Прочетен: 3694 Коментари: 0 Гласове:
Последна промяна: 05.07.2019 22:00
Procoptodon was a genus of giant short-faced kangaroo living in Australia during the Pleistocene epoch. P. goliah, the largest known kangaroo that ever existed, stood approximately 2 m (6.6 ft). They weighed about 232 kg (511 lb). Other members of the genus are smaller, however, and Procoptodon gilli is the smallest of all of the sthenurine kangaroos, standing ~1m tall. During the Pleistocene Australia had a variety of animals that loosely resembled those still living today but on a much grander scale, from giant three meter long wombats like Diprotodon to four meter plus goannas like Varanus priscus. Procoptodon for its part was essentially a giant kangaroo, although its full size has been the subject of mis-interpretation by some authors. Procoptodon itself stood no more than two metres high, but it could use its long arms to reach up to three meters high, a figure that has in the past been erroneously presented as the full height of the animal.
Procoptodon seems to have been one of the more abundant members of the Australian Pleistocene megafauna and seems to have been active in different habitats wherever there was ample growth of plants to support the population. These areas included the growth of tall plants, shrubs and trees that would have been out of reach for many of the animals of the time, and this is where the large size of Procoptodon comes in. First by being tall, the shoulders are higher up off the ground, which immediately gives Procoptodon a reach advantage over smaller kangaroos. The long arms also had hands that had two enlarged fingers tipped with curved claws which could quite conceivably have been used to wrap around tall branches and pull them down to the mouth, much like how the giant ground sloths of the Americas lived during this time. Procoptodon also had forward facing eyes which would have granted it the all-important depth perception that would have been required so that it knew exactly how far it had to reach in order to pull down the next branch.
How Procoptodon ate can also be revealed in the shape and proportions of the skull. Shorter faced animals usually have the adaptation of a shorter snout so that they can more easily process food with the rear teeth. This is a simple principal where the point of jaw articulation is actually the fulcrum of the mechanism that allows an animal to open and close its mouth and allows the jaw closing muscles to focus more force upon shearing through food. In Procoptodon this food could have been parts of sclerophyll plants that were soft and nutritious within, but had a tough exterior to protect the inner parts from drying in the harsh Australian climate. The dentary (lower jaw) was fused and well developed so that it could easily withstand the stresses of the more powerful jaw action. The teeth were also well adapted for this with low crowns that exhibited extra folds to increase their food processing potential.
Despite its large size, Procoptodon would have been prey to the larger predators of the time such as Thylacoleo, better known as the marsupial lion, that is often envisaged as dropping down from trees to hit is prey from above. Also was the aforementioned Varanus priscus, a huge monitor lizard that could have lain in denser areas of vegetation to surprise any unsuspecting Procoptodon that ventured too close. Procoptodon was not completely defenceless however, although its best defence against predators would have been speed. Most of the metatarsals of the foot were reduced with the exception of the fourth digit that had become so enlarged that in life Procoptodon would have been seen to have but a single toe. This single toe was actually stronger and would have been less susceptible to injury that several toes that would have meant more but smaller and weaker bones. The leg bones were also proportionately more robust than those of smaller kangaroos with the larger surface areas providing enlarged anchor points of tendons that attached to the proportionately more powerful leg muscles that would have been necessary to propel the larger and heavier body. Used correctly these legs would have also been a considerable weapon against predators, as well as rival Procoptodon since kangaroos can be observed today balancing on their tails while kicking out at an opponent or something they perceive as a threat.
The disappearance of Procoptodon from Australia seems to coincide with the arrival of the first humans on the continent, although the precise date remains a matter of debate with some sources claiming that Procoptodon may have survived to as recently as just under twenty thousand years ago, while others remain steadfast to the disappearance occurring forty to fifty thousand years ago. The cause of their extinction is also debated, but the main theory is effects of people that comes in two parts. The first is that Procoptodon may have been hunted by early humans for food, although it seems unlikely that people would or even could have hunted one of the most common large marsupials of the time into extinction. A contributing effect is that of fire stick farming where vast expanses of land are set alight to encourage fresh growth of plants that are more easily consumed than the existing growths already there. This would cause a shift in the availability of plant types that may have suited other herbivorous animals better than Procoptodon, leading to increased strain upon the species.
Some species from the genus Sthenurus were similar in size as well.
Sthenurus ("strong tail") is an extinct genus of kangaroo. With a length of about 3 m (10 ft), some species were twice as large as modern extant species. Sthenurus was related to the better-known Procoptodon.The subfamily Sthenurinae is believed to have separated from its sister taxon, the Macropodinae (kangaroos and wallabies), halfway through the Miocene and then its population grew during the Pliocene.
Research by Darren R. Grцcke from Monash University, analysed the diets of fauna at various fossil site localites in South Australia, using stable carbon isotope analysis 13C/12C of collagen. He found that at older localities like Cooper Creek the species of Sthenurus were adapted to a diet of leaves and twigs (browsing). This was due to the wet climate of the time period between 132,000-108,000 years (TL and uranium dating), which allowed for a more varied vegetation cover.
At the Baldina Creek fossil site 30,000 years (C14 dating), the genus had transitioned to a diet of grass-grazing. During this time, the area was open grasslands with sparse tree cover as the continent was drier than today. But at Dempsey"s Lake (36-25,000 years) and Rockey River (19,000 C14 dating), their diet was of both grazing and browsing. This analysis may be because of a wetter climatic period. The overall anatomy of the genus did not alter in response to the change in diet and dentition did not adapt to the varying toughness of the vegetation between grasses, shrubs and trees.
Other animals found in the Cuddie Springs habitat include the flightless bird Genyornis, the red kangaroo, Diprotodon, humans and many others.
Examination skeletal remains of Sthenurus from Lake Callabonna, northern South Australia revealed that as the animals were trapped as they floundered in the clay mud while attempting to cross the floor of the lake during tow-water or dry times. The data shows that three closely allied sthenurine species coexisted sympatrically at Lake Callabonna: a new giant taxon, S. stirlingi, an intermediate-sized S. tindalei, and the considerably smaller S. andersoni. Comparative osteology of these Sthenurus species with Macropus giganteus emphasizes how different sthenurine kangaroos were from extant kangaroos, especially with the sthenurines" short, deep skulls, long front feet with very reduced lateral digits, and the monodactyl hind feet.
Teapot Creek, a tributary of the MacLaughlin River in the Southern Monaro, southeastern New South Wales contains a sequence of terraces. The highest and oldest of these terraces was reported to contain the remains of fossil mammals found in Plio-Pleistocene fossil deposits elsewhere in Eastern Australia. Sthenurus atlas, S. occidentalis, and S. newtonae are some of the species identified from the fossils found in the terrace.
Examining the structure and lifestyle of this specific species is difficult due to the fact that not much has surfaced in regards to them. However, even within the rarity of discoveries relating to the kangaroo-like species, scientists were able to use their findings in order to learn more about their lifestyles. For example, scientists broke down the few bones that they had discover during the process of isotope analysis (which is the study of the distribution of certain isotopes that ease the process of drawing conclusions when determining food chains) and retrieved material which allowed them to draw the conclusion regarding their paleodiet. These animals were herbivores because the material they retrieved drew back to the plantation that was Australia (where their bones were found) had.
In anatomy they had a tail shorter but stronger than present species of kangaroo, and only one toe instead of three like the red kangaroo. At the end of the foot was a small hoof like nail suited for flat terrain; this toe is considered their fourth toe.
Their skeletal structure was very robust with powerful hind limbs, broad pelvis, longer arms and phalanges than modern species and a short neck. Their phalangel bones that make up their fingers may have been used to hold stems and twigs. These unique adaptations suited their feeding habits of browsing in the case of S. occidentalis, but other species were most likely grazers.
The estimated body mass of the largest species is thought to be two hundred and forty kilograms which is nearly three times the size of extant species. Due to the giant height and heavy weight of the biggest species, it is possible that this species did not hop as a form of locomotion but performed a bipedal for of walking similar to humans. This gait would be done at slow speeds since hopping at slow speeds would be a waste of energy. Pentapedal movement or bipedal hopping no longer seems to be an option for these massive kangaroos.
There was a morphological difference between the scapulae (or shoulder blade) of the Sthenurine and the extant as well as the extinct macropodids.
They possessed a short deep skull which was suited for eyes with stereoscopic vision; this allowed for better vision.
Unlike modern kangaroos, which are plantigrade hoppers, Sthenurus was an unguligrade biped, walking in a similar fashion to hominids.
Paleospecies S. stirlingi had a large, dolichocephalic skull with a more elevated braincase position and an inflamed nasal frontal region in comparison to the contemperaneous skull of the S. tindelai. S. andersoni skull fossils show a dome-like forehead that is unique to S. andersoni among other otherdolichocephalic sthenurines. This is attributed to the continuous high vaulting of the frontals above the orbits and the line of the rostrum.
These structures were tough and strongly enameled, useful for tough vegetation and with a striation pattern.
In paleospecies S. stirlingi fossil evidence shows that tooth row curves medially (anteriorly and posteriorly) from a line tangential to the labial side of the molars at the anterior ridge of the masseteric processes.
The fossils of teeth may also suggest that the sthenurines and macropodines shared a common ancestor. They share many synapomorphic character states. They each have well developed lophs on molars and both lack a posthypocristid.
From evidence gathered at Cuddie Springs according to Judith Field and Richard Fullagerit (as cited in Macey 2003) it is known that Native Australians inhabited the same habitat as that of Sthenurus and various other extant and extinct species of animal. At this locality there seems to be a lack of any specific tools suitable for hunting. Instead there are tools used to cut meat off the bone, as there is blood residue left on the stone tools. Any material made of wood for hunting like the boomerang and spear has either not survived intact or was not used by the people of the time in this locality. While this evidence may suggest that human contact with the Sthenurus and all Australian megafauna could have caused the extinction of these mammals, some studies show the extinction was probably under way before human contact. The Sthenurus were herbivores and when a great climate change began to occur they did not change their eating habits. This probably had a much larger impact on the extinction of this particular genus.
Palorchestes
1. Palorchestes azael 2. Nimiokoala greystanesi 3. Diprotodon optatum 4. Wakaleo alcootaensis
Palorchestes ("ancient leaper or dancer") is an extinct genus of terrestrialherbivorousmarsupial of the familyPalorchestidae. The genus was endemic to Australia, living from the Late Miocene subepoch through the Pleistocene epoch (around 11.6 mya – 11,000 years ago), and thought to be in existence for approximately 11.59 million years.
One species, Palorchestes azael, was almost as large as a horse, being around 2.5 metres (8.2 ft) in length with a weight of about 200 kilograms (440 lb), and had four powerful legs.The appearance of the animal"s nasal bones suggests that it possessed a short proboscis, leading to the nickname of the "marsupial tapir". Since it is unrelated to tapirs, this similarity in nose shape is an example of convergent evolution. Palorchestes front legs bore large claws, similar to those of a koala, which it probably used to pull down leaves and strip the bark from trees.
The long symphysis at the lower jaw of all Palorchestes species indicates that the tongue was long and protrudible, like that of a giraffe.
Fossilized remains of Palorchestes azael have been found at the Naracoorte Caves fossil site in Australia.
The generic name was coined by Sir Richard Owen, who first found what he thought was the fragmentary jaw of a prehistoric kangaroo. It was not until more postcranial elements were found did anyone realize that Palorchestes was actually a diprotodontid, and not a kangaroo.
Zygomaturus
Zygomaturus is an extinct giant marsupial from Australia during the Pleistocene. It had a heavy body and thick legs and is believed to be similar to the modern pygmy hippopotamus in both size and build. The genus moved on all fours. It lived in the wet coastal margins of Australia and became extinct about 45,000 years ago. Zygomaturus also is believed to have expanded its range toward the interior of the continent along the waterways. It is believed to have lived solitarily or possibly in small herds. Zygomaturus probably ate reeds and sedges by shoveling them up in clumps with its lower incisor teeth.
It was a large animal, weighing 500 kg (1100 lbs) or more and standing about 1.5 m (4.9 ft) tall and 2.5 m (8.2 ft) long.
Тагове:
Encyclopedia Largest Prehistoric Animals...
Encyclopedia Largest Prehistoric Animals...
