Pachyrhizodus fossils were first collected from Cambridgeshire, England in the 1840s and were very fragmentary, only a partial maxilla (SMB.9097) and were described as a species of Raphiosaurus in 1842 by Richard Owen. The type remains of Pachyrhizodus consisted of a maxilla (BMNH 49014) from the Lower Cretaceous of Sussex, England and was originally thought to be a mandible that Louis Agassiz dubbed Pachyrhizodus in 1850,Dixon, F. (1850): Geology and Fossils of the Tertiary and Cretaceous Formations of Sussex. – 422 pp.; London (Longman, Brown, Green & Longmans). with Frederick Dixon creating the species name basalis for the specimen. Over the next few years, many Pachyrhizodus species would be named only from England until in 1872, Edward Drinker Cope described large remains from the Smoky Hill Chalk of Kansas of several new species.Cope, E. D, 1872, On the families of fishes of the Cretaceous Formation of Kansas: Proceedings of the American Philosophical Society, v. 12, p. 327-357. During the 19th century, several complete and partial skeletons of Pachyrhizodus were collected from England, many of which belonging to P. basalis and P. subulidens.Forey, P. L. (1977). The osteology of Notelops Woodward, Rhacolepis Agassiz and Pachyrhizodus Dixon (Pisces: Teleostei), Bull. Brit. Mus. Nat. Hist. (Geol.), 28, 125–204. In 1899, Alban Stewart described the mandibles of another species, P. minimus, from Kansas and it is the most commonly discovered species of Pachyrhizodus.Stewart, A. (1899). Pachyrhizodus minimus, a new species of fish from the Cretaceous of Kansas. Kansas University Quarterly, 8(1), 37-38.Everhart, M. J., (2005) Oceans of Kansas: A Natural History of the Western Interior Sea. Indiana University Press, Bloomington, 220 p. Since the 19th century, many complete skeletons and species have been described from many regions.Bartholomai, A. (1969). The Lower Cretaceous elopoid fish Pachyrhizodus marathonensis (Etheridge Jr.). Stratigraphy and Palaeontology. Australian National University Press, Canberra, 249-263.Giersch, S., Frey, E., Stinnesbeck, W., & González González, A. H. (2010). Pachyrhizodus caninus Cope, 1872 (Teleostei, Crossognathiformes) from the early Turonian of Vallecillo (Mexico). Neues Jahrbuch für Geologie und Paläontologie, Abhandlungen, 258, 219-228. P. caninus specifically has been discovered in the United States, Mexico, and New Zealand.Shimada, K. (2015). Body form and paleoecology of the large Late Cretaceous bony fish, Pachyrhizodus caninus. Cretaceous Research, 52, 286-291.
