However, additionally the order monotremata have:
- Many reptilian characteristics (e.g. an egg tooth is present in young to help them break open their shell)
- A bird like skull with an elongated rostrum
- No teeth - they chew their food using a tongue and a horny plate on the roof of the mouth (echidnas) or some groups have horny gums (e.g. the platypus)
- A pectoral girdle splayed as in reptilians
- A pelvic girdle that is distinctly mammalian
Monotremes have a very distinctive form of reproduction, unique among all animals. This is reflected in the name of the animals which means 'one-holed creature' and refers to a common opening found at the posterior ends of all monotremes, through which waste products and eggs are excreated. Inside this hole two viginas seperate off, this structure is complemeneted by a two pronged penis in the males.
This structure, named the cloaca, is involved in another feature of the monotremes - the process of laying eggs. Subsequently this feature has led many people to believe that the order is very primitive, as it is a feature shared with their descendents, the dinosaurs. However, although they have retained such features, the order is not primitive. A unique mammalian form of reproduction has arisen as a consequence of the isolation of these mammals millions of years ago.
Only two families remain within the Monotremata Order; the Echidnas and Platypus.
As mentioned they are unique among animals in that they both lay eggs, but suckle their young with milk. Therefore it follows that they have unusual courtship and reproductive behaviours. We can only speculate about the behaviour of the other extinct families within this order, from that of the Echidna and Platypus.
Images used, with permission, from Wikipedia
Author: Catrin Roberts
Last updated: 23.11.83
Return to Fossil groups home page