Diprotodontia

Diprotodontia is the largest living order of marsupials. It contains approximately 155 different species found in Australasia. This group includes many animals that people recognize easily, such as kangaroos, wallabies, koalas, and wombats. It also includes various types of possums. These animals are vital to the biological diversity of the Australasian region. While many species are well-known today, the order has a very long and complex history.

Scientists identify members of Diprotodontia using two specific anatomical traits. The first trait is their unique dental structure. The name comes from Ancient Greek words meaning "two front teeth." These animals possess a pair of large, procumbent incisors on the lower jaw. Their jaws are typically short in shape. Most species have three pairs of upper incisors. However, wombats are an exception and only have one pair. The second identifying trait is called syndactyly. This refers to the fusing of the second and third digits of the foot. The claws themselves remain separate, but the digits are joined up to the base.

Syndactyly is often viewed as an adaptation to assist with climbing. Many modern diprotodonts have evolved to be strictly terrestrial, or ground-dwelling. This means they live on the land rather than in trees. The history of tree-kangaroos illustrates how these adaptations can shift. It appears these animals were arboreal, meaning they lived in trees, in the distant past. They later moved to the ground and developed long, kangaroo-like feet. Eventually, they returned to the trees. They developed a novel climbing method and changed the shape of their hind feet.

Dietary habits among diprotodonts are mostly herbivorous. This means most species eat plants. However, there are several interesting exceptions to this rule. The Potoroidae family is almost unique among vertebrates because they are largely fungivorous. This means they primarily eat fungus. Some other species are insectivorous, eating insects, or omnivorous, eating both plants and animals. In the past, some groups were much more predatory. The extinct thylacoleonids, known as "marsupial lions," were the only group to exhibit carnivory on a large scale.

The fossil record provides a window into the ancient history of this order. The earliest known fossils date back to the Late Oligocene. This period occurred between 23.03 and 28.4 million years ago. Large gaps exist in the fossil record in Australia, and there is almost no record in New Guinea. This suggests the order began to diverge much earlier than the oldest fossils show. Some extinct members were massive. The Diprotodon was as large as a hippopotamus. There were also extinct families like the Diprotodontidae, which were giant wombats.

Many large diprotodonts became extinct approximately 50,000 years ago. This coincided with the arrival of humans in Australia. This extinction included many types of Australian megafauna. Scientists believe this may have happened because of direct hunting by humans. It was also likely caused by widespread habitat changes. Human activities, specifically the use of fire, changed the environment significantly. This shift in the landscape likely made it difficult for the largest, least athletic animals to survive.

Taxonomy, or the classification of these animals, is divided into several suborders. One suborder is Vombatiformes, which includes wombats and koalas. Another major group is the Phalangeriformes. Within these groups, there are many different families and superfamilies. For example, the Macropodiformes include kangaroos and wallabies. The Petauroidea superfamily includes animals like sugar gliders and striped possums. The Phalangeroidea superfamily includes brushtail possums and cuscuses. This complex classification helps scientists understand how these different species are related to one another.