prototheria
/ˌproʊtoʊˈθɪriə/
noun
- A subclass of mammals that lay eggs instead of giving birth to live young, including the platypus and echidnas.
- Prototheria are the most primitive group of living mammals.
- Scientists study Prototheria to understand the early evolution of mammals.
- The platypus belongs to Prototheria, a subclass of egg-laying mammals.