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16.12.2015 15:43 - Encyclopedia Largest prehistoric animals Vol.1 Vertebrates part1 Mammals ch.1 Carnivores - Saber-toothed cats,sequel
Автор: valentint Категория: Забавление   
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Homotherini
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Homotherini is an
extinct tribe of carnivoran mammals of the family Felidae.The tribe is commonly known ascimitar-toothed cats.These saber-toothed cats were endemic to North America, Europe, Asia, Africa, and South America from the Miocene to Pleistocene living from c. 23 Ma until c. 12,000 years ago.
Compared to the usually massively built dirk-toothed phenotype, apparent in Smilodon, Megantereon and the feliform Barbourofelis (just to list a few), their upper canines were smaller than those of equally sized cats of that phenotype, but they had serrated edges. The scimitar-toothed phenotype has also evolved independently in other mammal families.
Based on mitochondrial DNA sequences extracted from fossils, the lineage of Homotherium is estimated to have diverged from that of Smilodon about 18 Ma ago.
The scimitar tooth form was used to assist in the hunting of herbivorous megafauna. With its hyper sharp and serrated form it was perfect for ripping flesh off of downed prey. However, if this tooth would come into contact with bone it could get caught, serrations worn off, or even completely broken thus leaving the organism without a food source, leading to starvation and death.
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There is a debate about how both the scimitar-tooth and the dirk-tooth evolved in felines and other mammals. the two sides of the debate revolve around whether it was derived from a sexual dimorphic trait or if it was completely natural selection that drove the creation of these phenotypes. The argument for sexual dimorphic origins stems from the fact that in mammals sexual dimorphic traits manifest as tools for males to compete for females. It is believed that the scimitar-tooth and the dirk-tooth were originally only in males for use in competition but then with the rise of mega-herbivores it became favorable for females to take up the trait as well. The natural selection side of the debate argues that the scimitar and dirk-tooth both evolved because of the unfilled niche of predation of megaherbivores so the trait evolved to take advantage of said niche.



Giant European Homotherium - Homotherium crenatidens
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Also known as the “Scimitar cat”, Homotherium was one of the most successful felines in prehistoric times, being found in North and South America, Europe, Asia and Africa. It adapted well to a variety of habitats, including the sub-arctic tundra and survived for five million years until its extinction 10,000 years ago.

Homotherium was seemingly a pack hunter, adapted to fast running and active mostly during day (thus avoiding competition with other, nocturnal predators). It had very long forelegs and shorter hind legs, which gave it a slightly hyena-like appearance. Although Homotherium is not very famous for its size, some fossil remains of a Scimitar cat unearthed recently in the North Sea suggest that they could reach 400 kgs (882lbs) in weight, being larger than modern day Siberian tigers.

If you are wondering what these enormous, pack-hunting cats ate, some paleontologists believe that they were quite skilled mammoth hunters, although their ability to run at high speed would allow them to chase after fleet-footed animals as well.



Nimravidae
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1. Hoplophoneus 2. Barbourofelis 3. Eusmilus 4. Nimravus 5. Dinictis
Nimravids look like cats, and in all likelihood they probably hunted like cats too, but there are a number of differences. The most clearly definable trait that identifies nimravids requires the preservation of the skull. The precise part of the skull that you need to look at is the auditory bulla, a rounded growth towards the rear and on the underside of the skull that forms part of the ear structure. In true cats the auditory bulla is chambered, split into more than one segment. In nimravids however the auditory bulla is a single chamber with no bony division.
Other nimravid characteristics are harder to spot and usually require an expert eye trained in the differences to identify. In more laymen’s terms, the skulls of nimravids are generally more primitive than true cats, although this should come as no surprise since nimravids appear tens of millions of years before the cats. Nimravid paws are also more like those of canids and adapted more for life on the ground rather than climbing up and through trees. Another additional difference is the proportionately shorter legs of nimravids as well as their more plantigrade postures (walking with the foot bones in contact with the ground) whereas true cats are digitigrade (walking on just their toes).
Nimravids tend to possess enlarged canine teeth, although the extent to which they are enlarged can vary considerably between genera. Some like
Hoplophoneus had teeth so large that they were in proportion to later machairodonts like Smilodon. However the canine teeth of nimravids were not as refined as the later machairodonts, with the teeth often slightly thicker. Also while the lower jaws of machairodonts are adapted to accommodate the upper canines, nimravids typically have enlarged flanges of bone that extended down from the lower jaw to help protect the upper canines when the jaws were closed.
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Briefly returning to the teeth, the differences in canine size and form between nimravid genera is probably down to different kinds of prey specialisation. The large curved sabre-like teeth of some genera were better suited for work on larger prey where the large teeth could easily sink into a soft spot like the throat where there was less chance for the relatively weak teeth to break against the preys bones. The genera with shorter, rounder canines however probably specialised in hunting smaller prey where tooth contact with bones was more likely to happen. Here the smaller size would reduce the chance of contact with bone while the more conical form reinforced the teeth against breakage on occasions when the teeth did strike bone. In addition the genera that had more heavily serrated teeth may have hunted animals with thicker and/or tougher skin that was more easily sliced thanks to the serration.
Nimravid fossils first appear in the later stages of the Eocene with most known from North America, though Asian fossils are also known from approximately this time. During this period the planet had entered a cooling phase which saw the beginning of a gradual reduction in tropical forests to more open scrub. In these ecosystems nimravids were likely ambush hunters of mammals such as primitive horses like
Hyracotherium and oreodonts. As the Oligocene progressed the global cooling and the climate change continued, but the nimravids seem to have thrived during this era and remained one of the main types of predatory mammals across Eurasia and North America.
By the Miocene however the Nimravids seem to have been on the decline. Out of nine established nimravid genera known in 2012, only three of these were known to have Miocene aged fossils. Two of these,
Dinictis and Nimravus only seem to have made it as far the Aquitanian, the first stage of the Miocene. The only genus at this time known to have made it as far as the late Miocene (specifically the Tortonian period) is Pogonodon. This decline coincides with the on-going climate change towards grassy plains, something that saw the types of available prey changing, possibly to the point where nimravids could only continue to survive by specialising in their hunting behaviour. Nimravids do not seem to have been the only predator group affected though, with others dominant groups such as the creodonts, mesonychids and entelodonts reducing in the number of genera before disappearing completely in the Miocene.
The one main group of predators that bucked this trend and thrived in the Miocene where the amphicyonids, better known as the ‘bear dogs’. It was probably competition from these and other more advanced predators that forced the remaining nimravids into the side-lines where they had to eek a living in the few locations that could support their method of hunting, until these areas also disappeared and the nimravids with them. So far no nimravid remains are known from any later than the Tortonian period around nine million years ago.


The largest
nimravid was Quercylurus
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Most nimravids were relatively small cat-like mammals that ranged between one and two metres in length, but Quercylurus was a giant when compared to these, something which leads to the popular comparison of Quercylurus being the size of a brown bear. This size would make Quercylurus comparable to some of the larger creodont predators such as Sarkastodon from Asia and denotes a specialisation towards hunting powerful prey animals. Scavenging may have also been an option where Quercylurus could have used its larger size to drive away smaller predators from their kills.
There is some uncertainty about the future validity of Quercylurus, particularly with regards to another nimravid called Dinailurictis. There has been some suggestion that Dinailurictis should actually be treated as a synonym to Quercylurus, as well as other suggestions that both are actually species to the Nimravidae type genus Nimravus. However the largest confirmed specimens of Nimravus are only around one hundred and twenty centimetres long, less than half the length of Quercylurus. For this reason most researchers continue to treat Quercylurus as a distinct genus from Nimravus, though the line between it and Dinailurictis is a little more blurry. Dinailurictis lived at a later time than Quercylurus and while this could indicate a longer temporal span for Quercylurus, an alternative interpretation would be Quercylurus being the ancestor to Dinailurictis.
Quercylurus acquired its name from the Quercy phosphorites of France, deposits that contain many mammals including another nimravid called Eofelis.


Barbourofelidae
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The Barbourofelidae is an extinct family of the mammalian order Carnivora of the suborder Feliformia that lived in North America, Eurasia and Africa during the Miocene epoch (16.9—9.0 Ma) and existed for about 7.9 million years.
Barbourofelidae were previously classified as a subfamily of the extinct Nimravidae, but are now thought to be taxonomically closer to the Felidae than to the Nimravidae. Barbourofelids first appear in the fossil record in the Early Miocene of Africa. By the end of the Early Miocene, a land bridge had opened between Africa and Eurasia, allowing for a faunal exchange between the two continents. Barbourofelids migrated at least three times from Africa to Europe.
Genus Ginsburgsmilus, Prosansanosmilus, Sansanosmilus and Barbourofelis
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Ginsburgsmilus is an extinct genus of carnivorous mammal of the family Barbourofelidae that was endemic to Africa during the early Miocene. There is only one known specimen of Ginsburgsmilus napakensis, dated to 20-19 mya.
Prosansanosmilus is an extinct genus of mammalian carnivores of the suborder Feliformia, family Barbourofelidae, which lived in Europe during the Miocene epoch (16.9—16.0 mya), existing for approximately 0.9 million years.
Sansanosmilus is an extinct genus of carnivorous mammal of the family Barbourofelidae endemic to Europe and Asia, which lived during the Miocene, 13.6—11.1 mya, existing for approximately 2.5 million years.
Barbourofelis is an extinct genus of large, mostly carnivorous, mammals of the family Barbourofelidae. The genus was endemic to North America during the Miocene, living from 13.6—5.3 Ma and existing for approximately 8.3 million years. Thought to be lion-sized, it had the longest canines of all barbourofelids. It had a very robust constitution; the largest individuals of B. fricki are thought to have weighed up to 380 kg (829 lbs). They had very prominent flanges on the lower jaws and an unusually shaped skull. The barbourofelids were probably very muscular, resembling a bear-like lion or lion-like bear. Although the nimravid family did evolve into cat-like forms, they left no descendents among modern cats.

 

The largest barbourofelids was Barbourofelis fricki in size - length - 2,3 m, height - 90 cm, weight - 180-300 kg.
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The largest species known as Barbourofelis fricki was living in North America, having reached the size of a modern lion, but has superior in weight, due to its unusually strong physique. It had a very robust constitution and largest individuals of B. fricki are thought to weight up to 300 kg. The skull of Barburofelis was shortened to a greater degree than in kind of saber-toothed cats Smilodon  and hypertrophied upper canines were perhaps even more advanced. The lower jaw, as well as saber-toothed predators have all been relatively weak, the lower teeth are not large, the set of teeth is shortened. On the lower jaw bone, there were specific processes that are characteristic for the early saber-toothed cats, but more pronounced than in the past. A very interesting structure of the rear limb girdle of Barburofelis. The pelvis of the predator was more extended than that of the cat with more developed iliac bones, which may suggest that barburofelis was more stable, rising on the feet and striking the front, as is often done in modern cats.

 

 




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Автор: valentint
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