Machairodus (from , 'knife' and 'tooth') is a genus of large machairodont or ''saber-toothed cat'' that lived in Africa, Eurasia and North America during the late Miocene. It is the animal from which the subfamily Machairodontinae gets its name and has since become a wastebasket taxon over the years as many genera of sabertooth cat have been and are still occasionally lumped into it.
History of research
Machairodus was first named in 1832, by German Naturalist Johann Jakob Kaup. Though its remains had been known since 1824, it was believed by Georges Cuvier that the fossils had come from a species of bear, which he called Ursus cultridens (known today as Megantereon) 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 nimravids) were lumped into the genus Machairodus, including but not limited to Sansanosmilus, Megantereon, Paramachairodus, Amphimachairodus, Nimravides, and Homotherium 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 irtyschensis and Machairodus ischimicus were described in 1936. Machairodus robinsoni was described in 1976. It was at one point referred to the genus Miomachairodus. Machairodus laskarevi was described in 1978. Machairodus alberdiae was first described in 1981, and extensively compared and retained as valid in 2019. Machairodus kurteni was described in 1991. It was later referred to the genus Amphimachairodus.
Description
In general Machairodus was similar in size to a modern lion or tiger, at long and standing about at the shoulder.
M. aphanistus from the Mediterranean late Miocene is known to be rather tiger-like in size and skeletal proportions, with a mass of to . It was similar to the related Nimravides of North America. The skeleton also indicates that this species would have possessed good jumping abilities.
M. alberdiae was contemporary with M. aphanistus in Cerro de los Batallones fossil deposits and was smaller and more primitive in anatomical features and would not have exceeded .
M. horribilis of China is the one of largest known species of the genus, weighing around . This is comparable in size to the much later Smilodon populator. Its skull, measuring upwards of in length, is one of the largest known skulls for any machairodont, with only a recently described S. populator skull rivaling it in size, with the latter cat outweighing M. horribilis at .
The species M. lahayishupup of North America was also quite large; fossil humerus bones measuring attributed to the species suggest that this cat was far larger than a modern lion, which has a humerus. It is estimated to have weighed between 241 and 348 kg, with a mean weight of 277 kg; one particularly large specimen was estimated to weigh 410 kg. Until its discovery, no true species representative of the genus Machairodus had been described from North America, as they had been reassigned to other genera, such as Nimravides and Amphimachairodus. Its presence in North America suggests that either there was a widespread population of this genus of cat throughout Africa, Eurasia and North America or simultaneous instances of independent evolution in machairodonts on multiple continents during the Miocene.
Overall, 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. However, a skull of M. horribilis was shown to be similar to extant pantherines in some cranial characters, suggesting new evidence for the diversity of killing bites even in the largest saber-toothed carnivorans, offering an additional mechanism for the mosaic evolution leading to functional and morphological diversity in sabertooth cats.