We Don’t Need No Stinkin’ Placentas!
It is commonly believed that marsupials, such as the kangaroos and cuddly koalas, are ‘primitive’ and ‘inferior’ when compared to placental mammals, which includes rats, cats, whales and humans. In certain regions of the world, and among certain species, this claim has some validity; nonetheless, as a sweeping generalization, it is erroneous, and fails to address biological fitness and natural adaptation in a meaningful way.
As an analogy, consider the claim that reptiles are patently ‘inferior’ to mammals. And yet lizards and snakes have competed along side mammals for tens of millions of years, successfully controlling many ecological niches; furthermore, reptiles dominate a number of predator niches in Australia that might be open to birds or mammals on other continents. Why?
As ectotherms, reptiles deploy an energy efficient and flexible low metabolism, making them better suited for surviving droughts and erratic food supplies. Many snakes and lizards, without suffering ill effects, can go months without feeding; large pythons and crocodiles, in fact, have gone years without a meal. Perhaps the skeptic, while pontificating on the grand superiority of the mighty mammal, might try skipping meals for several months straight while sticking to a regular routine.
It is true that certain placental mammals have been highly successful in competition with Australian marsupials. The dingo, arriving somewhere between four and ten thousand years ago, undoubtedly usurped much of the Thylacine’s ecological niche on the mainland. It has been assumed that the dingo arrived in boats from Indonesia no more than 4000 years ago, but new genetic studies suggest an earlier arrival.
The thylacine, sometimes called the marsupial wolf, or Tasmanian Tiger, was a remarkably dog-like animal. Although only remotely related to dogs–a mouse and a whale, for example, are more closely related–the thylacine evolved some convergent characteristics with the dog. Essentially, in convergent evolution, similar modes of life and similar environmental pressures can produce similar biological forms in even distantly related species.
Observers noted that the remarkable thylacine was a prodigious jumper. Dingoes never reached Tasmania, which separated from mainland Australia about 12,000 years ago. Before the arrival of the Europeans, the Thylacine remained safe in Tasmania until thoughtlessly exterminated in an orgy of bounties and shootings. The busy Europeans did much the same to the indigenous people of Tasmania until, much like the persecuted Thylacines, the last one died in captivity.
Rabbits, foxes, and cats are all introduced placental mammals that have run amok on the Australian continent: the rabbit, by breeding into devouring hordes and stripping all vegetation like waves of locusts; the fox and cat, as relentless predators, driving small native marsupials into the maw of extinction.
Ironically, the greatest introduced scourge in Australia, other than humans, may turn out to be not a brainy mammal at all, but a puffy, clumsy, warty simpleton of an amphibian: the noxious Marine Toad (Rhinella marinus), native to Mexico and Central America. Formerly placed in the genus Bufo, the creature is known as the Cane Toad in Australia. A few thousand were released in Queensland in 1935, with the idea of controlling the sugar cane beetle.
The toad is immensely toxic to almost all predators in Australia, and as it expands its range, it is clearly responsible for severe declines of many native snakes, lizards, and small mammals. The Australian Death Adder (genus Acantophis), for example, appears to be devastated by the invasive toads. The gravest threat to Acanthophis hawkei, now listed as vulnerable, are Cane Toads moving into its habitat. Many species of monitor lizards (Varanus), which are aggressive and opportunistic predators, are killed off in catastrophic numbers when trying to consume the poisonous toads.
Can anything eat the toad and live to tell about it?
According to the Australian Museum: “Predators of Cane Toad tadpoles in Australia include dragonfly nymphs, water beetles, Saw-shelled Turtles and Keelback Snakes. Keelbacks also eat young toads; laboratory tests have shown that they can tolerate low levels of toad toxins. Young or adult Cane Toads are eaten by wolf spiders, freshwater crayfish, Estuarine Crocodile, crows, White-faced Heron, kites, Bush Stone-curlew, Tawny Frogmouth, Water Rat and the Giant White-tailed Rat. Some predators eat only the toad’s tongue, or attack its belly and eat only the mildly poisonous internal organs.”
With enough time, some Australian predators may evolve coping mechanisms to detoxify the toads for safe consumption. Or ‘learn’ to avoid them completely. According to research conducted by award-winning herpetologist Rick Shine and his colleagues, the impact of the toad on native species, over time, may not be as apocalyptic as initially feared. In the meantime, the Cane Toads, an amphibious version of the Mongol Hordes, continue their ever expanding terrestrial and aquatic invasion of Australia.
Kangaroos vs. Ungulates
The first European description of a wallaby was made by the Dutchman Francisco Pelsaert in 1629 off the coast of Western Australia. Sir Joseph Banks, the botanist/biologist on Captain Cook’s ship the Endeavour, was stunned by the sight of kangaroos. Hoping to obtain a specimen, he set his greyhound lose on several kangaroos only to see the fleet marsupials easily outrun it over the rough terrain.
Kangaroos are extraordinary beasts that defy the mundane. It is not the odd pouches and offbeat reproduction that stand out because those are shared with all the marsupials of Australia and the Americas. “Kangaroos are among the strangest of all mammals…because they hop,” points out biologist Terence Dawson. He adds, “…hopping is very uncommon among vertebrates…being used only by frogs and some small desert mammals. Apart from kangaroos and their relatives, no vertebrates larger than about 5 kg hop. There is no evidence in fossil history of other large hopping mammals.”1.
Only the six largest species are known as kangaroos; the smaller species are generally called wallabies. Both words were borrowed from Aboriginal languages. The kangaroos are grazers, feeding on grasses. At slow speeds, kangaroos seem awkward and inefficient, using their tail to help support their reduced front limbs while ‘walking’. Several studies have shown, however, that at higher speeds hopping is much more energy efficient than running in other mammals. In kangaroos, Dawson notes, “Energy can be stored for re-use in elastic fibrous tissues, such as tendons, in the same manner as energy is stored in the spring of a pogo stick or in the rubber of a bouncing ball.” Red kangaroos, the largest species, can maintain speeds of 40 km/h for a couple of kilometers; bursts of 65-70 km/h have been reported in the wild.
Dawson’s research, in conjunction with University of Colorado physiologist Rodger Kram, confirms the astounding versatility of kangaroo biomechanics. “Kangaroos are really special mammals,” said Dawson. “Work over the past half century has turned the notion that they belong to an inefficient, primitive group of mammals totally on its head.” Kangaroos use their tails, effectively, as a powerful fifth limb. During exercise, they can increase their metabolism 50 times above the rest state.
To truly appreciate the evolutionary genius of the kangaroos, match them against placental ungulates such as sheep and cattle in the harsh Australian outback with its brutal droughts, scorching heat, and sketchy vegetation. The remarkable reproductive biology of the kangaroo is also well suited to the Australian climate and terrain. Large red kangaroos, for instance, develop a single offspring, giving birth after 33 days to an ‘infant’ that weighs less than a gram! This blind, naked little creature makes an epic journey, leaving the birth canal, crawling over the mother’s fur, seeking to safely reach the pouch. Once inside, fastening itself to a teat, it continues its development.
The female kangaroo, after giving birth, can mate again. She can then ‘hold’ that fertilized zygote in limbo for the future. If the first offspring is successfully reared, only then does the zygote begin its development. But if the first infant dies, then the female automatically resets the schedule, and the second egg starts development immediately. And in just over a month this replacement can be born. This is, in fact, a remarkably adaptable and responsive reproductive cycle. The key is that the mother invests far less resources in these babies, at least in the en utero phase of development, than a placental mammal mother does.
Most of Australia is desert or erratically arid except for coastal strips. As John Alcock writes, “A red kangaroo in the outback can have no guarantee that conditions favorable for the survival of her youngster will persist over the months needed for its full development. Devastating drought could settle in at any time. By giving birth so ‘prematurely,’ a female kangaroo avoids the costs of preparing a complex placenta, and this avoids the risks associated with giving birth to a large-bodied neonate. If drought conditions make it impossible to sustain a current offspring, she can end her parental investment simply by removed the joey from her pouch.”2.
The mother survives to try to reproduce again when conditions warrant it. If heavy rains suddenly appear and grass grows luxuriantly, then she is ready with the fertilized zygote held in reserve. A whitetail deer, in contrast, invests six months of demanding gestation into its offspring before birth. In what way is the kangaroo reproductive system inferior? The assertion reveals a fundamental misunderstanding of the interplay between natural selection, biodiversity, and environmental demands.
Kangaroos are marvelously adapted in other ways to the arid conditions in Australia. According to Dawson, kangaroos only drink about 10% of the amount of water sheep require. In research conducted at Fowlers Gap, NSW, kangaroos watered only about once a week. For two centuries ranchers slaughtered kangaroos for supposedly competing with domestic animals; most research, however, shows that competition is minimal and primarily occurs during droughts.
The ‘Eggstreme’ Monotremes
One of the most widespread and ‘successful’ mammal species in Australia, the echidna, uses an even more ancient, ‘primitive’, and retro mode of reproduction: it goes about producing babies the good old fashioned way, by laying eggs. In contrast to birds, the single leathery egg is retained internally, as the female deposits it directly inside the pouch.
After ten days, the baby hatches and, since mama echidnas lack nipples, begins feeding on milk secreted from two milk patches. In the interests of a good scrabble word, the baby echidna is known as a puggle. Despite being mild mannered and harmless, the echidna gets its name from a fierce Goddess, half woman and have giant snake, cited numerous times in Greek mythology. Aside from the egg laying, there are a number of other unusual features in the monotremes.
For example, once the baby begins to develop protective spines, the mother echidna digs a hole and dumps the baby into the burrow, returning every five days to nurse it until it is weaned at seven months! The penis of the male echidna has four ‘heads’, although it only uses one pair of ‘heads’ at a time for breeding. As they develop, adult echidnas shed their teeth and live primarily on ants and termites. In captivity, echidnas refuse to reproduce at all.
The platypus, limited to fresh water streams in Eastern Australia, is the other monotreme found on the continent. When the first specimen arrived at the British Museum in 1799, it was suspected of being a hoax, some kind of mole or beaver stitched artfully together with the cadaver of a duck. Who would go to all that trouble? Possibly Chinese sailors, who apparently liked to play practical jokes on European explorers.
The male platypus has a spine on each hind leg capable of delivering a shot of venom. Although not lethal to humans, it generates intense pain, enough to incapacitate the victim. Smaller mammals such as dogs have been killed by a platypus ‘sting’. Although not currently endangered, the platypus is threatened, primarily by pollution and destruction of its freshwater habitat.
Humans and Marsupials
Aborigines used an assortment of techniques for hunting kangaroos and other game—and these varied from region to region. Drawing on the research of Dorothy Tunbridge, an ethnographer who worked with the Adnyamathanha people of the Flinders Range in South Australia, Dawson sites a number of weapons and technologies. Hunters used a waddy—a throwing club—and boomerangs, both made from heavy mulga wood, as well as short spears, deep pit traps, blinds, and nets made from either wallaby tail sinew or plant fiber. These nets could stretch 90 meters in length.
Once the animals were butchered and briefly cooked in ground ovens, parts of the kangaroos were divvied up based on age and social status. There were food taboos that made certain parts of the animals off limits to uninitiated young men and single women.
According to Tunbridge’s research and inquiries among the Adnyamathanha, it appears that 30 out of 45 species of mammals became extinct in the Flinders Range within 50 years of the arrival of Europeans. How did the European colonists respond to such a wondrous creature? Kangaroos were hunted for meat, chased by dogs for sport, and then exterminated in huge numbers as pests for daring to compete with cattle and sheep.
Beginning in the mid 19th century massive numbers were killed for the leather and skin industry. Researcher Martin Denny demonstrated that half a million skins a year passed through the Melbourne market alone throughout the second half of the 19th century. In the late 20th century as many as 3 million a year were ‘harvested’ for skins and dog-food. It is testimony to the resilience of the larger species that they have survived this systematic plunder. Widespread shooting for skins or as ‘pests’ is still done in Australia, particularly in Queensland.
On my travels in outback Queensland, I occasionally came upon ‘hunting’ teams in battered trucks and rusty Land Rovers, overloaded with the bloody carcasses of Eastern Grey kangaroos. In one encounter, the bodies were hung from racks and bounced and swayed as the pickup made its way slowly down a rough dirt road. A gruesome mobile slaughter house, the men who emerged from the truck, filthy and blood-spattered, reminded me of the Morlocks in the 1960 film, The Time Machine, which starred, coincidentally, Australian Rod Taylor.
Although several of the smaller wallaby species are endangered—some have already gone extinct—the living kangaroos, fortunately, are fairly safe. Both the Eastern Greys and Reds may number close to ten million in the wild. They may have actually expanded their range in the arid interior thanks to stock ponds and tanks.
Kangaroos have their magnanimous side, too. While checking for storm damage under a tree, Australian farmer Len Richards was knocked out by a falling branch, suffering serious head injuries. Lulu, an eastern grey kangaroo raised as a pet, stood guard over Richards’ unconscious body and “barked like a dog” to attract help, the farmer’s daughter said. “She was obviously trying to get our attention because she never acts like that,” 17-year-old Celeste Richards said. “It went on for about 15 minutes, so we went outside to investigate and saw Lulu standing upright with her chest puffed out over dad’s body. If it wasn’t for her, my dad could have died. Lulu is my hero,” she added.
The kangaroo, which is half-blind, was adopted by the family when they found her in the pouch of her mother, who had been killed by a car. “Lulu and Dad are very close, and she follows him around,” Celeste explained.3.
 John Alcock, The Kookaburras’ Song, (University of Arizona Press 1988) P.111.
 Associated Press, September 22, 2003.