April 29, 2014 Sculpted by Climate Change: Wombats Down Under
The Australian continent has experienced some extreme climates during the past 65 million years. Its fauna and flora are testament to those extremities. The genus Eucalyptus, with some 700 species or so, is an excellent example of floral adaptations. Australian fauna, in particular the marsupials, have also been sculpted by climate change.
In the early 1990s I conducted my PhD studies in the subalpine snow gums forests of Mt. Stirling in the Victorian Alps. For 36 consecutive months I spent at least one week in the wild. During the winter months I back country skied into my research site.
The array of critters that I encountered during my visits were phenomenal including large awkward flying lyre birds, bounding rock wallabies and deadly king copper snakes. The most intriguing creatures I’ve ever encountered and had the pleasure of observing were wombats.
Wombats are large burrowing, massive flat skulled herbivores. They have short powerful front claws and they excel at digging. At 3.3 feet (1 meter) long and 4.3 feet (1.3 meters) high this 77-pound (35-kilogram) tunneler has been rightfully likened to the “hobbit” of the Australian forest.
Though they may appear at first glance to be cumbersome these beasts can accomplish feats greater than Cirque du Soleil performers. For instance, they are able to flatten their bodies within 4 inches (10 centimeters) of the ground. Also, they can attain speeds of 25 miles per hour (40 kilometers per hour) and maintain it for 164 yards (150 meters). Wombats are excellent swimmers and strong wrestlers.
They have thick hides with a one-centimeter layer of skin and a plate of bone muscle and cartilage on their backs. In their burrow they can squeeze under and intruder entering their tunnel and slam them against the roof.
There are three species of wombats. The bare-nosed or common wombat of southeastern Australia has a population of about one million. The southern hairy-nosed species of south Australia has a stable population of about 300,000. The largest species weighing a whopping 88 pounds (40 kilograms) is the northern hairy-nosed of Queensland. They are the rarest animal in Australia and may be the rarest mammal in the world.
Wombats have incredibly efficient metabolism as recorded by the lowest plasma concentration of thyroid hormones of any mammal. They are low-intake feeders, three times more efficient than kangaroos.
The key to wombat digestion is a very slow fermentation of starches and proteins from fungi, roots and grasses that are absorbed by the stomach and small intestines. A bacterium in their gut ferments the vegetation extracting every last drop of energy. The process may take several weeks.
Wombat pooh is the driest of any mammal because they are the most efficient consumer of water that mammalian evolution has produced.
Wombats have complex brains with intelligence equal to that of primates.
Wombats are marsupials and except during breeding they are solitary critters. Marsupials give birth to live young – essentially a fetus – that develops inside the mothers pouch. Wombats usually give birth to one offspring, rarely two, after one month of gestation. The young pup is about the size of a jelly-bean weighing five grams. About eight months later they leave the pouch weighing 4.4 pounds (2 kilograms). By the time they reach two years a common wombat can weigh 49 pounds (22 kilograms). They can live at least 15 years in the wild.
Interestingly, marsupials are a later evolutionary development than the placental mammals, because they can discard their fetuses at any time. Wombat-like creatures, possums and kangaroos date back to 35 million years.
Fossilized teeth of wombats show that over the last 25 million years that they adapted from a once lush rainforest continent to its present day aridity. The crowns of wombat teeth have become higher and higher over time until their roots finally disappeared.
The onset of desertification from ice ages replaced forests with grasslands. Today, their 24 rootless ever-growing teeth are specially designed to grind low-grade vegetation. In addition, wombats possess split lips which enable them to pick choice green stems off the ground.
Specialized teeth have enabled this large herbivore to live underground in burrows. It evolved to burrow in order to escape the heat; below ground burrows are cooler. In the winter the reverse is true.
Above 4,921 feet (1,500 meters) on Mt. Stirling snow cover can stick around for up to three months each year. Soil temperatures never freeze, and as a matter of fact, 3 feet (0.9 meter) beneath the surface is much warmer than the snow covered ground surface.
Every two or three days in the winter a wombat will leave its tunnel and venture into the snow. One of my most memorable moments on Mt. Stirling occurred in the winter of 1995. There was 3 feet (0.9 meter) of snow on the ground and I witnessed a mother wombat piggy-backing her young.
Wombat tunnels can extend for 66 feet (20 meters) horizontally under the ground and they mimic the pattern of tree roots in their branching configuration.
During the last Ice Age – the Pleistocene – fossils from the Gregory River in Riversleigh, Queensland showed that one species of wombat reached an astounding weight of 551 pounds (250 kilograms). I cannot even begin to imagine the size of its burrows!
Wombats are survivors and therefore they have thrived in Australia for millions of years. They have endured ice ages and prolonged aridity on the driest continent on Earth. They are water conservationists extraordinaire. And with global warming that is an important adaptation especially since Australia experiences extreme drought interspersed with intense flooding.
Earth Dr Reese Halter is an award-winning broadcaster and distinguished biologist. He’s the author of The Incomparable Honeybee
Text © by Dr Reese Halter 2014. All rights reserved.