Scimitartooths, dirktooths, sabertooths – the clade Machairodontinae

The earliest members of felines (Felidae) appeared on the European continent during late Oligocene and early Miocene. Some consider that the leopard-sized Pseudaelurus quadridentatus was the mutual ancestor of the sabertooths (Machairodontinae). Their clade currently branches into three separate lineages: the Metailurini, Homotherini, and Smilodontini. Although many descriptions have been written about these meat-eaters, we will introduce just some of them, the more famous and lesser known ones.

The members of Metailurini are often called the false sabertooths – their canines are not as distinct as those of the others, therefore their origin is still unclear. Metailurus (currently including two species) was described by Otto Zdansky in 1924, based on approximately 8 million years old skull fragments found in China. Metailurus major was mostly similar to its supposed predecessor, P. quadridentatus – in contrast, Metailurus parvulus was somewhat smaller and more agile.

For a long time, both these species were known only from a few fossils, until almost complete skeletons have been recovered several decades ago. Detailed studies have been conducted on the Bulgarian M. major in 2001 and the Greek (Kerassia) M. parvulus in 2006.Their muscular and long hind limbs suggest that they excelled at leaping, making this ability very useful at hunting.

At the end of the 19th century, paleontologists separated machairodontines into two diverse groups; however, their assumptions were only based on the shape of the lengthened canines. Shortly after, more differences have been observed, when remains in perfect condition were unearthed in France, Senèze, during the 20th century. The canines of the scimitartooths (homotherins) were more curved and only slightly flattened with jagged edges. Their bodies were supported by relatively lengthy limbs. In turn, the canines of dirktooths (smilodontins) were more straight and flat with smoothly knurled margins. Their robust bauplan and shorter legs were also their most distinguishing features.

Machairodus horribilis (© Péter Hutzler).

Machairodus, a member of scimitartooths, became famous thanks to Georges Cuvier (1769-1832). His story is as ironic as it is laughable, since the well-known naturalist, who frequently bragged about his ability to name the tooth-bearer by simply looking at it, has made a huge mistake. Eight years after Cuvier’s thesis was published, the German naturalist J. J. Kaup made his colleagues aware of a mistake: the examined fossils belonged to a feline instead of a bear! Misidentifications like this made it impossible to tell how many species of Machairodus were there. Deng Tao and coauthors expanded the list with a new one in October 2016 – a study about one of the biggest sabertooth cats that ever lived was published in the journal Vertebrata PalAsiatica.

Before the study was published, it has been speculated that the largest species of Machairodus (as big as lions or tigers) first appeared at the end of the evolutionary history of the taxon. However, Machairodus horribilis, as Tao and colleagues named the new scimitartooth, was clearly an exception. This carnivore lived during the late Miocene (some 11,6–5,3 millions of years ago) in what is today China. Its remains were recovered in the northwestern part of the country, in the Gansu Province. They had been gathering dust on the shelves of a warehouse for decades before they were found and examined. The 41,5 centimeters long skull most likely belonged to an adult male: according to the estimates, the heaviest animals could weigh as much as 400 kilograms. The fossils partly resembled early sabertooths, and partly the modern big cats.

Unlike its sabertooth relatives, Machairodus horribilis could open its mouth to only 70 degrees (for comparison, Smilodon could open theirs to 120 degrees). It is highly probable that they were ambush predators. However, hunting in open, plain areas were challenging for them – mostly because of their size and the lack of covering. The main prey of this feline might have been the short-legged horses Hipparion platyodus.

Some remains were also discovered in Hungary. Members of Machairodus are known from Csákvár and Baltavár (the two towns have merged and are now simply called Bérbaltavár). These Hungarian cats lived during the late Miocene, some 12 millions of years ago (this period is also known as the Pannonian). Though as yet unofficial, it might have belonged to the widespread species Machairodus aphanistus. As large as lions (~220 kilograms), they were likely the apex predators of this area.

The machairodontine Homotherium is at least 4 million years old. It originated from either Africa or Asia. According to Russian paleontologist Marina Sotnikova, Machairodus kurteni was its predecessor (found in today’s Kazakhstan). These sabertooths conquered North-America; from Europe, through the Bering land bridge. The Friesenhahn Cave is considered to be one of their most important fossil sites, as the bones found here gave us a glimpse into the lives of local felines. Homotherium serum had long and strong forelimbs, shorter hindlimbs, and its back was arching backwards, giving it a look similar to that of a hyena. 70 milk teeth of young mammoths found in this cavern could possibly mean that they were specialized in hunting down smaller proboscideans. Something similar can be perceived nowadays as well: calfs of African elephants – which wander away from their groups, especially when 2-4 years old – are highly endangered by lions.

Homotherium serum (© Péter Hutzler).

Even though Homotherium was relatively widespread, only poorly preserved remains were found. We can conclude from Homotherium fossils – found along the coastline of the Northern Sea – that these animals could withstand harsh weather conditions, camouflaging themselves with the color of their pelts.

Talking about sabertooth cats, most people immediately think of Smilodon. The most popular among the three species is Smilodon fatalis. Owing to the Rancho La Brea locality in Los Angeles, it has numerous fans worldwide. Buried in tar pits, its remains are exceptionally well preserved. Following the study of the rich assemblage (more than 1200 specimens) we can accurately recreate the biology of these extinct predators. It shouldn’t surprise that the battles they fought left some marks on the bones, just as sicknesses, fractures, and developmental abnormalities have. The size and structure of their brains are mostly resembling those of big cats, therefore some tend to think that dirktooth cats lived in smaller packs and hunted together, like the lions do.

Smilodon had set their foot several times in South America. As the time had been passing, separate species had evolved on the exotic landmass. Smilodon poulator was the greatest of its kind. Its fossils are known from Brazil and Venezuela, as well as the eastern part of the Andeans and the south of Patagonia. In 2015, distinctive footprints were found near the coast of Miramar, Argentina. Lead researchers Mariano Magnusson and Daniel Boh both hypothesize that the almost 20 centimeters wide marks were left by a Smilodon populator, some 50 thousand years ago. This outstanding ichnofossil got its own scientific name, Smilodonichnum miramarensis.

No matter how awe-inspiring these creatures were, they eventually shared the same cruel fate. Some were overpowered by new species in the never ending fight for survival, others were unable to keep up with the ever-changing environment. Scimitar- and dirktooths’ last representatives could have met our ancestors, so we can’t rule out the possible influence of human impact on their disappearance.

Featured image © Péter Hutzler.

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