Overview: In June of 1993, moviegoers attending the premier of Jurassic Park came face-to-screen with the fearsome and cunning Velociraptor, arguably the most menacing dinosaurian threat in the whole movie, even more so than the famous Tyrannosaurus rex. However, these “Velociraptors” had a big problem. It wasn’t just that their hand posture was wrong or that they should have been feathered. The biggest problem with the Jurassic Park Velociraptors was that they were misnamed. That’s right, they weren’t actually Velociraptors, rather they were based “in almost every detail” on Velociraptor’s larger American cousin Deinonychus, described by John Ostrom in 1969. The reason for the name switch? The author of the book (Michael Crichton) thought Velociraptor sounded cooler and the folks working on the movies followed suit. But despite Hollywood publicity wrongfully going to Velociraptor, Deinonychus itself has been one of the most influential dinosaurs in paleontology, helping to kick off the “Dinosaur Renaissance”, and revolutionizing the way we think about both dinosaurs and birds!
Discovery: The first remains of Deinonychus were discovered by legendary paleontologist Barnum Brown of the American Museum of Natural History in 1931 in the Cloverly Formation near Billings, Montana. He informally called it “Daptosaurus” but never got around to describing it. Deinonychus teeth were also found by Brown during the same expedition. Over three decades later in 1964, equally legendary paleontologist John Ostrom of the Yale Peabody Museum led an expedition to the Cloverly Formation which recovered over 1,000 Deinonychus bones, likely belonging to three individuals, and in 1969, based on these bones as well as Brown’s “Daptosaurus”, Ostrom described and named Deinonychus antirrhopus. Deinonychus’s name fittingly means “Terrible Claw” in Greek, named for the fearsome sickle-shaped “killing claws” on the second toe of each foot. The species name, antirrhopus, is also Greek, meaning “counterbalancing" in reference to the likely purpose of its stiffened tail. Since then, many more Deinonychus discoveries have made. It is well-known from both the Cloverly Formation of Montana and Wyoming as well as from the Antlers Formation of Oklahoma. Remains attributed to Deinonychus have also been found in the Arundel Clay of Maryland and the Ruby Ranch Member of the Cedar Mountain Formation of Utah.
Evolution: Deinonychus was a member of the famous Dromaeosauridae or “raptors”. In fact, the fame of the Dromaeosauridae came largely because of Deinonychus’s importance in the world of paleontology as well as its on-screen roll in Jurassic Park which helped to popularize raptors among the general public. Within Dromaeosauridae, Deinonychus was a member of Eudromaeosauria, a clade containing many of the larger derived dromaeosaurs to the exclusion of the smaller Microraptorinae and the strange Unenlagiinae. Eudromaeosauria included velociraptorines such as Velociraptor, saurornitholestines such as Saurornitholestes, and dromaeosaurines like Utahraptor. And it included Deinonychus. However, where exactly Deinonychus fits within Eudromaeosauria has been debated. It is often found to be a velociraptorine or a dromaeosaurine, and sometimes it is classified on its own outside of the major subfamilies.
Dromaeosaurs likely first appeared sometime in the mid-Jurassic Period. This is inferred from phylogenetic relationships as the Jurassic fossil record is almost entirely lacking in dromaeosaur remains. They shared a close ancestry with the troodontids with which they form the clade Deinonychosauria (“terrible clawed lizards”) and with the avialans, the bird lineage. Eudromaeosaurs likely appeared near the end of the Jurassic, possibly in Europe, based on isolated teeth. In the Cretaceous, dromaeosaurs diversified and spread and came to great ecological prominence. Eudromaeosaurs had sturdier builds, larger claws, and stronger jaws adapted to tackle larger prey than other deinonychosaurs. By 115 million years ago Deinonychus had appeared in North America.
Description: Deinonychus was bipedal like other theropods and fairly robustly built by dromaeosaur standards, yet still fairly lightly built compared to larger theropods. It had relatively long arms with large hands bearing three fingers, each tipped with a sharp and wickedly curved claw. Its legs were built for a combination of speed and strength. They were the short legs of a sprinter, with a proportionally long tibia associated with speed in theropods. However, the metatarsal bones were short, trading speed for power. It had four toes on each foot. Digit I, the hallux, never touched the ground. Digits III and IV (the outer toes) bore the animal’s weight and were tipped with claws. But Digit II is largely what made Deinonychus famous. The inner toe was held off the ground via hyperextension and bore an enlarged laterally flattened sickle-shaped claw nicknamed the “killing claw”. All dromaeosaurs and troodontids had “killing claws”, but they were proportionally larger in eudromaeosaurs, and Deinonychus had especially large ones. With the keratin sheath it would have had in life, the killing claws of Deinonychus may have approached five inches in length!
The skull of Deinonychus was more robust than Velociraptor’s but still had large opening called fenestrae to lighten the skull. Its jaws were lined with about 70 short, curved blade-like teeth. Its bite force, once thought to have been rather weak, is now thought by some to have been stronger than a modern hyaena’s and comparable to a similarly sized alligator, though this is still debated.
Deinonychus was a warm-blooded animal and like other dromaeosaurs it would have been covered in feathers like a bird. It, like other deinonychosaurs, had a proportionally large brain, and brain proportions more similar to a bird than a reptile, thus it was probably an animal of quite respectable intelligence and possibly more bird-like in its behavior. It had large eyes and keen binocular vision like a hawk and would have had a well-developed sense of smell. Its bones were light but strong like a bird’s and it probably had an avian style respiratory system.
Behavior and Ecology: Deinonychus lived between 115 and 108 million years ago in North America. Its habitat in Montana, Wyoming, and Oklahoma consisted of a lush flood plain covered in swamps, deltas, and subtropical forests, possibly somewhat resembling modern-day Louisiana, though since flowering plants had only recently evolved, the flora would have been dominated by non-flowering plants, like conifers, cycads, and ferns. Grass would have been conspicuously absent.
Deinonychus shared this habitat with a variety of other dinosaurs. Sauropods like Sauroposeidon towered over the landscape and browsed on the treetops, while nodosaurid ankylosaurs like Sauropelta and ornithopods like Zephyrosaurus and Tenontosaurus grazed beneath them. These ornithopods are known to have been prey for Deinonychus, and there is abundant evidence that Tenontosaurus was the preferred prey of Deinonychus, despite the fact that Tenontosaurus was somewhere in the ballpark of 10x the weight of Deinonychus!
Ostrom and others hypothesized that Deinonychus hunted in packs to take down such large prey, however more recent studies suggest this was unlikely. Permanent pack structures are extraordinarily rare in reptiles and birds, plus evidence from isotope analysis of Deinonychus suggests that juvenile Deinonychus ate different prey than the adults, ergo the parents were not providing food for the offspring, and thus pack-hunting seems unlikely. Additionally, reanalysis of Deinonychus bonebeds once thought to represent a pack hunt, show that the raptors were actually fighting each other, likely competing for food during a lean season. However some birds of prey as well as and crocodilians are known to form loose temporary coalitions to take down prey, so it is not impossible that at least temporary hunting parties could have formed, though the fossil evidence suggests that they were more likely to be territorial with each other rather than share. Many birds of prey form pair bonds and also hunt as pairs, and this could also be a possibility for Deinonychus.
Regardless of how social Deinonychus was, it may not have needed teamwork to take down large prey. Studies on modern birds of prey suggest that the killing claws of dromaeosaurs had similar functions to the talons of hawks and eagles and the killing claws of seriemas. That is, their primary purpose is pinning and grasping prey, both in the killing and the consuming of said prey, which often overlaps (Dr. Grant was likely correct when he told that kid “You are alive when they begin to eat you..”). Some birds of prey, are capable of taking prey equal to or greater than their own body weight, with some like Golden Eagles preying upon the likes of sheep, goats, deer, pronghorns, and even caribou! To do this, they either drive their prey off of cliffs, or dig their talons into their back and hold on until the herbivore keels over from shock and exhaustion, often beginning to feed before the animal has even gone down. Big game hunting dromaeosaurs like Deinonychus may have used their claws to similar effect on Tenontosaurus, allowing them to potentially solo prey much, much larger than themselves.
Deinonychus was an adept hunter, but it didn’t have the predatory niche all to itself. It had to compete with the giant carcharodontosaur Acrocanthosaurus. Adult Acrocanthosaurus may have been niche portioned, preferring to hunt sauropods, thus avoiding much direct competition with Deinonychus, though they may have occasionally stolen Deinonychus kills, as large carnivores often do. But juvenile Acrocanthosaurus likely competed with Deinonychus directly for many of the same foods. Despite this however, Deinonychus seems to have been highly successful throughout its environment, leading to one of the best fossil records for any dromaeosaur. And if the remains in Utah and Maryland are indeed Deinonychus, then it may have had a near pan-continental range!
It is unclear how much parental care Deinonychus gave its young after hatching. The young were born hyper-precocious and apparently hunted for themselves. However, this does not preclude them staying their parents’ territory and receiving protection from one or both parents as is seen in crocodilians. And while post-hatch care may have been minimal, hard fossil evidence suggests Deinonychus practiced dedicated nest care and directly incubated its eggs like modern birds.
Extinction and Legacy: Deinonychus’s success seems to have come to an end around 108 million years ago. Part of the reason for its extinction may have been related to the formation of the Western interior Seaway, which had fully split North America in two north to south by 100 million years ago. As this seaway began to form, Deinonychus may have found its heartland increasingly shrinking as the ocean transgressed over the low-lying center of North America which Deinonychus called home. Whatever the cause of its extinction, it has left a lasting legacy on both paleontology and popular culture that lives on to this day.
Before the discovery of Deinonychus, dinosaurs were generally thought of as slow, lumbering, stupid, and lizard-like. Primitive evolutionary dead ends. But Ostrom and a number of other paleontologists led a great effort to change the dogma surrounding dinosaurs. It was called the “Dinosaur Renaissance” and Deinonychus was its poster boy. Deinonychus, and intelligent, fast, bird-like, potentially social creature was the opposite of how dinosaurs had been portrayed for nearly 100 years. It helped to reshape how scientists thought about dinosaurs and it showed us just how bird-like dinosaurs really were and led to another great realization: that birds are themselves dinosaurs.
And then there’s the cultural impact of Deinonychus with the general public which cannot be denied. There’s its portrayal as the “Velociraptors” in the Jurassic Park Franchise of course, as well as its appearance in paleoart, games, and documentaries (all with varying degrees of accuracy). It, either directly or indirectly, has captured the minds of millions and launched the dromaeosaurs into fame perhaps exceeded only by T-rex. Deinonychus may be extinct but in our public conscience, it is alive and thriving!
Today Deinonychus can be seen in museums such as the Yale Peabody Museum in New Haven, Connecticut, USA, the American Museum of Natural History in New York City, New York, USA, and the Field Museum of Natural History in Chicago, Illinois, USA. Life-sized life reconstructions of Deinonychus, with and without feathers, can be seen at The Dinosaur Museum in Blanding, Utah, USA.