There are a lot of questions about dinosaurs. When did the dinosaurs first appear on Earth? Where did dinosaurs live? Why did the dinosaurs die out? Were there any swimming dinosaurs? Why did the dinosaurs die out? Were dinosaurs social animals? What colors were dinosaurs? and...

The oldest dinosaur types are known from rocks in Argentina and Brazil and are about 230 million years old. The most primitive of these types, Eoraptor, was a small meat-eating dinosaur. Because Eoraptor's skeleton shows some advanced skeletal features, older dinosaurs may yet be found. Dinosaurs went extinct about 65 million years ago (at the end of the Cretaceous Period), after living on Earth for about 165 million years. If all of Earth time from the very beginning of the dinosaurs to today were compressed into 365 days (1 calendar year), the dinosaurs appeared January 1 and became extinct the third week of September. (Using this same time scale, the Earth would have formed approximately 18.5 years earlier.) By comparison, people (Homo sapiens) have been on earth only since December 31 (New Year's eve). The dinosaurs' long period of dominance certainly makes them unqualified successes in the history of life on Earth.

Some dinosaurs were social creatures. Recently discovered evidence indicates that they travelled together and that some may even have migrated (because dinosaur fossils have been found above the Arctic Circle, where food supply would have been seasonal). 

 

Grouped hadrosaur nest sites have been found with badly crushed eggshells and skeletons of baby dinosaurs (with slightly wo teeth) still in the nests, suggesting that some babies stayed in their nests after hatching and probably were fed by parents.

Direct fossil evidence for dinosaur skin color is unknown. Paleontologists think that some dinosaurs likely had protective coloration, such as pale undersides to reduce shadows, irregular color pattes ("camouflage") to make them less visible in vegetation, and so on. Those dinosaurs that had enough armor, such as the stegosaurs and ceratopsians, may not have needed protective coloration but may have been brightly colored as a waing to predators or as a display for finding a mate. Most dinosaurs probably were as brightly colored as mode lizards, snakes, or birds.

 

Approximately 700 species have been named. However, a recent scientific review suggests that only about half of these are based on fairly complete specimens that can be shown to be unique and separate species. These species are placed in about 300 valid dinosaur genera (Stegosaurus, Diplodocus, etc.), although about 540 have been named. Recent estimates suggest that about 700 to 900 more dinosaur genera may remain to be discovered.

 

 

Most dinosaur genera presently contain only one species (for example, Deinonychus) but some have more (for example, Iguanodon). Even if all of the roughly 700 published species are valid, their number is still less than one-tenth the number of currently known living bird species, less than one-fifth the number of currently known mammal species, and less than one-third the number of currently known spider species.

 

Dinosaurs probably communicated both vocally and visually. The chambered headcrests on some dinosaurs such as Corythosaurus and Parasaurolophus might haved been used to amplify grunts or bellows. Defensive posturing, courtship behavior, and territory fights probably involved both vocal and visual displays. 

 

An angry Triceratops bull shaking his head at you, even silently, would have made himself very clearly understood!

 

Estimates of dinosaur speeds vary because several different methods are used to calculate them. One recent estimate suggests that an average person might have been able to to outrun an adult Tyrannosaurus (although you probably would not volunteer to try). The two basic approaches for estimating dinosaur speed are comparing to recorded speeds of mode animals of similar body size and build, and measuring distances between fossil footprints in a trackway and using these distances to calculate estimated speed. 

Walking-speed estimates for medium-sized bipedal (two-legged) dinosaurs vary from 4 kph to 6 kph, and peak running-speed estimates vary from 37 kph to 88 kph. The highest figure (88.6 kph) is the same as the peak speed of the currently fastest land animals, such as the North American prongho "antelope" (Antilocapra americana), and very probably is too high.

 

Some dinosaurs ate lizards, turtles, eggs, or early mammals. Some hunted other dinosaurs or scavenged dead animals. Most, however, ate plants (but not grass, which hadn't evolved yet). Rocks that contains dinosaur bones also contain fossil pollen and spores that indicate hundreds to thousands of types of plants existed during the Mesozoic Era. 

 

Many of these plants had edible leaves, including evergreen conifers (pine trees, redwoods, and their relatives), fes, mosses, horsetail rushes, cycads, ginkos, and in the latter part of the dinosaur age flowering (fruiting) plants. Although the exact time of origin for flowering plants is still uncertain, the last of the dinosaurs certainly had fruit available to eat.

 

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