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Prototheria

plural noun
Pro·​to·​the·​ria

Definition of Prototheria 

: a subclass of Mammalia that is coextensive with Monotremata or in some classifications includes both Monotremata and Allotheria and that is represented in the recent fauna solely by the egg-laying platypus and echidnas

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History and Etymology for Prototheria

New Latin, from prot- + -theria

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