| Trinisaura Temporal range: Late Campanian
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Scientific classification 
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| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Clade: | Dinosauria |
| Clade: | †Ornithischia |
| Clade: | †Neornithischia |
| Clade: | †Ornithopoda |
| Clade: | †Elasmaria |
| Genus: | †Trinisaura Coria et al., 2013 |
| Type species | |
| †Trinisaura santamartaensis Coria et al., 2013
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Trinisaura is a genus of ornithopod dinosaur that lived during the late Campanian stage of the Upper Cretaceous, around 73 to 72 million years ago in what is now James Ross Island off the coast of northern Antarctica near Patagonia. It is known from a single, incomplete postcranial skeleton that includes several vertebrae, a partial pelvis, and nearly complete right hindlimb. The fossils were collected in 2008 by paleontologists Juan Moly and Rodolfo Coria from the sandstone of the Snow Hill Island Formation. It remained undescribed in the collections of the Museo de La Plata until its description by Coria and colleagues in 2013, being the basis of the novel genus and species Trinisaura santamartaensis. The genus name is to commemorate the efforts of Argentine geologist Trinidad "Trini" Diaz and the Latin root -sauros, meaning "lizard". The species name is after Santa Marta Cove, where the fossils were collected.
Trinisaura has been classified as a basal (early-diverging or "primitive") member of the clade Ornithopoda along with other ornithischians that had lived in the former supercontinent of Gondwana, which lived during the Cretaceous. Its only known skeleton comes from a subadult, with a small size of 1.5 metres (4.9 ft). Trinisaura was very lightly built and bipedal, with long legs built for running and a rigid tail to aid in balance during locomotion. Trinisaura is distinct from its relatives in a variety of ways, such as the shape of the ischium (back pelvic bone) and a large deltopectoral crest on the humerus (upper arm bone). Trinisaura is also noted to have a slower growth rate than genera that lived in warmer climates, an adaptation to colder temperatures of the Antarctic.
During Trinisaura's existence, Antarctica had just recently broken off from the rest of Gondwana, causing it to evolve distinct traits due to geographic isolation. It was found in the lower layers of the Gamma Member of the Snow Hill Island Formation, which preserves only one other named dinosaur, the ankylosaur Antarctopelta, in addition to a variety of aquatic animals like sharks and cephalopods. The climate during the Upper Cretaceous was much warmer than it is today, and the continent was blanketed in forests.