Chapter 7 – Theropoda – Reptiles with Beastly FeetCladogram (in back of textbook) will be provided at the testing center for the exam!- The second major branch of the Saurischia is the Theropoda (means “beast foot”). These are meat-eating dinosaurs, except for only one type that may have preferred plants. - They include the smallest dinosaur, Microraptor, weighing less than half a pound, as well as the 10,000 pound T. rex and the slightly larger Gigamotosaurus. - Theropods have the following diagnostic features:o Carnivorous (meat-eating) teeth that were laterally compressed, recurved, and often serrated like a steak knife. o Thin, hollow bones that served to lighten the skeleton for rapid locomotion. - Other features THAT DO NOT NEED TO BE MEMORIZED include three main clawed fingers, long metatarsals (upper-foot bones) and bowed femurs (thigh bones).- The first theropods were small, bipedal forms weighing between fifty and 170 pounds. Very little is known about these rare animals. o Ceratosaurs – Spitters/Cannibals? By the Late Triassic period, new types of theropods known as ceratosaurs showed up. They had four fingers and a distinctive gap between the premaxilla and the maxilla where a lower tooth went. These critters had very long necks and have been found in the hundreds. It was originally thought that these animals were cannibals – that is, that they ingestedeggs containing infants of their own species. However, later testing confirmed that thestomach contents were not eggs with baby Ceratosaurs but rather the remains of a crocodile supper! - The first-known big theropod was the fifteen-to-twenty-foot-long ceratosaur, Dilophosaurus. This was the spitter from Jurassic Park. It sported two strange crests on its head, but the poisoin-spitting image portrayed in the movie is fantasy. - Finally, there was the twenty-foot-long Ceratosaurus (horn lizard) that had a horn on its nose. o Tetanurans (fused tails) The diagnostic features of the Tetanurae are- Hands half as long as the entire arm (this is true even for the T. rex with its diminutive arms)- A boot-like process on the pubis (one of the hip bones) There were two major groups of Tetanurans – the carnosauris (the giant theropods) and the coelurosauria (generally small theropods but inclusive of giant tyrannosaurs). - The carnosaurs from the Early Jurassic to Early Cretaceous Periods were over fifteen feet long and were large-headed killers.o The most well-known carnosaurs were the allosaurs from the Middle Jurassic to Early Cretacous Periods. They had sharp teeth and huge claws on their hands and are often depictedattacking the giant Sauropods. Allosaurus, for which the group was named, had a ver light skull. However, despite its fragil appearance, it could endure enormous stresses. The bones were ideally positioned to do this. However, despite the considerable strength of the skull, the bite forces for this 1.4-ton animal were remarkably low, just over 500 pounds, which is about what a wolf generates. (Some feel this is a gross underestimate.) Whatever the bite force really was, it was enough for it to be able to penetrate flesh and bone of its prey. o Spinosaurs are a little-known group of carnosaurs with bizarre snouts like those of fish-feeding crocodilians. They may well have fed near the water. One of these, Baryonyx, was found in England twenty-five years ago with the remains of fish and juvenile Iguanadon bones in its stomach region. This was the first new dinosaur found in England in one hundred years, and thus, it caused quite a sensation. It also sported an enormous claw on each hand. Spinosaurus, for which the group was named, lived in Egypt during the late Cretaceous. It had a similar snout to the Baryonyx but also had an enormous fin on its back with spines five feet tall. The first remains of this rare animal were collected by German paleontologists. These first Spniosauruses were type specimens, the all-important ones used to name, describe, and serve as future-reference for comparison with other specimens. They were blown to smithereens by British bombers in WWII. - The other major groups of tetanurans was the Coelurosauria from the Cretaceous Period of Asia and Western North America. o Key features of the Coelurosauria are Pubis longer than the ischium (hip bones) Long forelimbs (half of the length of the backbone) They also had the following features that don’t need to be memorized – fused clavicles, fused sternum, slender hands with long second and third fingers) o An interesting coelurosaurian group was the ornithomimosaurs (bird mimic dinosaurs) from the late Cretaceous Period of Asia and North America. Many of these species look like ostriches and all probably had horny bills. They had duck-like bills with pointed but not recurved claws and could run at similar speeds to the ostrich of today (35 miles an hour). They were probably omnivorous (eaters of plants and animals). Ornithomimosaurs are characterized by ostrich-like body form and a lack of teeth (except for very small teeth in early forms and one recently found with vestigial teeth). These animals were the real “big birds,” as some of them attained sizes comparable to those of tyrannosaurs.o Another subdivision of the coelurosaurs were the tyrannosaurs. They are characterized by reduced forelimbs with only two functional fingers. o A poorly known group of coelurosaurian dinosaurs were the segnosaurs from the Cretaceous Period of Alaska. The best-known segnosaur from the Early Cretaceous Period of China is known as Alxasaurus. It had huge forelimbs with enormous claws, a very short ail, and parosauropod-like teeth. Segnosaurs were probably the only herbivorous theropods. They were curiously found both in lakes and rivers. o Another weird, toothless coelurosaurian group was the Oviraptora (the egg-stealers). They had deep, highly fenestrated lower jaws. Stomach contents show that they fed upon lizards. They were good parents and sat atop their nests, but these nests originally were thought of as Protoceratops’ nests, hence why they were thought to be egg-stealers. o Deinonychosaurs – killer feet Deadly meat-eaters with enlarged killing claws on their feet. The diagnostic feature of the Deinonychosauria is an enlarged claw on the second toe, a key sign of agility since they had to balance on one foot to use it. They also had pubis
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