Most people think of dinosaurs as big, ferocious and extinct reptiles. That's largely true, but there are some misconceptions. Dinosaurs came in all shapes and sizes. Dinosaurs were the largest land animals of all time, but a great number of dinosaurs were smaller than a turkey.
Dinosaurs first appeared between 247 and 240 million years ago. They ruled the Earth for about 175 million years until an extinction event 65.5 million years ago wiped out all of them, expect for the avian dinosaurs. Scientists don't agree entirely on what happened, but the extinction likely was a double or triple whammy involving an asteroid impact, choking chemicals from erupting volcanoes, climate change and possibly other factors.
Flying on
Only the big, classic dinosaurs are extinct. Birds are living dinosaurs, most experts believe. Think of that next time a pigeon strafes you.
Fossils show that some of the more advanced dinosaurs had feathers or feather-like body covering, but many of them didn't fly and probably didn't even glide.
Hip check
Dinosaur fossils were first recognized in the 19th century. In 1842, paleontologist Richard Owen coined the term dinosaur, derived from the Greek deinos, meaning "terrible" or "fearfully great," and sauros, meaning "lizard" or reptile." Scientists classify dinosaurs into two orders — Saurischians and Ornithischians— based on the structure of the bones in their hips. (This saurischian and ornithischian grouping is now disputed. See the "Family tree update" section below to learn more.)
Family tree update
In 2017, a metaphorical bombshell hit the paleontology world regarding the dinosaur family tree. A study published in the journal Nature suggested that this hip-oriented classification was incorrect. Rather, theropods are likely close cousins with the ornithischian dinosaurs, and the two groups — the theropods and Ornithischia — form a newly identified group known as Ornithoscelida, the researchers said.
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