The oldest fossil animals with Sioux inspired names are technically the variously assigned Brontosaurus or Apatosaurus yahnahpin. A yahnahpin is a breastplate and graced the sauropod's name in reference to the well preserved gastralia, or belly ribs, that were recovered in the fossil remains. These remains date from the Jurassic of Wyoming and the information known about the animal and shared online is mostly in the domain of message boards and academic squabbles. The best description of the material comes from the Wyoming Geological Association Field Conference of 1994, which is, unfortunately, not available online.
Another dinosaur that prominently features the Sioux language is Dakotadon lakotaensis. The name refers to a Sioux tribe, the Dakota, and the Lakota Formation of South Dakota. The name of the formation, of course, refers to another Sioux tribe, the Lakota. Originally named Iguanodon lakotaensis in 1989 by Weishampel and Bjork, the species was reassigned to a new genus as Dakotadon by Paul in 2008. Still an iguanodontid, Dakotadon is a basal member of its family and has been suggested, but not yet shown to be, a synonym for another basal iguanodontid, I. bernissartensis. The arguments continue over the phylogenetic position of the dinosaur, but the basal position is not very contentious. The fossil is important to the fauna of North America as well as being important as a representation of the Sioux language because it represents the only universally accepted iguanodontid from the continent.