Apatosaurus had a small head, a long slender neck, and a long tail that was almost one and one-half times longer than the rest of the body. Scientists believe that its tail was its main defense against attack by flesh-eating dinosaurs. Apatosaurus's barrel-like body was supported by thick, heavy legs. The forelimbs were shorter than the hind limbs, and the animal's long spine counterbalanced the front part of its body against its heavy, muscular tail. The vertebrae also lengthened its neck, which was 6 m (20 ft) long. Apatosaurus had an elongated skull with short, pointed teeth. The nostrils were located high on its head, directly above and in front of the eyes. Apatosaurus skeletons are usually found headless, however, because the skull and neck connections were fragile. When Marsh discovered the first Apatosaurus fossils, he mistakenly paired them with the skull of the Camarasaurus, a smaller relative. Consequently, Apatosaurus was depicted as having Camarasaurus's flat-nosed head and peglike teeth until the late 1970s, when scientists corrected the error.
In North America, Apatosaurus inhabited vast, low plains dotted with lakes and crossed by tree-lined streams. The climate was semiarid, broken by a rainy season. The young dinosaurs grew rapidly, reaching maturity within about ten years. The enormous bulk of the adult animals suggests that they grazed in an environment with abundant vegetation. Long necks and powerful thumb claws (which allowed the dinosaurs to stand firmly in place) indicate that the animals could span a wide arc, reaping a broad swath of vegetation without walking much. These features also suggest that Apatosaurus grazed primarily on low plants, such as ferns. Apatosaurus's size gave it other advantages. Adults may have had a low metabolism because they were so large. If so, they could maintain a constant body temperature, subsist on low-quality food, and better survive droughts and famines. Evidence also indicates that they tended to avoid Diplodocus but may have associated occasionally with Stegosaurus. Fossil evidence indicates that the natural life span of Apatosaurus averaged about 100 years.
Ankylosaurae, family of plant-eating dinosaurs found worldwide during the later Cretaceous period, which ended about 65 million years ago. The heavily armored ankylosaurs were medium-sized ornithischian (bird-hipped) dinosaurs that ranged from 4.5 to 10 m (15 to 33 ft) long. They moved on all fours, and their broad, low bodies were covered with rows of bony plates, which ended in a clublike tail. Some species had spines on the head, along the back, or on the tail. They were related to the stegosaurs, another type of armored dinosaur that lived earlier. The slow-moving ankylosaurs probably resembled armadillos, and their fossils usually occur in regions that were once swampy.
Brachiosaurus, genus of large dinosaurs, of the suborder Sauropoda, that flourished during the Late Jurassic period. Its forelegs were slightly longer than its hind legs. Brachiosaurus was about 24 m (about 80 ft) long, weighed about 80 metric tons, and was about 12.6 m (43 ft) tall at the head. Fossil remains of the animal have been found in the western United States as well as in eastern Africa. Brachiosaurus, according to recent research, was a land dweller that probably fed on tall foliage.
Camptosaurus, genus of plant-eating, beaked dinosaurs of the Late Jurassic period, about 140 million years ago. The largest adult camptosauruses were more than 7 m (23 ft) long. They had heavy bodies but could rear up and walk on two legs as well as four. The genus is probably linked to the later iguanodon and hadrosaur dinosaurs.
Corythosaurus, dinosaur genus of the Late Cretaceous period, about 90 million years ago. The name, from a Greek word for helmet, refers to the hollow crest on the heads of these herbivorous duckbills, or hadrosaurs, which walked bipedally and could be more than 9.5 m (30 ft) long. The animals had hundreds of small teeth. The crest may have been for sexual or aggressive display, or perhaps was a resonating chamber through which sounds were amplified.
Diplodocus, genus of dinosaurs of the suborder Sauropoda. One of the largest of the dinosaurs, it lived during the Jurassic period, inhabiting the western part of what is now the United States. Fossil specimens indicate that the reptile attained lengths of up to 26.5 m (87 ft). It was relatively slender, however, and somewhat less bulky than the related Apatosaurus. Diplodocus was a quadruped with a long neck, a low body, and a long tail. A vegetarian, it had a small head with slender teeth and probably grazed in marshes and shallow water.
Hadrosaurus, genus of dinosaur in the suborder Ornithopoda. Their fossilized remains are in Cretaceous rocks of New Jersey and Wyoming. These large dinosaurs, which reached about 11 m (about 35 ft) in length, were characterized by a flattened bill, resembling that of a duck, with which they grasped the marsh grass and other vegetation that constituted their food. The bill, unlike that of a duck, contained many small teeth. Their hides were thick but not covered by armor. Their heads were large, and their tails were thick and heavy. The hadrosaurs moved about swampy pools on their thick, three-toed hind limbs. Many hadrosaurs had elaborate bony crests on their skulls.
Iguanodon, genus of large, herbivorous dinosaurs, of the suborder Ornithopoda, that lived worldwide during the Early Cretaceous period. Iguanodon weighed as much as 4.5 metric tons, attained a length of 7.5 m (25 ft), and stood up to 4.5 m (15 ft) tall on stout hind legs. The three toes of the feet and four of the five digits of the shorter forelimbs were equipped with flat, hooflike claws; the hand's first digit, a bony, spike-shaped thumb situated at a right angle to the other fingers, may have been used for defense. Iguanodon's long, flat head ended in a horny beak, and its jaws contained teeth that somewhat resemble those of the iguana lizard - hence, the name. These animals may have browsed in packs and probably assumed a four-legged stance while eating.
Maiasaura means "good mother." Dr. Jack Horner gave it this name because he saw evidence that it took good care of its babies — feeding them chewed up plants while they were newly hatched babies — too weak to leave the nest. Maisaura is just one of two dinosaurs with a female name. The other is Laellynasaura named for a little girl, Laellyn Rich, who asked her parents to find her a dinosaur. Since they are dinosaur scientists, they did!
Plateosaurus (Greek for "flat lizard"), large, plant-eating, early dinosaur that lived in central Europe in the late Triassic Period (about 231 million to 213 million years before present). A member of the suborder Sauropodamorpha, Plateosaurus fossils are the most common examples of the oldest group of plant-eating dinosaurs, the prosauropods. Plateosaurus had a long, thin neck similar to the necks of later, giant, plant-eating sauropods such as Apatosaurus, but it was not as large as its later cousins. Plateosaurus was, however, the largest dinosaur of its time, growing to a length of 10 m (30 ft). This animal was the first high browser, using its long tail to balance itself as it reared up on its hind legs to graze on vegetation that other herbivores (plant-eaters) could not reach. Fossil footprints left on paths used by prosauropods show that some prosauropods walked on two legs and some walked on four legs, but paleontologists do not know which method of locomotion Plateosaurus preferred. Its hand had a large claw on the thumb that may have been used to pull down high branches and to defend itself against attackers. The long, horselike skull had a jaw lined with a row of small, narrow, serrated, leaf-shaped teeth designed for stripping the vegetation from tree branches. Plateosaurus had no chewing teeth, so it used stones (gastroliths) in its gizzard to grind up its food before it reached the stomach.
Protoceratops (Greek for "first horned-face"), small, plant-eating dinosaur living in Mongolia in the late Cretaceous Period (about 97 million to 65 million years before present). A member of the suborder Ceratopsia, Protoceratops grew to a length of about 1.8 m (6 ft) and was fully quadrupedal (walked on four legs). It had a short tail and a small bony neck frill at the back of its skull where its strong jaw muscles attached. Windowlike holes in the frill made the skull light so that the animal could make fast, defensive movements. Protoceratops held its head low for grazing, using its parrotlike beak to snip off low foliage. It had no horns - in their place were bony bumps above the eyes and nose. Its body was more delicate than later ceratopsians, such as Triceratops, but sturdier than the earlier Cretaceous ceratopsian Psittacosaurus.
The first Protoceratops fossils were discovered during the 1920s expeditions led by American paleontologist Roy Chapman Andrews to the red sandstones of Bayn-Dzak ("Flaming Cliffs") in the Gobi Desert of Mongolia. Many complete skeletons were found, including young Protoceratops and the very first nests of dinosaur eggs - which scientists assumed belonged to Protoceratops. Another trip to the Gobi Desert in 1971 revealed a Protoceratops fossil with its beak closed firmly around the forearm of a Velociraptor fossil, whose hind claw was embedded in the ceratopsian's belly. They had died from their battle wounds and had been preserved for over 70 million years. New finds in the 1990s indicate that some nests thought to contain Protoceratops eggs belonged to the small meat-eating dinosaur Oviraptor instead.
Psittacosaurus (Greek for "parrot lizard"), plant-eating dinosaur that lived in northeastern Asia and possibly Germany in the early Cretaceous Period (about 144 million to 97 million years before present). Psittacosaurus was a relatively small, agile animal, growing to a length of only about 1.5 m (4.5 ft). It had four fingers on its powerful hands. Its long hind limbs and short forelimbs show that it spent far more time on two legs than later members of its suborder (Ceratopsia), but the strength of the forelimbs indicates that this dinosaur probably sometimes moved on all four legs.
True to its name, Psittacosaurus had a strong parrotlike beak. The little bone that formed the core of its upper beak links Psittacosaurus with the ceratopians (Greek for "horned lizard"). Psittacosaurus was the most primitive of dinosaurs of this suborder, with only small cheek horns and hardly any of the neck frill of later ceratopians such as Protoceratops and Triceratops. The large jaw muscles of Psittacosaurus ran along the side of the head into spaces at the back of the skull like those of later ceratopians, but Psittacosaurus lacked the grinding cheek teeth of those later dinosaurs. To compensate for the inability to grind food in its mouth, the animal swallowed small pebbles (gastroliths) to grind up its food in its gizzard.
Sauroposeidon fossils were found in 1994 and have turned out to be one of the biggest dinosaurs that ever walked the earth. The neck bones of a giant sauropod that would have been tall enough to look into a sixth-story window. The paleontologists named the new dinosaur species Sauroposeidon, after the Greek god of the sea and earthquakes, Poseidon. A larger relative of Brachiosaurus, Sauroposeidon stood 18 m (60 ft) tall and weighed about 55 metric tons.
As with the Brachiosaurus, the giant dinosaur had a long neck that enabled it to feed off the high branches of trees, where few other dinosaurs could reach. The neck of Sauroposeidon was about 12 m (40 ft) long. The paleontologists found that the bones were riddled with air pockets, which lightened the bones and made moving the dinosaur's great bulk easier.
Sauroposeidon lived about 110 million years ago, during the Cretaceous Period. At that time, the location where the bones were found was on the edge of a great sea that today is the Gulf of Mexico. The scientists said that the dinosaur was probably common throughout what is now the Southern United States.
Stegosaurus, genus of plant-eating ornithischian (bird-hipped) dinosaurs known for the large triangular plates along the crest of the back. Stegosaurus's armor accounts for its name, which is derived from the Greek words stego, "cover," and sauros, "lizard." These plates, as well as a number of spikes on the tail, render Stegosaurus one of the most recognizable of all dinosaurs. It lived on low plains in the interior of North America, Europe, Africa, and Asia during the late Jurassic Period, about 150 million years ago.
The plates along Stegosaurus's spine served both as protection and as a means of regulating body heat. A few well-preserved skeletons demonstrate that the plates were arranged in an alternating row along the crest of the back. Scientists believe that the primary function of the plates was to absorb and give off heat. Fossil evidence indicating that the plates had a rich supply of blood vessels supports this theory. Tests of models in wind tunnels have shown that the plates also could have aided in the removal of body heat by channeling wind currents across the plates' surfaces. This process may have regulated the animal's body temperature. The number and size of the plates suggest that Stegosaurus either lived in hot, tropical environments (similar to present-day India) or often had to shed large quantities of heat generated by the fermentation of food in its digestive system. While the animal had a low metabolic rate, it nevertheless appears to have given off high levels of body heat. Various large animals in existence today, including elephants, have slow digestive systems and give off large amounts of body heat.
Pairs of spikes projected sideways from the tail. They were obviously used for defense. As a further defense, an "apron" of small bones embedded in the skin protected the throat.
Stegosaurus had a beak and small, weak teeth. These features indicate that it chewed poorly. Its small teeth could not aid in digestion, so the animal ate soft food that fermented slowly within its massive body.
Stegosaurus was about 4.5 m (15 ft) long and weighed from 3.5 metric tons to 6.5 metric tons. Its head was extremely small in proportion to its body size. The tiny size of its jaws relative to its large body implies a low feeding rate. Minimal food requirements and the ability to store fat enabled the animal to survive lean, dry seasons, when it may have presented an attractive source of nourishment to meat-eating dinosaurs.
Stegosaurus resembled a giant porcupine, with a high back and nimble forelimbs with which it could maneuver to strike its tail spikes into oncoming attackers. This rugged animal was adapted to living on food of poor quality that may have been available only seasonally and in harsh environments. Stegosaurus lived in close association with the sauropods, such as Apatosaurus and Diplodocus, of the late Jurassic Period.
Triceratops, genus of four-legged, plant-eating dinosaurs that lived during the Cretaceous Period, more than 65 million years ago. Triceratops had three horns on its skull — one on its snout and one above each eye. The name is derived from the Greek words treis, "three"; kerat, "horn"; and ops, "face." Triceratops was one of the largest horned dinosaurs. Triceratops belonged to a diverse group of ornithischian ("bird-hipped") dinosaurs called ceratopsians ("horn-face").
An adult Triceratops was approximately 8 m (26 ft) long and weighed up to 12 metric tons. Skulls of adults were 2.5 m (8 ft) long and ended in a narrow, birdlike beak. Within the beak, its teeth were compressed into rows that resembled large shears. The animal could open its jaws sideways to gather foliage by rotating the joint between its head and neck. Once the food was gathered, the animal then rotated its head back and chopped up the food between its powerful jaws.
The horn on top of the nose was short and thick. The two horns over the eyes were sharp, and they could grow up to 3 feet (0.9 meter) long.
The underside of the neck frill contained a dense network of blood vessels. Fossil evidence indicates that heat was radiated from the frill through these blood vessels, in much the same way elephants transport blood to their ears to radiate heat. Unlike the frill of most horned dinosaurs, the frill of Triceratops was a solid sheet of bone, with no openings to lighten it.
Thick, strong legs supported the dinosaur's heavy body. Triceratops had a short, heavy tail, which it may have held straight out or dragged on the ground. Some scientists believe that Triceratops could gallop like a rhinoceros.
The animal's large size suggests that Triceratops inhabited an environment with an abundant food supply. Partly healed puncture wounds in their skulls indicate that they fought one another like modern horned mammals, such as male goats and deer. However, some paleontologists believe that Triceratops' horns may have played a role in species recognition between males and females and in other aspects of social behavior, particularly in group dominance and mating.
PlantEaters