The tubb's rotund shape is unique. There is no other animal like it anywhere. It evolved from the basal ornithopods that were present on the Australian continent in the Cretaceous period. The related crackbeaks must have evolved there as well, and spread to the Asia along the island chains.
The Tubb, Pigescandens robustus, is a slow-moving, arboreal, koala-like basal ornithopod, native to the temperate forests of southeastern and southwestern Australia, in The New Dinosaurs: An Alternative Evolution.
Not all tree-living animals are active jumpers. Up in the topmost branches of the Eucalyptus trees of the southeastern and southwestern corners of the Australian continent lives a silvery blob, about 70 centimeters (2 feet) long. This is the tubb, a clumsy-looking creature moving sluggishly up and down the silvery grey branches of the Eucalyptus trees, feeding on nothing but the bluish foliage. At first glance it is difficult to imagine that both the tubb and the crackbeak are evolved from the same ancestor, Fulgurotherium, yet there are clues. The hind feet have four toes, the first of which point backwards and allow the animal to grasp branches. The hands have five fingers, the outer two of which are opposable. The deep head has powerful jaw muscles and a sharp beak, for breaking off food from the trees.
The tubb is a placid animal, moving slowly and eating nothing but Eucalyptus leaves and twigs. It has neither armor nor speed for defense. Its only protection from enemies, such as birds and pterosaurs, is in its distasteful flesh. Its body tissues store up the poisons that are present in the leaves and bark that it eats.
The other physical features, however, are quite different. The body is round and not suited for rapid movement. The legs are more suited for grasping trunks than for swinging along branches. The tail is short and stubby. It is the two opposable fingers on the hand that reveal the tubb to be closely related to the crackbeak. Of the modern basal ornithopods in other parts of the world, only the taddey of the Indomalayan ecozone possesses this feature.