初一的课本也有!
Dinosaurs,oneofthemostsuccessfulgroupsofanimals(intermsoflongevity)thathaveeverlived,evolvedintomanydiversesizesandshapes,withmanyequallydiversemodesofliving.Theterm"Dinosauria"wasinventedbySirRichardOwenin1842todescribethese"fearfullygreatreptiles,"specificallyMegalosaurus,Iguanodon,andHylaeosaurus,theonlythreedinosaursknownatthetime.ThecreaturesthatwenormallythinkofasdinosaurslivedduringtheMesozoicEra,fromlateintheTriassicperiod(about225millionyearsago)untiltheendoftheCretaceous(about65millionyearsago).Butwenowknowthattheyactuallyliveontodayasthebirds.
Somethingstokeepinmindaboutdinosaurs:
•Noteverythingbiganddeadisadinosaur.Alltoooften,bookswritten(ormoviesmade)forapopularaudienceincludeanimalssuchasmammoths,mastodons,pterosaurs,plesiosaurs,ichthyosaurs,andthesail-backedDimetrodon.Dinosaursareaspecificsubgroupofthearchosaurs,agroupthatalsoincludescrocodiles,pterosaurs,andbirds.althoughpterosaursarecloserelations,theyarenottruedinosaurs.Evenmoredistantlyrelatedtodinosaursarethemarinereptiles,whichincludetheplesiosaursandichthyosaurs.MammothsandmastodonsaremammalsanddidnotappearuntilmanymillionsofyearsafterthecloseoftheCretaceousperiod.Dimetrodonisneitherareptilenoramammal,butabasalsynapsid,i.e.,anearlyrelativeoftheancestorsofmammals.
•Notalldinosaurslivedatthesametime.Differentdinosaurslivedatdifferenttimes.DespitetheportrayalsinmovieslikeKingKongandJurassicPark,noStegosauruseversawaTyrannosaurus,becauseTyrannosaurusdidn'tappearonthesceneuntil80orsomillionyearsfollowingtheextinctionofstegosaurs.ThesamegoesforApatosaurus("Brontosaurus")—it'sboneswerealreadywell-fossilizedbythetimeT.rexcamealong.
•Dinosaursarenotextinct.Technically.Basedonfeaturesoftheskeleton,mostpeoplestudyingdinosaursconsiderbirdstobedinosaurs.Thisshockingrealizationmakeseventhesmallesthummingbirdalegitimatedinosaur.Soratherthanreferto"dinosaurs"andbirdsasdiscrete,separategroups,itisbesttorefertothetraditional,extinctanimalsas"non-aviandinosaurs"andbirdsas,well,birds,or"aviandinosaurs."Itisincorrecttosaythatdinosaursareextinct,becausetheyhaveleftlivingdescendantsintheformofcockatoos,cassowaries,andtheirpals—justlikemodernvertebratesarestillvertebrateseventhoughtheirCambrianancestorsarelongextinct.