“ Imperobator. Hunters. Like most dinosaurs, they are warm-blooded. But to stay warm, they need a lot of food, so they must make a kill every few days if they can. ”
Imperobator (Powerful Warrior) is a genus of paravian theropod dinosaur that lived in the Snow Hill Island Formation, James Ross Island, Antarctica, 71 - 70 million years ago, during the Maastrichtian stage of the Late Cretaceous Period. While its full relationship with dromaeosaurs was initially a subject of debate, studies in 2023 and 2024 suggest that Imperobator is an unenlagiine,[1][2] a medium-sized dromaeosaurid maniraptoran predator around the size of Deinonychus.[3]
Initially nicknamed the "Naze dromaeosaur" when it was described in 2007, it was soon discovered that Imperobator lacked some key dromaeosaur traits, most notable of these being the absence of a sickle claw on the second toe of each foot. This appeared to indicate that, while not a true dromaeosaur, Imperobator developed a body plan similar to its paravian relatives due to convergent evolution. However, with the discovery of Diuqin lechiguanae (Mapudungan for "Bird of Prey"), a Santonian (86 - 83 million years in age) unenlagiine taxon discovered in the Bajo de la Carpa Formation of Neuquén Province in Patagonian Argentina, it has been tentatively suggested that Imperobator is a member of the unenlagiine subfamily of dromaeosaurs, with Diuqin representing a transitional stage between the older members like Unenlagia and later species like Imperobator and Austroraptor,[1][2][3] with the latter being exceptionally large for a non-avian paravian dinosaur, rivaling the size of the largest dromaeosaurs like Utahraptor, Dakotaraptor (controversial due to being a possible chimera, a fossil reconstructed with the remains of more than one animal species),[6] and Achillobator.
Based on just one unusual foot, 45 centimeters (18 inches) long,[DN 1]Imperobator was believed to stand higher than the average human, being around 2 meters (6 feet, 7 inches) tall,[7] making it appear to be as large as its Argentinian relative Austroraptor. However, a 2024 study suggests that it is only half the size of Austroraptor, and more in line with the size of Deinonychus, around 2 - 3.4 meters (6 feet, 7 inches - 11 feet, 2 inches) in body length, albeit heavier than its estimated mass of 100 kilograms (221 pounds). Furthermore, this same study proposes that the supposed second metatarsal (bone before the toe) of Imperobator is in fact the fourth metatarsal of its right foot. This suggests that the idea of Imperobator supposedly not having the recognizable sickle toe of other dromaeosaurs was derived from assumptions based on the wrong toe, which, in turn, could mean that Imperobator may have had a sickle claw on its second toe after all, though that remains to be discovered and confirmed.[5][3]
As an unenlagiine, Imperobator likely shared the same slender build and fish-eating adaptations as Austroraptor (e.g. narrow snout and conical teeth similar to those of spinosaurids), in sharp contrast to its portrayal on Prehistoric Planet as a predator more heavily-built than animals of similar size and form.[1][2]
Prehistoric Planet's Portrayal[]
Imperobator concept art by Gabriel N. Ugueto
On Prehistoric Planet, it appears that Imperobator took some design cues from a polar bear, with dark scales (as shown by the area around their eyes and the front of their snouts, as well as parts of their upper legs and tails, which are not as heavily-feathered as the rest of the body) beneath a thick coat of what appears to be translucent feathers (similar to the translucent fur of polar bears) that can appear white, gray, or black, or even have a faint yellowish or greenish tint, due to lighting, viewing angles, or dirt and grime. The feathers of their arms and pygostyles (tail fans) also come in black. While overall sleek in form, they appear robust compared to similar animals. This design choice was done to avoid the tendency to portray dinosaurs in cold regions with coats as white as snow,[DN 2] a plan that is seen early on in the concept art made by Gabriel N. Ugueto.[PhP 1]
Like Atrociraptor, the unidentified Alaskan troodontid, and Dromaeosaurus, Imperobator is depicted with legs that are heavily feathered like those of a booted eagle, in contrast with other paravians in the series like Velociraptor, which have bare legs. This trait is likely an adaptation for the cold environment it lived in.
“ In the far south of the planet, on the islands of the Antarctic peninsula, winter brings months of freezing temperatures. Here, too, being part of a family brings benefits. ”
Imperobator lived 71 - 70 million years ago in the Snow Hill Island Formation, James Ross Island, Antarctica. During that time, Earth's climate was much warmer and more humid than today, thus, Antarctica would have had a climate similar to those of modern-day volcanic arcs supporting large, dense conifer forests, cycads, and ginkgos. Even back then, however, much like Antarctica today, the inhabitants of the island had to endure a long period of cold, dark months during the winter, and hence had to adapt to the freezing temperatures as snow and ice cover up the temperate forests of the region.[DN 3]
A frozen lake, half a mile in width
While Imperobator is only known from the Snow Hill Island Formation, it may have also lived in the later López de Bertodano Formation like Morrosaurus (which was confirmed to have lived in the area), an idea supported by fragments of a theropod found in the region.[4] If Imperobator is proven to be an unenlagiine dromaeosaur, it would serve as further proof of the connection between South America and Antarctica given their similarities in fauna.[1][2]
Paleofauna[]
“ A Morrosaurus. A plant eater for whom winter is inevitably a very hard time. Imperobators specialize in hunting such prey. ”
Imperobator is the largest land predator discovered thus far in the Snow Hill Island Formation. It coexisted with animals like the bird Antarcticavis, the heavily-armored parankylosaur Antarctopelta, and indeterminate animals like an iguanodontid, a titanosaur, and a pterodactyloid pterosaur with a wingspan of 4 - 5 meters (13 - 16 feet). As a swift theropod that likely matched a human in size, Imperobator would have likely targeted the similarly sized and similarly quick elasmarians like Trinisauria, Morrosaurus, and Biscoveosaurus (which may or may not also be Morrosaurus). The area is also known for its sea life, like the elasmosaur Vegasaurus, the tylosaurine mosasaur Taniwhasaurus, several fish, and corals.
Social Behavior, Hunting Tactics, and Feeding Preferences[]
The Imperobators get up and prepare to hunt
“ Fresh snow muffles the sound of their footsteps, enabling them to move undetected through the forest in search of prey. ”
Due to the harsh conditions, Imperobators form family packs of at least five to help in conserving heat (by huddling together) and hunt prey for the whole group with the cooperation of several of the members. They are shown to be intelligent enough to take advantage of the environment, like the cover of the trees and the soft snow, to help conceal them and soften the sound of their footsteps, making them more stealthy as they hunt and stalk for prey in the forests of Antarctica.
The Imperobators spread their feathered arms out as they run and leap
“ The Imperobators' long, feathered tails give them remarkable maneuverability. ”
On Prehistoric Planet, the different maneuvering methods of both predator and prey are shown. The Imperobators are depicted using their forearms and tails (which constantly swing as they run) to balance themselves, control their descent, and help steer their bodies while running, serving as brakes, much like a ship's rudder or a cheetah's long tail. The Morrosaurus, on the other hand, is seen using the mass of its tail to shift its center of gravity and make sharp turns.[DN 4] In the fifth segment of Islands, it was this skill that ultimately allowed the ornithopod to get away from its pursuers, at least, in that specific encounter. The maneuvering methods of both animals are not necessarily superior or inferior to each other; instead, the success or failure of a predator's hunt or prey's evasion depends on factors both within and beyond their control, like individual fitness, the terrain, and even sheer luck.
Given support for the theory that Imperobator might be a unenlagiine like Austroraptor, it may have instead been a sleek, primarily piscivorous animal.[1][2][3] This does not necessarily invalidate its capability to ambush and pursue prey like Morrosaurus, as a study in 2020 suggests that unenlagiines were better at chasing prey than other dromaeosaurs due to their more gracile physique. Assuming that Imperobator possesses the smooth, conical, spinosaurid-like teeth of Austroraptor, it can use its teeth both for the primary purpose of gripping slippery fish, but also for seizing larger land-based animals, as the conical shape of teeth matching its body size would be resistant enough to withstand the stresses of large, struggling prey.[8]
Imperobator observing the Morrosaurus from behind cover
In the fifth, penultimate segment of Islands, deep within a freezing hillside forest, a family of five Imperobators are viewed through a thermal camera. To get food for the pack and maintain the heat they have, three of them set off to find food. The three hunters travel downhill, the snow muffling the sounds of their feet, enabling to move undetected as they search for prey. In the forest, a lone Morrosaurus is seen struggling to forage for food through the snow, with the Imperobators slowly approaching it from the cover of the trees. Sensing their presence, the Morrosaurus immediately runs down the slope of the snowy hill, its hunters rushing out to pursue it.
The Imperobators chase the Morrosaurus across a frozen lake
“ The chase has reached the very edge of the forest. Beyond lies a frozen lake, half a mile wide. The clear, open space could give the faster Morrosaurus an advantage. But the frozen surface is treacherous. With the Imperobator closing in, it isn't much of a choice. ”
Upon exiting the forest, the Morrosaurus is greeted by a frozen lake. While it can better use its superior speed in this open area to lose its pursuers, the elasmarian hesitates due to the possible dangers of frozen, slippery surface, which could potentially be fragile in some places. Left with no choice due to the hunters closing in on it, the ornithopod rushes across the frozen lake, the three theropods just right behind. Swinging its tail to shift its center of gravity, the Morrosaurus makes a tight turn, avoiding the jaws of one of the Imperobators in a nick of time, causing the hunter to slip as its two other packmates behind it continue the chase.
Imperobators after a failed hunt
“ A misplaced step, a chance for the Morrosaurus to sprint beyond the predators' reach. But this is an island, so hunters and hunted will almost certainly meet again. ”
As the Morrosaurus ultimately gets away, the two other Imperobators halt their pursuit. In frustration, one snaps in the direction of the Morrosaurus, likely insisting that the hunt be continued, while the other, just as exasperated, snaps back, forcing the other to flinch away. As vexing as the situation is for the theropods, it is clear that the hunt is over and their prey has evaded them, though only for that specific encounter. With nothing more that could be done about the matter, the Imperobators cut their losses and walk away.
Gallery[]
Join us for a story you've never heard, on a scale you've never witnessed
↑ 4.04.1Olivero, E.B.; Ponce, J.J.; Marsicano, C.A.; Martinioni, D.R. (2007). "Depositional settings of the basal Lopez de Bertodano Formation, Maastrichtian, Antarctica". Revista de la Asociación Geológica Argentina. 62 (4): 521–529.
