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The Dinosaur Portal Introduction Dinosaurs are a diverse group ofreptiles of thecladeDinosauria. They first appeared during theTriassicperiod, between 243 and 233.23 million years ago (mya), although the exact origin and timing of theevolution of dinosaurs is a subject of active research. They became the dominant terrestrialvertebrates after theTriassic–Jurassic extinction event 201.3 mya and their dominance continued throughout theJurassic andCretaceous periods. Thefossil record shows thatbirds arefeathered dinosaurs,having evolved from earliertheropods during theLate Jurassicepoch, and are the only dinosaur lineage known to have survived theCretaceous–Paleogene extinction event approximately 66 mya. Dinosaurs can therefore be divided intoavian dinosaurs—birds—and the extinctnon-avian dinosaurs, which are all dinosaurs other than birds. Dinosaurs are varied fromtaxonomic,morphological andecological standpoints. Birds, at over 11,000 livingspecies, are among the most diverse groups of vertebrates. Using fossil evidence,paleontologists have identified over 900 distinctgenera and more than 1,000 different species of non-avian dinosaurs. Dinosaurs are represented on every continent by bothextant species (birds) and fossil remains. Through most of the 20th century, before birds were recognized as dinosaurs, most of the scientific community believed dinosaurs to have been sluggish andcold-blooded. Mostresearch conducted since the 1970s, however, has indicated that dinosaurs were active animals with elevatedmetabolisms and numerous adaptations for social interaction. Some wereherbivorous, otherscarnivorous. Evidence suggests that all dinosaurs wereegg-laying, and thatnest-building was a trait shared by many dinosaurs, both avian and non-avian. (Full article...) Selected article Iguanodon is agenus ofornithopoddinosaur that lived roughly halfway between the first of the swiftbipedalhypsilophodontids and the ornithopods' culmination in theduck-billed dinosaurs. Many species of Iguanodon have been named, dating from theKimmeridgianage of theLate JurassicPeriod to theCenomanian age of theLate Cretaceous Period fromAsia,Europe, andNorth America. However, research in the first decade of the 21st century suggests that there is only one well-substantiated species namedI. bernissartensis, that lived from the lateBarremian to the earliestAptian ages (Early Cretaceous) inBelgium, between about 126 and 125 million years ago. Iguanodon's most distinctive features were its large thumb spikes, which were possibly used for defence againstpredators, combined with long prehensile fifth fingers able to forage for food. Named in 1825 byEnglishgeologistGideon Mantell, Iguanodon was the second dinosaur formally named, afterMegalosaurus. A large, bulkyherbivore, Iguanodon is a member ofIguanodontia, along with the duck-billedhadrosaurs. (see more...) Topics
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