Machairodus

***Machairodus*** is a genus of large that lived in , , and from the to the . It is the animal from which the family Machairodontidae gets its name and has since become a over the years as many genera of sabertooth cat have been and are still occasionally lumped into it.

*Machairodus* was first named in 1832, by German Naturalist . Though its remains were known since 1824, it was believed by that the fossils had come from a species of bear, which he called "Ursus cultridens" (known today as ) based on composite sample of teeth from different countries, species and geologic ages, leading to what would become a long series of complications. Kaup however, recognized the teeth as those of felids and promptly reclassified the existing specimens as *Machairodus*, including *M. cultridens* in it. The name quickly gained acceptance and by the end of the 19th Century, many species of felid or related feliform (such as ) were lumped into the genus *Machairodus*, including but not limited to , *Megantereon*, , , , and among others. This would eventually turn *Machairodus* into something of a wastebasket taxon, which would be rectified with the discoveries of more complete skeletons of other machairodonts.

*Machairodus* was similar in size to a modern lion, standing about 1 m (3.3 feet) at the shoulder. The species once referred to *Machairodus coloradensis* was apparently significantly larger, about 1.2 m (3.9 feet) at the shoulder, according to skeletal and life reconstructions.[3] If accurate, this would have made *M. coloradensis* one of the largest felids. However *M. coloradensis*, along with *M. kurteni* and *M. giganteus*, has been reassigned to the genus *Amphimachairodus* and by extent, the Homotherini based on both morphology and its time of appearance in North America.[1] *Nimravides catacopsis* also has been separated from *Machairodus*, as the two are too different in regards to autapomorphies to be synonymous.[1] However, the species *Machairodus horribilis*, which stands as the largest known species of the genus, is comparable in size to the much later *Smilodon populator*, weighing in at around 404.6 kg (892 pounds). Its skull, measuring upwards of 16 in (41 centimetres) in length, is the largest known skull for any machairodont.[4]

The skull of *Machairodus* was noticeably narrow compared with the skulls of extant pantherine cats, and the orbits were relatively small. The canines were long, thin and flattened from side to side but broad from front to back like the blade of a knife, as in *Homotherium*. The front and back edges of the canines were serrated when they first grew, but these serrations were worn down in the first few years of the animal's life.

*Machairodus* was about 2 m (6.6 feet) long and probably hunted as an ambush predator. Its legs were too short to sustain a long chase, so it most likely was a good jumper, and used its canines to cut open the throat of its prey. Its teeth were rooted to its mouth and were not too delicate, unlike most saber-toothed cats of the time, which had extremely long canines which hung out of their mouths. The fangs of *Machairodus*, however, were able to more easily fit in its mouth comfortably while being long and effective for hunting.[5] Despite its great size, the largest example of *Machairodus*, *M. horribilis* was better equipped to hunt relatively smaller prey than *Smilodon*, as evidenced by its moderate jaw gape of 70 degrees, similar to the gape of a modern lion.[

The fossil species assigned to the genus *Machairodus* were divided by Turner into two grades of evolutionary development, with *M. aphanistus* and the North American "*Nimravides*" *catacopis* representing the more primitive grade and *M. coloradensis* and *M. giganteus* representing the more derived grade. The characteristics of the more advanced grade include a relative elongation of the forearm and a shortening of the lumbar region of the spine to resemble that in living pantherine cats. Subsequently the more derived forms were assigned a new genus, *Amphimachairodus*, which includes *M. coloradensis*, *M. kurteni* and *M. giganteus*. In addition, *M. catacopsis* was reclassified as *N. catacopsis*.

*Machairodus* seemed to prefer open woodland habitat, as evidenced by finds at , which is of age. As a top predator at Batallones, it would have hunted large herbivores of the time. Such herbivores would have included horses like , the hornless rhinoceros , the mastodon , the suid , silvatherid giraffes and boselaphine antelope. *Machairodus* would have competed for such prey with the , fellow machairodonts and , the bear , and the small . While *Indarctos* and *Magericyon* would likely have been strongly competitive with *Machairodus* for food, *Promegantereon*, *Paramachairodus* and *Protictitherium* likely were less potential rivals. Evidence also exists indicating that Machairodus may have been prone to with *Magericyon*, possibly living in slightly different habitats, with the machairodont preferring more heavily vegetated habitats while the bear-dog hunted in the more open areas. Dietary preferences may also have played a role in the coexistence between these two large predators at Batallones. Based on its jaw gape, the largest species, *M. horribilis* was probably a hunter of relatively slow-moving horses.

*Machairodus aphanistus* fossils recovered from Batallones reveal a high percentage of tooth breakages, indicating that unlike later machairodonts, due to a lack of protruding incisors *Machairodus* often used its sabers to subdue prey in a manner similar to modern cats; this was a more risky strategy that virtually ensured that damage to their saber teeth often occurred.