Scientific name: Diprotodon sp. Scientific classification:
Phylum: Chordata Class: Mammalia Order: Diprotodontia Family: Diprotodontidae When did it become extinct? The most recent remains of a diprotodon are the 30,000-
year-old bones from Cuddie Springs in southeastern Australia. Where did it live? The diprotodons were found only in Australia.
Like all of the landmasses on earth, Australia was once home to an array of large animals known as megafauna. The Australian assemblage of giant beasts included massive
marsupials, big flightless birds, and monster reptiles. Today, these are all gone, and the largest living marsupial is the red kangaroo (Macropus rufus). A fully grown male stands around 1.8 m tall and weighs in at about 90 kg. Thousands of years ago, the red kangaroo was even larger than it is today, but it was still dwarfed by the largest of the diprotodons, which were up to 1.8 m at the shoulder, 4 m in length, and 3 tonnes in weight—the only land animals alive today that are larger are the elephant, hippopotamus, and two species of rhinoceros. These giant marsupials looked a lot like big wombats, and the living wombats and koalas are actually the closest living relatives of these extinct beasts. There were several species of diprotodons—experts disagree on the exact number—but they ranged in size from 500-kg, bear-sized creatures to the aforementioned giants.
For hundreds of thousands of years, these giant marsupials were very widespread, as their bones have been found all over Australia. In some places, such as Lake Callabonna in South Australia, lots of diprotodon skeletons have been found together. Hair thought to be from a diprotodon has also been found as well as footprints preserved in the hardened surfaces of old lake beds. These impressions show that the diprotodon had hairy feet, and we can assume that the whole animal was covered with fur and was not naked like a rhinoceros. These footprints, the places in which they have been found, and the delicate skeletal structure of the diprotodon's feet suggest that these were animals that spent a lot of their time padding around on the soft earth and mud bordering lakes and rivers.
The diprotodon had a big skull, and like its feet, this was also quite fragile, with lots of hollow spaces. In the way of teeth, the skull contained four molars in each jaw, three pairs of upper incisors, and one pair of lower incisors. From this dentition, we can deduce that the diprotodons were herbivorous—probably browsers, rather than grazers, as their incisors enabled them to strip vegetation from branches. The molars, with their flat surfaces, ground the food before it was swallowed. In the skeletal remains of some diprotodons found at Lake Callabonna, the remains of saltbush were identified where the stomach would have been. This plant is far from nutritious, and it is likely that they only ate such things when they were starving, for example, during the dry season. So we know these marsupials were browsers, but what effect did this have on their activity; were they energetic creatures, always dashing about on the Australian plains, or did they lead a more sedate lifestyle? If the modern wombats are anything to go by, the diprotodons may have had a very slow metabolic rate, enabling them to make the very best of low-energy plant food. If this were the case, then they probably only moved with any urgency when they really needed to.
Like all marsupials, diprotodons had a pouch. There are even bones of adult female di-protodons that are accompanied by the tiny skeletons of their joeys, which were in the pouch when their mothers died. Marsupial babies are born at a very early stage of development. Little more than embryos, they struggle through their mother's fur to the pouch and latch onto one of the teats inside. The teat expands in their mouth, and they're locked in place for the next few months, swallowing their mother's milk. When the diprotodon baby outgrew the pouch, it ventured out into the wide world, keeping close to its mother and retreating to its furry refuge at the first sign of danger, in much the same way as a kangaroo joey.
Today, Australia is bereft of its large, native land predators, but thousands of years ago, this land was home to several creatures that could have made short work of a young di-protodon that had wandered too far from its mother. There was the marsupial lion, with its formidable claws and teeth, and it is likely that this predator killed and ate young di-protodons, and even the adults of the smaller species. The thylacine was another animal that may have preyed on these big, lumbering marsupials, and although it is unlikely that an individual marsupial lion or thylacine could have overpowered and killed the largest, fully grown diprotodons, these extinct predators may have hunted in groups to bring down prey much larger than themselves. In Tasmania, the hind limb bones of one of the smaller diprotodons were found with partially healed teeth marks, thought to be work of the marsupial lion. Saltwater crocodiles (Crocodylus porosus) can still be seen in Australia today, and these giant reptiles must have been more than a match for an adult diprotodon. Thousands of years ago, crocodiles were not the only murderous reptiles capable of preying on diprotodons: the giant monitor lizard, Megalania, also stalked the land (see the entry "Giant Monitor Lizard" later in this chapter).
These great, pouched plant munchers are, unfortunately, no longer with us. They disappeared, along with most of the Australian megafauna, around 30,000 to 40,000 years ago, just before the peak of the last ice age. The reason for the disappearance of Australia's large mammals is a mystery, but the widely held theory today is that they succumbed to a combination of climate change and human activity. Several thousand years before they became extinct, the earth's climate cooled significantly, and Australia's arid interior expanded to cover over 70 percent of the continent. The diprotodons needed a lot of greenery to sustain their considerable bulk, and as this died back and the standing water disappeared, they may have slowly perished. The ancestors of the Australian Aborigines first reached Australia at least 50,000 years ago; there is little direct evidence of humans hunting the diprotodon, but there is evidence from the Cuddie Springs site suggesting that people may have scavenged from the carcasses of these animals or ambushed them at water holes. It has also been suggested that humans altered Australian habitats by starting bushfires as a way of clearing land or driving prey from cover. However, of the 69 species of extinct Australian mammal known today, only 13 are known to have lived within the period of human occupation. Perhaps people just accelerated a process that had started well before they arrived.
♦ It has been suggested that the diprotodons were semiaquatic like the hippopotamus, spending most of their time in lakes and rivers, browsing on aquatic vegetation.
♦ The fact that Australian Aborigines lived alongside diprotodons in some parts of Australia for thousands of years is the reason why some people believe that the stories of the bunyip, a terrible aquatic beast, are based on folk memories of living diprotodons. The bunyip is said to be a dangerous animal that will kill any creature that ventures into its aquatic home. However, it is often the case that due to huge stretches of time, the recollections of extinct animals that persist in folk memories are often massively distorted.
Further Reading: Wroe, S., M. Crowther, J. Dortch, andJ. Chong. "The Size of the Largest Marsupial and Why It Matters." Proceedings of the Royal Society of London B: Biological Sciences 271 (2004): S34-S36; Wroe, S., and J. Field. "A Review of the Evidence for a Human Role in the Extinction of Australian Megafauna and an Alternative Interpretation." Quaternary Science Reviews 25 (2006): 2692-2703.
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