Zhou, Zhonghe (October 2004). "The origin and early evolution of birds: discoveries, disputes, and perspectives from fossil evidence" (PDF). Naturwissenschaften. Berlin: Springer Science+Business Media. 91 (10): 455–471. Bibcode: 2004NW.....91..455Z. doi: 10.1007/s00114-004-0570-4. ISSN 0028-1042. PMID 15365634. S2CID 3329625. Archived from the original (PDF) on July 21, 2011 . Retrieved November 6, 2019. Dinosaur bones 'used as medicine' ". BBC News. London: BBC. July 6, 2007. Archived from the original on August 27, 2019 . Retrieved November 4, 2019. Hadrosauriformes (ancestrally had a thumb spike; large quadrupedal herbivores, with teeth merged into dental batteries) Those dinosaurs which returned to four-legged stance kept all four legs under their body. This is much more efficient than the sprawling legs of a lizard. By human standards, dinosaurs were creatures of fantastic appearance and often enormous size. As such, they have captured the popular imagination and become an enduring part of human culture. The entry of the word "dinosaur" into the common vernacular reflects the animals' cultural importance: in English, "dinosaur" is commonly used to describe anything that is impractically large, obsolete, or bound for extinction. [329]

At the time of the K-Pg extinction, the Deccan Traps flood basalts of India were actively erupting. The eruptions can be separated into three phases around the K-Pg boundary, two prior to the boundary and one after. The second phase, which occurred very close to the boundary, would have extruded 70 to 80% of the volume of these eruptions in intermittent pulses that occurred around 100,000 years apart. [304] [305] Greenhouse gases such as carbon dioxide and sulfur dioxide would have been released by this volcanic activity, [306] [307] resulting in climate change through temperature perturbations of roughly 3°C (5.4°F) but possibly as high as 7°C (13°F). [308] Like the Chicxulub impact, the eruptions may also have released sulfate aerosols, which would have caused acid rain and global cooling. [309] However, due to large error margins in the dating of the eruptions, the role of the Deccan Traps in the K-Pg extinction remains unclear. [270] [271] [310] However, researchers do not agree regarding whether these structures share a common origin between lineages (i.e., they are homologous), [251] [252] or if they were the result of widespread experimentation with skin coverings among ornithodirans. [253] If the former is the case, filaments may have been common in the ornithodiran lineage and evolved before the appearance of dinosaurs themselves. [246] Research into the genetics of American alligators has revealed that crocodylian scutes do possess feather-keratins during embryonic development, but these keratins are not expressed by the animals before hatching. [254] The description of feathered dinosaurs has not been without controversy in general; perhaps the most vocal critics have been Alan Feduccia and Theagarten Lingham-Soliar, who have proposed that some purported feather-like fossils are the result of the decomposition of collagenous fiber that underlaid the dinosaurs' skin, [255] [256] [257] and that maniraptoran dinosaurs with vaned feathers were not actually dinosaurs, but convergent with dinosaurs. [245] [256] However, their views have for the most part not been accepted by other researchers, to the point that the scientific nature of Feduccia's proposals has been questioned. [258] Scientists will probably never be certain of the largest and smallest dinosaurs to have ever existed. This is because only a tiny percentage of animals were ever fossilized and most of these remain buried in the earth. Few of the specimens that are recovered are complete skeletons, and impressions of skin and other soft tissues are rare. Rebuilding a complete skeleton by comparing the size and morphology of bones to those of similar, better-known species is an inexact art, and reconstructing the muscles and other organs of the living animal is, at best, a process of educated guesswork. [144] Comparative size of Argentinosaurus to the average human Chiappe, Luis M.; Witmer, Lawrence M., eds. (2002). Mesozoic Birds: Above the Heads of Dinosaurs. Berkeley: University of California Press. ISBN 978-0-520-20094-4. LCCN 2001044600. OCLC 901747962. It is now certain (from fossils discovered in China: see Jehol biota) that small theropods had feathers. This fits well with the idea that they were warm-blooded, and that the origin of birds can be traced to a line of small theropods.Holtz, Thomas R. Jr. 2007. Dinosaurs: the most complete, up-to-date encyclopedia for dinosaur lovers of all ages. New York: Random House. ISBN 978-0-375-82419-7 Weishampel, David B; Dodson, Peter and Osmólska, Halszka (eds) 2004. The Dinosauria. 2nd ed. Berkeley: University of California Press. ISBN 0-520-24209-2

Ornithopoda (various sizes; bipeds and quadrupeds; evolved a method of chewing using flexible skulls and many teeth)Holtz, Thomas R. Jr. (2007). Dinosaurs: the most complete, up-to-date encyclopedia for dinosaur lovers of all ages. New York: Random House. ISBN 978-0-375-82419-7. Dinosaurs began in the Upper Triassic, about 230 million years ago (mya). [3] The earliest date of a dinosaur fossil is that of Eoraptor and Herrerasaurus from Argentina, and Saturnalia from Brazil, 237 to 228 mya. [4] The Cretaceous–Paleogene extinction event, which occurred approximately 66million years ago at the end of the Cretaceous, caused the extinction of all dinosaur groups except for the neornithine birds. Some other diapsid groups, including crocodilians, dyrosaurs, sebecosuchians, turtles, lizards, snakes, sphenodontians, and choristoderans, also survived the event. [126] Nesbitt, Sterling J. 2011. The early evolution of Archosaurs: relationships and the origin of major clades. Bulletin of the American Museum of Natural History. New York: American Museum of Natural History. 2011 (352): 1–292. doi:10.1206/352.1. hdl:2246/6112. ISSN 0003-0090. S2CID 83493714. Based on fossil evidence from dinosaurs such as Oryctodromeus, some ornithischian species seem to have led a partially fossorial (burrowing) lifestyle. [174] Many modern birds are arboreal (tree climbing), and this was also true of many Mesozoic birds, especially the enantiornithines. [175] While some early bird-like species may have already been arboreal as well (including dromaeosaurids) such as Microraptor [176]) most non-avialan dinosaurs seem to have relied on land-based locomotion. A good understanding of how dinosaurs moved on the ground is key to models of dinosaur behavior; the science of biomechanics, pioneered by Robert McNeill Alexander, has provided significant insight in this area. For example, studies of the forces exerted by muscles and gravity on dinosaurs' skeletal structure have investigated how fast dinosaurs could run, [136] whether diplodocids could create sonic booms via whip-like tail snapping, [177] and whether sauropods could float. [178] Communication

Nexus of basal coelurosaurs" (used by Tweet to denote well-known taxa with unstable positions at the base of Coelurosauria)Restoration of four macronarian sauropods: from left to right Camarasaurus, Brachiosaurus, Giraffatitan, and Euhelopus St. Fleur, Nicholas (8 December 2016). "That thing with feathers trapped in amber? It was a dinosaur tail". New York Times . Retrieved 8 December 2016.

Osborn, H.F. (1912). "Integument of the iguanodont dinosaur Trachodon". Memoirs of the American Museum of Natural History. 1: 33–54. Fourth trochanter (projection where the caudofemoralis muscle attaches on the inner rear shaft) on the femur (thigh bone) is a sharp flange Alvarez, Walter (1997). T. rex and the Crater of Doom. Princeton, NJ: Princeton University Press. ISBN 978-0-691-01630-6. LCCN 96049208. OCLC 1007846558 . Retrieved November 4, 2019. Currie, Philip J.; Koppelhus, Eva B.; Shugar, Martin A.; Wright, Joanna L., eds. (2004). Feathered Dragons: Studies on the Transition from Dinosaurs to Birds. Life of the Past. Bloomington, IN: Indiana University Press. ISBN 978-0-253-34373-4. LCCN 2003019035. OCLC 52942941. Sternberg, Charles Mortram (1966) [Original edition published by E. Cloutier, printer to the King, 1946]. Canadian Dinosaurs. Geological Series. Vol.54 (2nded.). Ottawa: National Museum of Canada. LCCN gs46000214. OCLC 1032865683.Cnemial crest on the tibia (protruding part of the top surface of the shinbone) arcs anterolaterally (curves to the front and the outer side) Main article: Chicxulub crater Luis (left) and his son Walter Alvarez (right) at the K-T Boundary in Gubbio, Italy, 1981 The Chicxulub Crater at the tip of the Yucatán Peninsula; the impactor that formed this crater may have caused the dinosaur extinction. A major change in outlook came in the 1960s, when it was realised that small theropods were probably warm-blooded. [20] The question of whether all theropods or even all dinosaurs were warm blooded is still undecided.