A dinosaur pertains to any of the animals of the clade Dinosauria. This group of animals first appeared in the Triassic period (243 to 233.23 million years ago). They were reptiles that became dominant during Triassic, Jurassic, and Cretaceous. They are now extinct after the Cretaceous-Paleogene extinction event (66 million years ago). The only modern-day animals from dinosaur lineage are the birds (from the theropod ancestry). Dinosaurs include the ankylosaurids, stegosaurus, ceratopsians, ornithopods, theropods, and sauropodomorphs.(1) As for the other prehistoric animals such as ichthyosaurs, mosasaurs, pelycosaurs, and pterosaurs, they are considered as dinosaurs in some references but in stricter definition, they are not because they lack the erect hind limb posture of a true dinosaur.(2) A true dinosaur would, therefore, be one that had an erect hind limb posture. They were bipedal except for some quadrupedal, although they could shift between bipedalism and quadrupedalism. They were horned or crested and with bony armor and spines. While some dinosaurs could grow as high as 59 feet or to a length of 130 feet like the sauropod dinosaurs, others were only as high as humans or even smaller such as Xixianykus that was about 20 inches long.
- Langer, M. C., Ezcurra, M.D., Bittencourt, J. S., and Novas, F. E. (2010). “The origin and early evolution of dinosaurs”. Biological Reviews. 85 (1): 65–66, 82. doi:10.1111/j.1469-185x.2009.00094.x.
- Lambert, D. & the Diagram Group (1990). The Dinosaur Data Book. New York: Avon Books. p. 288. ISBN 978-0-380-75896-8.
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