The maxilla of "Bathygnathus "was found around 1845 in a community in the north of Prince Edward Island called French River. The bone was uncovered by a landowner named Donald McLeod in a layer of shale at the bottom of his well. This layer was part of a red sandstone formation that bears similarities to younger Triassic sandstones in the United Kingdom, leading geologists to think that the deposit dated back to the Triassic rather than the Permian. Canadian geologist John William Dawson purchased the fossil and was the first to recognize its significance. Dawson brought it to the attention of American paleontologist Joseph Leidy, who described it to the Philadelphia Academy of Natural Sciences in 1854. Leidy identified the bone as a lower jaw, a mistake that was not corrected until English paleontologist Richard Owen reinterpreted it as an upper jaw in 1876. Leidy erected the new genus and species "Bathygnathus borealis", which means "northern deep jaw" in Greek as a reference to the height of the jaw and its discovery in Canada. He identified it as belonging to a dinosaur, although he never called "Bathygnathus" a dinosaur in the paper (Dawson later described it as "a "carnivorous reptile"... one of that giant "reptile aristocracy" which constituted the highest animal type in the middle or secondary period of geologic time"). Leidy compared "Bathygnathus" with "Thecodontosaurus" from the Triassic red beds of the United Kingdom, one of the first dinosaurs to have been described scientifically.