Troll_Man
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WWD: cf. Australovenator wintonensis
🕑 Added 2023-07-14 08:33:02 +0000 UTCOne of the more notorious animals featured in the series was the "polar allosaur" that was the primary antagonist in "Spirits of the Ice Forest". It should be well known now that there is no such animal, although the details on its true identity are a bit murkier. Although it is widely thought to actually be Australovenator, this is impossible given that this species was only excavated in 2006, a full eight years after production of WWD, and was not described until 2009.
In reality, the polar allosaur was based on a single fragmentary ankle bone found in the Wonthaggi Formation which was considered to belong to a species of Allosaurus or an Allosaurus-like animal (it was never officially given a name, but was sometimes referred to, informally, as "Allosaurus robustus") in a 1981 study. This was the prevailing idea, and often repeated in dinosaur media from the 1980s onward, until it was reevaluated with new studies, starting in the 2000s, as most likely belonging to either a megaraptoran or abelisaur. WWD is probably the last real appearance of the idea of the animal as an Allosaurus relative.
The classification of the ankle bone as Allosaurus, despite the massive geographical and temporal difference, was used as evidence that Australia was a prehistoric refugium where forms otherwise extinct managed to cling on in isolation (alongside the discovery of Koolasuchus, but we'll get to that next), but of course its reclassification into a megaraptoran/abelisaur deflates that idea considerably, since both of those two groups were extremely widespread across Gondwana during the Cretaceous.
Far more being rare at the time, allosaurs, or more broadly, carnosaurs, were the dominant land predators of the Early-Mid Cretaceous, including some of the largest carnivores to ever walk the Earth, with carnosaurs known from every continent, except Antarctica, around the period of the episode's temporal setting. Megaraptorans were one of the three groups of large theropod carnivores which lasted until the very end of the Mesozoic (although they may not actually be carnosaurs...).
Australovenator's discovery helped the idea that this bone belonged to a megaraptoran so much that even the BBC website started referring to the WWD polar allosaur as Australovenator, but this genus is only known from a much younger and more northern fossil formation outside of it being found much too late. Unnamed megaraptorans are known from the Eumeralla Formation and would have been the region's apex predators however, including fossils likely indicating a very Australovenator-like animal (although slightly smaller in size) which were described in a 2019 study and is used here (since it's marginally more complete than one ankle bone, with one ankle bone, two teeth, and two claws, and is about the same size as the polar allosaur in the episode).
So here we mention the elephant in the room: the classification of megaraptorans. For decades their exact placement amongst theropod groups has bounced around. Megaraptor has gone being thought of as a dromaeosaur, a spinosaur, an advanced allosauroid, a basal coelurosaur, possibly even a tyrannosaur. Currently the two main ideas being bounced around is that the group is that they are either advanced allosauroids or basal tyrannosaurs, but it's not even close to being conclusive. If megaraptorans do turn out to be allosauroids, it would mean the original idea of "Allosaurus robustus" being a "polar allosaur" would technically be correct.
I've given the megaraptoran a speculative shaggy, feathered coat here owing to the animal being well within the size range of having feathers, it living in a temperate, seasonal climate, and its possible ancestry as a coelurosaurs (for which feathers are known even in very basal species). Notably, many megaraptoran fossils are known from areas of high latitudes at the time, including Antarctica, which seems to suggest they were well-adapted to these seasonal, wintery climates.
