Megaraptora is a clade of carnivorous theropod dinosaurs with controversial relations to other theropods. Pterosaurs are known to have been eaten by theropods. Like most theropods, abelisaurids were carnivorous bipeds. "Carcharodontosaurus" were compared with isotopic compositions from contemporaneous theropods, turtles, and crocodilians. Dinosaurs are now extinct, except for birds, which are theropods. Ornithomimosaurs belonged to the clade Maniraptoriformes of coelurosaurian theropods, which also includes modern birds. The dinosaurs also developed smaller forms, including the feather-bearing smaller theropods. The first confirmed non-carnivorous fossil theropods found were the therizinosaurs, originally known as segnosaurs. Birds belong to the dinosaurs as members of the theropods. Large fenestrae (openings) in the skull reduced weight, as in all carnivorous theropods. Feathers or feather-like structures are attested in most lineages of theropods. Some Mesozoic flying theropods however had more developed deltoideus. The global radiation of these carnivorous theropods occurred in two steps. Its coordination and balance would not have been as important as for carnivorous theropods. In reality, "Velociraptor", like many other maniraptoran theropods, was covered in feathers.