Imperobator

## ImperobatorPowerful Warrior

* Second known non-avian theropod from Antarctica after *Cryolophosaurus*
* Exhibits insular gigantism

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***“ 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. ”***

― **David Attenborough**, *Islands*
***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 is an ongoing subject of debate, a 2023 study suggests that *Imperobator* is a large unenlagiine like the similarly-sized *Austroraptor*.

## Description

### Size and Physique

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 a new unenlagiine taxon in northeast Patagonia in 2023, it's been tentatively suggested that *Imperobator* is a member of the unenlagiine subfamily of dromaeosaurs, representing a transitional stage between the older members like *Unenlagia* and later species like *Austroraptor*, which, much like *Imperobator*, is exceptionally large for a non-avian paravian dinosaur, rivaling the size of the largest dromaeosaurs like *Utahraptor* and *Achillobator*. It's possible that *Imperobator* gained its large size due to insular gigantism, a phenomenon also observed in the Romanian pterosaur *Hatzegopteryx* and the extinct Haast's Eagles of New Zealand (the largest eagles to ever exist), and subsequently passed on its larger size to later unenlagiines like *Austroraptor*.

Based on just one unusual foot, 45 centimeters (18 inches) long, *Imperobator* is believed to be 2 meters (6 feet, 7 inches) tall. Assuming that *Imperobator* is indeed an exceptionally-sized unenlagiine like *Austroraptor*, it would have had a probable length of 5 - 6 meters (16 - 20 feet) and a possible weight ranging around 250 - 370 kilograms (550 - 815 pounds), though this would also mean that *Imperobator* would have likely shared the same slender build and fish-eating adaptations as *Austroraptor* (e.g. narrow snout and conical teeth much like spinosaurids), in sharp contrast to its portrayal on Prehistoric Planet as a predator more heavily-built than animals of similar size and form.

### Prehistoric Planet's Depiction

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 (much like 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.

Much 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.

## Habitat

*Main: Snow Hill Island Formation*

Main: Snow Hill Island Formation

***“ 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. ”***

― **David Attenborough**, *Islands*
*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.

While *Imperobator* is only known from the Snow Hill Island Formation, it may have also lived in the much later López de Bertodano Formation, much like *Morrosaurus* (which was confirmed to have lived in the area), an idea supported by fragments of a non-avian theropod found in the region. 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.

## Behavior

***“ Fresh snow muffles the sound of their footsteps, enabling them to move undetected through the forest in search of prey. ”***

― **David Attenborough**, *Islands*
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' long, feathered tails give them remarkable maneuverability. ”***

― **David Attenborough**, *Islands*
During their segment, the different maneuvering methods of both predator and prey are shown. The *Imperobators* use their forearms and their 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, uses the mass of its tail to shift its center of gravity and make sharp turns, a skill that ultimately allowed it to get away from its pursuers.

Given the theory that *Imperobator* might be a large unenlagiine like *Austroraptor*, it may have instead been a sleek, primarily piscivorous animal. This does not necessarily invalidate its capability to ambush and pursue prey like *Morrosaurus*, as one study suggests that unenlagiines were better at chasing prey than other dromaeosaurs due to their more gracile physique.

## Appearance

* Abraham Lake, Alberta, Canada
* Callaghan Valley, British Columbia, Canada
* Alvie and Dalraddy Estates, Scotland

**Islands**, Segment V
**Setting**
Snow Hill Island Formation, James Ross Island, James Ross Archipelago, Antarctica

**Filming Location**

* Abraham Lake, Alberta, Canada
* Callaghan Valley, British Columbia, Canada
* Alvie and Dalraddy Estates, Scotland

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 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. ”***

― **David Attenborough**, *Islands*
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.

***“ 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. ”***

― **David Attenborough**, *Islands*
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 it is, they must accept that the hunt is over and their prey has evaded them, though only for that specific encounter. With that, the *Imperobators* cut their losses and walk away.

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## References

### General

1. ↑ 1.0 1.1 1.2 1.3 1.4 1.5 1.6 New Insights into Unenlagiine (Theropoda: Paraves: Dromaeosauridae) Diversity, Paleoecology, and Paleobiogeography Derived from Late Cretaceous Fossils from Patagonia and Antarctica
2. ↑ 2.0 2.1 Olivero, 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.
3. ↑ 3.0 3.1 Phylogeny of a new gigantic paravian (Theropoda; Coelurosauria; Maniraptora) from the Upper Cretaceous of James Ross Island, Antarctica
4. ↑ Differential locomotor and predatory strategies of Gondwanan and derived Laurasian dromaeosaurids (Dinosauria, Theropoda, Paraves): Inferences from morphometric and comparative anatomical studies

### Dr. Darren Naish

1. ↑ The unusual foot of *Imperobator*.
2. ↑ The winters of prehistoric Antarctica would have still covered the land in snow and ice, hence, animals back then would have needed to adapt to these changes.
3. ↑ Different maneuvering techniques were planned for both *Imperobator* and *Morrosaurus*.

### Prehistoric Planet

1. ↑ 1.0 1.1 1.2 Based on the stated length and weight of *Austroraptor* in the Swamps episode, "Twenty feet from head to tail, and weighing over 800 pounds", as well as *Austroraptor's* minimum length and weight estimate.
2. ↑ 2.0 2.1 2.2 2.3 I Know Dino: The Big Dinosaur Podcast, Episode 443: Dinosaurs on Islands. Featuring Prehistoric Planet 2