Definition of prototherian in English:

prototherian

noun

Zoology
  • A mammal of the group Prototheria, which comprises the monotremes and their extinct relatives.

    • ‘Extant mammals, including prototherians (egg-laying mammals) and therians (marsupial and placental mammals), probably last shared a common ancestor about 160 million years ago.’

adjective

Zoology
  • Relating to or denoting prototherians.

    • ‘They had a common ancestor more recently than either had with the monotremes or, probably, any other prototherian group.’
    • ‘In his classification of prototherian mammals Hopson queried the allocation of Haramiyidae to the Multituberculata.’

Pronunciation:

prototherian

/ˌprəʊtə(ʊ)ˈθɪərɪən/