title: Olson's Extinction and the latitudinal biodiversity gradient of tetrapods in the Permian.
abstract: The terrestrial vertebrate fauna underwent a substantial change in composition between the lower and middle Permian. The lower Permian fauna was characterized by diverse and abundant amphibians and pelycosaurian-grade synapsids. During the middle Permian, a therapsid-dominated fauna, containing a diverse array of parareptiles and a considerably reduced richness of amphibians, replaced this. However, it is debated whether the transition is a genuine event, accompanied by a mass extinction, or whether it is merely an artefact of the shift in sampling from the palaeoequatorial latitudes to the palaeotemperate latitudes. Here we use an up-to-date biostratigraphy and incorporate recent discoveries to thoroughly review the Permian tetrapod fossil record. We suggest that the faunal transition represents a genuine event; the lower Permian temperate faunas are more similar to lower Permian equatorial faunas than middle Permian temperate faunas. The transition was not consistent across latitudes; the turnover occurred more rapidly in Russia, but was delayed in North America. The argument that the mass extinction is an artefact of a latitudinal biodiversity gradient and a shift in sampling localities is rejected: sampling correction demonstrates an inverse latitudinal biodiversity gradient was prevalent during the Permian, with peak diversity in the temperate latitudes.
authors.affiliation: Museum für Naturkunde, Leibniz-Institut für Evolutions- und Biodiversitätsforschung, Invalidenstraße 43, 10115 Berlin, Germany neil.brocklehurst@mfn-berlin.de.
authors.forename: Neil
authors.identifier: http://orcid.org/0000-0003-2650-5480
authors.initials: N
authors.lastname: Brocklehurst
authors.affiliation: Evolutionary Studies Institute and School of Geosciences, University of the Witwatersrand, Private Bag 3, Johannesburg 2050, South Africa.
authors.forename: Michael O
authors.initials: MO
authors.lastname: Day
authors.affiliation: Evolutionary Studies Institute and School of Geosciences, University of the Witwatersrand, Private Bag 3, Johannesburg 2050, South Africa.
authors.forename: Bruce S
authors.initials: BS
authors.lastname: Rubidge
authors.affiliation: Museum für Naturkunde, Leibniz-Institut für Evolutions- und Biodiversitätsforschung, Invalidenstraße 43, 10115 Berlin, Germany.|Evolutionary Studies Institute and School of Geosciences, University of the Witwatersrand, Private Bag 3, Johannesburg 2050, South Africa.|Institut für Biologie, Humboldt-Universität zu Berlin, Invalidenstraße 110, Berlin, 10115, Germany.
authors.forename: Jörg
authors.initials: J
authors.lastname: Fröbisch
mesh_terms: D000818:Animals; D044822:Biodiversity; D053476:Extinction, Biological; D005580:Fossils; D009656:North America; D012426:Russia
keywords: Olson's Extinction; Permian; Tetrapoda; latitudinal biodiversity gradient; sampling bias