Abelisaurus is a genus of abelisaurid theropod dinosaur from the Late Cretaceous Period of what is now South America. It was a bipedal carnivore that probably reached 7 to 9 meters (25 to 30 feet) in length, although it is known from only one partial skull. The generic name recognizes Roberto Abel as the discoverer of the specimen and former director of the provincial Museum of Cipolletti in Argentina, where the specimen is housed. There is one named species, A. comahuensis, which honors the Comahue region of Argentina, where the fossil was found. Both genus and species were named and described by Argentine paleontologists Jose Bonaparte and Fernando Novas in 1985, who placed it in the newly-created family Abelisauridae.

Acrocanthosaurus is a genus of theropod dinosaur that existed in what is now North America during the mid-Cretaceous Period, approximately 125 to 100 million years ago. Acrocanthosaurus was a bipedal predator. As the name suggests, it is best known for the high neural spines on many of its vertebrae, which most likely supported a ridge of muscle over the animal's neck, back and hips. Acrocanthosaurus was one of the largest theropods, approaching 12 meters (40 ft) in length, and weighing up to about 2.4 metric tons (2.65 short tons). Large theropod footprints discovered in Texas may have been made by Acrocanthosaurus, although there is no direct association with skeletal remains.

Aerosteon

Aerosteon is a genus of tetanuran theropod dinosaur from the Late Cretaceous period of Argentina. Its remains were discovered in 1996 in the province of Mendoza. They show evidence of a bird-like respiratory system, hence the name. Aerosteon was a 9 metre (30 ft) long bipedal carnivorous dinosaur that lived approximately 84 million years ago during the Santonian stage.

Afrovenator ("African hunter") is a genus of theropod dinosaur from the Early Cretaceous Period of northern Africa. It was a bipedal predator, with a mouthful of sharp teeth and three claws on each hand. Judging from the one skeleton known, this dinosaur was approximately 30 feet (9 meters) long from snout to tail tip.

Albertosaurus ("Alberta lizard") is a genus of tyrannosaurid theropod dinosaur that lived in western North America during the Late Cretaceous Period, more than 70 million years ago. The type species, A. sarcophagus, was restricted in range to the modern-day Canadian province of Alberta, after which the genus is named. Scientists disagree on the content of the genus, with some recognizing Gorgosaurus libratus as a second species. As a tyrannosaurid, Albertosaurus was a bipedal predator with tiny, two-fingered hands and a massive head with dozens of large, sharp teeth. It may have been at the top of the food chain in its local ecosystem. Although relatively large for a theropod, Albertosaurus was much smaller than its more famous relative Tyrannosaurus, probably weighing less than 2 metric tons.

Alectrosaurus ("Unmarried lizard") is a genus of tyrannosauroid theropod dinosaur from the Late Cretaceous Period of Inner Mongolia. It was a bipedal carnivore with a body shape similar to its much larger relative, Tyrannosaurus rex. Alectrosaurus was much smaller though, most likely less than five meters (17 ft) long.

Alioramus ("'Different branch") is a genus of tyrannosaurid theropod dinosaur from the Late Cretaceous period of Asia. The type and only species, A. remotus, is known from a partial skull and three metatarsals recovered from Mongolian sediments which were deposited in a humid floodplain between 70 to 65 million years ago. These remains were named and described by Russian paleontologist Sergei Kurzanov in 1976. Its relationships to other tyrannosaurid genera are unknown, but some experts believe Alioramus is closely related to the contemporaneous Tarbosaurus, or is a juvenile of that genus.

Allosaurus was a large bipedal predator with a large skull, equipped with dozens of large, sharp teeth. It averaged 8.5 meters (30 ft) in length, though fragmentary remains suggest it could have reached over 12 meters (39 ft). Relative to the large and powerful hindlimbs, its three-fingered forelimbs were small, and the body was balanced by a long, heavy tail. It is classified as an allosaurid, a type of carnosaurian theropod dinosaur. The genus has a complicated taxonomy, and includes an uncertain number of valid species, the best known of which is A. fragilis. The bulk of Allosaurus remains have come from North America's Morrison Formation, with material also known from Portugal and possibly Tanzania. It was known for over half of the 20th century as Antrodemus, but study of the copious remains from the Cleveland Lloyd Dinosaur Quarry brought the name Allosaurus back to prominence, and established it as one of the best-known dinosaurs.

Alxasaurus ("Alxa Desert lizard") is a genus of therizinosauroid theropod dinosaur from the Early Cretaceous Period of Inner Mongolia. It is one of the earliest known members of the superfamily Therizinosauroidea, but it still possessed the body shape - including the long neck, short tail, and long hand claws - of later therizinosauroids. Like other members of this group, it was a bipedal herbivore with a large gut to process plant material. Several specimens are known and the largest was a little over 12 feet (3.8 m) long.

Aucasaurus was a genus of medium-sized theropod dinosaur from Argentina that lived during the Santonian stage. It was smaller than the related Carnotaurus, although the arms were longer. The type skeleton is complete to the thirteenth caudal vertebra, and so is relatively well understood, and is the most complete abelisaurid yet described. However, the skull is damaged, causing some paleontologists to speculate that it was involved in a fight shortly prior to death.

Austroraptor ("Southern thief") was a genus of dromaeosaurid dinosaur that lived about 70 million years ago during the Cretaceous period in what is now modern Argentina. The type species for the genus, Austroraptor cabazai, was described in late 2008 by Fernando Novas of the Museo Argentino de Ciencias Naturales. The fossil specimen was discovered in the Late Cretaceous deposits located in the Río Negro Province of Argentina. The species was named in honor of Alberto Cabaza, who founded the Museo Municipal de Lamarque where the specimen was partially studied.

Avimimus ("Bird mimic"), was a genus of bird-like maniraptoran dinosaur that lived in the late Cretaceous in what is now Mongolia, around 70 million years ago. Avimimus was a small dinosaur with a length of 1.5 m (5 ft). The skull was small compared to the body, though the brain and eyes were large. The size of the bones which surrounded the brain and were dedicated to protecting it are large. This is also consistent with the hypothesis that Avimimus had a proportionally large brain.

Bambiraptor is a 75 million year old bird-like dinosaur discovered by scientists at the University of Kansas, Yale University, and the University of New Orleans. When living, Bambiraptor would have stood no more than 0.3 meter (1 ft) off the ground, reached 0.7 meter (2.3 ft) in length, and weighed only two kilograms (4.4 lb), although this specimen appears to be a juvenile,it is therefore certainly possible that Bambiraptor is really just a juvenile Saurornitholestes, but no one can be positive. Because of its small size, it was christened Bambiraptor feinbergi, after the familiar Disney movie character and the surname of the wealthy family who bought and donated the specimen to the new Graves Museum of Natural History in Florida.

Baryonyx ("Heavy claw") is a genus of carnivorous dinosaur first discovered in clay pits just south of Dorking, England, and later reported from fossils found in northern Spain and Portugal. It contains one species, Baryonyx walkeri. Its fossils have been recovered from formations dating from early Cretaceous Period, around 130-125 million years ago. Baryonyx is one of the few known piscivorous (fish-eating) dinosaurs, with specialized adaptions like a long low snout with narrow jaws filled with finely serrated teeth and gaffe hook-like claws to help it hunt its main prey.

Beipiaosaurus is a genus of therizinosauroid theropod dinosaur. Its fossils were found in Liaoning Province, China and have been dated to the early Cretaceous Period, about 125 million years ago. The exact classification of therizinosaurs had in the past been hotly debated, since their prosauropod-like teeth and body structure indicate that they were generally herbivorous, unlike typical theropods. Beipiaosaurus, being considered to be a primitive therizinosauroid, has features which suggest that all therizinosauroids, including the more derived Therizinosauridae, to be coelurosaurian theropods, not sauropodomorph or ornithischian relatives as once believed. A recently discovered specimen preserved a complete skull as well as a significant covering of unique, elongated feathers.