| Thylacoleo Temporal range: latePliocene—latePleistocene | |
|---|---|
 | |
| Skeletal diagram ofT. carnifex (top) and restored musculature based on living marsupials (bottom) | |
Scientific classification | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Mammalia |
| Infraclass: | Marsupialia |
| Order: | Diprotodontia |
| Family: | †Thylacoleonidae |
| Genus: | †Thylacoleo Owen, 1859 |
| Type species | |
| †Thylacoleo carnifex | |
| Species | |
| |
Thylacoleo ("pouch lion") is anextinctgenus of carnivorousmarsupials that lived inAustralia from the latePliocene to theLate Pleistocene (until around 40,000 years ago), often known asmarsupial lions. They were the largest and last members of the familyThylacoleonidae, occupying the position ofapex predator within Australian ecosystems. The largest and last species,Thylacoleo carnifex, approached the weight of alioness. The estimated average weight for the species ranges from 101 to 130 kg (223 to 287 lb).[1]
The firstThylacoleo fossil findings, discovered byThomas Mitchell were found in the 1830s in the Wellington Valley of New South Wales, though not recognised as such at the time. The generic holotype, consisting of broken teeth, jaws, and a skull was discovered by a pastoralist, William Avery, near Lake Colungolac from which the speciesThylacoleo carnifex was described byRichard Owen.[2] It was not until 1966 that the first nearly-complete skeleton was found. The only pieces missing were a foot and the tail. Currently, theNullarbor Plain of West Australia remains to be the greatest finding site. These fossils now reside at the Australian Museum.[3][4]
The genus was first published in 1859, erected to describe the type speciesThylacoleo carnifex. The new taxon was established in examination of fossil specimens provided toRichard Owen. The familial alliance takes its name from this description, the so-called marsupial lions ofThylacoleonidae.
The colloquial name "marsupial lion" alludes to the genus name, which was named after its superficial resemblance to the placental lion and its ecological niche as a large predator.
Genus:Thylacoleo (Thylacopardus) – Australia's marsupial lions, that lived from about 2 million years ago, during the Late Pliocene Epoch and became extinct about 40,000 years ago, during theLate Pleistocene Epoch. Three species are known:
Fossils of other representatives of Thylacoleonidae, such asMicroleo andWakaleo, date back to the Late Oligocene Epoch, some 24 million years ago.[9]
T. hilli was described byNeville Pledge in a study published in the records of the South Australia Museum in 1977. The holotype is a third premolar, discovered at a cave inCurramulka in South Australia, exhibiting the carnivorous characteristics of the genus and around half the size ofT. carnifex. This tooth was collected by Alan Hill, a speleologist and founding member of the Cave Exploration Group of South Australia, while examining a site known as the "Town Cave" in 1956; the specific epithethilli honours the collector of the first specimen.[8] Material found amidst the fauna atBow River in New South Wales, dated to the earlyPliocene, was also referred to the species in 1982.[10]A fragment of an incisor, unworn and only diagnosable to the genus, was located at a site in Curramulka, close to the Town Cave site, and referred to the species for the apparent correlation in size when compared to the better knownT. carnifex.[11]
The marsupial lion is classified in the order Diprotodontia along with many other well-known marsupials such as kangaroos,possums, and thekoala. It is further classified in its ownfamily, theThylacoleonidae, of which threegenera and 11species are recognised, all extinct. The term marsupial lion (lower case) is often applied to other members of this family. Distinct possum-like characteristics ledThylacoleo to be regarded as members ofPhalangeroidea for a few decades. Though a few authors continued to hint at phalangeroid affinities for thylacoleonids as recently as the 1990s, cranial and other characters have generally led to their inclusion withinvombatiformes, and as stem-members of the wombat lineage.[12] Marsupial lions and other ecologically and morphologically diverse vombatiforms were once represented by over 60 species ofcarnivorous,herbivorous,terrestrial andarboreal forms ranging in size from 3 kg to 2.5 tonnes. Only two families represented by fourherbivorous species (koalas and three species of wombat) have survived into modern times and are considered the marsupial lion's closest living relatives.[13]
The ancestors ofthylacoleonids are believed to have beenherbivores, something unusual for carnivores. They are members of theVombatiformes, an almost entirely herbivorous order of marsupials, the only extant representatives of which arekoalas andwombats, as well as extinct members such as thediprotodontids andpalorchestids.[14] The group first appeared in the LateOligocene. The earliest thylacoleonids likeMicroleo were small possum-like animals,[15] with the group increasing in size during theMiocene, with representatives like the leopard-sizedWakaleo. The genusThylacoleo first appeared during thePliocene, and represented the only extant genus of the family from that time until the end of thePleistocene. The youngest representative ofThylacoleo and the thylacoleonids,T. carnifex, is the largest known member of the family.[14] The earliest thylacoleonids are thought to have been arboreal (tree dwelling) animals,[16] whileThylacoleo is thought to be terrestrial with some climbing capabilities.[17]
T. carnifex is thelargest carnivorousmammal known to have ever existed in Australia, and one of the largestmetatherian carnivores known (comparable toThylacosmilus andBorhyaena species, but smaller thanProborhyaena gigantea). Individuals ranged up to around 75 cm (30 in) high at the shoulder and about 150 cm (59 in) from head to tail. Measurements taken from a number of specimens show they averaged 101 to 130 kg (223 to 287 lb) in weight, although individuals as large as 124–160 kg (273–353 lb) might not have been uncommon, and the largest weight was of 128–164 kg (282–362 lb). This would make it comparable to female lions and femaletigers in general size.[17] Estimates of the size ofT. carnifex based on dental remains are typically dubious, in contrast to estimates based on proximal limb bone circumference.[18]
Like other thylacoleonids,Thylacoleo had blade-like thirdpremolar teeth in the upper and lower jaws, that functioned as thecarnassial teeth, with these teeth being present much further forwards in the jaw than in other mammals.[19][20] Compared to earlier thyacoleonids, the third premolars were considerably enlarged.[21]Thylacoleo also had a proportionally large pair of firstincisors in the upper and lower jaws, which functioned analogously to other carnivorescanine teeth.[19][22] They also had true canines but they served little purpose as they were stubby and not very sharp.[23] Compared to earlier thylacoleonids, the number ofmolar teeth was reduced.[21]
Pound for pound,T. carnifex had the strongest bite of anymammal species, living or extinct; aT. carnifex weighing 101 kg (223 lb) had a bite comparable to that of a 250 kg Africanlion, and research suggests thatThylacoleo could hunt and take prey much larger than itself.[20] Larger animals that were likely prey includeDiprotodon spp. andgiant kangaroos. It seems improbable thatThylacoleo could achieve as high a bite force as a modern-day lion; however, this might have been possible when taking into consideration the size of its brain and skull. Carnivores usually have rather large brains when compared toherbivorous marsupials, which lessens the amount of bone that can be devoted to enhancing bite force.Thylacoleo however, is thought to have had substantially stronger muscle attachments and therefore a smaller brain.[24] Some later studies questioned the ability of the canine teeth to deliver a killing bite.[25]
Using3D modeling based onX-ray computed tomography scans, marsupial lions were found to be unable to use the prolonged, suffocating bite typical of living big cats. They instead had an extremely efficient and unique bite; the incisors would have been used to stab at and pierce the flesh of their prey while the more specialised carnassials crushed thewindpipe, severed thespinal cord, and lacerated the majorblood vessels such as thecarotid artery andjugular vein. Compared to an African lion which may take 15 minutes to kill a large catch, the marsupial lion could kill a large animal in less than a minute.[dubious –discuss] The skull was so specialized for big game that it was very inefficient at catching smaller animals, which possibly contributed to its extinction.[26][27]
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Thylacoleo had highly mobile and powerful forelimbs used to grapple prey, with eachmanus having a single very large retractable hooked claw set on large semi-opposable thumbs, which are suggested to have been used deal a killing blow.[25]
The hind feet had four functional toes, the first digit being much reduced in size, but possessing a roughened pad similar to that ofpossums, which may have assisted with climbing. The discovery in 2005 of a specimen which included complete hind feet provided evidence that the marsupial lion exhibitedsyndactyly (fused second and third toes) like other diprotodonts.[28]
Its strong forelimbs and retracting claws mean thatThylacoleo possibly climbed trees and perhaps carried carcasses to keep the kill for itself (similar to theleopard today).[29] The climbing ability would have also helped them climb out of caves, which could therefore have been used as dens to rear their young.[30] Specialised tail bones calledchevrons strengthened the tail, likely allowing the animal to use it to prop itself up while rearing on its hind legs, which may have been done when climbing or attacking prey.[30]
Thelumbar region is relatively rigid and straight, and suggests that the lower back was relatively inflexible.[30]
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WhenThylacoleo was first described by Richard Owen, he considered it to be a carnivore, based on the morphology of its skull and teeth.[2] However other anatomists, such asWilliam Henry Flower disagreed. Flower was the first to placeThylacoleo with the Diprotodonts, noting its skull and teeth to be laid out more like those of thekoala and thewombat, and suggested that it was more likely a herbivore. Owen did not disagree with Flower's placement ofThylacoleo with the Diprotodonts, but still maintained that it was a carnivore, despite its herbivorous ancestry.[31] Owen found little support in his lifetime, despite the pointing out ofThylacoleo's retractable claws, something only found in mammalian carnivores,[4] and its lack of any ability to chew plant material.[31] In 1911, a study by Spencer and Walcott claimed that certain marks on the bones of megafauna had been made byThylacoleo, but according to Horton (1979) they were not sufficiently rigorous, resulting in their arguments being strongly challenged by later scholars, such as Anderson (1929), and later Gill (1951, 1952, 1954), thereby leaving the issue unresolved.[32]
Besides the most common hypothesis that it was an active predator, a variety of other theories existed in the late 19th to early 20th centuries as to the diet and feeding ofThylacoleo, with hypotheses of it being a scavenger filling the ecological niche ofhyenas,[33] being a specialist of crocodile eggs,[29] or even a melon-eater.[34] As late as 1954, doubts were still being raised as to whether it was actually a hypercarnivore.[25]
In 1981, another paper was published arguing that certain cuts to bones of large marsupials had been caused byThylacoleo. This paper by Horton and Wright was able to counter earlier arguments that such marks were the result of humans, largely by pointing out the presence of similar marks on the opposite side of many bones. They concluded that humans were extremely unlikely to have made the marks in question, but that if so "they had set out to produce only marks consistent with whatThylacoleo would produce".[32] Since then, the academic consensus has emerged thatThylacoleo was a predator and a hypercarnivore.[25]
The marsupial lion's limb proportions and muscle mass distribution indicate that, although it was a powerful animal, it was not a particularly fast runner. Paleontologists conjecture that it was anambush predator, possibly using leaping.[30] Incisions on bones of the extinct large kangarooMacropus titan, and the general morphology ofThylacoleo suggests that it fed in a similar manner to modern cheetahs, by using their sharp teeth to slice open the ribcage of their prey, thereby accessing the internal organs. They may have killed by using their front claws as either stabbing weapons or as a way to grab their prey with strangulation or suffocation.[32]
Like many predators, it was probably also an opportunisticscavenger, feeding oncarrion and driving off less powerful predators from their kills. It also may have shared behaviours exhibited by recentdiprotodont marsupials such as kangaroos, like digging shallow holes under trees to reduce body temperature during the day.[35]
Trace fossils in the form of claw marks and bones from caves inWestern Australia analyzed by Gavin Prideaux et al. indicate marsupial lions could also climb rock faces, and likely reared their young in such caves as a way of protecting them from potential predators.[36]
Analysis of finds on the Nullabor Plain suggests thatThylacoleo carnifex inhabited open, arid environments similar to those found across much of Australia today.[37]
A 1985 study suggested thatThylacoleo carnifex was an apex predator that primarily fed on large bodied prey, which may have included the large kangaroosSthenurus,Procoptodon,Protemnodon,Macropus andOstphranter as well as possibly the largest Australian marsupial, the rhinoceros-sized vombatoidDiprotodon.[38]
Thylacoleo is thought to have become extinct around 40,000 years ago as part of theLate Pleistocene megafauna extinctions, essentially simultanteously with the vast majority ofAustralian megafauna. It has been contested as to the relative importance of climatic change vs the impact of recently arrivedIndigenous Australians (who arrived in Australia around 50-60,000 years ago) in the extinctions. There is limited evidence of human interaction with extinct megafauna in Australia.[39]
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