Dinosaur Size
Dinosaurs are divided into two large groups according to the arrangement of the pelvic structure those with reptile-like pelvis (order Saurischia) and those with birdlike pelvis (order Ornithischia). Further divisions are based on feeding habits, two or four-footed posture, and the presence of armor in the body.
The Stegosaurus was ornithischian, of the group Stegosauria (having body armor). It was over 20 feet long and had distinctive large bony plates arranged along the backbone. The skull was small; this large creature had a brain of 2 1/2 ounces, about the size of a walnut. An enlargement of the spinal cord in the hip region controlled the large hind limbs and a tail that contained four sharp spikes. Stegosaurus’ tail was the animal's chief means of protection.
Apatosaurus is one of the largest land animals ever known on the earth with a length of about 70 feet. Other similar dinosaurs include Brachiosaurus which measures up to 80 feet in length and Diplodocus which measures over 80 feet long. These dinosaurs weighed anywhere from 35 to 50 tons. They would have required consuming large amounts of vegetation to sustain such massive bodies. In some dinosaurs, the nostrils were positioned on top of their heads, this would have allowed the dinosaur to stay almost completely submerged in water; they were quadrupeds.
Allosaurus was a carnivorous bi-pedal dinosaur that grew over 30 feet in length. Allosaurus had a large head and jaws with serrated teeth. These anatomical features would have enabled the dinosaur to attack dinosaurs which were larger than it. Allosaurus was a Saurischian dinosaur, a group of theropods, which walked on their three-toed hind legs like modern birds.
Ornitholestes is a rather small, bi-pedal dinosaur, although flourishing in the upper Jurassic and Cretaceous period, strongly resembles the ancestors of dinosaurs, prehistoric reptiles of the order Thecodontia, which lived millions of years before in the early Triassic Period. Like the thecodonts, Ornitholestes could run swiftly on its two hind legs. It was about 6 feet long and probably weighed little more than a turkey. It had sharp, pointed teeth and preyed on small animals; It also ate insects and eggs of dinosaurs.
Tyrannosaurus is often called the "King of the dinosaurs". With its knife knife-like teeth, huge jaws, length of 50 feet, and 6 to 8 ton weight, it did not disdain to attack even the largest sauropods such as the Apatosaurus and Brachiosaurus. Tyrannosaur also belongs to the Saurischia group. It stood on two powerful legs and was able to maintain its balance with aid from its muscular tail. Tyrannosaurus forelimbs were quite small.
Struthiomimus whose name means "ostrich-imitator," bore a visual resemblance to the large bird we know today. Ornithomimus was a Saurischian dinosaur with very long hind legs, a long neck and bird-like feet. These ostrich-dinosaurs did not have teeth but had beaks for eating fruits, insects, and small animals.
Trachodon is classified in the order Ornithischia. It has a duck-bill jaw structure and also one of the later members of the ornithopods. It alternately walked on all fours and was able to stand on its hind legs for short periods of time. Duck-bills lived in and around water, they were herbivores.
Triceratops is an Ornithischian dinosaur and was the most distinctive member of the group Ceratopsia "horned-dinosaurs." Triceratops skull included three large horns and a bony frill above the neck which grew to about 6 1/2 feet in length. Adult triceratops would grow up to 20 feet in length. It was among the last dinosaurs to live in the late Cretaceous Period. Although a herbivore, its obvious defensive anatomical features enabled it to survive in this period.
Ankylosaurus belongs to the group Ankylosauria "armored dinosaurs". Ankylosaurus was covered heavily with body armor, such as bony plates and spines. Ankylosaurus grew up to 33 feet when an adult, and would have been a tough opponent to the well known Tyrannosaurus.