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Machairodus horribilis
Topic Started: Nov 8 2016, 04:19 PM (526 Views)
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Machairodus horribilis

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The biggest of the sabertooth cats, Machairodus horribilis, combined its lengthy canines with size and strength.
Credit: Courtesy of T. Deng/IVPP, artwork by Y. Chen

Temporal range: Late Miocene (11.6 million to 5.3 million years ago)

Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Carnivora
Family: Felidae
Subfamily: †Machairodontinae
Tribe: †Machairodontini
Genus: †Machairodus
Species:Machairodus horribilis

Machairodus horribilis belonged to the genus Machairodus of large machairodontine saber-toothed cats that lived in Europe, Asia, Africa and North America during the Miocene through Pleistocene living from 11.6mya—126,000 years ago, existing for approximately 11.5 million years.

According to the size of the skull (NWU 48Wd0001), M. horribilis from Longjiagou is estimated to have had a body weight of about 405 kg (893 lbs) as a living animal.

M. horribilis from Longjiagou has the largest skull of any sabertooth cat, but it likely did not exhibit the predatory behavior of derived taxa such as Smilodon or Homotherium, and instead hunted comparatively smaller preys. Derived predatory behaviors apparently have evolved several times independently in sabertooth cats along with changes of habitats and preys through the whole evolutionary history of sabertooth cats (Antón, 2013), as has clearly occurred in some ungulates, especially tooth crown changes in the family Equidae (Mihlbachler et al., 2011). The mixture of primitive and derived morphological characteristics in the cranium of M. horribilis is consistent with previously observed mosaic evolutionary patterns in early machairodontines, and additionally provides evidence that gigantism may be one of several mechanisms to increase gape prior to the evolution of the full suite of anatomical features associated with more efficient killing bite mechanism (Antón, 2013). Future discoveries of postcranial elements belonging to M. horribilis would allow these functional morphological interpretations to be further tested.

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Saber-Toothed Cat Had a Huge Skull, But a Puny Bite

A newly described fossil skull from one of the largest of the saber-toothed cats, Machairodus horribilis, is the biggest saber-toothed skull ever found, and is helping scientists understand the diversity of killing techniques used by these extinct and fearsome predators.

The skull was excavated from the Longjiagou Basin in Gansu Province, China, but languished in storage for decades before researchers rediscovered it in a collection room and identified it in the new study.

And while M. horribilis may have had the biggest skull of the saber-toothed cats, it didn't necessarily have the biggest bite. When scientists analyzed the skull alongside its saber-toothed cousins, they estimated that it couldn't stretch its jaws as wide as some of the other extinct cats, which likely affected what type of prey it hunted and how it brought them down.

M. horribilis lived in the steppes and forests of northwestern China during the late Miocene epoch (11.6 million to 5.3 million years ago). The skull's upper surface measures 1.4 feet (415 millimeters) in length, and likely represents an adult male. Its incisors are arranged in a "gentle arch" and its signature upper canines are serrated on both edges, the study authors wrote.

Reconstructing an ancient bite

They noted that some of the fossil's features resembled those seen in primitive saber-toothed cats. But certain aspects of the skull shape were more like the skulls of modern lions and leopards, suggesting that M. horribilis may have had a range of motion in its jaw similar to large cats alive today.

Clues in both the shape and the surface texture of the fossil helped the scientists determine how the jaw may have moved in life, according to study co-author Z. Jack Tseng, a professor of pathology and anatomical sciences at the State University of New York at Buffalo.

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M. horribilis's skull shares features with both primitive sabertooths and modern big cats.
Credit: Courtesy of T. Deng/IVPP, artwork by Y. Chen

"The surface of bones preserves ridges and bumps that indicate where muscles once attached, so paleontologists and anatomists can reconstruct the lines of action of the major muscle groups," Tseng told Live Science in an email.

"The joints of the jaw — one on each side between the upper and lower jaws, and one down the middle between the two halves of the lower jaw — provide clues as to the mobility and range of motion possible in the animal’s bite."

But when it came to using its knife-like teeth for killing, M. horribilis was "a lightweight" compared with some other saber-tooths, Tseng added. It lacked the shallower jaw joints that allowed other cats' jaws to open wider — to enclose and rip out the throats of large prey. The jaws of M. horribilis just didn't stretch wide enough to do that, he said.

A burly predator

However, M. horribilis probably made up for that disadvantage with its bulk, Tseng said. The researchers estimated that it weighed nearly 900 pounds (400 kilograms), which would have given it a size and strength advantage over even large prey, which it probably killed by ripping open the throat "and causing massive blood loss," the study authors wrote.

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Short-legged horses may have been hunted by M. horribilis in the steppes of northwestern China, millions of years ago.
Credit: Courtesy of T. Deng/IVPP, artwork by Y. Chen

"We found evidence of short-legged, probably slower-running horses in the same fossil assemblage," Tseng said. "Those horses are good candidates as this cat's main prey."

Their findings emphasize how even highly specialized adaptations — like extra-long canines — can be used by different species in different ways, even in closely related groups such as saber-toothed cats.

"Cats continue to surprise us," Tseng added. "We now think gigantism is one of those mechanisms for intermediate saber-tooths to get by as predators."

The findings were published online Oct. 25 in the journal Vertebrata PalAsiatica.


Journal Reference:
Deng T, Zhang Y X, Tseng Z J et al., 2016. A skull of Machairodus horribilis and new evidence for gigantism as a mode of mosaic evolution in machairodonts (Felidae, Carnivora). Vertebrata PalAsiatica, 54(4): 302−318

Sabertooth cats were extinct carnivorans that have attracted great attention and controversy because of their unique dental morphology representing an entirely extinct mode of feeding specialization. Some of them are lion-sized or tiger-sized carnivorans who are widely interpreted as hunters of larger and more powerful preys than those of their modern nonsaber-toothed relatives. We report the discovery of a large sabertooth cat skull of Machairodus horribilis from the Late Miocene of northwestern China. It shares some characteristics with derived sabertooth cats, but also is similar to extant pantherines in some cranial characters. A functional morphological analysis suggests that it differed from most other machairodont felids and had a limited gape to hunt smaller preys. Its anatomical features provide new evidence for the diversity of killing bites even within in the largest saber-toothed carnivorans and offer an additional mechanism for the mosaic evolution leading to functional and morphological diversity in sabertooth cats.

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