Antarctopelta

AntarctopeltaAntarctic Shield
Classification
Domain	Eukaryota
Kingdom	Animalia
Phylum	Chordata
Subphylum	Vertebrata
Superclass	Tetrapoda
Clade	Sauropsida
Class	Reptilia
Clade	Archosauria Avemetatarsalia Ornithodira Dinosauria Ornithischia Thyreophora Ankylosauria Parankylosauria
Species	Antarctopelta oliveroi
Presence
Location	Snow Hill Island Formation, James Ross Island, Antarctica
Temporal Range	71 - 70 million years ago, Maastrichtian Stage, Late Cretaceous Period
Episodes	Ice Worlds (Segment 5)
Characteristics
Height	1.2 meters (4 feet)
Length	4 - 6 meters (13 - 20 feet)
Mass	350 kilograms (770 pounds)
Diet	Herbivorous
Possibly possesses a tail sword like its relative, Stegouros

“ The Southern Hemisphere has its own species of dinosaurs. These three are young Antarctopelta, small plant-eating dinosaurs. They're also one of this world's most heavily-armored animals. Even so, youngsters are safer together. ”

― David Attenborough, Ice Worlds

Antarctopelta (Antarctic Shield) is a genus of parankylosaurian 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.

Paleobiology

Like other ankylosaurs, Antarctopelta was a stocky, herbivorous quadruped protected by armor plates embedded in the skin. Although a complete skeleton has not been found, the species is estimated to have been a medium-sized animal, 4 - 6 meters (13 - 20 feet) long and weighing 350 kilograms (770 pounds).

Antarctopelta was originally classified as a primitive nodosaurid, being reconstructed with the appearance of one on the show. Even so, for many years, the ankylosaurs of Gondwana were enigmatic, as their strange features made their exact placement in the ankylosaur clade hard to ascertain. However, in 2021 (just one year before the first season of Prehistoric Planet was aired, too late to make adjustments to), clarifications were finally made in a paper about Stegouros elengassen (ancient Greek for "Roofed Tail"), an ankylosaur found in 2018 in the Dorotea Formation (75 - 72 million years old) of southern Chile. Rather than possessing a tail club, Stegouros had seven pairs of flattened tail osteoderms (along with an eighth pair of small, knob-shaped osteoderms by the tail tip) which the authors of the study have compared to a "macuahuitl", an ancient Aztec weapon with razor-sharp obsidian teeth that made it seem like a combination of a sword, a war club, a saw, and a paddle.

From here, the research study describing Stegouros established a new group of ankylosaurians, encompassing Antarctopelta, Stegouros, Kunbarrasaurus ieversi (which lived in Australia around 105 - 100 million years ago), and possibly Patagopelta cristata (which is known from the Allen Formation of Argentina). This clade, known as "Parankylosauria" (Near Fused Lizards), is made up of small ankylosaurs that migrated to the Southern Hemisphere and thus evolved to be quite distinct from their ankylosaurid and nodosaurid relatives in the north, with their clade likely going as far back 167 million years ago, possibly even before the first euankylosaurians (true fused lizards). For this reason, they retained traits more like those of primitive thyreophorans and stegosaurs, most noticeable of these being their strangely long, slender limbs and their thin pelvic shield, tougher than the thin, superficial sheets found over stegosaur hips, but less robust than the pelvic shields of euankylosaurs. Although yet to be proven, given its close relationship to Stegouros, it is possible that Antarctopelta also possessed a macuahuitl-like tail, an intimidating defense against predators like Imperobator.

Paleoecology

Paleoenvironment

Main: Snow Hill Island Formation

Main: Snow Hill Island Formation

“ In the Antarctic, ice clings to the highest mountains even in the summer months, but now, with temperatures falling, and the days shortening, the polar winter is spreading once more across the land. Animals must now prepare for its return. ”

― David Attenborough, Ice Worlds

Antarctopelta 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.

Paleofauna

Antarctopelta coexisted with animals like the bird Antarcticavis, the fleet-footed elasmarian ornithopods Morrosaurus, Trinisauria, and Biscoveosaurus (which may or may not also be Morrosaurus), and indeterminate animals like an iguanodontid, a titanosaur, and a pterodactyloid pterosaur with a wingspan of 4 - 5 meters (13 - 16 feet). Given its armor and possible macuahuitl-like weaponry, Antarctopelta would not have been targeted frequently by the theropod Imperobator, the largest predator known so far in the Snow Hill Island Formation. However, while Imperobator is better meant to hunt elasmarians, it would not have entirely avoided going after Antarctopelta, especially when opportunities (e.g. the presence of a sick or incapacitated Antarctopelta) and certain circumstances (e.g. lack of other suitable prey in the area) make attacking the parankylosaur a viable choice. The area is also known for its sea life, like the elasmosaur Vegasaurus and the tylosaurine mosasaur Taniwhasaurus, as well as several fish and corals.

Social Behavior

“ This far south, the plants on which they depend stop growing for months on end. As winter approaches, these juveniles spend more time resting. Sheltering together conserves heat, and therefore energy. ”

― David Attenborough, Ice Worlds

Generally, adult ankylosaurs are found alone, supporting the idea that they are solitary animals. But some bonebeds suggest that some ankylosaurs lived gregariously at some point in their lives, with several Pinacosaurus mass-burial sites indicating that they were more likely to group up as juveniles. However, such mass death assemblages may also be caused by other factors, like natural disasters (e.g. floods) forcing animals together, consequently killing or depositing them in the same place. Furthermore, when fully grown, ankylosaurs were capable of fending for themselves alone.

“ With powerful front limbs, they can enlarge this winter den. But each time they return, they've grown a little bigger. Their den seems a little smaller, and the brotherly bond starts to wear a little thin. ”

― David Attenborough, Ice Worlds

While all these findings appear to only concern euankylosaurs (as hints that could shed light on parankylosaur social lifestyle are yet to be found), it is reasonable to believe that parankylosaurs lived in a similar manner. Prehistoric Planet portrays the Antarctopelta living in closely-knit groups, likely comprised of siblings. However, as they gradually grow larger, the juveniles must separate from one another and embark on independent journeys. This separation is necessary due to limitations in resource sharing, as they become too large to inhabit their original rocky den together. Prehistoric Planet also depicted other animals living in this way, with juveniles grouping up, and adults living alone, as demonstrated by Alcione, Therizinosaurus, Zalmoxes, Isisaurus, Tarchia, and Nostoceras.

Appearance

The fifth, penultimate segment of Ice Worlds takes place in Antarctica, just right when autumn is heralding the return of winter. Layers of snow and frost, once limited to just the highest of areas, begin to crawl back down to the lower regions, with the glaciers once more building up, and a river cascading down the side of a mountain slowly being claimed by the ice. In the forest, three young Antarctopelta prepare for winter hibernation. As they journey through the woods, one of them tries to pick some of the remaining vegetation from the roots of a tree. It is clear, however, that, in a short while, there will be little to no food, hence, the next few months would be a time of rest rather than a time of feeding. The three juveniles eventually find the small cave in which they rest in every winter. Unfortunately, this time, given their size, only two of the three ankylosaurs can fit in the cave. With his brothers making it clear that he can no longer share the den with them, the third Antarctopelta dejectedly sets off on his own to look for a place to rest.

“ For every growing animal, this is a vulnerable time, a time when they need to separate and each take its first tentative steps to find a territory of its own. ”

― David Attenborough, Ice Worlds

As his brothers sleep snugly in their den, the young Antarctopelta lies uncomfortably in the open, on the leaf-littered floor of the forest, with the noticeable increase in fog indicating the short time left before the cold times really close in. Unable to properly sleep, he is left with no other choice but to get up and continue the search for shelter and avoid the freezing winter.

Antarctic hadrosaur herd crosses paths with a young Antarctopelta

“ Herds of hadrosaurs are once again on the move. With little to eat, these huge herbivores return to look for food in warmer lands, leaving others to endure the freezing polar winter. ”

― David Attenborough, Ice Worlds

The Antarctopelta eventually makes it to an open, stony field, coming across a herd of hadrosaurs searching for warmer areas where there is more food. One hadrosaur tries to check for food from a log, to no avail. For a moment, this individual and the Antarctopelta regard each other before continuing on their journey down opposite paths, the Antarctopelta searching for a place to rest in and wait the incoming winter out, the hadrosaurs looking for a more bountiful region that can sustain them.

“ Finding a suitable territory can take animals far from the place where their lives began. It's a search that many will not survive. A cave, perhaps. ”

― David Attenborough, Ice Worlds

Once more in a forest, the Antarctopelta makes his way down the woodland's rugged, treacherous grounds. Eventually, however, he finds himself facing down the mouth of a large cave.

“ Even in the coldest months, the temperature in most caves hardly varies. But he is not the first to be attracted by this one. This cave glows. These are the tiny lures of fungus gnat larvae that produce light to attract their insect prey. This is the perfect place for an Antarctopelta to escape the worst winter weather. He'll be safe beneath these strange living stars, while outside, snow begins to fall. ”

― David Attenborough, Ice Worlds

Walking down a stony slope, the Antarctopelta takes a good look of the large, warm cavern, its ceiling lit up by the whitish-blue glow of silky threads, the lures of fungi to attract insects for them to eat. Having found refuge from winter at last, the Antarctopelta makes his way to a corner of the cave and curls up to take his well-earned rest.