Balaur is a uniquely specialized species of carnivorous theropod dinosaur. It lived in what is now Romania during the latter part of the Late Cretaceous. Balaur was described by scientists in August 2010, and was named after the balaur, a dragon of Folklore of Romanian folklore. It is known from a single partial skeleton representing the type specimen. Having been described as a "beefy version of the predatory Velocirapto, its name is Romanian language for 'stocky dragon'.Unlike its other relatives within the dromaeosaur family, which includes Velociraptor, Deinonychus, and the four-winged Microraptor gui, this raptor had not just one but two large, retractable, sickle-shaped claws on each foot, and its limbs were proportionally shorter and heavier than those of its other relatives. Given these and nearly twenty other derived traits, the new genusBalaur was Biological classification created for this one species. As with other dinosaurs from Hațeg, such asMagyarosaurus, a dwarf sauropod,its aberrant features are argued to show the effects of its island habitat on its evolution.Balaur is a dromaeosaurid theropod dinosaur estimated to have lived about 70 million years ago in the late Cretaceous (Maastrichtian). Its bones were shorter and heavier than those of other dromaeosaurs. While the feet of most dromaeosaurs bore a single, large "sickle claw" on the second toe which was held retracted off the ground, Balaur had large retractable sickle claws on both the first and second toes of each foot.In addition to its strange feet, Balaur is unique for its status of being the most complete nonavialan theropod from the late Cretaceous of Europe. It also possesses a great number of additional autapomorphies, including a reduced and presumably nonfunctional third manual digit.The first small bones belonging to Balaur bondoc consisted of six elements of the front limbs. Named specimens FGGUB R. 1580-1585, these were discovered in 1997 in Romania by Dan Grigorescu, but the morphology of the arm was so unusual that scientists could not correctly combine them, mistaking them for the remains of a oviraptorosaur. The first partial skeleton was discovered in September 2009 in Romania, approximately 2.5 kilometers north of Sebeș, along the Sebeș river in the Sebeș Formation dating from the early Maastrichtian, and was given the preliminary field number SbG/A-Sk1. Later it received the holotype inventory number EME VP.313. The discovery was made by the geologist and paleontologist Mátyás Vremir of the Transylvanian Museum Society of Cluj Napoca who sent them for analysis to Zoltán Csiki of the University of Bucharest.The findings were described on August 31, 2010, in the Proceedings of the National Academy of Sciences. The 1997 specimens indicate an individual about 45% longer than the holotype; they were also found in a younger stratum.
Little is known about the behavior of Balaur, but Csiki speculates that it may have been one of the apex predators in its limited island ecosystem, because no larger teeth have ever been found in Romania. He also believes that it likely used its double sickle claws for slashing prey, and that the atrophied state of its hands indicates that it probably did not use them to hunt. One of the original discoverers indicated that it "was probably more of a kickboxer than a sprinter" compared to Velociraptor, and was probably able to hunt larger animals than itself. However, the hunting behavior as well as its typical prey are not known.
Italian paleontologist Andrea Cau has speculated that the aberrant features present in Balaur may have been a result of this dromaeosaurid being omnivorous or herbivorous instead of carnivorous like typical dromaeosaurids. The lack of the third finger may be a sign of reduced predatory behavior and the robust first toe could be interpreted as a weight-supporting adaptation rather than a weapon. These characteristics are consistent with the relatively short, stocky limbs and wide, swept-back pubis, which may indicate enlarged intestines for digesting vegetation as well as reduced speed.