Dimetrodon borealis

Dimetrodon borealis, formerly known as Bathygnathus borealis, is an extinct species of pelycosaur-grade synapsid that lived about 270 million years ago, during the Early Middle Permian period. A partial maxilla or upper jaw bone from Prince Edward Island in Canada is the only known fossil, which was discovered around 1845 during the course of a well excavation in Spring Brook in the New London area and its significance was recognized by geologists John William Dawson and Joseph Leidy. It was originally described by Leidy in 1854 as the lower jaw of a dinosaur, making it the first purported dinosaur to have been found in Canada, and the second to have been found in all of North America (the first was Clepsysaurus from Pennsylvania, now known to be a phytosaur rather than a dinosaur). The bone was later identified as that of a sphenacodontid pelycosaur, specifically a species of Dimetrodon.