[3] This makes it larger and more robust in skeletal build than many of its relatives, including the fellow Antarctic genus Trinisaura,[1] only 1.5 metres (4.9 ft) in length.

This in turn formed a clade with other ornithopods of Patagonia and Antarctica, particularly Trinisaura, Gasparinisaura, Anabisetia, Notohypsilophodon, Talenkauen and Macrogryphosaurus in a group called Elasmaria, whose members are distinguished by their adaptation to a running lifestyle which would be reflected by the narrow foot with a thin fourth metatarsal which indicates a high speed running; subsequently expanded chevrons, a feature that is associated with a greater surface area for attachment of the lateral muscles of the tail, which would give good control of the movements of this; and a curved humerus which demonstrates the absence of a deltopectoral ridge and therefore that the front leg was not used for walking.

[1] Cladogram based in the phylogenetic analysis of Rozadilla et al., 2016: Hypsilophodon Thescelosaurus Gasparinisaura Morrosaurus Trinisaura Macrogryphosaurus Notohypsilophodon Talenkauen Anabisetia Parksosaurus Kangnasaurus Rhabdodontidae Tenontosaurus Dryomorpha Based on the hindlimb anatomy of Morrosaurus and other elasmarians, notably the slim metatarsus, it's thought they were very capable runners, distinguishing them from other herbivorous dinosaurs they lived alongside.

Elements of relatives not preserved in Morrosaurus such as expanded chevrons and distinctive bony intercostal plates along the torso would've further aided their cursorial abilities by improving tail balance and musculature control as well as breathing efficiency.

Ornithischian dinosaurs living in polar regions in the Northern Hemisphere (such as Edmontosaurus and Pachyrhinosaurus) typically show different growth rates than relatives from lower latitutes, owing to the extreme temperatures of their environments, but studies have failed to find the same signs in Antarctic animals.

[5] The discovery of Morrosaurus was concurrent with the first evidence of a previously hypothesized uniting clade of ornithopod dinosaurs from the continents that had comprised Gondwana.

The distinction between fauna of this part of the world as compared with the northern hemisphere equivalent Laurasia had long been noted, but evidence was traditionally lacking for a biogeographic link for dinosaurs between the different Gondwanan regions.

[1] This contrasted with existing recognition of links between the flora and marine invertebrate fauna between Patagonia, Antarctica, Australia, and New Zealand, termed the Weddellian Bioprovince.

[1][6] The recognition of Morrosaurus and Trinisaura as Antarctic elasmarians closely related to animals from South America constituted important evidence of such ties between these continents existing in dinosaurs as well.