among the most common mammals known from the late Paleocene Cernay fauna of the Paris Basin. The persistence of pleuraspidotheriids in the UCF suggests that the Pontide terrane was connected, at least intermittently, to western Europe during the Paleocene. The absence of rodents and other ubiquitous Laurasian mammals in the UCF indicates that any direct geographic links between the Pontide terrane and the Eurasian mainland were severed prior to the Paleocene-Eocene boundary. Multiple mammals must have colonized the Pontide terrane by rafting across parts of the Tethys Sea during the Eocene. Overwater colonization of the Pontide terrane occurred both from the north (the herpetotheriid and the omomyid) and the south (the polydolopimorph and the embrithopod), reflecting the convergent tectonic setting and monsoonal patterns of precipitation characterizing this part of Tethys during the Eocene.