The distribution of certain dasycladacean algae (Chlorophyceae) in the Jurassic of Europe and adjacent parts of Africa and southwestern Asia is summarized. The isocrymal limits for different groups of living dasycladaceans are indicated. The Middle Jurassic dasycladacean distribution, when plotted on the ‘Pangaea stage of continental displacement 180 Ma B.P.’ (Owen 1976) shows that, on the then Earth’s surface, there is a marked line of distribution limitation, now inferred as isocrymal in origin. Beyond this the very limited records available suggest either a more limited temperature tolerance in the Middle Jurassic dasycladacean flora than exists in the living dasycladacean flora, or a distribution due to the effects of increased solar radiation on an Earth of smaller diameter than at present.

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