Theropod

Theropoda ( or, from Greek θηρίον "wild beast" and πούς, ποδός "foot") or theropods are a dinosaur suborder that is characterized by hollow bones and three-toed limbs. They are generally classed as a group of saurischian dinosaurs, although a 2017 paper has instead placed them in the proposed clade Ornithoscelida as the closest relatives of the Ornithischia. 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 (Ma) 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.

Theropods exhibit a wide range of diets, from insectivores to herbivores and carnivores. Strict carnivory has always been considered the ancestral diet for theropods as a group, and a wider variety of diets was historically considered a characteristic exclusive to the avian theropods (birds). However, discoveries in the late 20th and early 21st centuries showed that a variety of diets existed even in more basal lineages. All early finds of theropod fossils showed them to be primarily carnivorous. Fossilized specimens of early theropods known to scientists in the 19th and early 20th centuries all possessed sharp teeth with serrated edges for cutting flesh, and some specimens even showed direct evidence of predatory behavior. For example, a Compsognathus longipes fossil was found with a lizard in its stomach, and a Velociraptor mongoliensis specimen was found locked in combat with a Protoceratops andrewsi (a type of ornithischian dinosaur). The first confirmed non-carnivorous fossil theropods found were the therizinosaurs, originally known as segnosaurs. First thought to be prosauropods, these enigmatic dinosaurs were later proven to be highly specialized, herbivorous theropods. Therizinosaurs possessed large abdomens for processing plant food, and small heads with beaks and leaf-shaped teeth. Further study of maniraptoran theropods and their relationships showed that therizinosaurs were not the only early members of this group to abandon carnivory. Several other lineages of early maniraptors show adaptations for an omnivorous diet, including seed-eating (some troodontids) and insect-eating (many avialans and alvarezsaurs). Oviraptorosaurs, ornithomimosaurs and advanced troodontids were likely omnivorous as well, and some early theropods (such as Masiakasaurus knopfleri and the spinosaurids) appear to have specialized in catching fish.