Smilodon //, is an
extinct genus of
machairodont felid. It is perhaps the best known
saber-toothed cat and lived in
North America during the
Pleistocene epoch (2.5
mya—10,000 years ago). Several fossils have been found with one of the largest collections taken from the
La Brea Tar Pits. Three species of the genus are known and they vary in size and build.
Overall,
Smilodon was more robustly built than any modern cat, with particularly well-developed forelimbs and exceptionally long upper
canines.
Its jaw had a bigger gape than modern cats and its upper canines were
slender and fragile, being adapted for precision killing. These
attributes made
Smilodon a specialized hunter of large herbivores like
bison and
camels.
Smilodon likely lived in closed habitats like forests and bush
which would have provided cover for ambushing prey. Its reliance on
large animals may have been the cause of its extinction. Scientists
debate over whether
Smilodon was a social animal. Comparison of
predator responses to distress calls and the prevalence of healed
injuries suggest it was social, while its small brain size and vegetated
habitat suggest it was more solitary. Some fossils show signs of
ankylosing spondylitis, trauma and
arthritis.
Smilodon went extinct 10,000 years ago.
Etymology
Restoration of
Smilodon fatalis
The nickname "saber-tooth" refers to the extreme length of their
maxillary canines. Despite the colloquial name "saber-toothed tiger",
Smilodon is not closely related to the
tiger (or any other living felid); the latter belongs to subfamily
Pantherinae, whereas
Smilodon belongs to subfamily
Machairodontinae. The name
Smilodon comes from
Greek:
σμίλη, (
smilē), "
carving knife"
[1] +
ὀδoύς (
odoús), "tooth" (whose stem is
odont-, as seen in the
genitive case form
ὀδόντος,
odóntos).
[2]
Classification
Smilodon populator skeleton
The
genus Smilodon was named and described by the
Danish naturalist and
palaeontologist Peter Wilhelm Lund in 1842. He found the
fossils of
Smilodon populator in caves near the small town of
Lagoa Santa, in the
state of
Minas Gerais,
Brazil.
[3] It is grouped with several species of
saber-toothed cats in the subfamily
Machairodontinae within the family
Felidae. An early
ancient DNA analysis suggested that
Smilodon be grouped with modern cats (subfamily
Felinae)
[4] However, a 2005 study found that
Smilodon belonged to a separate lineage.
[5]
Another study published a year later confirmed this, showing that the
Machairodontinae diverged early from the ancestors of modern cats and
were not closely related to any living feline species.
[6] The skull and mandible morphology of the earliest saber-toothed cats were similar to that of
clouded leopards. The lineage further adapted to precision killing of large animals with elongated
canine teeth and wider gapes, in the process sacrificing high bite force.
[7] Smilodon belongs to the
tribe Smilodontini, which are known as "dirk-toothed cats". These cats were defined by their long slender canines with fine
serrations.
[8]
Species
A number of
Smilodon species have been described, but today usually only three are recognized.
[9]
- Smilodon gracilis, 2.5 million–500,000 years ago; the smallest and earliest species, estimated at 55 to 100 kg (120 to 220 lb) in weight[10] was the successor of Megantereon
in North America, from which it probably evolved. This species reached
the north of South America in the early Pleistocene, along with Homotherium.[11] The other Smilodon species probably derived from this species. As its specific name suggests, this species is the most lightly built of the genus.[3] In terms of size, it was intermediate between S. fatalis and S. populator.[9]
- Smilodon fatalis, 1.6 million–10,000 years ago, replaced S. gracilis in North America and invaded western South America as part of the Great American Interchange.[12] It ranged from 160 to 280 kg (350 to 620 lb).[10] and reached a shoulder height of 100 cm (39 in) and body length of 175 cm (69 in).[13] Sometimes two additional species are recognized, S. californicus and S. floridanus, but usually they are considered to be junior synonyms of S. fatalis.[14]
- Smilodon populator, 1 million–10,000 years ago; occurred in the eastern parts of South America and was larger than the North American species.[15] It is perhaps the largest known felid with a body mass range of 220 to 400 kg (490 to 880 lb).[10][16] It stand at a shoulder height of 120 cm (47 in).[9] Compared to S. fatalis, S. populator had a more elongated and narrow skull, higher positioned nasals, more massive metapodials and slightly longer forelimbs relative to hindlimbs.[12]
Description and anatomy
Smilodon fatalis shown to scale
Smilodon was around the size of a modern lion or tiger but was more robustly built. It had a reduced
lumbar region, high
scapula, short tail, broad limbs with relatively short feet and long canines.
[9][17] The brain of
Smilodon was relatively small compared to other cat species.
[18] In reconstructing the facial appearance of
Smilodon,
Miller (1969) proposed that it looked very different from a typical
cat: having a lower lip line (to allow its mouth to open so wide without
tearing the facial tissues), a more retracted nose and lower placed
ears.
[19] However this is disputed, and Antón, et al. (1998) write that the facial features of
Smilodon were overall no different than that of other cats.
[20]
There is some dispute over whether
Smilodon was
sexually dimorphic. Some studies of
Smilodon fatalis fossils have found little difference between the sexes.
[21][22] Conversely a 2012 study found that while fossils of
S. fatalis show less variation in size among individuals than modern
Panthera, they do appear to show the same difference in some traits between the sexes.
[23]
Limbs
Smilodon had shorter and more massive limbs than other
felines. It had well developed flexors and extensors in its forearms,
which enabled it to pull down and securely hold down large prey so it
could deliver a killing bite without endangering the vulnerable elongate
canines. Analysis of the cross-sections of
S. fatalis humeri
indicated that they were strengthened by cortical thickening to such an
extent that they would have been able to sustain greater loading than
those of extant big cats, or of the extinct
American lion. However, the thickening of
S. fatalis femurs was within the range of extant felids.
[24] The
heel bone of
Smilodon was fairly long which suggests it was a good jumper.
[9]
Teeth and jaws
Smilodon skull with jaws positioned to show wide gape
Smilodon is most famous for its relatively long
canines, which are the longest found in the saber-toothed cats, at about 28 cm (11 in) long in the largest species
Smilodon populator.
[9] Those of
S. fatalis reached their full size in 18 months at a growth rate of 7 mm/month.
[25] These canine teeth were slender and had fine serrations.
[8]
They were fragile and could not have bitten into bone; thus, these cats
did not use their long teeth while taking down prey, due to the risk of
breaking. Only when their prey was totally subdued did they use their
teeth to slash the throat.
[24]
Despite being more powerfully built than other large cats,
Smilodon actually had a weaker bite. Modern big cats have more pronounced
zygomatic arches, while
Smilodon had smaller zygomatic arches which restricted the thickness and therefore power of the
temporalis muscles, and thus reduced
Smilodon's bite force. Analysis of its narrow jaws indicates it could produce a bite only a third as strong as that of a lion.
[26]
There seems to a be a general rule that the saber-toothed cats with the
largest canines had proportionally weaker bites. However, analyses of
canine bending strength (the ability of the canine teeth to resist
bending forces without breaking) and bite forces indicate that the
saber-toothed cats' teeth were stronger relative to the bite force than
those of modern "big cats".
[27] In addition,
Smilodon's gape could have reached almost 120 degrees,
[28] while that of the modern lion reaches 65 degrees.
[29] This makes the gape wide enough to allow
Smilodon to grasp large prey despite the long canines.
[20]
Paleoecology and paleobiology
Skeleton depicted climbing a branch
Smilodon was perhaps the most recent of the saber-toothed cats and lived during the
Pleistocene epoch (2.5
mya—10,000 years ago).
[9] Fossils of the genus have been found throughout the Americas.
[30] In particular, numerous specimens have been discovered in the
La Brea Tar Pits in
Los Angeles, California and the
Talara Tar Seeps in Peru.
[13] Smilodon likely lived in "closed" habitat (forest and bush).
[31]
Diet and hunting
S. californicus and
Canis dirus fight over a
Mammuthus columbi carcass in the La Brea Tar Pits, by
Robert Bruce Horsfall (1913)
Smilodon was an
apex predator and primarily hunted large mammals like
bison,
camels,
ground sloths,
horses and
mastodons.
Isotopes preserved in the bones of
S, fatalis in the La Brea Tar Pits reveal that
ruminants like bison and camels were most commonly taken by the cats.
[32] In addition, isotopes preserved in the enamel of
S. gracilis specimens from Florida show that this species feed on the pig-like
Platygonus and the llama-like
Hemiauchenia.
[33] Isotopic studies of
dire wolf and
American lion bones show an overlap with
S. fatalis in prey, which suggests that they were competitors.
[32] The amount of prey available to these predators in the La brea area was likely comparable to modern
East Africa.
[34]
Smilodon was likely an ambush predator and concealed itself in dense vegetation.
[35]
It probably used its great upper-body strength to wrestle prey to the
ground, where its long canines could deliver a deep stabbing bite to the
throat which would generally cut through the
jugular vein and/or the
trachea and thus kill the prey very quickly.
[24][36] By contrast, modern cats kill large prey with a suffocating bite.
[24] An alternate hypothesis suggests that
Smilodon
targeted the belly of its prey. However, this is disputed as the
curvature of their prey's belly would likely have prevented the cat from
getting a good bite.
[37] Smilodon probably avoided eating bone and would have left enough food for scavengers.
[38] Smilodon itself may have scavenged dire wolf kills.
[39]
Social behavior
Scientists debate whether
Smilodon was social. One study of African predators found that social predators like
lions,
spotted hyenas respond more to the distress calls of prey than solitary species. Since
Smilodon fatalis
fossils are common at the La Brea Tar Pits and were likely attracted by
the distress calls of stuck prey, this could mean that La Brea
S. fatalis were social as well.
[40]
Critics claim the study neglects other factors, such as body mass
(heavier animals are more likely to get stuck then lighter ones),
intelligence (some social animals like the American lion may have
avoided the tar when they saw their fellow group members getting
caught), lack of visual and olfactory lures, the type of audio lure, and
the length of the distress calls (the actual distress calls of the
trapped prey animals would have lasted longer than the calls used in the
study). In addition, they note that solitary cats like tigers are known
to aggregate around a single carcass.
[41] The authors of the original study have responded to these criticisms.
[42]
Another argument for sociality is based on the healed injures in several
Smilodon fossils which would suggest that the animals needed others to provide it food.
[43] This argument has been questioned, as cats can recover quickly from even severe bone damage and an injured
Smilodon could survive as long as it had access to water.
[44] Some researchers have argued that
Smilodon's brain would have been too small for it to have been a social animal.
[18] However, an analysis of brain size in living big cats found no correlation between brain size and sociality.
[45] Another argument against
Smilodon being social is based on it being an ambush hunter in closed habitat which would likely have negated sociality.
[44]
Skull of immature
Smilodon
Whether
Smilodon was sexual dimorphic has implications for its reproductive behavior. Based on their conclusions that
Smilodon fatalis
had no sexual dimorphism, Van Valenburgh and Sacco (2002) suggest that
if the cats were social they would likely have lived in monogamous pairs
(along with offspring) with no intense competition among males for
females.
[21] Likewise, Meachen-Samuels and Binder (2010) conclude that aggression between males was less pronounced in
S. fatalis than the American lion.
[22] However, Christiansen and Harris (2012) find that as
S. fatalis did exhibit some sexual dimorphism, there would have been evolutionary selection for competition between males.
[23]
In recent years, Smilodon cubs have been found in tar pits close to
the Rancho La Brea site, near the bones of larger adults. Unlike the
mature specimens, juvenile Smilodon had smaller saber teeth which were
used more for cutting flesh away from bones than killing prey. This
likely infers that they were coming in to feed after the adults had made
a kill and fed on parts of the kill that were inaccessible to the
adults. In attempting to feed, the cubs and subadults would also become
mired and starve to death. This behavior was recently revealed in
popular culture in the first episode of the 2013 BBC documentary
miniseries "Ice Age Giants".
[46]
Mortality
Several
Smilodon fossils show signs of
ankylosing spondylitis,
hyperostosis and trauma;
[47] some also had
arthritis which gave them fused vertebrae. One study of 1,000
Smilodon skulls found that 30% of them had eroded
parietal bones,
which is where the largest jaw muscles attach. They also showed signs
of microfractures, and the weakening and thinning of bones possibly
caused by mechanical stress from the constant need to make stabbing
motions with the canines.
[48]
Extinction
Smilodon went extinct 10,000 years ago, along with most of the Pleistocene megafauna, in the
Quaternary extinction event.
Its extinction may be linked to the decline and extinction of large
herbivores, which were replaced by smaller and more agile ones like
deer. Hence
Smilodon could have been too specialized at hunting large prey and may have been unable to adapt.
[24] However, a 2012 study of
Smilodon
tooth wear found no evidence that they were limited by food resources.
Other explanations include climate change and competition with humans.
[49]
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