Instruct: Given a question, retrieve documents that answer the question.
Query: When did the Smilodon live?
Smilodon is a genus of the extinct machairodont subfamily of the felids. It is one of the most famous prehistoric mammals, and the best known saber-toothed cat. Although commonly known as the saber-toothed tiger, it was not closely related to the tiger or other modern cats. "Smilodon" lived in the Americas during the Pleistocene epoch (2.5 mya–10,000 years ago). The genus was named in 1842, based on fossils from Brazil. Three species are recognized today: S. gracilis, S. fatalis, and S. populator. The two latter species were probably descended from "S. gracilis", which itself probably evolved from "Megantereon". The hundreds of individuals obtained from the La Brea Tar Pits in Los Angeles constitute the largest collection of "Smilodon" fossils.
On occasion, the bone of a fossilised predator is preserved well enough to retain recognizable proteins that belong to the species it consumed when alive. Stable isotope analysis of these proteins has shown that "Smilodon" preyed mainly on bison and horses, and occasionally ground sloths and mammoths, while "Homotherium" often preyed on young mammoths and other grazers such as pronghorn antelope and bighorn sheep when mammoths were not available.
Fossils of "Smilodon" were discovered in North America from the second half of the 19th century onwards. In 1869, American paleontologist Joseph Leidy described a maxilla fragment with a molar, which had been discovered in a petroleum bed in Hardin County, Texas. He referred the specimen to the genus "Felis" (which was then used for most cats, extant as well as extinct) but found it distinct enough to be part of its own subgenus, as "F." ("Trucifelis") "fatalis". The species name means "fate" or "destiny", but it is thought Leidy intended it to mean "fatal". In an 1880 article about extinct American cats, American paleontologist Edward Drinker Cope pointed out that the "F. fatalis" molar was identical to that of "Smilodon", and he proposed the new combination "S. fatalis". Most North American finds were scanty until excavations began in the La Brea Tar Pits in Los Angeles, where hundreds of individuals of "S. fatalis" have been found since 1875. "S. fatalis" has junior synonyms such as "S. mercerii", "S. floridanus", and "S. californicus". American paleontologist Annalisa Berta considered the holotype of "S. fatalis" too incomplete to be an adequate type specimen, and the species has at times been proposed to be a junior synonym of "S. populator". Swedish paleontologists Björn Kurtén and Lars Werdelin supported the distinctness of the two species in 1990.
During the 1830s, Danish naturalist Peter Wilhelm Lund and his assistants collected fossils in the calcareous caves near the small town of Lagoa Santa, Minas Gerais, Brazil. Among the thousands of fossils found, he recognized a few isolated cheek teeth as belonging to a hyena, which he named "Hyaena neogaea" in 1839. After more material was found (including canine teeth and foot bones), Lund concluded the fossils instead belonged to a distinct genus of felid, though transitional to the hyenas. He stated it would have matched the largest modern predators in size, and was more robust than any modern cat. Lund originally wanted to name the new genus "Hyaenodon", but realizing this had recently become preoccupied by another prehistoric predator, he instead named it "Smilodon populator" in 1842. He explained the Ancient Greek meaning of "Smilodon" as ("smilē"), a scalpel or two-edged knife, and "οδόντος" ("odontús"), tooth. This has also been translated as "tooth shaped like double-edged knife". He explained the species name "populator" as "the destroyer", which has also been translated as "he who brings devastation". By 1846, Lund had acquired nearly every part of the skeleton (from different individuals), and more specimens were found in neighboring countries by other collectors in the following years. Though some later authors used Lund's original species name "neogaea" instead of "populator", it is now considered an invalid "nomen nudum" ("naked name"), as it was not accompanied with a proper description and no type specimens were designated. Some South American specimens have been referred to other genera, subgenera, species, and subspecies, such as "Smilodontidion riggii", "Smilodon" ("Prosmilodon") "ensenadensis", and "S. bonaeriensis", but these are now thought to be junior synonyms of "S. populator".
Another argument for sociality is based on the healed injuries in several "Smilodon" fossils, which would suggest that the animals needed others to provide it food. This argument has been questioned, as cats can recover quickly from even severe bone damage and an injured "Smilodon" could survive if it had access to water. The brain of "Smilodon" was relatively small compared to other cat species. Some researchers have argued that "Smilodon"'s brain would have been too small for it to have been a social animal. An analysis of brain size in living big cats found no correlation between brain size and sociality. Another argument against "Smilodon" being social is that being an ambush hunter in closed habitat would likely have made group-living unnecessary, as in most modern cats. Yet it has also been proposed that being the largest predator in an environment comparable to the savanna of Africa, "Smilodon" may have had a social structure similar to modern lions, which possibly live in groups primarily to defend optimal territory from other lions (lions are the only social big cats today).
In his 1880 article about extinct cats, Cope also named a third species of "Smilodon", "S. gracilis". The species was based on a partial canine, which had been obtained in a cave near the Schuylkill River in Pennsylvania. Cope found the canine to be distinct from that of the other "Smilodon" species due to its smaller size and more compressed base. Its specific name refers to the species' lighter build. This species is known from fewer and less complete remains than the other members of the genus. "S. gracilis" has at times been considered part of genera such as "Megantereon" and "Ischyrosmilus". "S. populator", "S. fatalis" and "S. gracilis" are currently considered the only valid species of "Smilodon", and features used to define most of their junior synonyms have been dismissed as variation between individuals of the same species (intraspecific variation). One of the most famous of prehistoric mammals, "Smilodon" has often been featured in popular media and is the state fossil of California.
A Smilodon appeared for the first time in episode 2.3, where it is responsible for a number of deaths at a theme park. When the team hear of this, Connor wonders why the Anomaly detector he has recently built didn't detect an Anomaly in the theme park; it is later revealed that the Smilodon had came through its Anomaly as a cub years before the events of the episode, and had been kept as a pet by a ranger called Valerie who had lost control of it as it became more aggressive and turned man-eater upon maturing; she was certain that her pet would never hurt her after all she had done for it over the years, but was proved wrong when it later killed her. At the end of the episode, Oliver claims the cat is dead, killed by an apparent heart attack after being tranquillised; Nick questions how this could have happened when it was a perfectly healthy animal. Oliver is revealed to have been lying in episode 2.7, where it is revealed he has built up his own army of creatures that his men have kidnapped from their own time and that the Smilodon is now one of the creatures in his army. He tries to use it to kill Connor, Abby, Jenny and Caroline, but Nick tricks him into opening the prison and the Smilodon escapes. It is later lured back to the prison along with the other creatures by Nick, Helen and Stephen; it then participates in killing Stephen. It is assumed that the creatures turned on and killed each other after killing Stephen and that the Smilodon, and the rest of Oliver's creatures, are all dead.
Whether "Smilodon" was sexually dimorphic has implications for its reproductive behavior. Based on their conclusions that "Smilodon fatalis" had no sexual dimorphism, Van Valkenburgh and Sacco suggested in 2002 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. Likewise, Meachen-Samuels and Binder (2010) concluded that aggression between males was less pronounced in "S. fatalis" than in the American lion. Christiansen and Harris (2012) found that, as "S. fatalis" did exhibit some sexual dimorphism, there would have been evolutionary selection for competition between males. The structure of the hyoid bones suggest that "Smilodon" communicated by roaring, like modern big cats. The ability to roar may have implications for the social life of "Smilodon".
The jaws of machairodonts, especially more derived species with longer canines, such as "Smilodon" and "Megantereon", are unusually weak. Digital reconstructions of the skulls of lions and of "Smilodon" show that the latter would have fared poorly with the stresses of holding onto struggling prey. The main issue was the stresses suffered by the mandible: a strong force threatened to break the jaw as pressure was placed on its weakest points.
Dimetrodon ( or , meaning "two measures of teeth") is an extinct genus of synapsids that lived during the Cisuralian (Early Permian), around 295–272 million years ago (Ma). It is a member of the family Sphenacodontidae. The most prominent feature of "Dimetrodon" is the large neural spine sail on its back formed by elongated spines extending from the vertebrae. It walked on four legs and had a tall, curved skull with large teeth of different sizes set along the jaws. Most fossils have been found in the southwestern United States, the majority coming from a geological deposit called the Red Beds of Texas and Oklahoma. More recently, fossils have been found in Germany. Over a dozen species have been named since the genus was first described in 1878.
The Talara Tar Seeps in Peru represent a similar scenario, and have also produced fossils of "Smilodon". Unlike in La Brea, many of the bones were broken or show signs of weathering. This may have been because the layers were shallower, so the thrashing of trapped animals damaged the bones of previously trapped animals. Many of the carnivores at Talara were juveniles, possibly indicating that inexperienced and less fit animals had a greater chance of being trapped. Though Lund thought accumulations of "Smilodon" and herbivore fossils in the Lagoa Santa Caves were due to the cats using the caves as dens, these are probably the result of animals dying on the surface, and water currents subsequently dragging their bones to the floor of the cave, but some individuals may also have died after becoming lost in the caves.
"Sinosauropteryx" lived in what is now northeastern China during the early Cretaceous period. It was among the first dinosaurs discovered from the Yixian Formation in Liaoning Province, and was a member of the Jehol Biota. Well-preserved fossils of this species illustrate many aspects of its biology, such as its diet and reproduction.
"Dimetrodon" was a quadrupedal, sail-backed synapsid. Most "Dimetrodon" species ranged in length from and are estimated to have weighed between . The largest known species of "Dimetrodon" is "D. angelensis" at and the smallest is "D. teutonis" at . The larger species of "Dimetrodon" were among the largest predators of the Early Permian, although the closely related "Tappenosaurus", known from skeletal fragments in slightly younger rocks, may have been even larger at an estimated in total body length. Although some "Dimetrodon" species could grow very large, many juvenile specimens are known.
The team discovered the remains of the largest dinosaur to walk in the southern parts of Africa , namely a 190-million-year-old fossilised egg of a Massospondylus dinosaur. This dinosaur lived in the Late Triassic and Early Jurassic, a period from about 230-million years ago to about 185-million years ago. The Massospondylus wandered about in great herds, migrating back and forth between what would millions of years later become Southern Africa and Russia, when the southern super-continent, Gondwana, was still intact. The rocks that were laid down during this period are called the Stormberg Group of rocks, and it is in rocks of the Stormberg Group that the fossils of Massospondylus and other dinosaurs were found. Massospondylus dinosaurs hatched from eggs not much larger than a hen’s egg, but grew into big creatures 5 to 6 metres long. They had large bodies, long necks and small heads, and long tails.
220,000,000 BC, Late Triassic (Arizona) − This episode follows the evolution of the first dinosaurs and other prehistoric creatures in the late Triassic period.152,000,000 BC, Late Jurassic (Colorado) − This episode follows the story of a young female "Diplodocus" and her brothers and sisters in the late Jurassic period.149,000,000 BC, Late Jurassic (Oxfordshire) − This episode follows the life of several baby "Ophthalmosaurus" and a bull "Liopleurodon" in the late Jurassic period.127,000,000 BC, Early Cretaceous (Brazil) − This episode follows a male "Ornithocheirus" on his long journey to the mating grounds in the early Cretaceous period.106,000,000 BC, Early Cretaceous (Antarctica) − This episode follows the hardships of an Antarctican "Leaellynasaura" clan in the early Cretaceous period.65,500,000 BC, Late Cretaceous (Montana) − This episode follows the final years of the dinosaurs and a mother "Tyrannosaurus rex" and her babies in the late Cretaceous period.49,000,000 BC, Early Eocene (Germany) − This episode follows the life of a mother "Leptictidium" and her babies in the dense forests of Germany in the early Eocene epoch.36,000,000 BC, Late Eocene (Pakistan) − This episode follows the sea journey of a pregnant female "Basilosaurus" search for food in the late Eocene epoch.25,000,000 BC, Late Oligocene (Mongolia) − This episode follows the life of a young "Paraceratherium" and his mother from his birth in the late Oligocene epoch.3,200,000 BC, Late Pliocene (Ethiopia) − This episode follows the hardships of an "Australopithecus" group and a young called Blue in the late Pliocene epoch.1,000,000 BC, Early Pleistocene (Paraguay) − This episode follows a male "Smilodon" called Half-Tooth after he lost his territory in the early Pleistocene epoch.30,000 BC, Late Pleistocene (North Sea, Belgium, and Swiss Alps) − This episode follows a herd of woolly mammoth journey to the Alps in the last Ice Age of the late Pleistocene epoch.This episode details a list of animals from the first season that the developers thought were the most impressive creatures on Earth.
Recent molecular phylogenetic studies suggest that most placental orders diverged late in the Cretaceous period, about 100 to 85 million years ago, but that modern families first appeared later, in the late Eocene and early Miocene epochs of the Cenozoic period. Fossil-based analyses, on the contrary, limit the placentals to the Cenozoic. Many Cretaceous fossil sites contain well-preserved lizards, salamanders, birds, and mammals, but not the modern forms of mammals. It is likely that they simply did not exist, and that the molecular clock runs fast during major evolutionary radiations. On the other hand, there is fossil evidence from of hoofed mammals that may be ancestors of modern ungulates.
Hurum, Zhe-Xi Luo, and Kielan-Jaworowska suggested in 2006 that the spurs on the ankles of Mesozoic mammals (such as "Catopsbaatar") were homologous with those of monotremes, and were a basal (or "primitive") feature lost by later therian mammals. The male platypus uses the spur to deliver venom from a gland, but it is unknown if the extinct groups were venomous as well. Mesozoic mammals were mostly small (with exceptions such as the fox-sized "Repenomamus") and, although they were too small to be prey for large theropod dinosaurs, smaller theropods, large lizards, crocodiles, and birds could have fed on them. For example, mammal jaws have been found in the abdomen of a specimen of the small theropod "Sinosauropteryx"; the jaws belonged to "Zhangheotherium", which also had spurs, and the multituberculate "Sinobaatar". Since dinosaurs dominated Earth during the Mesozoic, this period has been called the "dark ages" of mammalian history. The spur, which would have been more effective if venomous, was probably used as a defensive weapon by small, early mammals. It could also have been used during intraspecific competition or predation.
The pelvic bones of "Catopsbaatar" specimen PM120/107 may not have been fused because fusion occurred late in development, because it was a sexually dimorphic feature only occurring in males (unfused pelvic bones might have enabled expansion of the birth canal in females), or pelvic fusion may be a taxonomic difference between "Catopsbaatar" and other multituberculates. Unlike with other mammals, the pelvis of multituberculates was very narrow; in other genera where the pelvis is known, each half of the pubis and ischium were fused together, forming a keel. The length and rigidity of the keel indicate that the pelvis could not have spread during birth. Because there would be little space for the passage of an egg (egg-laying monotremes have wide ischial archs), Kielan-Jaworowska suggested in 1979 that multituberculates were viviparous (gave live birth) and that the newborns were extremely small—similar to those of marsupials.
This species of wildebeest seems to have evolved around 2.5 million years ago. The black wildebeest is believed to have diverged from the blue wildebeest to become a distinct species around a million years ago, in the mid- to late Pleistocene. Fossil evidence suggests that blue wildebeest were quite common in the Cradle of Humankind in the past. Apart from eastern Africa, fossils are commonly found in Elandsfontein, Cornelia, and Florisbad.
Mosasaurs (from Latin "Mosa" meaning the 'Meuse river', and Greek σαύρος "sauros" meaning 'lizard') are an extinct group of large marine reptiles containing 38 genera in total. Their first fossil remains were discovered in a limestone quarry at Maastricht on the Meuse in 1764. Mosasaurs probably evolved from an extinct group of aquatic lizards known as aigialosaurs in the Early Cretaceous. During the last 20 million years of the Cretaceous period (Turonian-Maastrichtian ages), with the extinction of the ichthyosaurs and pliosaurs, mosasaurs became the dominant marine predators. They became extinct as a result of the K-Pg event at the end of the Cretaceous period, about 66 million years ago.
Hair, structurally similar to that of modern mammals and associated with bones of the Mongolian multituberculate "Lambdopsalis", has been identified in coprolites (fossilised feces) of carnivorous mammals from the Palaeocene Epoch. This indicates that multituberculates had hair for insulation, similar to modern mammals (and possibly fossil mammals), a feature probably related to homeothermy (warm-bloodedness).
A number of partial fossil remains of "Secodontosaurus" have been identified from its characteristic long skull and jaws. The postcranial skeletal material from different individuals includes parts of the backbone with clear evidence of a tall sail very similar to that of "Dimetrodon". The limbs and tail are incomplete but probably resembled those of "Dimetrodon" as well. Like "Dimetrodon", "Secodontosaurus" would have had a short neck, robust body, short limbs, and a long tail. In light of such similarities, some skeletal remains with missing or fragmentary skulls that were previously identified as "Dimetrodon" may in fact belong to "Secodontosaurus". A key noncranial difference can be found in the axis neck vertebra, which has a tall and broad neural spine in "Dimetrodon" but has a lower neural spine in "Secodontosaurus".
Despite the colloquial name "saber-toothed tiger", "Smilodon" is not closely related to the modern tiger (which belongs in the subfamily Pantherinae), or any other extant felid. A 1992 ancient DNA analysis suggested that "Smilodon" should be grouped with modern cats (subfamilies Felinae and Pantherinae). A 2005 study found that "Smilodon" belonged to a separate lineage. A study published in 2006 confirmed this, showing that the Machairodontinae diverged early from the ancestors of modern cats and were not closely related to any living species. The following cladogram based on fossils and DNA analysis shows the placement of "Smilodon" among extinct and extant felids, after Rincón and colleagues, 2011:
"Smilodon" started developing its adult saber-teeth when the animal turned one-and-a-half years of age, shortly after the completion of the eruption of the cat's baby teeth. Both baby and adult canines would be present side by side in the mouth for an 11-month period, and the muscles used in making the powerful bite were developed at about one-and-a-half years old as well, eight months earlier than in a modern lion. After "Smilodon" turned around 20 months of age, the infant teeth were shed while the adult canines grew at an average growth rate of per month during a 12-month period. They reached their full size at around 3 years of age, later than for modern species of big cat. Juvenile and adolescent "Smilodon" specimens are extremely rare at Rancho La Brea, where the study was performed, indicating that they remained hidden or at denning sites during hunts, and depended on parental care while their canines were developing.
Radiocarbon analysis of human remains from the cave returned dates of 2390+/-145 B.P. and 1690+/-115 B.P. These remains were collected from an upper zone approximately 16-feet above the saber-tooth bones. The human remains are believed to be from the Woodland Period and originated thousands of years after the "Smilodon" find. According to Guilday (1977), collagen from the "Smilodon" remains returned radiocarbon dates of 9410+/-155 B.P. and 10,035+/-650 B.P. These dates are extremely late for the presence of "Smilodon" in the Southeast, both contemporaneous with the Dalton horizon and overlapping Paleoindian occupations along the Cumberland River by at least 1,000 years. As such, the dates for the "Smilodon" remains from the First American site should be regarded with some skepticism.
The question of sociality is still controversial. Strong support for the traditional concept of a solitary "Smilodon" is found in its brain. Most social predators, including humans, grey wolves, and lions, have brains that are slightly larger than those of their loner relatives. "Smilodon" had a relatively small brain, suggesting less ability for complex cooperative behaviors, such as hunting in groups. The high numbers of "Smilodon" in the tar pits is often dismissed as evidence for a social nature because the golden eagle, a species still extant, is solitary and yet is found in the pits in similar numbers. The social grey wolf and coyote lived in the region, but their fossils in the pits are rare.