Sauroposeidon
The press release in 1999 immediately garnered international media attention, which led to many (inaccurate) news reports of "the largest dinosaur ever!". While "Sauroposeidon" likely represents the tallest known dinosaur taxon, it does not hold records for either the longest or most massive. "Patagotitan" or "Argentinosaurus" make better candidates for the title "World's Largest Dinosaur" (presuming to ignore, as is conventional, "Amphicoelias"), though incomplete fossil evidence makes exact rankings impossible.
Dinosaur
Using one of the above definitions, dinosaurs can be generally described as archosaurs with hind limbs held erect beneath the body. Many prehistoric animal groups are popularly conceived of as dinosaurs, such as ichthyosaurs, mosasaurs, plesiosaurs, pterosaurs, and pelycosaurs (especially "Dimetrodon"), but are not classified scientifically as dinosaurs, and none had the erect hind limb posture characteristic of true dinosaurs. Dinosaurs were the dominant terrestrial vertebrates of the Mesozoic, especially the Jurassic and Cretaceous periods. Other groups of animals were restricted in size and niches; mammals, for example, rarely exceeded the size of a domestic cat, and were generally rodent-sized carnivores of small prey.