Winters and biogeography: Diploptera cockroaches and biotic sorting in greenhouse and icehouse climates

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Abstract We examine the effects of mean annual temperature (MAT) and coldest month mean temperature (CMMT) on Eocene and modern distributions of the cockroach genus Diploptera de Saussure, 1864. Today, Diploptera range in parts of the Sino–Japanese, Oriental, and Oceanian Realms with upper mesothermal to megathermal MAT and mild CMMT. In the Eocene greenhouse world, Diploptera ranged from microthermal to megathermal climates, with two published species in Wyoming, USA, four new species that we name ( Diploptera reticulata , Diploptera rothi , Diploptera simeoptera , and Diploptera praecisus ), and eight incertae sedis specimens from Messel, Germany; British Columbia, Canada; and Washington, USA. All of these localities had mild winters with few if any frost days, and so the ranges of modern and Eocene Diploptera are constrained by CMMT, not MAT. This is consistent with a tropical/temperate mix of fossil taxa in microthermal Eocene plant and insect communities being explained by mild CMMT. It does not, however, explain why taxa that today inhabit temperate climates mixed with tropical taxa in Eocene upper mesothermal to megathermal climates. This might be due to their cold tolerance evolving after the Eocene with the onset of cold extra-tropical winters, only then establishing their modern temperate association. Therefore, thinking of them as tropical or temperate organisms in the greenhouse Eocene is not appropriate. To survive in post-Eocene extra-tropical latitudes, animals and plants either adapted to colder winters, went extinct, were restricted to reduced extra-tropical mild winter refugia, or, like Diploptera , retreated to the tropics. UUID: http://zoobank.org/3cfa2688-6001-4499-8a48-a83de9f6bb26

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