Acinonyx pardinensis

Acinonyx pardinensis
Skull, Firenze
Conservation status
Extinct
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Mammalia
Order:	Carnivora
Family:	Felidae
Genus:	Acinonyx
Species:	A. pardinensis
Binomial name
Acinonyx pardinensis Croizet & Joubart, 1828

The giant cheetah (Acinonyx pardinensis) is an extinct species of big cat; its closest living relative is the modern cheetah.

Morphology

the skull of modern Acinonyx jubatus. The similarities between the two species are strong (note the small canines and domed frontal bone over large nasal passages).

The lifestyle and physical characteristics of the giant cheetah were probably similar to that of its modern relative, except that the giant cheetah was the height of a lion at the shoulder (but, due to its light build, it weighed considerably less than a lion). It was roughly twice the size of today's cheetahs, putting it at around 120 kilograms (260 lb), and about 200 centimetres (79 in) from head to rump, not including a 140 centimetres (55 in) tail. Its reconstructed shoulder height was at 90 centimetres (35 in). It was a specialized sprinter with long limbs just like the modern cheetah and a back that was slightly longer. This back was highly flexible and allowed great propulsion during a sprint.

depicting the forced inhalation and exhalation of Acinonyx while sprinting by shifting of abdominal (green) and thoracic (red) cavities beneath the skeleton (blue)

Just as with the modern cheetah, almost every aspect of Acinonyx pardinesis was specialized for running. The muzzle is short, nasal passage large for increased air intake during a strenuous sprint. To make room for the enlarged nasal passage, the maxilla was reduced and the anchorage for the canine roots was less, resulting in shorter canine roots and a shorter, more stout external canine, a characteristic seen in the modern cheetah. To lighten the weight of the animal, bone girth is reduced and the skeleton is lean and light, excellent for running but not fighting or coping with injuries, severe or minor. Its thoracic cavity was consumed by large lungs and a powerful heart. The intestines were probably shorter, to lighten the animal, and muscles not used for running were reduced. The diaphragm was connected to the movement of its gait and with the stretching phase of a stride, the expansion of space in the abdominal cavity pulled the diaphragm down and forced the animal to inhale, while the contractile phase compressed the lungs and forced air out, so it had no control over its breathing while running, a commonality of most quadruped sprinters. It was a fragile animal that could be killed by a simple sprain (if it meant the individual could not run well enough to hunt). Its tail was long, probably thickly furred, and relatively heavy; it was used as a counterweight to aid in quick directional changes when chasing prey.

One of the most complete skulls of this species is from the well-known French site of Saint-Vallier, but the best collection of postcranial bones came from the older site of Perrier in the Massif Central, including vertebral column and long bones of one individual were found. Unfortunately, the metacarpals were not recovered and so subsequent reconstructions depict them at the same length as the modern Acinonyx.

Distribution and habitat

Giant cheetahs were present in Europe during the Early and Middle Pleistocene. The giant cheetah was found in Germany, France, and also in China and India. European cheetahs occurred alongside jaguars and leopards at some Middle Pleistocene localities, and it is possible that competition among the three contributed to the cheetah's decline. Its large mass and more worn claws (when compared to modern cheetahs) suggest it was less adapted to climbing, an ability that would continue to evolve until modern-day cheetahs appeared.

Hunting

Skull

It could have preyed upon anything from small, contemporary muntjac deer, mountainous ibex and bighorn sheep, to elk and possibly sambar, prey that was considerably larger than the modern cheetah's ideal prey, the thomson's gazelle. The modern cheetah utilizes a specific hunting style seen nowhere else in the cat family : on open plains, it locates prey and walks directly towards a group or individual, without crouching, with head and tail down. When it comes within suitable distance (usually 50 yards), it sprints forward. The chase is fast and takes many turns until the cheetah uses an enlarged dew claw to hook the hind leg of the prey or smack its flanks to either knock it off balance or damage its Achilles tendon. When the prey falls to the ground, the cheetah suffocates it with a throat clamp, and after resting, eats as much as it can on the spot before being chased off by larger predators or occasionally having eaten all it can. This sequence of a chase over an open area and the hooking of the back leg is unique and often necessary for the cheetah: prey that does not flee is addressed with a great deal of confusion on the cheetah's part and is often left unharmed if it cannot be coaxed to flee.

Due to the skeletal structure of Acinonyx pardinensis, it is very likely that the larger species used a similar approach to hunting: it, too, bore a large dew claw and the lean form was definitely built for running. A stalk, sprint, trip, and kill was probably a commonality of the large species' hunting tactics. The modern cheetah almost always uses a throat clamp to suffocate prey and it is likely that this species of Acinonyx used this method of killing. Due to the small canines and weaker jaw muscles of both species, a muzzle clamp (seen in lions) or severing of the spinal cord (seen in jaguars) is generally not an option, so a throat clamp would have been used most prominently.

Lifestyle and behavior

Fossil leg

Within the same species, as shown in the modern species Panthera onca, the South American jaguar and Panthera tigris, the Asian tiger, individuals in higher and colder areas acquire larger sizes. The fossil record for cheetahs is scarce. In contrast to Smilodon fatalis, severe injuries lead to death and there is no sign of cooperation as seen in the latter species of machairodont. Fossils suggest a lifestyle similar to the modern cheetah species: solitary, except for mothers a cubs and possibly siblings as seen with cheetah brothers, more specialized hunting tactics that narrow the number of species being hunted and therefore increasing the size of a territory and causing the species to be spread out more thinly than the much more adaptable modern Panthera pardus, or leopard. Vertebrate paleontologist Alan Turner suggests that "since it had the bodily proportions of the living cheetah, and since running speed is a reflection of stride length for a given stride frequency, such large animals may also have been capable of running somewhat faster than their living relatives, although greater weight may have countered any advantage of greater size. Whether they needed to run faster is less clear." The motivation for Acinonyx pardinensis achieving large size could be to keep warm, to move faster, to subdue larger prey, or a combination of the three.

On the same field as the modern cheetah, it would have been a relatively successful hunter, very wary of injuries, and rarely came into contact with others of its species. It would have been cautious, preferred fleeing to fighting and would have been wary of prey that was too large and capable of injuring the cheetah. Cooperative hunting would generally have been out of the question and mortality rates in the young would have been high. The modern cheetah must stop running after about 60 seconds, or when its body temperature rises over 104 degrees Fahrenheit and this large species would have had these confines as well.