Palaeosaurus

''Palaeosaurus'' (or ''Paleosaurus'') is a genus of indeterminate archosaur known from two teeth found in the Bromsgrove Sandstone Formation and also either the Magnesian Conglomerate or the Avon Fissure Fill of Clifton, Bristol, England (originally Avon). It has had a convoluted taxonomic history.

Richard Owen's mistake of associating prosauropod skeletal remains with the carnivorous teeth which Riley and Stutchbury called ''Palaeosaurus'', combined with Friedrich von Huene's '' Teratosaurus minor'', which was also a combination of carnivore and prosauropod remains, led paleontologists to view prosauropods as carnivorous animals for quite a long time. This error was included in several textbooks and other dinosaur reference works.

History and classification

Nineteenth century

In the autumn of 1834, surgeon Henry Riley (1797–1848) and the curator of the Bristol Institution, Samuel Stutchbury (15 January 1798 – 12 February 1859), began to excavate " saurian remains" at the quarry of Durdham Down, at Clifton, presently a part of Bristol, which is part of the Magnesian Conglomerate. In 1834 and 1835, they briefly reported on the finds. They provided their initial description in 1836, naming two new genera: ''Palaeosaurus'' and ''Thecodontosaurus''. In 1836 Riley and Stutchbury briefly and informally published on two new fossil teeth (the holotype tooth of ''P. platyodon'' is listed under BRSMG *Ca7448/3 and the holotype tooth of ''P. cylindrodon'' is listed under BRSMG *Ca7449/4. Both are now listed under the latter species) found in or near the city of Bristol, England, which they called ''Palaeosaurus cylindrodon'' and ''Palaeosaurus platyodon''.A series of posts to th
Dinosaur Mailing List
by George Olshevsky, regarding the history of ''Palaeosaurus''

/ref> Riley and Stutchbury did not mean to assign these species to Saint-Hilaire's genus of teleosaurids; they simply did not know the name had been used. ''Thecodontosaurus'' was also named in this publication. Only in 1840 do Riley and Stutchbury fully describe their two species of ''Palaeosaurus'', each based on a single sharp tooth from the Late Triassic Period. The spellings were then corrected to read ''Paleosaurus cylindrodon'' and ''Paleosaurus platyodon''.

In 1842, Sir Richard Owen created the name Dinosauria. In the same publication, he attempted to redescribe Riley and Stutchbury's ''Paleosaurus'' and ''Thecodontosaurus'', which he did not consider to be dinosaurs. Not knowing of the change in spelling, he changed the name back to ''Palaeosaurus'', and this spelling was followed by all subsequent authors until 1959. Owen assigns other bones to ''Palaeosaurus'', which would later be re-classified to the prosauropod dinosaur ''Thecodontosaurus''. Contrary to Owen, in 1870, Thomas Henry Huxley described both ''Thecodontosaurus'' and ''Palaeosaurus'' as dinosaurs for the first time. He considered ''Palaeosaurus platyodon'' to be synonymous with ''Thecodontosaurus antiquus'', most likely due to the ''Thecodontosaurus'' bones that Owen assigned to the former genus. However, Huxley regarded ''P. cylindrodon'' as an unrelated carnivorous theropod.

American paleontologist Edward Drinker Cope named a third species, ''Palaeosaurus fraserianus'', in 1878, for an isolated tooth found in Triassic rocks in Pennsylvania. Today these are regarded as belonging to an indeterminate sauropodomorph dinosaur unrelated to ''Palaeosaurus''. In 1881, a fourth species is created, ''Palaeosaurus stricklandi''; these are now recognized to be those of a phytosaur.

Twentieth century

Von Huene, in 1908, recognized the tooth of ''Palaeosaurus platyodon'' belonged to a phytosaur and placed it into the new genus ''Rileya'', forming the new combination '' Rileya platyodon''.

One of the holotype teeth of ''P. cylindrodon'', presumably BRSMG *Ca7448/3, was destroyed during World War II, in 1940. The other tooth survives to this day.

In 1959 German paleontologist Oskar Kuhn, for the first time since 1840, recognized that the genus ''Palaeosaurus'' created by Riley and Stutchbury in 1836 was preoccupied and created the new generic name ''Palaeosauriscus'' to contain ''Palaeosaurus cylindrodon'' and all other species that had previously been described under ''Palaeosaurus''.

In 1964, Owen's mis-classified specimens caused American Edwin Harris Colbert to classify prosauropods into two groups – Palaeosauria, which included ''Palaeosaurus'' and ''Teratosaurus'', thought to be carnivorous because of the chimaeric nature of ''Palaeosaurus''; and Plateosauria, which included ''Thecodontosaurus'' and ''Plateosaurus'', which had been described with the correct skulls, and therefore were correctly described as a herbivorous group.

Twenty-first century

''Thecodontosaurus'' was redescribed by a team of paleontologists led by Michael Benton in 2000, which placed Owen's misclassified material under the genus ''Thecodontosaurus'' rather than ''Palaeosaurus'', and this is still followed today. Most of the skeletal bones ever assigned to ''Palaeosaurus cylindrodon'' and ''P. platyodon'' were also reassigned to ''Thecodontosaurus''. The genera ''Rileya'' and ''Palaeosauriscus'', as well as the species ''Palaeosaurus cylindrodon'' and ''Palaeosaurus platyodon'', were all declared ''nomina dubia''.

In 2007, Peter Galton, reviewing the archosaurian fossils of the 1834 Bristol finds, reaffirmed the identification of the two teeth and humeri of ''Palaeosaurus platyodon'' (''Rileya'') as belonging to a phytosaur, and regarded ''P. cylindrodon'' (''Palaeosauriscus'') as an indeterminate archosaur. He agreed with Benton that ''Rileya'' is dubious, but suggested that ''Palaeosauriscus'' may be valid, based on its now-destroyed tooth with a "subcircular cross-section and fine, obliquely inclined denticles".

''Efraasia'' and ''Sellosaurus''

In 1932, Von Huene assigned new material to ''Palaeosaurus''; numerous prosauropod bones were found in Germany. Because of Owen's ''Thecodontosaurus'' bones misassigned to ''Palaeosaurus cylindrodon'', the species was thought to be a prosauropod. Von Huene therefore referred his new species to ''Palaeosaurus'', creating the name ''P. diagnostica''.

In 1973, Peter Galton, a British paleontologist, moved the species into its own genus, creating the new combination ''Efraasia diagnosticus''. For several decades, most scientists considered ''Efraasia'' a junior synonym of ''Sellosaurus''; however, in 2003 Adam Yates, another British palaeontologist, redescribed the bones assigned to ''Sellosaurus''. He resurrected the genus ''Efraasia'' for some of these bones, to which he also assigned the bones that had been first described as ''Teratosaurus minor'' as well (although leaving out the teeth, which were recognized as non-dinosaurian). Like Galton in 1973, Yates's ''Efraasia'' also included the remains previously known as ''Palaeosaurus diagnosticus'', although unlike Galton, Yates calls the species ''Efraasia minor'', synonymizing both species. ''E. minor'' was claimed to have priority because von Huene described ''Teratosaurus minor'' several pages before ''Palaeosaurus diagnosticus'' in his 1908 publication. The name ''minor'' therefore, would take precedence over ''diagnostica'' for this species.

Species

Type species: "''Palaeosaurus''" ''cylindrodon'' (''nomen dubium'') Riley and Stutchbury 1836 (an indeterminate archosauromorph later renamed the type species of ''Palaeosauriscus cylindrodon'', as ''Palaeosaurus'' was pre-occupied)

Other species:
*"''Palaeosaurus''" ''fraserianus'' (''nomen dubium'') Cope 1878 (an indeterminate sauropodomorph later renamed to ''Palaeosauriscus fraserianus'')
*"''Palaeosaurus''" ''platyodon'' (''nomen dubium'') Riley and Stutchbury 1836 (an indeterminate phytosaur later renamed the type species of the genus '' Rileyasuchus'')
*"''Palaeosaurus''" ''stricklandi'' (''nomen dubium'') Davis 1881 (an indeterminate phytosaur later transferred to the genus ''Palaeosauriscus'')
*"''Palaeosaurus''" ''diagnosticus'' Fraas, 1912 (alternatively spelled ''P. diagnostica'', described by Eberhard Fraas in 1912, and re-classified as ''P.''? ''diagnosticus'' be von Huenn in 1936; now assigned to ''Efraasia''.

See also

*'' Rileyasuchus''
*''Efraasia''

References

{{Taxonbar, from=Q7126497

Late Triassic reptiles of Europe
Prehistoric reptile genera
Prehistoric archosaurs
Fossil taxa described in 1840
Taxa with lost type specimens