The third group, the monotremes , are far less diverse and less well known. They are warm-blooded, have hair, and produce milk just like other mammals, but they lay eggs and do not give live birth like marsupials and placentals. A fourth major group, the Multituberculata , are entirely extinct, though they were once widespread and successful. You can follow the quagga in her quest for more mammalian knowledge by clicking on the group of your choice in the image below. Mammals themselves are part of a larger tetrapod group called the Synapsida .
Synapsids make up one of the two largest groups of amniote vertebrates.
Note that not all synapsids were mammals. A non-mammalian member of Synapsida is Thrinaxodon . The Thrinaxodon exhibit is of special interest because it uses CAT-scan technology to view the internal structure of a Thrinaxodon skull. An audio introduction to Mammals from The Encyclopedia of Mammals by David Macdonald. Read about the recent discovery of an early mammal fossil in Australia at the Dinosaur Dreaming site in Australia.