• WordNet 3.6
    • n Synapsida extinct reptiles of the Permian to Jurassic considered ancestral to mammals
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Century Dictionary and Cyclopedia
    • synapsida A subclass of Reptilia having the roof of the cranium solid, or with a single, large supratemporal opening, the squamosal large, the quadrate reduced and fixed, and the coracoid and procoracoid separate or suturally united. Contrasted with Diapsida.
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