Dinosauria: Meat Eaters

[T-Rex]

Albertosaurus, formerly known as Gorgosaurus, genus of carnivorous dinosaur that lived in Alberta and Montana in the Late Cretaceous period from about 100 million years ago to the time of the extinction of the dinosaurs, about 65 million years ago. Not quite as large as the related Tyrannosaurus, the bipedal Albertosaurus had a similar appearance and weighed up to about 3 tons.

Allosaurus, genus of large, carnivorous dinosaurs of the suborder Theropoda, that flourished approximately 150 million years ago during the Late Jurassic period. These saurischian (lizard-hipped) dinosaurs reached 12 m (40 ft) in length, stood more than 4.5 m (15 ft) tall, and weighed up to 3.6 metric tons.
Allosaurus was an obligatory biped; it walked on stout hindlegs with large birdlike feet (with three toes pointing forward and a small inner toe pointing backward), while using its heavy tail for balance. The digits of the feet and the hands of the shorter forelimbs were equipped with sharp, grasping claws. The jaws of its huge head (1 m/3 ft long) were filled with about 70 long, serrated teeth that enabled Allosaurus to bolt enormous chunks of flesh. Holes in the skull lightened the weight of the dinosaur's large head. It had a bony crest above each eye.

Fossil remains of Allosaurus have been found in Wyoming and Colorado.

Carcharodontosaurus, or "shark-toothed reptile," was found in Africa. At five feet four inches long, the skull of this theropod was a bit longer than the largest known skull of Tyrannosaurus rex.

Coelophysis (Greek for "hollow bone"), small, meat-eating, early dinosaur that lived in the eastern and southwestern United States in the late Triassic Period (about 231 million to 213 million years before present). A member of the suborder Theropoda, Coelophysis was a slender, graceful, fast predator with long jaws filled with curved daggerlike teeth. It grew to a length of up to 3 m (10 ft) and probably ran on two or four legs. It inhabited highland forest areas.

In December 1880 American dinosaur-fossil-hunter David Baldwin discovered a few fragmented bones in a dried-up river bed near Ghost Ranch, New Mexico. In 1947 and again in 1980 the site was reopened and many complete skeletons were found. Paleontologists estimate that several thousand dinosaur fossils have yet to be excavated from this site.

It is unusual to find so many meat-eating dinosaur fossils together. Unlike plant-eaters, which tend to live and travel in herds, most meat-eaters are solitary or travel in small packs. Coelophysis probably died from drowning in a flash flood or from becoming stuck in a mudtrap. Young Coelophysis remains found in the ribcages of two adult Coelophysis were once thought to be evidence of live birth rather than egg laying. But the advanced stage of development of the skeletons indicates that the young Coelophysis were probably eaten by the adults. Cannibalism is also known to occur in living meat-eaters, especially when food is scarce.

Compsognathus, genus of tiny, carnivorous, birdlike dinosaurs that lived during the Late Jurassic period. Compsognathus was about 60 cm (2 ft) long and weighed a little more than 3 kg (6.5 lb). It had remarkably birdlike legs and feet; the shorter forelimbs ended in delicate hands with two grasping digits and one smaller digit. The jaws of its small pointed head contained many sharp teeth. The bipedal Compsognathus used its long, slender tail for balance as it ran after prey, which probably included insects and small lizards and mammals. Two specimens of Compsognathus have been found, one in 1861 in the same sequence of limestone layers in southern Germany that contained Archaeopteryx, and one in the south of France in 1978.

Deinonychus (Greek deinos, "terrible"; onychos, "claw"), genus of small, bipedal, flesh-eating dinosaurs, of the suborder Theropoda, that lived during the Early Cretaceous period, which began about 136 million years ago. Fully grown, this fierce theropod stood as high as 1.5 m (5 ft), measured 2.75 m (9 ft) in length, and weighed up to 80 kg (175 lb). Deinonychus was a strong runner and carried its body horizontally on long, robust hind legs with its tail rigidly stretched out behind for balance as it attacked its prey. The jaws of its relatively large head were equipped with large, serrated teeth. Three toes of the hindlimbs were armed with long, recurved claws, one of which earned the animal its name: the second toe bore a 13 cm (5 in) sickle-shaped, retractable claw that must have been a formidable offensive weapon. Deinonychus is known from fossil remains found in Montana.

Eoraptor, dog-sized dinosaur that lived during the late Triassic Period, about 228 million years ago. Scientists believe Eoraptor may resemble the common ancestor of all dinosaurs. An Eoraptor ran upright on its hind legs, which were more than twice as long as its arms. Its skull and skeleton about 1 m (3 ft) long were discovered in northwestern Argentina in 1992. Eoraptor had sharp teeth in the back of its jaw (not all of its teeth were curved and serrated). At the front of the jaw, its teeth were leaf-shaped like those of some plant-eating dinosaurs. It had three-toed feet. Its hands had five fingers, but it only used the three longest fingers on each hand to handle prey. These three fingers ended in large claws. The fourth and fifth fingers were probably too small to be of use.
Eoraptor bones were first found in 1991.

Giganotosaurus (Greek for "giant southern lizard"), very large meat-eating dinosaur that lived in South America in the late Cretaceous Period (about 97 million to 65 million years before present). A member of the suborder Theropoda, Giganotosaurus is known only from fragmentary fossil remains. Paleontologists believe that Giganotosaurus may be the largest meat-eating, or carnivorous, dinosaur that ever existed. The femur (thighbone) of Giganotosaurus fossils was longer than the femur of any Tyrannosaurus (previously the largest known meat-eating dinosaur) fossil, but some paleontologists believe the legs of Tyrannosaurus and Giganotosaurus were about the same length. Weighing somewhere between 6 and 8 tons and growing to a length of over 13 m (43 ft), Giganotosaurus appears to have been more heavily built than the largest tyrannosaur. Even though Giganotosaurus ran on two legs like Tyrannosaurus, and both were gigantic meat-eaters, Giganotosaurus lived nearly 30 million years before Tyrannosaurus walked on the earth, and the two dinosaurs do not appear to be closely related.

The first Giganotosaurus bones were found in 1995 by an amateur Argentine fossil hunter, Ruben Carolini, after whom the fossil species Giganotosaurus carolinii is named. The remains include parts of the 1.5-m (5-ft)-long skull and jaws, as well as the hips and parts of the backbone. The form of the hip suggests that it was more closely related to Allosaurus than to Tyrannosaurus.

Ornitholestes (Greek for "bird robber"), small, meat-eating, birdlike dinosaur of the suborder Theropoda that lived in North America in the late Jurassic Period (about 163 million to 144 million years before present). Everything that is known about Ornitholestes comes from only one fossil specimen, Ornitholestes hermanii, found in the Bone Cabin Quarry of Wyoming in 1903. Weighing around 15 kg (30 lb) and having a length of about 2 m (6.7 ft), Ornitholestes was balanced at the hips by a long, whiplike tail, which allowed it to lean forward. Its long hands had a short first finger next to two long fingers. This anatomy has led some paleontologists to speculate that the first finger worked like the human opposable thumb, allowing the dinosaur to grasp objects tightly in its sharply clawed hands.
The teeth of Ornitholestes were large and serrated like those of other meat-eating dinosaurs. It probably preyed on small plant-eating dinosaurs and mammals. Ornitholestes had a heavily built skull that contained large eyes above short jaws and robust teeth. Although the skull is sometimes reconstructed as having a small horn on the end of the snout, many paleontologists believe this is probably a distortion produced by crushing of the skull during fossilization, rather than an original feature.

Oviraptor (Latin for "egg thief") was a small, probably meat-eating, dinosaur that resembled an ostrich and lived in southern Mongolia in the late Cretaceous Period (about 97 million to 65 million years ago). A member of the suborder Theropoda, Oviraptor grew to a length of up to 2.7 m (9 ft). It walked upright, balancing itself with its heavy tail, and had long, powerful forelimbs.
This dinosaur had a short head and a strong, curved, toothless beak. Bony prongs inside its mouth appear similar to the throat tooth of egg-eating snakes and may have been used to pierce eggs held in the beak. Oviraptor probably lived near lakes where it may have fed on freshwater mussels, crushing the shells with its powerful beak. This dinosaur had a hornlike crest on its nose that some paleontologists think may have been used to part branches as it moved quickly through shrubs, much as the cassowary bird uses its crest today.
The first Oviraptor fossil was discovered in 1923. Oviraptor was so named because this first specimen was found near a nest of eggs that was assumed to belong to Protoceratops, a small -about 1.8 m (6 ft) long- dinosaur with a bony frill around its face. The Oviraptor, paleontologists assumed, had died in the act of stealing eggs from the Protoceratops's nest. In the early 1990s, however, a type of egg previously identified as belonging to Protoceratops was found to contain an Oviraptor embryo. In 1995 a fossil of Oviraptor was found still sitting on its eggs in a classic brooding position..

Struthiomimus (Greek strouthion,"ostrich"; mimos,"mimic"), genus of swift, ostrich-size dinosaurs of the suborder Theropoda, that lived about 75 million years ago during the Late Cretaceous period. Like an ostrich, Struthiomimus had a small head with a beak and large eyes, a long neck, a short body, long and slender yet powerful legs, and birdlike feet. It stood 2 m (7 ft) tall, its long tail gave it an overall length of 3.5 m (12 feet), and its weight was probably about 200 kg (about 440 lb). The front limbs, long for a biped, had three grasping claws. This toothless theropod may have subsisted mainly on the eggs of other dinosaurs.

Troodon nested in colonies, guarded its clutches and baby-sat its young, even hauling food back to feed the babies.

Tyrannosaurus was a large, two-legged, meat-eating dinosaur of the family Tyrannosauridae, in the suborder Theropoda (beast-footed). It lived in the late Cretaceous Period, about 65 million years ago. The name Tyrannosaurus is derived from the Greek words tyrannos, "tyrant," and sauros, "lizard."
Tyrannosaurus rex wasn't called Tyrannosaurus rex by other dinosaurs. But it was the first name given that animal. It was also, mistakenly called dynamosaurus, but we stick with the 1905 name "Tyrannosaurus rex."
Tyrannosaurus reached 12.5 m (41 ft) in length and weighed over 5 metric tons. The skull of Tyrannosaurus was large and flexible and grew as long as 41/2 feet (135 centimeters), and contained a brain comparable in size to those of modern reptiles. The bridge of the nose contained wartlike knobs and pits. The animal had a broad field of vision but could focus its eyes directly to the front.
Tyrannosaurus had short arms with few nerves running through them. This insufficient development of nerves suggests that the arm movements must have been unwieldy and clumsy. Its barrel-shaped chest indicates that the lungs were very large. The legs were long and slender, and the animal was obviously very swift despite its enormous weight. A latticework of bones protected its stomach and other internal organs.
Tyrannosaurus probably preferred open terrain, such as broad game trails and open forests, where it could move its large body and see unimpeded by brush. It had great speed and agility for its size - the length of its legs suggests that it could reach 35 km/h (22 mph) when charging. It also could lie in ambush upon a strong extension of its pelvis, its chin on the ground, watching for prey with its high-placed eyes. The uniform temperature of its body suggests that Tyrannosaurus had a metabolic rate higher than that of other reptiles. Therefore, it would have had to eat more often. Its stomach could hold more than half a metric ton of flesh, which it would consume every few weeks. Scientists have found a 2-liter (2.1-qt) lump of fossilized dung that contains direct evidence of its prey: partly digested bone fragments of young plant-eating dinosaurs. Further evidence of its diet includes a Triceratops pelvis that exhibits deep punctures and grooves made by Tyrannosaurus teeth. Like most active carnivores, Tyrannosaurus probably also fed on the decaying bodies of dinosaurs killed by starvation and floods. Tooth marks on some Tyrannosaurus skulls indicate that the animals fought with one another by biting on the face.