Diprotodon
Encyclopedia
Diprotodon, meaning "two forward teeth", sometimes known as the Giant Wombat or the Rhinoceros Wombat, was the largest known marsupial that ever lived. Along with many other members of a group of unusual species collectively called the "Australian megafauna
", it existed from approximately 1.6 million years ago until extinction some 46,000 years ago (through most of the Pleistocene epoch
).
Diprotodon species fossil
s have been found in sites across mainland Australia
, including complete skulls and skeleton
s, as well as hair and foot impressions. Female skeletons have been found with babies located where the mother's pouch would have been. The largest specimens were hippopotamus
-sized: about 3 metres (9.8 ft) from nose to tail, standing 2 metres (6.6 ft) tall at the shoulder and weighing up to 2786 kilograms (6,142.1 lb).
They inhabited open forest
, woodland
s, and grassland
s, possibly staying close to water, and eating leaves, shrubs, and some grasses.
The closest surviving relatives of Diprotodon are the wombat
s and the koala
. It is suggested that diprotodonts may have been an inspiration for the legends of the bunyip
, as some Aboriginal
tribes identify Diprotodon bones as those of "bunyips".
The first recorded Diprotodon remains were discovered in a cave near Wellington
in New South Wales
in the early 1830s by Major Thomas Mitchell who sent them to England for study by Sir Richard Owen. In the 1840s Ludwig Leichhardt
discovered many Diprotodon bones eroding from the banks of creeks in the Darling Downs of Queensland
and when reporting the find to Owens commented that the remains were so well preserved he expected to find living examples in the then unexplored central regions of Australia.
The majority of fossil finds are of demographic groups indicative of diprotodonts dying in drought conditions. For example, hundreds of individuals were found in Lake Callabonna
with well preserved lower bodies but crushed and distorted heads. It is theorised several family groups sank in mud while crossing the drying lake bed. Other finds consist of age groupings of young or old animals which are first to die during a drought.
Diprotodon superficially resembled a rhinoceros
without a horn. Its feet turned inwards like a wombat’s, giving it a pigeon-toed appearance. It had strong claws on the front feet and its pouch opening faced backwards. Footprints of its feet have been found showing a covering of hair which indicates it had a coat similar to a modern wombat.
Until recently it was unknown how many species of Diprotodon had existed. Eight species are described although many researchers believed these actually represented only three at most while some estimated there could be around twenty in total.
Recent research compared the variation between all of the described Diprotodon species with the variation in one of Australia’s largest living marsupials the Eastern Grey Kangaroo
and found the range was comparable, with a near continent-wide distribution. This left only two possible Diprotodon species differing only in size with the smaller being around half the size of the larger. According to Gause’s “competitive exclusion principle
” no two species with identical ecological requirements can coexist in a stable environment. However, both the small and large diprotodonts coexisted throughout the Pleistocene and the size difference is similar to other sexually dimorphic
living marsupials. Further evidence is the battle damage common in competing males found on the larger specimens but absent from the smaller. Dental morphology also supports sexual dimorphism, with highly sexually dimorphic marsupials, such as the grey kangaroo, having different tooth sizes between males and females, but both sexes having the same dental morphology. An identical dental morphology occurs in the large and small Diprotodon. The taxonomic implication is that Owen’s original Diprotodon optatum is the only valid species.
A single sexually dimorphic species allows behavioral interpretations. All sexually dimorphic species of over 5 kg in weight exhibit a polygynous
breeding strategy. A modern example of this is the gender segregation of elephant
s where females and the young form family groups while lone males fight for the right to mate with all the females of the group. This behavior is consistent with fossil finds where adult/juvenile fossil assemblages usually contain only female adult remains.
argue that diprotodonts, along with a wide range of other Australian megafauna
, became extinct shortly after humans arrived in Australia about 50,000 years ago.
Some older researchers including Richard Wright argue on the contrary that diprotodont remains from several sites, such as Tambar Springs and Trinkey and Lime Springs suggest that Diprotodon survived much longer, into the Holocene
. Other more recent researchers, including Lesley Head and Judith Field, favor an extinction date of 28 000 - 30 000 years ago, which would mean that humans coexisted with Diprotodon for some 20 000 years. However, opponents of "late extinction" theories have interpreted such late dates based on indirect dating methods as artifact
s resulting from redeposition
of skeletal material into more recent strata
, and recent direct dating results obtained with new technologies have tended to confirm this interpretation.
Australia has undergone a very long process of gradual aridification since it split off from Gondwanaland about 40 million years ago. From time to time the process reversed for a period, but overall the trend has been strongly toward lower rainfall. The recent ice age
s produced no significant glaciation in mainland Australia but long periods of cold and very dry weather. This dry weather during the last ice age may have killed off all the large diprotodonts.
Critics point out a number of problems with this theory. First, large diprotodonts had already survived a long series of similar ice ages, and there does not seem to be any particular reason why the most recent one should have achieved what all the previous ice ages had failed to do. Also, climate change apparently peaked 25,000 years after the extinctions. Finally, even during climatic extremes, some parts of the continent always remain relatively exempt: for example, the tropical north stays fairly warm and wet in all climatic circumstances; alpine valleys are less affected by drought, and so on.
The "blitzkrieg theory" is that human hunters killed and ate the diprotodonts, causing their extinction. The extinctions appear to have coincided with the arrival of humans on the continent, and in broad terms, Diprotodon was the largest and least well-defended species that died out. Also, similar hunting-out happened with the megafauna
of New Zealand, Madagascar and many smaller islands around the world (such as New Caledonia, Cyprus, Crete and Wrangel Island), and at least in part, in the Americas
—probably within a thousand years or so. Recent finds of Diprotodon bones which appear to display butchering marks lend support to this theory. Critics of this theory regard it as simplistic, arguing that (unlike New Zealand and America) there is little direct evidence of hunting, and that the dates on which the theory rests are too uncertain to be relied on.
on which they depended. In particular, early Aborigines are thought to have been fire-stick farmers
using fire regularly and persistently to drive game, open up dense thickets of vegetation, and create fresh green regrowth for both humans and game animals to eat. Evidence for the fire hypothesis is the sudden increase in widespread ash deposits at the time that people arrived in Australia, as well as land-management and hunting practices of modern Aboriginal people as recorded by the earliest European settlers before Aboriginal society was devastated by European contact and disease
. Evidence against the hypothesis is the fact that humans appear to have eliminated the megafauna of Tasmania
without using fire to modify the environment there.
The above hypotheses are not necessarily mutually exclusive. Each of proposed mechanisms can potentially support the other two. For example, while burning an area of fairly thick forest and thus turning it into a more open, grassy environment might reduce the viability of a large browser (an animal that eats leaves and shoots rather than grasses), the reverse could also be true: removing the browsing animals (by eating them, or by any other means) within a few years produces a very thick undergrowth which, when a fire eventually starts through natural causes (as fires tend to do every few hundred years), burns with greater than usual ferocity. The burnt-out area is then repopulated with a greater proportion of fire-loving plant species (notably eucalypt
s, some acacia
s, and most of the native grasses) which are unsuitable habitat for most browsing animals. Either way, the trend is toward the modern Australian environment of highly flammable open sclerophyllous forests, woodlands and grasslands, none of which are suitable for large, slow-moving browsing animals—and either way, the changed microclimate produces substantially less rainfall.
Australian megafauna
Australian megafauna are a number of large animal species in Australia, often defined as species with body mass estimates of greater than 30 kilograms, or equal to or greater than 30% greater body mass than their closest living relatives...
", it existed from approximately 1.6 million years ago until extinction some 46,000 years ago (through most of the Pleistocene epoch
Pleistocene
The Pleistocene is the epoch from 2,588,000 to 11,700 years BP that spans the world's recent period of repeated glaciations. The name pleistocene is derived from the Greek and ....
).
Diprotodon species fossil
Fossil
Fossils are the preserved remains or traces of animals , plants, and other organisms from the remote past...
s have been found in sites across mainland Australia
Australia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...
, including complete skulls and skeleton
Skeleton
The skeleton is the body part that forms the supporting structure of an organism. There are two different skeletal types: the exoskeleton, which is the stable outer shell of an organism, and the endoskeleton, which forms the support structure inside the body.In a figurative sense, skeleton can...
s, as well as hair and foot impressions. Female skeletons have been found with babies located where the mother's pouch would have been. The largest specimens were hippopotamus
Hippopotamus
The hippopotamus , or hippo, from the ancient Greek for "river horse" , is a large, mostly herbivorous mammal in sub-Saharan Africa, and one of only two extant species in the family Hippopotamidae After the elephant and rhinoceros, the hippopotamus is the third largest land mammal and the heaviest...
-sized: about 3 metres (9.8 ft) from nose to tail, standing 2 metres (6.6 ft) tall at the shoulder and weighing up to 2786 kilograms (6,142.1 lb).
They inhabited open forest
Forest
A forest, also referred to as a wood or the woods, is an area with a high density of trees. As with cities, depending where you are in the world, what is considered a forest may vary significantly in size and have various classification according to how and what of the forest is composed...
, woodland
Woodland
Ecologically, a woodland is a low-density forest forming open habitats with plenty of sunlight and limited shade. Woodlands may support an understory of shrubs and herbaceous plants including grasses. Woodland may form a transition to shrubland under drier conditions or during early stages of...
s, and grassland
Grassland
Grasslands are areas where the vegetation is dominated by grasses and other herbaceous plants . However, sedge and rush families can also be found. Grasslands occur naturally on all continents except Antarctica...
s, possibly staying close to water, and eating leaves, shrubs, and some grasses.
The closest surviving relatives of Diprotodon are the wombat
Wombat
Wombats are Australian marsupials; they are short-legged, muscular quadrupeds, approximately in length with a short, stubby tail. They are adaptable in their habitat tolerances, and are found in forested, mountainous, and heathland areas of south-eastern Australia, including Tasmania, as well as...
s and the koala
Koala
The koala is an arboreal herbivorous marsupial native to Australia, and the only extant representative of the family Phascolarctidae....
. It is suggested that diprotodonts may have been an inspiration for the legends of the bunyip
Bunyip
The bunyip, or kianpraty, is a large mythical creature from Aboriginal mythology, said to lurk in swamps, billabongs, creeks, riverbeds, and waterholes....
, as some Aboriginal
Indigenous Australians
Indigenous Australians are the original inhabitants of the Australian continent and nearby islands. The Aboriginal Indigenous Australians migrated from the Indian continent around 75,000 to 100,000 years ago....
tribes identify Diprotodon bones as those of "bunyips".
Discovery
Wellington, New South Wales
Wellington is a town in inland New South Wales, Australia located at the junction of the Macquarie and Bell Rivers. The town is the administrative centre of the Wellington Shire Local Government Area. The town is 362 kilometres from Sydney on the Great Western Highway and Mitchell Highway...
in New South Wales
New South Wales
New South Wales is a state of :Australia, located in the east of the country. It is bordered by Queensland, Victoria and South Australia to the north, south and west respectively. To the east, the state is bordered by the Tasman Sea, which forms part of the Pacific Ocean. New South Wales...
in the early 1830s by Major Thomas Mitchell who sent them to England for study by Sir Richard Owen. In the 1840s Ludwig Leichhardt
Ludwig Leichhardt
Friedrich Wilhelm Ludwig Leichhardt, known as Ludwig Leichhardt, was a Prussian explorer and naturalist, most famous for his exploration of northern and central Australia.-Early life:...
discovered many Diprotodon bones eroding from the banks of creeks in the Darling Downs of Queensland
Queensland
Queensland is a state of Australia, occupying the north-eastern section of the mainland continent. It is bordered by the Northern Territory, South Australia and New South Wales to the west, south-west and south respectively. To the east, Queensland is bordered by the Coral Sea and Pacific Ocean...
and when reporting the find to Owens commented that the remains were so well preserved he expected to find living examples in the then unexplored central regions of Australia.
The majority of fossil finds are of demographic groups indicative of diprotodonts dying in drought conditions. For example, hundreds of individuals were found in Lake Callabonna
Lake Callabonna
Lake Callabonna is a dry salt lake with little to no vegetation in northeastern South Australia, approximately southwest of the junction of South Australia, Queensland and New South Wales at Cameron Corner. It is an important site for late Pleistocene fossils...
with well preserved lower bodies but crushed and distorted heads. It is theorised several family groups sank in mud while crossing the drying lake bed. Other finds consist of age groupings of young or old animals which are first to die during a drought.
Taxonomy
Diprotodon was named by Owen (1838). It was assigned to Diprotodontidae by McKenna and Bell (1997). The historical classification of Diprotodon consisted of eight species (Diprotodon optatum Owen, 1838; Diprotodon australis Owen, 1844; D. annextans McCoy, 1861; D. minor Huxley, 1862; D. longiceps McCoy 1865; D. loderi Krefft, 1873a; D. bennettii Krefft, 1873b (nec D. bennettii Owen, 1877); and D. bennettii Owen, 1877 (nec D. bennettii Krefft, 1873b); based on size or slight morphological differences of single specimens collected from isolated geographic regions. Bimodal dental sizes, rather than a continuum of tooth sizes, and identical male and female dental morphology, indicate sexual dimorphism instead of separate species, thus providing strong evidence that the eight species are synonyms for D. optatum.Morphology
Rhinoceros
Rhinoceros , also known as rhino, is a group of five extant species of odd-toed ungulates in the family Rhinocerotidae. Two of these species are native to Africa and three to southern Asia....
without a horn. Its feet turned inwards like a wombat’s, giving it a pigeon-toed appearance. It had strong claws on the front feet and its pouch opening faced backwards. Footprints of its feet have been found showing a covering of hair which indicates it had a coat similar to a modern wombat.
Until recently it was unknown how many species of Diprotodon had existed. Eight species are described although many researchers believed these actually represented only three at most while some estimated there could be around twenty in total.
Recent research compared the variation between all of the described Diprotodon species with the variation in one of Australia’s largest living marsupials the Eastern Grey Kangaroo
Eastern Grey Kangaroo
The Eastern Grey Kangaroo is a marsupial found in southern and eastern Australia, with a population of several million. It is also known as the Great Grey Kangaroo and the Forester Kangaroo...
and found the range was comparable, with a near continent-wide distribution. This left only two possible Diprotodon species differing only in size with the smaller being around half the size of the larger. According to Gause’s “competitive exclusion principle
Competitive exclusion principle
In ecology, the competitive exclusion principle, sometimes referred to as Gause's law of competitive exclusion or just Gause's law, is a proposition which states that two species competing for the same resources cannot coexist if other ecological factors are constant...
” no two species with identical ecological requirements can coexist in a stable environment. However, both the small and large diprotodonts coexisted throughout the Pleistocene and the size difference is similar to other sexually dimorphic
Sexual dimorphism
Sexual dimorphism is a phenotypic difference between males and females of the same species. Examples of such differences include differences in morphology, ornamentation, and behavior.-Examples:-Ornamentation / coloration:...
living marsupials. Further evidence is the battle damage common in competing males found on the larger specimens but absent from the smaller. Dental morphology also supports sexual dimorphism, with highly sexually dimorphic marsupials, such as the grey kangaroo, having different tooth sizes between males and females, but both sexes having the same dental morphology. An identical dental morphology occurs in the large and small Diprotodon. The taxonomic implication is that Owen’s original Diprotodon optatum is the only valid species.
A single sexually dimorphic species allows behavioral interpretations. All sexually dimorphic species of over 5 kg in weight exhibit a polygynous
Polygyny
Polygyny is a form of marriage in which a man has two or more wives at the same time. In countries where the practice is illegal, the man is referred to as a bigamist or a polygamist...
breeding strategy. A modern example of this is the gender segregation of elephant
Elephant
Elephants are large land mammals in two extant genera of the family Elephantidae: Elephas and Loxodonta, with the third genus Mammuthus extinct...
s where females and the young form family groups while lone males fight for the right to mate with all the females of the group. This behavior is consistent with fossil finds where adult/juvenile fossil assemblages usually contain only female adult remains.
Date of extinction
Most modern researchers including Richard Roberts and Tim FlanneryTim Flannery
Timothy Fridtjof Flannery is an Australian mammalogist, palaeontologist, environmentalist and global warming activist....
argue that diprotodonts, along with a wide range of other Australian megafauna
Megafauna
In terrestrial zoology, megafauna are "giant", "very large" or "large" animals. The most common thresholds used are or...
, became extinct shortly after humans arrived in Australia about 50,000 years ago.
Some older researchers including Richard Wright argue on the contrary that diprotodont remains from several sites, such as Tambar Springs and Trinkey and Lime Springs suggest that Diprotodon survived much longer, into the Holocene
Holocene
The Holocene is a geological epoch which began at the end of the Pleistocene and continues to the present. The Holocene is part of the Quaternary period. Its name comes from the Greek words and , meaning "entirely recent"...
. Other more recent researchers, including Lesley Head and Judith Field, favor an extinction date of 28 000 - 30 000 years ago, which would mean that humans coexisted with Diprotodon for some 20 000 years. However, opponents of "late extinction" theories have interpreted such late dates based on indirect dating methods as artifact
Artifact (error)
In natural science and signal processing, an artifact is any error in the perception or representation of any visual or aural information introduced by the involved equipment or technique....
s resulting from redeposition
Deposition (geology)
Deposition is the geological process by which material is added to a landform or land mass. Fluids such as wind and water, as well as sediment flowing via gravity, transport previously eroded sediment, which, at the loss of enough kinetic energy in the fluid, is deposited, building up layers of...
of skeletal material into more recent strata
STRATA
Strata Marketing Inc. is a Chicago, Illinois-based software company involved in connecting media buyers and sellers. It is owned by Comcast. As of 2010, it processes about $50 billion worth of media buys annually.-History:...
, and recent direct dating results obtained with new technologies have tended to confirm this interpretation.
Climate change
Ice age
An ice age or, more precisely, glacial age, is a generic geological period of long-term reduction in the temperature of the Earth's surface and atmosphere, resulting in the presence or expansion of continental ice sheets, polar ice sheets and alpine glaciers...
s produced no significant glaciation in mainland Australia but long periods of cold and very dry weather. This dry weather during the last ice age may have killed off all the large diprotodonts.
Critics point out a number of problems with this theory. First, large diprotodonts had already survived a long series of similar ice ages, and there does not seem to be any particular reason why the most recent one should have achieved what all the previous ice ages had failed to do. Also, climate change apparently peaked 25,000 years after the extinctions. Finally, even during climatic extremes, some parts of the continent always remain relatively exempt: for example, the tropical north stays fairly warm and wet in all climatic circumstances; alpine valleys are less affected by drought, and so on.
Human hunting
Megafauna
In terrestrial zoology, megafauna are "giant", "very large" or "large" animals. The most common thresholds used are or...
of New Zealand, Madagascar and many smaller islands around the world (such as New Caledonia, Cyprus, Crete and Wrangel Island), and at least in part, in the Americas
Americas
The Americas, or America , are lands in the Western hemisphere, also known as the New World. In English, the plural form the Americas is often used to refer to the landmasses of North America and South America with their associated islands and regions, while the singular form America is primarily...
—probably within a thousand years or so. Recent finds of Diprotodon bones which appear to display butchering marks lend support to this theory. Critics of this theory regard it as simplistic, arguing that (unlike New Zealand and America) there is little direct evidence of hunting, and that the dates on which the theory rests are too uncertain to be relied on.
Human land management
The third theory says that humans indirectly caused the extinction of diprotodonts, by destroying the ecosystemEcosystem
An ecosystem is a biological environment consisting of all the organisms living in a particular area, as well as all the nonliving , physical components of the environment with which the organisms interact, such as air, soil, water and sunlight....
on which they depended. In particular, early Aborigines are thought to have been fire-stick farmers
Fire-stick farming
Fire-stick farming is a term coined by Australian archaeologist Rhys Jones in 1969 to describe the practice of Indigenous Australians where fire was used regularly to burn vegetation to facilitate hunting and to change the composition of plant and animal species in an area.Fire-stick farming had...
using fire regularly and persistently to drive game, open up dense thickets of vegetation, and create fresh green regrowth for both humans and game animals to eat. Evidence for the fire hypothesis is the sudden increase in widespread ash deposits at the time that people arrived in Australia, as well as land-management and hunting practices of modern Aboriginal people as recorded by the earliest European settlers before Aboriginal society was devastated by European contact and disease
Disease
A disease is an abnormal condition affecting the body of an organism. It is often construed to be a medical condition associated with specific symptoms and signs. It may be caused by external factors, such as infectious disease, or it may be caused by internal dysfunctions, such as autoimmune...
. Evidence against the hypothesis is the fact that humans appear to have eliminated the megafauna of Tasmania
Tasmania
Tasmania is an Australian island and state. It is south of the continent, separated by Bass Strait. The state includes the island of Tasmania—the 26th largest island in the world—and the surrounding islands. The state has a population of 507,626 , of whom almost half reside in the greater Hobart...
without using fire to modify the environment there.
Multiple causes
Eucalypt
Eucalypts are woody plants belonging to three closely related genera:Eucalyptus, Corymbia and Angophora.In 1995 new evidence, largely genetic, indicated that some prominent Eucalyptus species were actually more closely related to Angophora than to the other eucalypts; they were split off into the...
s, some acacia
Acacia
Acacia is a genus of shrubs and trees belonging to the subfamily Mimosoideae of the family Fabaceae, first described in Africa by the Swedish botanist Carl Linnaeus in 1773. Many non-Australian species tend to be thorny, whereas the majority of Australian acacias are not...
s, and most of the native grasses) which are unsuitable habitat for most browsing animals. Either way, the trend is toward the modern Australian environment of highly flammable open sclerophyllous forests, woodlands and grasslands, none of which are suitable for large, slow-moving browsing animals—and either way, the changed microclimate produces substantially less rainfall.
See also
Australian megafaunaAustralian megafauna
Australian megafauna are a number of large animal species in Australia, often defined as species with body mass estimates of greater than 30 kilograms, or equal to or greater than 30% greater body mass than their closest living relatives...