Labels:text | font | black and white | screenshot | paper | document OCR: All dinosaurs are grouped into two categories originally based on the structure of their pelvis (hipbones) - these are the ornithischian ("bird-hipped") dinosaurs and the saurischian ("lizard-hipped") dinosaurs. Restudy of both groups has resulted in other anatomical differences being thought crucial. The pelvis is the bony structure that connects the hindlimbs to the backbone. In all dinosaurs, the pelvis consisted of three bones on each side of the hip: two lower bones, the pubis and ischium; and an upper bone, the ilium, which was connected to the backbone. In ornithischian dinosaurs, the pelvis was very similar to that seen in living birds, with part of each pubis slanted back, parallel to the ischium. Ornithischians, all herbivorous (plant-eating), are divided into three subgroups. These are the thyreophorans ("shield-bearing" dinosaurs), ornithopods ("bird-footed" dinosaurs), and marginocephalians ("margined heads"). THYREOPHORANS Thyreophorans ("shield-bearing" dinosaurs) were a group of mainly quadrupedal (four-legged) ornithischians that fed by browsing on low-level vegetation. Their most distinctive feature was their protective body armor. There were three subgroups: scelidosaurs (a group of primitive "bird-hipped" dinosaurs); stegosaurs (a group of armored four-legged dinosaurs); and ankylosaurs (a group of armored dinosaurs). The most primitive, the scelidosaurs (a group of primitive "bird-hipped" dinosaurs), were relatively small, with bony studs protecting the neck and body. The stegosaurs (a group of armored four-legged dinosaurs) were medium-sized to large with an arched back. Their body armor consisted of two rows of tall, vertical bony plates (or sometimes spikes) along the neck, back, and tail; and two pairs of long tail spines. Stegosaurus, the largest stegosaur, grew up to 9 m (30 ft). The ankylosaurs were protected by bands of bony studs, plates, or spines, which covered the upper part of the barrel-shaped body and reinforced the broad skull. Many ankylosaurs had a tail club, which was swung like a mallet to defend against predators. Ankylosaurs reached lengths of up to 10 m (33 ft). ORNITHOPODS Ornithopods ("bird-footed" dinosaurs) were bipedal (two-legged), herbivorous ornithischian dinosaurs with a horned beak. They ranged in length from 2 m (6 1/2 ft) to 15 m (49 ft). Typically, they had feet with three walking toes ending in hooflike claws; hands with four or five fingers; and cheek teeth and jaws for effective chewing of vegetation. A diverse group, the ornithopods included hypsilophodonts (a group of two-legged "bird-hipped" dinosaurs), iguanodonts (a group of large two-legged "bird-hipped" dinosaurs), and hadrosaurs (duck-billed dinosaurs). Hypsilophodonts were small ornithopods that had long, slim hind legs adapted for fast running, and they may have moved in herds to protect themselves against predators. Iguanodonts (a group of large two-legged "bird-hipped" dinosaurs) were bulky, powerful ornithopods with thick, strong arms that may have supported them when they were walking on all fours to forage for food. Some had a large thumb-spike, which they may have used to stab an attacking predator. Hadrosaurs (duck-billed dinosaurs) had a toothless, ducklike bill, containing hundreds of self-sharpening cheek teeth. Some had a skull with a bony crest, which they may have used for making sounds. MARGINOCEPHALIANS Marginocephalians ("margined heads") were herbivorous ornithischians that had a narrow shelf or deep bony frill at the back of the skull. There were two subgroups: pachycephalosaurs ("thick-headed lizards") and ceratopsians ("horned-faced" dinosaurs). Pachycephalosaurs ("thick-headed lizards") were bipedal marginocephalians that had a thick, domed, or flat skull with knobs and sometimes spikes. They had a broad, stocky body and ranged in length from 90 cm to 4.6 m (3 ft to 15 ft). Male pachycephalosaurs may have used their domed head for bouts of head-butting when fighting over territory and females. Ceratopsians ("horned-faced" dinosaurs) were quadrupedal marginocephalians that had horns, a bony head frill, and a toothless, parrotlike beak used to chop vegetation. They ranged in length from 1.8 to 9 m (6 ft to 29 1/2 ft), and many lived in herds. The frill and horns of ceratopsians may have been used for display purposes, and may have differed in size between the sexes, much as antler size differs between male and female deer.
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