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- Omnivore
- An omnivore is an animal that eats both plants and meat. Humans are omnivores, most birds are omnivorous, and it is believed that a few dinosaurs had a mixed diet.
- Opabinia
- Imagine a swimming slug with five eyes on the top of its head and a single arm with its jaw on the end - this is the very peculiar creature known as Opabinia. It lived about 550 million years ago and its fossils have been found in western Canada and China. It is almost as if nature was experimenting with various designs for complex life forms to determine which would work best. Opabinia was a slow swimming, 3-inch-long (8 cm) hunter. Its excellent vision would have allowed it to easily spot its prey, but it would have only been able to catch those creatures too slow to escape. As there are no longer any five-eyed creatures, Opabinia became an interesting evolutionary dead end.
- Orbit
- The bony opening or cavity in which the eye is housed is called the orbit.
- Order
- See "Classification"
- Ornithischia
- This was a group of dinosaurs that included almost exclusively herbivorous (plant-eating) dinosaurs. The name means bird-hipped. This group included dinosaurs such as Stegosaurus, Triceratops, Ankylosaurus, and many more. What is curious is that it was not the bird-hipped dinosaurs that scientists believe evolved into birds, it was the lizard-hipped dinosaurs
- Ornithopod
- An herbivorous dinosaur that could walk on its hind legs (bipedal). These included dinosaurs such as Iguanodon and most hadrosaurs.
- Orthacanthus
- This is a primitive shark genus, from a family of prehistoric sharks known as xenacanths. They were freshwater predators that prowled shallow swamps and lagoons. Orthacanthus is indicative of the many types of fish that evolved to fill every ecological niche of the seas and waterways of the world. Sharks in particular evolved many hundreds of species - from small to enormous - in the Cenozoic. Some sharks even reached lengths of 60-feet or more. Orthacanthus and the xenacanths all had teeth with a double fang on each tooth, making them formidable weapons. The species shown was long and flexible, most likely an adaptation to moving through and around the plants and primitive trees found in paleozoic swamps. It grew to about 10 feet (3 m) and would have been a fearsome predator. Xenacanths became extinct in the Triassic and were replaced by the large reptiles such as phytosaurs.
- Osborn, Henry Fairfield
- Henry Fairfield Osborn established the Department of Vertebrate Paleontology at the American Museum of Natural History in New York City in 1891. Under his supervision, the museum amassed one of the most incredible dinosaur collections in the world and sponsored many of the most important fossil hunting expeditions ever undertaken, including those by Barnum Brown and Roy Chapman Andrews.
- Owen, Sir Richard
- An English scientist, Sir Richard Owen coined the word dinosaur. In 1841 Sir Richard examined the fossil remains of three huge prehistoric creatures - Iguanodon, Megalosaurus and Hylaeosaurus - and coined the word dinosaur, which means Terrible Lizard. More importantly, he established the Infraclass Dinosauria as an accepted taxonomic classification within the class Reptilia.
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