Kogaionidae

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Kogaionidae were a family of small, extinct mammals in the order Multituberculata. They lived from the Late Cretaceous to the Paleocene-Eocene boundary, roughly 66 to 55 million years ago, and are known from Europe, especially Hațeg Island in what is today Romania, where they were the dominant mammals while the island was isolated. This isolation led them to evolve unique ecological roles and traits.

The family includes genera such as Barbatodon, Hainina, Kogaionon, and Litovoi. Kogaionids are considered early members of Cimolodonta, a major subgroup of multituberculates, and many studies place them close to Taeniolabidoidea. A 2021 study even suggests they were among the most basal Cimolodonts, possibly descending from an eobaatarid-like ancestor.

Some kogaionids had red, iron-pigmented enamel, a feature seen in modern rodents and shrews, hinting at insect-eating habits. In Barbatodon the enamel pattern is more like that of shrews, supporting insectivory. On Hațeg Island, isolation produced unusual traits, such as extremely small brains in Litovoi and a small dome on the head in Barbatodon.

Kogaionids first appear in the Maastrichtian (late Cretaceous) of Romania, making them the only European multituberculates from that time in Europe. There is a doubtful Campanian record from Appalachia, but its identity is uncertain.

Their insectivorous lifestyle may have helped them survive the end-Cretaceous mass extinction. After Hațeg joined the rest of Europe in the Paleocene, fossils appear in France, Spain, Belgium, and Romania (Jisou). For a while they were common mammals in Europe, but by the Late Paleocene they declined as other multituberculate groups arrived from North America, eventually going extinct near the Paleocene-Eocene boundary (the PETM).