Homotherium

Taxobox
name = "Homotherium"
fossil_range = Early Pliocene to Late Pleistocene


image_width = 250px
image_caption = Skeleton of "Homotherium serum" from Friesenhahn cave, Texas Memorial Museum, University of Texas at Austin, Austin, Texas.
regnum = Animalia
phylum = Chordata
classis = Mammalia
ordo = Carnivora
familia = Felidae
subfamilia = †Machairodontinae
tribus = †Machairodontini
genus = †"Homotherium"
genus_authority = Fabrini, 1890
subdivision_ranks = Species
subdivision = †"Homotherium serum"
†"Homotherium latidens"
†"Homotherium aethiopicum"
†"Homotherium hadarensis"
†"Homotherium nestianus"
†"Homotherium nihowanensis"
†"Homotherium sainzelli"
†"Homotherium ultimum"
†"Homotherium crenatidens"

"Homotherium" is a genus of machairodontine saber-toothed cats, often termed 'scimitar cats', that lived approximately 5 million to 10,000 years ago in North America, South America, Eurasia and Africa. It first became extinct in Africa some 1.5 million years ago. In Eurasia it survived until about 30,000 years ago cite journal|last=Reumer|first=J.W.F.|coauthors=L. Rook, K. Van Der Borg, K. Post, D. Mol, J. De Vos|year=2003|title=Late Pleistocene survival of the saber-toothed cat "Homotherium" in northwestern Europe|journal=Journal of Vertebrate Paleontology|doi=10.1671/0272-4634(2003)23 [260:LPSOTS] 2.0.CO;2|volume=23|pages=260] . The last scimitar cat survived in North America until 10,000 years ago.

Anatomy

"Homotherium" reached 1.1 m at the shoulder and was therefore about the size of a lion. Compared to some other machairodonts, like "Smilodon" or "Megantereon", "Homotherium" had relatively shorter upper canines, but they were flat, serrated and longer than those of any living cat. Incisors and lower canines formed a powerful puncturing and gripping device. Among living cats, only the tiger ("Panthera tigris") has such large incisors, which aid in lifting and carrying prey. The molars of Homotherium were rather weak and not adapted for bone crushing. The skull was longer than in "Smilodon" and had a well-developed crest, where muscles were attached to power the lower jaw. This jaw had down-turned forward flanges to protect the scimitars. Its large canine teeth were crenulated and designed for slashing rather than purely stabbing.

It had the general appearance of a cat, but some of its physical characteristics are rather unusual for a large cat. The limb proportions of "Homotherium" gave it a hyena-like appearance. The forelegs were elongated, while the hind quarters were rather squat with feet perhaps partially plantigrade, causing the back to slope towards the short tail. Features of the hindlimbs indicate that this cat was moderately capable of leaping. The pelvic region, including the sacral vertebrae, were bear-like, as was the short tail composed of 13 vertebrae — about half the number in long-tailed cats.

The unusually large, square nasal opening, like that of the cheetah ("Acinonyx jubatus"), presumably allowed quicker oxygen intake, which aided in rapid running and in cooling the brain. As in the cheetah, too, the brain's visual cortex was large and complex, emphasizing the scimitar cat's ability to see well and function in the day, rather than the night, as in most cats.

Range and species

"Homotherium" probably derived from "Machairodus" and appeared for the first time at the Miocene-Pliocene border, about 5 million years agoAlan Turner: "The Evolution of the guild of larger terrestrial carnivores during the Plio-Pleistocene in Africa". Geobios, no 23, fasc. 3, p. 349-368, 1990.] . During the Pleistocene it occurred in vast parts of Eurasia, North America and until the middle Pleistocene (about 1.5 million years ago) even in Africa. There has also been a discovery of 1.8 million-year-old fossils in Venezuela [cite web
last = Sanchez
first = Fabiola
authorlink =
coauthors =
title = Saber-toothed Cat Fossils Discovered in Venezuela
work =
publisher = Associated Press
date = 2008-08-22
url = http://www.livescience.com/animals/080822-ap-cat-fossils.html
format =
doi =
accessdate = 2008-08-30] [cite web
last = Orozco
first = José
authorlink =
coauthors =
title = Sabertooth Cousin Found in Venezuela Tar Pit -- A First
work = [http://news.nationalgeographic.com/news/index.html National Geographic News]
publisher = National Geographic Society
date = 2008-08-22
url = http://news.nationalgeographic.com/news/2008/08/080822-scimitar-cat.html
format =
doi =
accessdate = 2008-08-30] , indicating that scimitar cats were able to invade South America along with "Smilodon" during the Great American Interchange. How long they lasted in South America is not yet evident. "Homotherium" survived in Eurasia and North America until about 30,000cite journal|last=Reumer|first=J.W.F.|coauthors=L. Rook, K. Van Der Borg, K. Post, D. Mol, J. De Vos|year=2003|title=Late Pleistocene survival of the saber-toothed cat Homotherium in northwestern Europe|journal=Journal of Vertebrate Paleontology|doi=10.1671/0272-4634(2003)23 [260:LPSOTS] 2.0.CO;2|volume=23|pages=260] and 10,000 years ago, respectively.

Several species ("nestianus", "sainzelli", "creantidens", "nihowanensis", "ultimum") are recognized from Eurasia, which differ mainly in the shape of the canines and in body size. But given the fluctuation range of the size of modern large cats, it is highly probable that all belong to just one species, "Homotherium latidens".

Two species described form the early Pleistocene of Africa are "Homotherium ethiopicum" and "Homotherium hadarensis". But they also hardly differ from the Eurasian forms. On the African continent the genus disappeared about 1.5 million years ago. In North America, a very similar species, "Homotherium serum" occurred from the latest Pliocene until the latest Pleistocene. Remains have been found at various sites between Alaska and Texas. In the southern parts of its range the American "Homotherium" co-existed with "Smilodon"; in the northern parts it was the only species of saber-toothed cat. The American "Homotherium" was originally described by the name "Dinobastis".

Despite "Homotherium"'s vast range and the large amount of fossil remains from Eurasia, Africa and North America, complete skeletons of this cat are relatively rare. One of the most famous sites of "Homotherium" remains is Friesenhahn cave in Texas, where 30 "Homotherium" skeletons were found, along with hundreds of juvenile mammoths and several dire wolves.

Diet and habitat

Friesenhahn cave in Texas contained the remains of over 30 "H. serum" individuals, which were discovered along with the remains of between 300 and 400 juvenile Columbian Mammoths ("Mammuthus columbii").cite journal|last=Rawn-Schatzinger|first=V.|year=1992|title=The scimitar cat "Homotherium serum" (Cope)|publisher=Illinois State Museum|journal=Report of Investigations|issue=47|pages=pp. 1–80] Besides mammoth, very few other potential prey species were found in the cave - it is therefore unlikely that "Homotherium" carried scavenged carcasses of already dead animals to the cave. Such specialization on prey of a particular species and age structure is not covenant with a scavenging lifestyle. For the same reason it is also unlikely that the dire wolves carried the mammoths into the cave. The worldwide association of "Homotherium" species with proboscidean (elephant and mastodon) and rhino remains, mainly those of juveniles, suggests that "Homotherium" preyed selectively on these tough-skinned animals and probably hunted in packs, carrying away the large animals it brought down. The decline of "Homotherium" could be due to the disappearance of large herbivorous mammals like mammoths in America at the end of the Pleistocene. In North America fossil remains of "Homotherium" are less abundant than those of its contemporary "Smilodon". For the most part it probably inhabited higher latitudes and altitudes, and therefore was likely to be well adapted to the colder conditions of the mammoth steppe environment.

The suggested large prey species make it probable that "Homotherium" hunted in packs. Reduced claws, relatively slender limbs and the sloping back indicate adaptations for endurance running in open habitats. [M. Anton et al.: Co-existence of scimitar-toothed cats, lions and hominins in the European Pleistocene. Implications of the post-cranial anatomy of "Homotherium latidens" (Owen) for comparative palaeoecology. Quaternary Science Reviews 24 (2004).]

References

* A. Turner: "The big cats and their fossil relatives". Columbia University Press, 1997.ISBN 0-231-10229-1

External links

* [http://www.lioncrusher.com//Machairodontinae.htm Saber-toothed Cats at Lioncrusher's Domain]
* [http://www.beringia.com/02/02maina7.html American Scimitar Cat]
* [http://www.wrecksite.eu/details.aspx?13463 Saber-toothed cat jaw]