Morrosaurus

Morrosaurus is an extinct genus of herbivorous elasmarian dinosaur that lived in the late Cretaceous in Antarctica. The only known species is the type Morrosaurus antarcticus.

Morrosaurus is an extinct genus of herbivorous elasmarian dinosaur that lived in the late Cretaceous in Antarctica. The only known species is the type Morrosaurus antarcticus. ==Palaeobiology== The hindlimb anatomy of Morrosaurus and other elasmarians, such as the slim shape of the , indicates they had adept running abilities compared to other herbivores in their ecosystem. Though unpreserved in Morrosaurus, fossils of its relatives show traits such an expanded and distinctive bony plates (intercostal plates) placed along the sides of the torso that would have granted them beneficial running traits such as strong balance, muscle control, and breathing efficiency. Though more primitive relatives such as Hypsilophodon were also strong runners, elasmarians show greater development in tail musculature and other running-associated traits than other ornithopods. Study of the histological properties of thin bone slices from the and fourth of Morrosaurus and the related Antarctic genus Trinisaura indicate they had similar growth strategies to South American relatives such as Gasparinisaura, which lived outside of the Antarctic Circle. This conforms to previous studies of Antarctic dinosaurs, but contrasts with those from the polar regions of the North Hemisphere (such as Edmontosaurus and Pachyrhinosaurus) that show distinct histology from relatives that lived in less extreme temperatures. Morrosaurus, Trinisaura, and Gasparinisaura all show variation in growth signs, with typical rapid growth intermittently interrupted and a trend towards slower growth towards age. This strategy of rapid growith but interruptions would have been a beneficial adaptation in the Antarctic region where resource availability varied throughout the year. Other more distantly related ornithopods and dinosaurs at much lower latitudes show similar cyclical growth strategies. Thus, elasmarians appear to have ancestrally possessed adaptations that allowed them to thrive at low latitudes rather than having acquired adaptations specifically for this geographic range. Growth rates were higher Morosaurus than Trinisaura, consistent with its larger body size. The only known specimen was a subadult that had reached sexual maturity but not completely ceased its growth (somatic maturity), a pattern seen in many dinosaurs. Fossils of newborns from Australia have been interpreted as strong evidence that elasmarians bred and resided in high latitude conditions year-round rather than migrating north for part of the year, as had been assumed by some in the past. ==Palaeobiogeography== The biogeographic nature of dinosaur faunas in the Southern Hemisphere was traditionally unclear. It had long been clear that Gondwana, compromising the modern southern continents, had a distinct fauna from Laurasia, the northern ones. Less evident, however, were signs of connections between the dinosaurs between these southern continents that would signify unifying biogegraphic exchange. Those found in Brazil and North Africa were distinct from those in Patagonia, India and Madagascar, and each differed from those in Australia and Antarctica, which seemed more similar to one another. Some authors had also suggested the southern continents acted as a refugium of primitive animals that had declined elsewhere in the world. Flora and marine invertebrate fauna, contrastingly, showed clear links across southern Gondwana, contiguous through Patagonia, Antarctica, Australia, and New Zealand. Together they form what is termed the Weddelian Bioprovince. Recognition of Antarctic taxa such as Morrosaurus and Trinisaura as being closely related to other elasmarians in South American demonstrated links between the dinosaurs on these continents. Later studies would expand the elasmarian group with Australian taxa as well as Kangnasaurus and Iyuku from Africa, expanding a distribution across Gondwana. Other groups of dinosaurs such as megaraptoran theropods, diamantinasaurian sauropods, and parankylosaurian ankylosaurs have more recently shown similar patterns of distribution. In particular, the dinosaurs of James Ross Island all appear to possess close relatives in the Patagonian region of South America. It is possible that, similar to what is seen with plants and marine reptiles, this terrestiral fauna extended to East Antarctica, Australia, and New Zealand, but Late Cretaceous fossils are incredibly sparse in these regions and their dinosaurian fauna remains largely unknown.

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