Goodbye Temnodontosaurus, hello Proteosaurus?

Proteosaurus lectotype

Illustration of the skull of NHMUK PV R 1158 from Home (1814), and photograph from McGowan (1974). Scale bar is 25 cm.

In 1811, Joseph Anning discovered the first complete ichthyosaur skull on the Jurassic Coast between Lyme Regis and Charmouth, England. The following year, his sister Mary Anning found a partial skeleton that belonged to the same individual. The Annings sold the whole specimen for £23 to the landowner Henry Henley, who then loaned it to William Bullock’s Museum of Natural History in London for study (Home, 1814; Torrens, 1995). It was there that Everard Home observed this ichthyosaur, and in 1814 he published the first description and illustrations of it (Home, 1814). When Bullock’s museum closed in 1819, the specimen was purchased by the British Museum (Natural History) and catalogued as BMNH R 1158 (Torrens, 1995). Its current number is NHMUK PV R 1158 (PV R 1158, n.d.).

In 1819, Home created the genus Proteosaurus for PV R 1158 and a number of other ichthyosaurs that he had studied (Home, 1819a;b). He did not include a species name, and thus did not fix a type species, but this is allowed for genera named before 1931 (ICZN Art. 12). He also did not designate a holotype out of the specimens that he described, so they are all syntypes of Proteosaurus (ICZN Art. 73.2). Owen (1840) was the first to refer PV R 1158 to the species Ichthyosaurus platyodon, which had been named by de la Beche in Conybeare (1822). I. platyodon was made the type species of the new genus Temnodontosaurus by Lydekker in Nicholson & Lydekker (1889). Since then, PV R 1158 has been referred to Temnodontosaurus platyodon (e.g., McGowan, 1974) and Proteosaurus has been forgotten.

However, Hay (1902) resurrected Proteosaurus and designated I. platyodon as its type species. Hay was the first to associate a species name with this genus and fix a type species, so his designation alone is valid (ICZN Art. 69.1 & 69.3). Although platyodon was not technically included in Proteosaurus by Home, material referable to this species does constitute one of the syntypes. I propose that NHMUK PV R 1158 should be the lectotype of Proteosaurus platyodon (ICZN Art. 74.1), and that the selection of NHMUK PV R 2003 as the neotype by McGowan (1974) be rejected. Since they have the same type species, Temnodontosaurus Lydekker in Nicholson & Lydekker, 1889 is an objective junior synonym of Proteosaurus Home, 1819. Additionally, the family name Temnodontosauridae McGowan, 1974 is a junior synonym of Proteosauridae Hay, 1902. 

Temnodontosaurus is currently in prevailing usage in the ichthyosaur literature. Proteosaurus has been used as a valid name after 1899 (Hay, 1902) and cannot be considered a nomen oblitum (ICZN Art. 23.9). Thus Temnodontosaurus cannot be made a nomen protectum, and the only way to conserve it would be to submit a petition to the ICZN to suppress Proteosaurus. The alternate option would be to accept Proteosaurus as the genus name for platyodon and related species and gradually phase out usage of Temnodontosaurus. I will leave this issue for ichthyosaur workers to decide.

References

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