Utahraptor ostrommaysi

By Nix, CC BY-NC 4.0

Etymology: Thief from Utah 

First Described By: Kirkland et al., 1993 

Classification: Dinosauromorpha, Dinosauriformes, Dracohors, Dinosauria, Saurischia, Eusaurischia, Theropoda, Neotheropoda, Averostra, Tetanurae, Orionides, Avetheropoda, Coelurosauria, Tyrannoraptora, Maniraptoromorpha, Maniraptoriformes, Maniraptora, Pennaraptora, Paraves, Eumaniraptora, Dromaeosauridae, Eudromaeosauria, Dromaeosaurinae  

Status: Extinct 

Time and Place: Between 129 and 120 million years go, from the Barremian to the Aptian ages of the Early Cretaceous 

Utahraptor is known from the Yellow Cat and Poison Strip members of the Cedar Mountain Formation 

Physical Description: Utahraptor was a very large raptor dinosaur, and had the associated bodily characteristics – a bulky trunk, shorter legs, long arms, large head, and long, stiffened tail. It was really and truly huge, about 7 meters long and 500 kilograms in weight – about the size of a modern Grizzley or Polar Bear, though they might have been heavier than previously thought. Like other raptors, it had huge sickle claws on its feet, and the claws were probably around 24 centimeters long – or even longer, if they had been covered in a keratin sheath as potentially thought. The skull of Utahraptor has not yet been described, so for now we can only say that it had a long, triangular head like other raptors, with sharp serrated teeth. As with other raptors, it would have been feathered – with very large wings for flapping, and a distinctively huge tail fan. The legs of Utahraptor would have been slightly less feathered, but still distinctive. In short, it was a big and fluffy bird-bear, and the largest predator in its environment. 

By Matt Martyniuk, CC BY-SA 3.0

Diet: Utahraptor was a large predator and, accordingly, ate large sources of food such as ornithopods and younger sauropods. 

By PaleoNeolitic, in the Public Domain

Behavior: As a raptor, Utahraptor would have been most analogous to a cat – probably stalking alone rather than in packs, and utilizing ambush behavior to trap its prey. Since it had somewhat stubby legs and wasn’t very fast at all, it couldn’t have relied on pursuit to attack its food, even if its food was just as slow as it was. Instead, these powerful legs helped Utahraptor to jump onto its food and surprise it, even from the ground where it spent its time. It then could use raptor prey restraint (RPR) to stay balanced on the prey, flapping its wings rapidly as the prey moved around and tried to escape. Those impossibly large sickle claws then were used to strategically stab at places where the prey would bleed out – important veins and arteries – rather than slash. In addition to this, Utahraptor would have been able to flap its wings rapidly and run up steep surfaces – a technique called Wing-Assisted Inclined Running (WAIR) –  even vertical ones, like cliff faces and trees. This allowed Utahraptor to reach strategic vantage points and search for prey – and even jump down onto it from high heights. These techniques allowed Utahraptor to not only hunt the similarly-sized Ornithopods of the time, but also potentially attack the even larger Sauropods with which it shared its home. When it needed a smaller snack, that large claw could be used to pin down struggling furry mammals and lizards, in order for Utahraptor to then take a bite. 

By Fred Wierum, CC By-SA 4.0

Though Utahraptor did not hunt in packs, that doesn’t mean it wasn’t social – and, indeed, there is considerable evidence not yet described that it lived in dense family groups. This would probably mean that adult Utahraptor would go out hunting on their own, while the little ones would gather their own food, before coming together in the same space for safety from other Utahraptor and just to spend the night. It is very likely that Utahraptor took care of its own young based on its relatives – and there’s hopefully more evidence on the way to corroborate this. This was a very complex social animal, using those fancy wings and tail fan to display to other Utahraptor – by holding up the wings and lifting the tail fan to display, it could communicate with others that it was a threat, that it wanted to mate, or to stay away from its nest. In general, it would have behaved very bird-like – walking around, bobbing its head, and moving its head to look for food and for each other rather than moving the eyes. And, like birds, it would have been very active, and warm-blooded. 

 

By Ashley Patch

Ecosystem: When the Cedar Mountain Formation supported Utahraptor, it was a very large floodplain environment, that periodically flash flooded and filled the valley with mud. This was a seasonally wet environment with a variety of rivers, forests, prairies, and open woodlands. The ecosystem had a short wet system and a very long, tedious dry season. Utahraptor shared this environment with countless creatures – the tuataran Toxolophosaurus, the turtle Glyptops, a variety of fish, the mammaliaform Cifelliodon, and – of course – other dinosaurs. There was the ankylosaur Gastonia, the large Iguanodon-like Ornithopods Cedrorestes, Hippodraco, and Iguanacolossus; the Sauropods Cedarosaurus and Mierasaurus; the Therizinosaurs Martharaptor and Falcarius; the Troodontid Geminiraptor; the Ornithomimosaur Nedcolbertia; and another raptor – Yurgovuchia! This gave Utahraptor a wide variety of things to hunt in its environment. 

By Emily Willoughby, CC By-SA 3.0

By the time of the later Poison Strip environment, things were changing rapidly in Cedar Mountain. Dry seasons were longer now, and a significant amount of sand was washing through the ecosystem. This made life higher in the floodplain, and probably eliminated many of the forests and river-woods that had been present prior to, leaving only a somewhat scrubland-esque plain. Accordingly, creature diversity actually went down – it was something of an ecosystem collapse. There was still food for Utahraptor to eat – the Ornithopod Planicoxa, and the sauropods Moabosaurus and Venenosaurus; but that was it. Utahraptor, thus, was living in a miniature extinction event – and disappears from the environment by the time the mud and rainy seasons returned in the Ruby Ranch Environment, and the large predator niche was replaced by the carnosaur Acrocanthosaurus. 

By Calum O’Halloran

Other: Utahraptor was the largest raptor known, and we actually have many fossils of it – but they’re trapped in a block! Well, there isn’t funding to remove them from the block, anyway. So much more could be (and will be, dammit!) written about this excellent dinosaur if it was adequately funded to be researched properly. Check out the Utahraptor Project if you want to learn more about Utahraptor – and consider donating! Literally every penny helps. Utahraptor is also one of the inspirations for the raptors of Jurassic Park, along with Deinonychus – though, obviously, those creatures do not resemble their real counterparts in the slightest. 

~ By Meig Dickson

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