Nearly complete specimens of "Dimetrodon" and "Edaphosaurus" (as ""Naosaurus"") had not been found yet by the first decade of the 20th century when American paleontologist E.C. Case produced his major monograph on the Pelycosauria in 1907. Case argued that the apparent lack of any associated elongate and cylindrical tail bones with the known fossils meant that "Dimetrodon" and ""Naosaurus"" must have had short tails in life. (Earlier, Cope had assumed that the animals had long tails as in most reptiles, an idea seen from his sketches and his advice to Charles R. Knight in 1897.) Based on the authority of Case, museums and artists at the time restored ""Naosaurus"" with a short tail. New fossil finds and research by A.S. Romer in the 1930s and 1940s showed that both "Dimetrodon" and "Edaphosaurus" had long tails, a feature similar to other "pelycosaurs" and seen as primitive.