Morrosaurus (El Morro Lizard, a reference to the site it was found in, El Morro on James Ross Island) is an extinct genus of herbivorous ornithopod dinosaur that lived in the Snow Hill Island and López de Bertodano Formations, James Ross Island, Antarctica, 71 - 66 million years ago, during the Maastrichtian stage of the Late Cretaceous Period.
Only known from a right hind leg, Morrosaurus, with a length of 4.6 - 5 meters (15 - 16 feet), is larger and more robust than its relatives, like Trinisaura, which, at 1.5 meters (5 feet) is around three times smaller.[1] Nevertheless, it is still very small, fast, and lightweight by ornithopod standards. It is part of a clade known as "Elasmaria", which consists of small, bipedal ornithopods that used to be grouped together in a now-invalid family known as "Hypsilophodontidae".
Growth[]
Despite the harsh, cold environment, Antarctic ornithischians like Morrosaurus likely grew rapidly, albeit with interruptions at certain times
In order to reduce the cost of maintaining and nourishing themselves, animals found in cold environments tend to have different growth rates compared to their relatives in lower latitudes. While this appears to be the case for ornithischians in the Northern Hemisphere like Edmontosaurus and Pachyrhinosaurus,[2] this did not appear to also be true for Antarctic ornithischians, which are not as derived as their northern counterparts. Comparisons with Australian ornithopods and the South American Gasparinisaura confirm that, rather than adjusting their growth rates in response to the extremely low temperatures of the Southern Hemisphere, elasmarians underwent rapid growth (that gradually slows down as the animal gets older) with periodic interruptions, though, like other dinosaurs, they reached sexual maturity well before growing to their full size.[3] Based off of Australian specimens, elasmarians may have taken 5 - 7 years to grow, much like the North American thescelosaurid Orodromeus.[4]
Prehistoric Planet's Portrayal[]
Morrosaurus concept art by Gabriel N. Ugueto
“ A Morrosaurus. A plant eater for whom winter is inevitably a very hard time. Imperobators specialize in hunting such prey. ”
Prehistoric Planet depicts Morrosaurus with a feathered coat in shades of brown and gray, thus avoiding the tendency to portray dinosaurs in cold regions with coats as white as snow,[DN 1] a plan that is seen early on in the concept art made by Gabriel N. Ugueto, which shows that the animal was originally intended to have more vivid integument.[PhP 1]
“ 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. ”
Morrosaurus 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 2]
Traces of Morrosaurus are also known from the López de Bertodano Formation, the successor of the Snow Hill Island Formation, indicating that it lived up to 66 million years ago, making it a likely witness and victim of the Cretaceous-Paleogene Extinction Event which wiped out three-quarters of life on Earth, including all non-avian dinosaurs.
Paleofauna[]
To maintain their warm-blooded metabolism, hunters like Imperobators need to feed on prey like Morrosaurus regularly
“ 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. ”
In the Snow Hill Island Formation, Morrosaurus 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). It also lived alongside smaller elasmarians like Trinisauria and Biscoveosaurus (which may or may not also be Morrosaurus). These elasmarians would have likely been preyed upon by the theropod Imperobator, the largest predator known so far in the Snow Hill Island Formation. 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.
In the López de Bertodano Formation, Morrosaurus lived alongside at least five bird species, an indeterminate hadrosaur, and an indeterminate theropod that may or may not be Imperobator.[5] The area is more recognized for its marine fauna, like the elasmosaurs Morturneria and Aristonectes and the (possibly tylosaurine) mosasaur Kaikaifilu, as well as several ammonites like Diplomoceras.
Feeding Preferences and Escape Tactics[]
Morrosaurus leaps down a snowy hillside to try and escape its pursuers
“ The Morrosaurus is faster than its pursuers. But it's outnumbered by the pack. ”
Based off of neonatal fossils of elasmarians in Australia, Morrosaurus was unlikely to be a migratory animal, instead residing all year round in harsh, low conditions.[4] As a consequence of this, however, it struggles during wintertime, forced to resort to digging for what ever sustenance is left buried in the snow-covered ground of the freezing forest. While the animal's social habits are unknown, Prehistoric Planet depicts Morrosaurus as a solitary animal. Without the safety provided by the numbers of a herd, the ornithopod is more vulnerable to getting targeted and cornered by predators, especially pack hunters like Imperobator, so Morrosaurus has to stay alert at all times.
Morrosaurus makes a sharp turn
On Prehistoric Planet, 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.[DN 3] 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.
Morrosaurus viewed from behind the cover of the trees
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.
Morrosaurus gets away from Imperobator
“ 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[]
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↑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.
