 Beginning in the late 1920s , paleontologist Alfred Romer restudied many Dimetrodon specimens and named several new species . In 1940 , Romer coauthored a large study with Llewellyn Ivor Price called " Review of the <unk> " in which the species of Dimetrodon named by Cope and Case were reassessed . Most of the species names considered valid by Romer and Price are still used today . 
