Paleobiogeography and Evolutionary History of Theropoda

As discussed in Chapter 10, theropods were among the first dinosaurs and their appearance as body fossils slightly preceded, or was contemporaneous with, the evolution of primitive ornithischians during the earliest part of the Late Triassic, slightly less than 230 million years ago. Tracks attributed to theropods, with some dispute over the actual identity of their tracemakers, are in Middle Triassic strata. Undoubted theropod tracks are relatively abundant in Upper Triassic rocks, where in some places they co-occur with skeletal material. Throughout the remainder of the Mesozoic, theropods subsequently diversified into a myriad of sizes and forms. These range from the crow-sized Microraptor to the multi-ton Giganotosaurus, both of the Early Cretaceous, to the bizarrely headed, toothless Oviraptor of the Late Cretaceous.

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