Dromaeosauridae

Dromaeosauridae is a family of feathered, meat-eating theropod dinosaurs within the coelurosaur group. They were mostly small to medium in size, active during the Cretaceous Period. Their name comes from Greek words meaning "running lizards," and they are commonly called raptors—a nickname made famous by *Jurassic Park*. Several dinosaur genera even include "raptor" in their own names, and popular culture often highlights their bird-like appearance and speculated behaviors.

Definitive fossils of this family have turned up in North America, Europe, and Asia. Some fossils from other continents were once thought to be dromaeosaurids, but are now often placed in a separate family called Unenlagiidae, which some researchers consider a distinct branch of Avialae. The earliest body fossils date to the Early Cretaceous, about 145 to 140 million years ago, and they survived until the end of the Cretaceous, 66 million years ago, when the Cretaceous–Paleogene extinction event occurred. Isolated teeth from the Middle Jurassic suggest they might have been around even earlier, but no body fossils from that period have been found.

**Description**

*Technical diagnosis*: Dromaeosaurids are identified by several skeletal features: short T-shaped frontals that form the front border of the supratemporal fenestra; a rearward overhanging shelf on the squamosal; a side process of the quadrate that connects to the quadratojugal; raised, stalked parapophyses on the dorsal vertebrae; a modified second toe; elongated chevrons and prezygapophyses on the tail vertebrae that span several vertebrae; and a subglenoid fossa on the coracoid.

*Size and build*: These dinosaurs ranged from small to medium. *Velociraptor* was about 1.5 to 2.07 meters long, while *Utahraptor*, *Dakotaraptor*, and *Achillobator* reached or exceeded 6 meters. Large size evolved at least twice: once among dromaeosaurines like *Utahraptor* and *Achillobator*, and again among unenlagiines like *Austroraptor* (5–6 meters). Isolated teeth from the Isle of Wight, England, suggest a possible third giant lineage, about the size of *Utahraptor* but shaped like velociraptorine teeth.

The dromaeosaurid body plan helped revive the idea that dinosaurs were active, fast, and closely related to birds. Robert Bakker’s illustration of *Deinonychus* in a running pose, for John Ostrom’s 1969 monograph, became one of the most influential paleontological reconstructions. Their build includes a relatively large skull with serrated teeth, a narrow snout (except in derived dromaeosaurines), and forward-facing eyes that suggest some binocular vision.

Like most theropods, they had a moderately long S-curved neck and a short, deep trunk. Their arms were long and could be folded against the body in some species, with three long fingers—the middle longest, the first shortest—ending in large claws. The hip had a large pubic boot projecting beneath the tail base. Their feet bore a large, curved claw on the second toe. The tail was slender, with long, low vertebrae that lacked transverse processes and neural spines after the 14th caudal vertebra. Ossified uncinate processes on the ribs have been found in several species.

*Foot*: Dromaeosaurids were bipedal, walking on their hind legs. But unlike most theropods, which used three toes on the ground, fossil footprints show that many early paravians, including dromaeosaurids, held the second toe off the ground in a hyperextended position, walking only on the third and fourth toes—a condition called functional didactyly. The enlarged second toe carried a large, curved, sickle-shaped claw that was retracted when walking. This claw is thought to have been used for capturing prey and climbing. In large predatory eudromaeosaurs, it was especially blade-like. One possible dromaeosaurid, *Balaur bondoc*, also had a highly modified first toe, held retracted with a sickle claw similar to the second. Similar claws are seen in modern seriemas.

*Tail*: Their tails were long. Most tail vertebrae had bony, rod-like extensions called prezygapophyses, and some species also had bony tendons. Ostrom proposed that these features stiffened the tail so it could only flex at the base, moving as a rigid lever. However, a well-preserved *Velociraptor mongoliensis* specimen shows an articulated tail curved horizontally in a long S-shape, suggesting it could bend side to side with considerable flexibility. This tail may have served as a stabilizer or counterweight while running or in the air. In *Microraptor*, an elongated, diamond-shaped fan of feathers is preserved at the tail tip, possibly used as an aerodynamic stabilizer and rudder during gliding or powered flight.