Romer, A. S.; Price, L. I. (1940). "Review of the Pelycosauria". Geological Society of America Special Papers. 28: 1–538. doi:10.1130/spe28-p1.
Laurin, M.; Reisz. R. R. (1996). "The osteology and relationships of Tetraceratops insignis, the oldest known therapsid". Journal of Vertebrate Paleontology. 16: 95–102. doi:10.1080/02724634.1996.10011287.
Conrad, J.; Sidor, C. A. (2001). "Re−evaluation of Tetraceratops insignis (Synapsida: Sphenacodontia)". Journal of Vertebrate Paleontology. 21: 1–117. doi:10.1080/02724634.2001.10010852.