page_title: Theropoda
section_title: Size
hierarchical_section_title: Theropoda / Biology / Size
context_page_description: Theropoda or theropods are a dinosaur clade that is characterized by hollow bones and three-toed limbs. They are generally classed as a group of saurischian dinosaurs. Theropods were ancestrally carnivorous, although a number of theropod groups evolved to become herbivores, omnivores, piscivores, and insectivores. Theropods first appeared during the Carnian age of the late Triassic period 231.4 million years ago and included the sole large terrestrial carnivores from the Early Jurassic until at least the close of the Cretaceous, about 66 Ma. In the Jurassic, birds evolved from small specialized coelurosaurian theropods, and are today represented by about 10,500 living species.
context_section_description: Tyrannosaurus was for many decades the largest known theropod and best known to the general public. Since its discovery, however, a number of other giant carnivorous dinosaurs have been described, including Spinosaurus, Carcharodontosaurus, and Giganotosaurus. The original Spinosaurus specimens (as well as newer fossils described in 2006) support the idea that Spinosaurus is longer than Tyrannosaurus, showing that Spinosaurus was possibly 3 meters longer than Tyrannosaurus though Tyrannosaurus could still be more massive than Spinosaurus. Specimens of Tyrannosaurus are estimated to be the most massive theropods known to science. There is still no clear explanation for exactly why these animals grew so much larger than the land predators that came before and after them.
  The largest extant theropod is the common ostrich, up to 2.74 m (9 ft) tall and weighing between 60 and 145 kg (140 - 320 lb).
  The smallest non-avialan theropod known from adult specimens is the troodontid Anchiornis huxleyi, at 110 grams in weight and 34 centimeters (1 ft) in length. When modern birds are included, the bee hummingbird Mellisuga helenae is smallest at 1.9 g and 5.5 cm (2.2 in) long.
  Recent theories propose that theropod body size shrank continuously over a period of 50 million years, from an average of 163 kilograms (359 lb) down to 0.8 kilograms (1.8 lb), eventually evolving into modern birds. This was based on evidence that theropods were the only dinosaurs to get continuously smaller, and that their skeletons changed four times as fast as those of other dinosaur species.
caption: Size comparison of selected giant theropod dinosaurs