Global palaeobiogeography of brachiopod faunas during the early Katian (Late Ordovician) greenhouse episode

• Quantitative global biogeography of 33 early Katian brachiopod faunas.
• Strong faunal endemism in Laurentia began at the Sandbian–Katian boundary.
• Endemism in Laurentia was influenced regionally by Taconic Orogeny.
• Endemism was also related to palaeoelatitudinal gradients within the tropics.

The early Katian (Late Ordovician) was marked by a major greenhouse episode and the early stage of a first-order marine transgression that led to the flooding of much of North America during the middle–late Katian. Multivariate analyses of 33 brachiopod faunas of early Katian (Trentonian, Chatfieldian, late Caradoc) age, including 252 rhynchonelliform genera, demonstrate that the “Trentonian brachiopod faunas” of Laurentia were already clearly differentiated into a Scoto-Appalachian fauna and an epicontinental fauna. Globally, four distinct faunal clusters are identified: Kazakhstan, Avalonia, epicontinental Laurentia, and Scoto-Appalachia. The Scoto-Appalachian fauna, which originated during the Sandbian, persisted into the early Katian and became most closely related to the brachiopod faunas along the western margins of Laurentia. The early Katian epicontinental faunas of Laurentia were more closely related to the coeval brachiopods of the Lithuanian–North Estonian confacies belts of Baltica than to the Scoto-Appalachian fauna. Palaeoecological control on the faunal endemism within Laurentia was attributable to isolation of Appalachian foreland basin by faulting and peripheral bulging during the early Taconic Orogeny, palaeolatitudinal faunal gradient from the subtropical Appalachia to mid-tropical epicontinental Laurentia, as well as different water depth, water temperature, and substrate types between the two palaeogeographical settings of Laurentia.