''Procoptodon''
is an extinct
genus
Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...
of giant short-faced (
sthenurine
Sthenurinae (from ''Sthenurus'', Greek for 'strong-tailed') is a subfamily within the marsupial family Macropodidae, known as 'short faced kangaroos'. No members of this subfamily are extant today, with all becoming extinct by the late Pleistocen ...
)
kangaroo
Kangaroos are four marsupials from the family Macropodidae (macropods, meaning "large foot"). In common use the term is used to describe the largest species from this family, the red kangaroo, as well as the antilopine kangaroo, eastern gre ...
s that lived in
Australia
Australia, officially the Commonwealth of Australia, is a Sovereign state, sovereign country comprising the mainland of the Australia (continent), Australian continent, the island of Tasmania, and numerous List of islands of Australia, sma ...
during the
Pleistocene
The Pleistocene ( , often referred to as the ''Ice age'') is the geological Epoch (geology), epoch that lasted from about 2,580,000 to 11,700 years ago, spanning the Earth's most recent period of repeated glaciations. Before a change was fina ...
Epoch. ''P. goliah'', the largest known kangaroo species that ever existed, stood at about .
They weighed about .
Other members of the genus were smaller, however; ''Procoptodon gilli'' was the smallest of all of the sthenurine kangaroos, standing approximately tall.
The genus is derived from ''
Simosthenurus
''Simosthenurus,'' also referred to as the short-faced kangaroo, is an extinct genus of megafaunal macropods that existed in Australia, specifically Tasmania, during the Pleistocene. Analysis of ''Simosthenurus'' fossils has contributed to the fi ...
'', making the latter genus
paraphyletic
In taxonomy (general), taxonomy, a group is paraphyletic if it consists of the group's most recent common ancestor, last common ancestor and most of its descendants, excluding a few Monophyly, monophyletic subgroups. The group is said to be pa ...
.
Description
![Procoptodon goliah](https://upload.wikimedia.org/wikipedia/commons/2/2a/Procoptodon_goliah.jpg)
''Procoptodon'' physiology was likely similar to that of the contemporary kangaroos; however, ''Procoptodon goliah'' was characterised by its large size. These sthenurines, or short-faced kangaroos, included species that were more than three times the size of the largest kangaroos living today. The largest, ''P. goliah'', was tall and weighed up to .
These animals lived alongside modern species of kangaroos, but specialised on a diet of leaves from trees and shrubs. ''Procoptodon were'' large and short-faced, distinguishable by their flat faces and forward-pointing eyes. On each foot, they had a single large toe or claw somewhat similar in appearance to a horse's hoof. On these unusual feet, they moved quickly through the open forests and plains, where they sought grass and leaves to eat. Their front
paws were equally strange; each front paw had two extra-long fingers with large claws. They may have been used to grab branches, bringing leaves within eating distance.
[Field, Judith and Wroe, Stephen]
Aridity, faunal adaptations and Australian Late Pleistocene extinctions
''World Archaeology''. Mar 2012, Vol. 44 Issue 1, p 56–74. 19p.
Distribution and habitat
''Procoptodon'' is mainly known for living in semiarid areas of
South Australia
South Australia (commonly abbreviated as SA) is a state in the southern central part of Australia. It covers some of the most arid parts of the country. With a total land area of , it is the fourth-largest of Australia's states and territories ...
and
New South Wales
)
, nickname =
, image_map = New South Wales in Australia.svg
, map_caption = Location of New South Wales in AustraliaCoordinates:
, subdivision_type = Country
, subdivision_name = Australia
, established_title = Before federation
, es ...
. These environments were harsh, characterised by vast areas of treeless, wind-blown sand dunes. However, the area around
Lake Menindee
The Menindee Lakes is a system of 9 large, but relatively shallow lakes, located in south-west New South Wales on the Darling (Barka) River, about 200 km upstream of the Darling River's junction with the River Murray. The Darling River is ...
, in western New South Wales, had a cooler, wetter climate at the time ''Procoptodon'' existed. The surrounding area was a mosaic of sclerophyll forest, woodland, savannah, and plains, but sand dunes would have also formed along the edges of the Menindee.
[ Fossilized footprints have also been found on Kangaroo Island.
]
Palaeobiology
Mobility
''Procoptodon'' was not able to hop as a mode of transportation, and would have been unable to accelerate sufficiently due to its weight.[ Broad hips and ankle joints, adapted to resist torsion or twisting, point to an upright posture where weight is supported by one leg at a time. Its broad hips also allowed for another important modification – large buttocks – a feature shared with other walking species.]
However, some ambiguity surrounds the possible locomotion of ''P. goliah''. Some research suggests that this species was perhaps the largest hopping mammal to have ever existed.[ Research suggests that the most optimal weight for a large hopping marsupial is roughly 50–60 kg. Larger animals, especially the massive ''P. goliah'', would be substantially more at risk of tendon breakage while hopping.][ If ''P. goliah'' were to have travelled by hopping, the highest possible balance between size and speed would have been peaked, because its body would have been the largest possible to be carried by this method of locomotion.][Webb, Steve. Corridors to Extinction and the Australian Megafauna. Burlington: Elsevier Science, 2013. Print.]
A more likely suggestion, based on the apparent anatomy allowed by the bone structure of ''P. goliah'', is that unlike modern kangaroos, which are plantigrade hoppers at high speeds and use their tails in pentapedal locomotion at slower speeds, ''Procoptodon'' was an unguligrade biped, walking in a fashion similar to hominid
The Hominidae (), whose members are known as the great apes or hominids (), are a taxonomic family of primates that includes eight extant species in four genera: '' Pongo'' (the Bornean, Sumatran and Tapanuli orangutan); ''Gorilla'' (the east ...
s. Locomotion mechanics and physiology have been investigated through the examination of musculoskeletal scaling patterns. The largest, ''P. goliah'', was tall and weighed up to . For ''P. goliah'', tendon stress was identified, which indicates limited locomotor capabilities, exposing a correlation between body mass and locomotion abilities. Ruptures in tendons demonstrate strain in elasticity of muscles in the limbs, which provides evidence that perhaps the hypothesised ability for ''P. goliah'' to hop may have been unlikely.[ Due to its locomotive performance, the species may have been vulnerable to human predation.][
Fossils of giant short-faced kangaroos have been found at the Naracoorte World Heritage fossil deposits in South Australia, ]Lake Menindee
The Menindee Lakes is a system of 9 large, but relatively shallow lakes, located in south-west New South Wales on the Darling (Barka) River, about 200 km upstream of the Darling River's junction with the River Murray. The Darling River is ...
in New South Wales, the Darling Downs in Queensland, and at many other sites. A full-sized, lifelike replica is on permanent display with other ancient native Australian animals at the Australian Museum.[
]
Diet and molar patterns
These animals lived alongside modern species of kangaroos, but specialised on a diet of leaves from trees and shrubs. Their robust skull architecture and shortened faces have been thought to be related to increased masseter muscles used to chew foods. Dental microwear Dental microwear analysis is a method to infer diet and behavior in extinct animals, especially in fossil specimens. Typically, the patterns of pits and scratches on the occlusal or buccal surface of the enamel are compared with patterns observed ...
of ''P. goliah'' supports a browsing diet. Large bicuspids
The premolars, also called premolar teeth, or bicuspids, are transitional teeth located between the canine and molar teeth. In humans, there are two premolars per quadrant in the permanent set of teeth, making eight premolars total in the mouth ...
, crenulated dental crown
In dentistry, a crown most commonly refers to a dental cap, a type of dental restoration that completely caps or encircles a tooth or dental implant. A crown may be needed when a large cavity threatens the health of a tooth. A crown is typically ...
s, and a massive bony jaw present in the fossil evidence of ''P. goliah'' would have been required to process and digest a substantial amount of leafy fodder. Stable isotopic data suggest its diet consisted of plants using a C4 photosynthetic
carbon fixation or the Hatch–Slack pathway is one of three known photosynthetic processes of carbon fixation in plants. It owes the names to the 1960's discovery by Marshall Davidson Hatch and Charles Roger Slack that some plants, when supp ...
pathway, typically associated with grasses. In this case, however, chenopod
Amaranthaceae is a family of flowering plants commonly known as the amaranth family, in reference to its type genus ''Amaranthus''. It includes the former goosefoot family Chenopodiaceae and contains about 165 genera and 2,040 species, making it ...
saltbushes found throughout semiarid Australia were considered a more likely source of the C4 signature. [An intensification in aridity during the second half of the Pleistocene propagated the evolutionary progression of ''P. goliah'' to adapt to an abundance of dry vegetation. Evidence that ''P. goliah'' was the most widely distributed species among the Pleistocene macropodids throughout the continent shows that this species was adapted to a tougher diet than any other extinct Pleistocene sthenurine. Similar to ''Macropus giganteus'', ''Procoptodon'' has Molar (tooth), molar patterns that indicate they had a similar, grassy, herbivorous diet (as opposed to leaves) and were grazers, but determining specific diets and preference of extinct herbivores is admittedly difficult. Through the study of isotopic composition of ''P. goliah'' tooth enamel, in addition to biomechanical bone features, dietary clues and feeding behavior have been deduced. The osteological characters furnish evidence of ''P. goliah''s ability to handle fibrous vegetables and salt consumption. This, in turn, leads to the belief that the species needed to be close to a water source to deal with salt intake; at the same time, though, some theories are beginning to arise that limb remains indicate the ability to travel distances both to and from water sources.[
]
Extinction
The genus was present until at least about 45,000 years ago before going extinct, although some evidence indicates it may have survived to as recently as 18,000 years ago. Its extinction may have been due to climate shifts during the Pleistocene,[ or to human hunting.] Those who support the hypothesis of a human-mediated extinction process cite that the arrival of humans to continental Australia occurred around the same time as the disappearance of this species. More evidence that this extinction was facilitated by human interaction is that the time period in which the extinction occurred was characterised by a relatively stable climate.[ However, no evidence of predation on or consumption of ''P. goliah'' by humans has been found in the fossil record.][
New evidence has been found, however, which shows humans arrived 10,000–15,000 years prior to extinction.]
Some researchers have speculated that the replacement of nutritious, fire-sensitive plants with less flammable, less nutritious flora brought about by human, fire-based deforestation in Australia played a large role in ''P. goliah'' and other Australian megafaunal extinctions about 50 thousand years ago ( kya). However, the diet of ''P. goliah'', primarily chenopods and ''Atriplex
''Atriplex'' () is a plant genus of about 250 species, known by the common names of saltbush and orache (; also spelled orach). It belongs to the subfamily Chenopodioideae of the family Amaranthaceae ''s.l.''.
The genus is quite variable and w ...
'' in particular, were less flammable and remained largely unaffected by fire. These diet patterns disprove theories that ''P. goliah'''s extinction was due in large part to a reduction in food supply from fire. At the same time, because of the kangaroos' elongated breeding cycles, their ability to increase population numbers after human predation was highly limited.[
]
Environmental factors
Kangaroos living in dry, arid environments have been shown to exhibit higher densities of tooth enamel
Tooth enamel is one of the four major Tissue (biology), tissues that make up the tooth in humans and many other animals, including some species of fish. It makes up the normally visible part of the tooth, covering the Crown (tooth), crown. The ...
, caused by indirect hydration through consuming herbaceous plants. Lower levels of this enamel in ''P. goliah'' teeth found in areas with similar environmental parameters compared to the modern grazing kangaroos suggests that it relied far more heavily on free-standing water sources such as lakes and streams.
Given the larger size of ''P. goliah'' and its tendency to favor larger, free-standing water sources, episodic droughts accumulating 55 kya in the southern interior region of Australia would have certainly affected its populations. Yet, records show that such droughts had characterised this region for the previous 7 million years, with ''P. goliah'' surviving multiple intensely dry episodes during this period. Any period of significant decreases in rainfall did not occur until 5,000–10,000 years after the approximate extinction of ''P. goliah'' 45–50 kya, 20 ky before the last glacial maximum of high aridity. These factors disprove speculations that such droughts could have played a significant role in the extinction of ''P. goliah''.
Some evidence supports both of the claims that the extinction of ''P. goliah'' may have been due to climate shift
In common usage, climate change describes global warming—the ongoing increase in global average temperature—and its effects on Earth's climate system. Climate change in a broader sense also includes previous long-term changes to E ...
s during the Pleistocene[ or to human hunting.] ''P. goliah'', depending heavily on free-standing water, was more vulnerable to drought. This can explain why the red kangaroo survived the increasing aridity and ''P. goliah'' did not. However, there is also evidence that suggests that humans could have a significant influence in the extinction of ''P. goliah''. ''P. goliah''s need for a constant free-standing source of water, plus its height and common habitat in open shrublands, made it more noticeable to human hunters, thus making it vulnerable to humans, who were also water-bound like it was.
References
{{Taxonbar, from=Q131971
Prehistoric macropods
Pleistocene mammals of Australia
Pleistocene marsupials
Prehistoric marsupial genera
Clawed herbivores
Fossil taxa described in 1873
Taxa named by Richard Owen