Introduction to Monotremata

Ornithorhynchus anatinus

The order Monotremata is a fairly ancient mammalian taxon. It includes two families, Ornithorhynchidae (Ornithorhynchus*) and Tachyglossidae (the echidnas, Tachyglossusand Zaglossus). Although considered mammals, monotremes have several characteristics not generally considered mammalian. Among these are oviparity, a cloaca (hence the name monotreme, Greek for "one hole"), lack of functional teeth, the presence of poison glands (Walker 1964), and milk secretion in a "mammary patch" rather than through teats. Like marsupials, they have anterior testes and a forked penis (Anderson and Jones 1967). Their range is limited to Australia, Tasmania, and New Guinea (Walker 1964).

*Don "The Mango King," Yungaburra, Queensland fruit stand proprietor and self-proclaimed platypus expert, disputes this account of platypus phylogeny. He places the platypus in Anatidae, the duck family (personal communication, 11/98).

Tachyglossus sp.

Echidnas

A young Tachyglossus

Specialized for digging to find food and escape predation
Have poor vision but excellent smell and hearing
Lack teeth, but use a long (15-18 cm) tongue to feed on ants and termites
Females develop and use a pouch (marsupium) during the breeding season
Humans appear to be only natural enemy -- can live up to 50 years in captivity
Genus Tachyglossus, the short-beaked echidna, occurs throughout Australia and Tasmania
Genus Zaglossus, the long-beaked echidna, occurs only in New Guinea

Source: Anderson and Jones, 1967

Platypus

Only one species: Ornithorhynchus anatinus
Total length around 650 mm, males are larger than females
Dives in freshwater lakes and streams for food
Feeds on aquatic invertebrates and vegetation
Lacks true teeth -- use "gum plates" to grind food
Closes eyes and ears when diving -- relies on electrosensory perception in bill

Can eat up to 1/2 body weight per day in captivity
Only sound is an uncommon, low "growl"
Nocturnal and crepuscular
Unlike echidnas, does not develop marsupium
Occurs only in southern and eastern Australia

Sources: Bethge, 1997; Anderson and Jones, 1967

All images courtesy http://www.healthsci.utas.edu.au/physiol/mono/Mainpage.html unless otherwise noted.

Main page

Introduction to
Monotremes

Thermal Biology

Evolutionary Implications
of Thermal Biology

Diving

Special Aspects
of Diving

Literature
Cited

This page is a class assignment for Animal Physiology at Davidson College. For questions or comments, please email Will White.