Biology of Australia The superfamily Protodontoidea has 2
families, diprotodontids and palorchestids. The diprotodontids
were similar in shape to wombats, and ranged from the size of a
sheep to that of a large hippopotamus. There were 2 families of
diprotodontids, Zygomaturines and Diprotodontines. Zygomaturines
have multi-cusped last upper premolars. Among the Riversleigh
diprotodontoids these were the most common and diverse. One of
the most common was Neohelos tirarensis, that seems to have
ranged far and wide across Australian habitats during the
Miocene. One genus, Nimbadon, is known from skulls and
articulated skeletons, was about the size of a labrador dog,
others reached the size of small cattle. A feature of these
animals was that they had very small brains. They are believed
to have eaten soft leaves. Gradually the smaller forms died out,
either becoming extinct or giving rise to larger forms. This
evolutionary pattern is common, being found in the fossil record
of many vertebrate groups. Most zygom