Animalia Life

Stegosaurs are a group of quite large (up to eight meters long), quadrupedal, ornithischian dinosaurs. That is, they have a pelvis in which the pubis points backward, and thus they are allied with all other herbivorous dinosaurs except the gigantic sauropods. Their closest relatives are the other armored dinosaurs, the ankylosaurs, with which they are grouped as Thyreophora ("shield bearers"), characterized by rows of plates along the back and sides of the body. The earliest stegosaurs are represented by fragmentary remains fromthe Middle Jurassic of England, but by the Late Jurassic they are well known from complete skeletons from Africa, Asia, Europe, and North America. The Late Jurassic was the most successful time for stegosaurs and they are particularly well known from articulated skeletons of Stegosaurus of this age from North America.Bythe Early Cretaceous their distribution had contracted to Europe, Africa, and China, and by the Late Cretaceous they are absent from all continents except India. India was separate from all the other continents from the Middle Jurassic onward as it drifted away from Africa and toward Asia, and this isolation may have protected the stegosaurs as they became extinct everywhere else.

Anatomy and Lifestyle
The best known stegosaur is Stegosaurus ("roofed reptile"), fromthe Late Jurassic of North America, and thus it is commonly used to typify the entire group. Stegosaurus had a small head with an unusually small brain, even for a dinosaur, and a narrow, horn-covered beak at the tip of the snout. The sides of the jaws were lined with leaf-shaped serrated teeth but these were not arranged in batteries and there is no evidence of the sophisticated grinding apparatus that was developed in some other herbivorous dinosaurs. However, Stegosaurus was a large animal and must have needed large quantities of plant food, so it is likely that it was a low-level browser that chopped up vegetation and then quickly passed it back to a large stomach, where it would have fermented, perhaps with the help of gastroliths (stomach stones) to further break it down. The most distinctive feature of Stegosaurus is the rowof vertical plates along the back. There has been some disagreement as to their relationship to each other, as they were set in soft tissue and not attached to the skeleton; however, it is generally agreed that they formed two parallel rows in which the plates were staggered. The plates are not optimally positioned for defense and it has been suggested that they were devices for thermoregulation, acting as radiators to gain or lose heat and help maintain a constant internal body temperature in animals that may have had an ectothermic metabolism (an internal temperature regulated by the ambient temperature, as in most modern reptiles). Experiments have shown that the plates were ideally shaped and positioned to do this. The surface of the plates is covered by fine grooves, indicating the presence of numerous blood vessels, and the plates themselves are hollow, implying that they were richly supplied with blood. Thus the animal could have flushed blood over the plates to cool itself if its internal temperature had risen too much, or to warm the blood by exposure to the sun if its internal temperature was dropping. The proportions of the legs in Stegosaurus show that it was not a fast runner, and thus as a large and relatively slow-moving herbivore it would have needed some means of defense against predators. This would undoubtedly have been the spike-bearing tail. Two pairs of spines projected laterally from the tip of the tail and could have inflicted severe injuries on an attacking carnivorous dinosaur as the tail was lashed from side to side while the animal backed toward the attacker.

Stegosaurus Facts

Classification:
Kingdom: Animalia
Subkingdom: Bilateria
Phylum: Chordata
Subphylum: Vertebrata
Class: Reptilia
Order: Ornithischia
Suborder: Thyreophora
Geographical location: North America, Europe, China, India, and Africa
Habitat: Terrestrial habitats
Gestational period: Unknown
Life span: Unknown
Special anatomy: Large, quadrupedal dinosaurs in which the head was small, the back was covered by a double row of large vertical plates, and the tail bore large spikes

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