SMILODON :THE SABER-TOOTH CAT

 Smilodon ( /ˈsmaɪlədɒn/), often called a saber-toothed cat or incorrectly a saber-toothed tiger, is an extinct genus of machairodonts. This saber-toothed cat was endemic to North and South America, living during the Pleistocene epoch (2.5 mya—10,000 years ago).

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" + ὀδoύς (odoús), "tooth", or in the genitive: ὀδoύς, ὀδόντος, odóntosThe genus Smilodon was described by the Danish naturalist and palaeontologist Peter Wilhelm Lund in 1841. He found the fossils of Smilodon populator in caves near the small town of Lagoa Santa, in the state of Minas Gerais, Brazil. A number of Smilodon species have been described, but today usually only three are recognized. Genetic evidence suggests the members of the genus diverged from the main lineage of modern cats (subfamily Felinae) around 14-18 million years ago.

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 was the successor of Megantereon in North America, from which it probably evolved. The other Smilodon species probably derived from this species.

Smilodon fatalis, 1.6 million-10,000 years ago, replaced Smilodon gracilis in North America and invaded western South America as part of the Great American Interchange. Matching the largest living cat, the Siberian tiger in size, it ranged from 160 to 280 kg (350 to 620 lb).[7] Sometimes two additional species are recognized, Smilodon californicus and Smilodon floridanus, but usually they are considered to be subspecies of Smilodon fatalis.

Smilodon populator, 1 million-10,000 years ago; occurred in the eastern parts of South America and it was perhaps the largest known felid with a body mass range of 220 to 360 kg (490 to 790 lb) possessing a massive chest and front legs, It was more than 1.40 m (55 in) high at the shoulder, 2.6 m (100 in) long on average and had a 30 cm (12 in) tail. Its upper canines reached 30 cm (12 in) and protruded up to 17 cm (6.7 in) out of the upper jaw.

The species of Smilodon were among the largest felids ever to live; the heaviest specimens of the massively built carnivore S. populator may have exceeded 400 kg (880 lb).

A fully-grown Smilodon weighed approximately 55 to 360 kg (120 to 790 lb), depending on species. It had a short tail, powerful legs, muscular neck and long canines. Smilodon was more robustly built than any modern cat, comparable to a bear. The lumbar region of the back was proportionally short, and the lower limbs were shortened relative to the upper limbs in comparison with modern pantherine cats, suggesting that Smilodon was not built for speed.

The largest species, the South American S. populator, had higher shoulders than hips and a back that sloped downwards, superficially recalling the shape of a hyena, in contrast to the level-backed appearance of S. fatalis, which was more like that of modern cats. However, while its front limbs were relatively long, their proportions were extremely robust and the forearm was shorter relative to the upper arm bone than in modern big cats, and proportionally even shorter than in S. fatalis. This indicates these front limbs were designed for power rather than fast running, and that S. populator would have had immense strength in its forequarters.Smilodon probably preyed on a wide variety of large game including bison, tapirs, deer, American camels, horses and ground sloths. As it is known for the saber-toothed cat Homotherium, Smilodon might have also killed juvenile mastodons and mammoths. Smilodon may also have attacked prehistoric humans, although this is not known for certain. The La Brea tar pits in California trapped hundreds of Smilodon in the tar, possibly as they tried to feed on mammoths already trapped. The Natural History Museum of Los Angeles County has many of their complete skeletons.

Restoration by Charles R. Knight

Modern big cats kill mainly by crushing the windpipe of their victims, which may take a few minutes. Smilodon’s jaw muscles were probably too weak for this and its long canines and fragile skull would have been vulnerable to snapping in a prolonged struggle or when biting a running prey. Research in 2007 concluded that Smilodon most likely 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. The leaders of this study also commented to scientific journalists that this technique may have made Smilodon a more efficient killer of large prey than modern lions or tigers, but also made it more dependent on the supply of large animals. This highly specialized hunting style may have contributed to its extinction, as Smilodon’s cumbersome build and over-sized canines would have made it less efficient at killing smaller, faster prey if the ecosystem changed for any reason.A later study concurred, finding that the forelimbs of Smilodon, more than those of any modern felid, were capable of minimizing the struggles of prey and positioning them for a quick kill with the predator's canines without them fracturing.

Smilodon became extinct at the end of the Pleistocene around 10,000 BC, a time which saw the extinction of many other large herbivorous and carnivorous mammals.

Prehistoric humans, who reached North America at the same time and are known to have hunted many of the species that disappeared, are often viewed as responsible for this extinction wave. Others have suggested that the end of the ice age caused the extinction. As the ice sheets retreated there would have been changing vegetation patterns. Grasslands expanded. The summers became more extreme and parts of North America began to dry out. However, this hypothesis does not explain why Smilodon and its ancestors as well as other megafaunal species successfully survived many previous interglacials, and then fairly suddenly died out over the entire contiguous land area of North and South America.

TORVOSAURUS :THE JURASSIC KING

Torvosaurus is a genus of large theropod dinosaur that lived during the Late Jurassic period (mid-late Kimmeridgian stage in North America, early Tithonian stage in Europe). The nameTorvosaurus means "savage lizard" and is derived from the Latin torvus ("savage") and the Greek σαυρος/sauros ("lizard").

 TORVOSAURS UP
ALLOSAURS DOWN 

Fossilized remains of Torvosaurus have been found in North America and Portugal. Torvosaurus reached 9 to 11 meters (30 to 36 ft) in length and an estimated weight of about 2 metric tons (2.2 tons), which made it the largest carnivore of its time, except for Epanterias (which may have been just a big Allosaurus) andSaurophaganax.

It was first discovered by James A. Jensen and Kenneth Stadtman in the rocks of the Morrison Formation at the Dry Mesa Quarry, Colorado in 1972. The genus and the type species T. tanneri were named and described in 1979 by Peter M. Galton and Jensen. The type specimen from Colorado was further described by Brooks Britt, and the Portuguese specimen by O. Mateus and M.T. Antunes.The size of Torvosaurus is not definitely known because only incomplete material has been found, but it was a large theropod. North American Torvosaurus material is estimated as belonging to an individual about 9.0 meters long (29 ft), with a weight of about 1.95 metric tons (2.15 tons).Material from Portugal indicates even larger animals. In 2006 a nearly complete maxilla found in Portugal was assigned to Torvosaurus tanneri. It measured 63 cm in length (2.13 ft), significantly larger than the 47 cm (1.54 ft) long maxilla of the American specimen (total skull length 118 cm [3.87 ft]). Based on this, a skull length of 158 cm (5.18 ft) was estimated for the Portuguese specimen. This is comparable to the largest T. rex skulls, and makes Torvosaurus the largest known Jurassic theropod (surpassing Saurophaganax/Allosaurus maximus and Edmarka), and among the largest of all theropods. A partial femur from another individual belongs to an animal estimated as 11 m (36 ft) long.Torvosaurus is related to the earlier Megalosaurus but is seemingly more advanced. Its classification is still uncertain but its family Megalosauridae is most commonly held as a basal branch of Tetanurae, less derived than carnosaurs or coelurosaurs, and likely related to the spinosaurids.

KELENKEN :THE TERROR BIRD

Kelenken is an extinct genus of giant flightless predatory birds of the family Phorusrhacidae or "terror birds".

These birds lived in the Middle Miocene, some 15 million years ago, in Argentina along with Argentavis. With a skull 28 inches (71 cm) long (including its 18 inch, 45.7 cm beak), it had the largest head of any known bird. The tarsometatarsus was about 45 cm long .Kelenken was one of the largest carnivorous birds of all time, possibly reaching 2.28 to 3 meters (7.5 to 10 feet) tall and weighing around 500 pounds (230 kg).It is not entirely clear how Kelenken captured and killed its prey. As a large flightless carnivore, Kelenken likely chased down and killed its prey with several bone-shattering blows from its massive beak. Another possibility is that it may have picked up its prey item, then proceeded to shake it vigorously in order break its back. It is also possible that Kelenken may have been a scavenger, driving off other animals with its impressive size, and ferocious looks.

DUNKLEOSTEUS

Dunkleosteus (From "(David) Dunkle" + osteus (οστεος, Greek: bone)) is a genus of prehistoric fish, one of the largest arthrodire placoderms ever to have lived, existing during the Late Devonian period, about 380-360 million years ago.This hunter, measuring up to 10 metres (33 ft) and weighing 3.6 tonnes (4.0 short tons), was a hypercarnivorous apex predator. Few other placoderms, save, perhaps, its contemporary, Titanichthys, rivaled Dunkleosteus in size.Dunkleosteus is a member of the pachyosteomorph arthrodires, and is more specifically usually placed in the family Dinichthyidae, a family composed mostly of large, carnivorous arthrodires like Gorgonichthys. Anderson (2009) suggests that because of its primitive jaw structure Dunkleosteus should be placed outside the family Dinichthyidae, perhaps close to the base of the clade Pachyosteomorpha, near Eastmanosteus, but this idea has yet to be tested.New studies have revealed several features in both its food and biomechanics as its ecology and physiology. Placodermi first appeared in the Silurian, and the group became extinct during the transition from the Devonian to the Carboniferous, leaving no descendants. The class lasted barely 50 million years, in comparison to the 400 million year long history of sharks.

In recent decades, Dunkleosteus has achieved recognition in popular culture, with a large number of specimens on display, and notable appearances in entertainment media. Numerous fossils of some species have been found in North America,Poland, Belgium and Morocco.Due to its heavily armoured nature, Dunkleosteus was likely a relatively slow, but powerful, swimmer. It is thought to have dwelled in diverse zones of inshore waters. Fossilization tends to have preserved only the especially armoured frontal sections of specimens, and thus it is uncertain what exactly the hind sections of this ancient fish were like. As such, the reconstructions of the hindquarters are often based on smaller arthrodires, such as Coccosteus, that had hind sections preserved.

The most famous specimens of Dunkleosteus are displayed at the Cleveland Museum of Natural History. Others are displayed at the American Museum of Natural History and in the Queensland Museum in Brisbane, Queensland.Instead of teeth, Dunkleosteus possessed two pairs of sharp bony plates which formed a beak-like structure. After studying a biomechanical model of the fish's jaws, scientists at the Field Museum of Natural History and the University of Chicago concluded that Dunkleosteus had the second most powerful bite of any fish (the giant Megalodon being the strongest). Dunkleosteus could concentrate a pressure of up to 8,000 pounds per square inch (55 MPa) at the tip of its mouth, placing Dunkleosteus in the same league as Tyrannosaurus rex and modern crocodiles as having the most powerful known bite.Dunkleosteus could open its mouth in one-fiftieth of a second, which would have caused a powerful suction that pulled the prey into its mouth,a food-capture technique used by many fish today.

ORNITHOCHEIRUS: THE T-REX OF THE SKIES

Ornithocheirus (from Greek "ορνις", meaning bird, and "χειρ", meaning hand) was a pterosaur from the Cretaceous period of Europe and South America. Based on poor fossil material, the genus has caused enduring problems of zoological nomenclature.

Fossil remains currently classified as Ornithocheirus have been recovered mainly from the Cambridge Greensand of England, dating to the beginning of the Albian stage of the late Cretaceous period, about 110 million years ago.Additional fossils from the Santana Formationof Brazil, dating to 112-108 million years ago, have been classified as species of Ornithocheirus.The original material of Ornithocheirus simus, recovered from England, indicates a mid-sized species with a wing span of 2.5 m (8 ft). Referred specimens attributed to Ornithocheirus simus(alternately called Criorhynchus simus) can reach 5 m (16 ft). Tropeognathus mesembrinus is also usually considered a part of the Ornithocheirus genus as O. mesembrinus, and reached over 6 m (20 ft) in wingspan.Both O. simus and O. mesembrinus bore distinctive convex "keeled" crests on their snouts.The upper crests arose from the snout tip and extended back to the nostril. An additional, smaller crest projected down from the lower jaw at the symphysis ("chin" area). While many ornithocheirids had a small, rounded bony crest projecting from the back of the skull, this was particularly large and well-developed in Ornithocheirus.Unlike the related Anhanguera and Coloborhynchus, which had an expanded rosette of teeth at the jaw tips, Ornithocheirus had straight jaws that narrowed toward the tip. Also unlike related pterosaurs, the teeth of Ornithocheirus were mostly vertical, rather than set at an outward-pointing angle. They also had fewer teeth than related species.The type specimen of Ornithocheirus simus is represented only by a broken piece of the upper jaw tip. While it does preserve several characteristic features of Ornithocheirus, it is nearly identical to comparable bones in o. mesembrinus, making clear distinction between these two species impossible.During the 19th century, in England many fragmentary pterosaur fossils were found in the Cambridge Greensand, a layer from the early Cretaceous, that had originated as a sandy seabed. Decomposing pterosaur cadavers, floating on the sea surface, had gradually lost individual bones that sank to the bottom of the sea. Water currents then moved the bones around, eroding and polishing them, until they were at last covered by more sand and fossilised. Even the largest of these remains were damaged and difficult to interpret. They had been assigned to the genus Pterodactylus, as was common for any pterosaur species described in the early and middle 19th century.