The Prototheria is a subclass of mammals. The name comes from Greek prōtos means 'first', and thēr, 'beast'. The only surviving animals in this subclass are the Monotremes.
There are two other subclasses, the Metatheria and the Eutheria. Metatheria contains the marsupials. All the other mammals are Eutherian.
Evidence is accumulating that the Prototheria is not a natural group, but alternative suggestions are not yet agreed.
- ↑ Zofia Kielan-Jaworowska, Richard L. Cifelli, and Zhe-Xi Luo 2004. Mammals from the Age of Dinosaurs: origins, evolution, and structure. New York: Columbia University Press.
- ↑ Benton, Michael J. 2005. Vertebrate palaeontology. 3rd ed. Oxford: Blackwell Publishing. ISBN 0-632-05637-1