FastCounter by bCentral
Who is the Bristol Dinosaur?
The Complicated Story of the Naming of the Bristol Dinosaur
Riley and Stutchbury named the two new genera Thecodontosaurus and Palaeosaurus in their 1836 paper, based on finds from the quarries on Durdham Down, Bristol. Since 1836, the history of these names has been rather tangled, and the story is told in full here. [Don't read this unless you are feeling strong and have a stiff drink to hand.]
In the 1836 paper, Riley and Stutchbury misspelled both species of Palaeosaurus, as P. cylindricum and P. Platyodon. In their 1837 paper, the genus Palaeosaurus is referred to in a footnote (p. 91), together with its two species P. cylindrodon and P. platyodon [both now spelled correctly], but the genus name is spelled Paleosaurus in a table on p. 94. The descriptive memoir (Riley and Stutchbury, 1840) offers full descriptions of the two species of Paleosaurus [note spelling], P. cylindrodon and P. platyodon, each based on a single tooth. Riley and Stutchbury also described a range of postcranial remains which were not clearly assigned to either Thecodontosaurus and Paleosaurus. Riley and Stutchbury (1836, 1837, 1840) named only the genus Thecodontosaurus; the specific name antiquus was added by Morris (1843: 211) in his Catalogue of British Fossils.
Richard Owen (1842:153-155) redescribed Thecodontosaurus and Paleosaurus (now spelled by him Palaeosaurus, the spelling generally used thereafter) in the same paper, and he attempted to divide the postcranial elements between the two taxa. There was no evidence though about which of these two supposedly different reptiles, named from their jaws or teeth, owned which bones of the skeleton.
Thomas Huxley came to Bristol to examine the Durdham Down material, and he (Huxley, 1870) separated Thecodontosaurus and Paleosaurus into two different dinosaurian groups based on their teeth. Seeley (1895) and Huene (1902, 1908a, b, 1914) re-described the Durdham Down specimens. Both Seeley and Huene divided the Durdham Down specimens between species of Paleosaurus and Thecodontosaurus, again without clear evidence of how to do it.
There has been continued and vigorous debate about the validity of the two species of Paleosaurus, P. platyodon and P. cylindrodon. Huxley (1870) assigned the P. platyodon holotype tooth to Thecodontosaurus, regarding it as having come from a larger species of that genus, while retaining P. cylindrodon as a megalosauroid theropod. Seeley (1895), on the other hand, retained T. antiquus and P. platyodon, but invalidated P. cylindrodon, and divided the postcranial remains from Durdham Down, on limited evidence, between the two species. Huene (1902:62-63) established the new phytosaur Rileya bristolensis on the basis of a humerus and two 'caudal vertebrae' from Durdham Down. Huene (1908a:240, b) identified P. platyodon as a phytosaur and, as the name Palaeosaurus was preoccupied, renamed the Bristol phytosaur Rileya platyodon (Riley and Stutchbury, 1836) and assigned further teeth and postcranial elements to it. Huene (1908a:214-216) divided the postcranial material from Bristol between two species of Thecodontosaurus, assigning the commoner lightly-built elements to T. antiquus, and the rarer more robust elements to T. cylindrodon.
There is no evidence that the teeth named P. platyodon pertain to the taxon Rileya. Nonetheless, the type tooth of P. platyodon, from the illustration (Riley and Stutchbury, 1840:pl. 29, fig. 5), is almost certainly a posterior maxillary or dentary tooth of a heterodont phytosaur, but it lacks generic and specific diagnostic characters, and must be termed a nomen dubium. Steel (1970:25) was first to designate P. platyodon as type species of Paleosaurus, a surprising decision, since P. cylindrodon has page priority. Nonetheless, this decision makes Paleosaurus a phytosaurian taxon, albeit an invalid one. The tooth taxon Paleosaurus cylindrodon (Riley and Stutchbury, 1840:pl. 29, fig. 4) cannot be identified more precisely than Archosauria incertae sedis. Hence, the species P. cylindrodon is also a nomen dubium.
It is now assumed that all the Durdham Down dinosaur remains belong to a single species, Thecodontosaurus antiquus, and that shape variations are an expression of sexual dimorphism (i.e. one set comes from males, the other from females). In addition, most of the postcranial remains assigned by Huene (1902, 1908b) to the purported phytosaur species, Rileya platyodon, are now returned to T. antiquus.
In conclusion, the generic names Paleosaurus, Palaeosaurus, Palaeosauriscus, Rileya, Rileyasuchus, and the species P. cylindrodon and P. platyodon are invalid, being based initially on single largely non-diagnostic teeth, together with later additions of generally non-diagnostic postcranial remains.
Riley and Stutchbury named the two new genera Thecodontosaurus and Palaeosaurus in their 1836 paper, based on finds from the quarries on Durdham Down, Bristol. Since 1836, the history of these names has been rather tangled, and the story is told in full here. [Don't read this unless you are feeling strong and have a stiff drink to hand.]
In the 1836 paper, Riley and Stutchbury misspelled both species of Palaeosaurus, as P. cylindricum and P. Platyodon. In their 1837 paper, the genus Palaeosaurus is referred to in a footnote (p. 91), together with its two species P. cylindrodon and P. platyodon [both now spelled correctly], but the genus name is spelled Paleosaurus in a table on p. 94. The descriptive memoir (Riley and Stutchbury, 1840) offers full descriptions of the two species of Paleosaurus [note spelling], P. cylindrodon and P. platyodon, each based on a single tooth. Riley and Stutchbury also described a range of postcranial remains which were not clearly assigned to either Thecodontosaurus and Paleosaurus. Riley and Stutchbury (1836, 1837, 1840) named only the genus Thecodontosaurus; the specific name antiquus was added by Morris (1843: 211) in his Catalogue of British Fossils.
 |
|
Richard Owen |
Thomas Huxley came to Bristol to examine the Durdham Down material, and he (Huxley, 1870) separated Thecodontosaurus and Paleosaurus into two different dinosaurian groups based on their teeth. Seeley (1895) and Huene (1902, 1908a, b, 1914) re-described the Durdham Down specimens. Both Seeley and Huene divided the Durdham Down specimens between species of Paleosaurus and Thecodontosaurus, again without clear evidence of how to do it.
 |
|
Thomas Huxley |
There is no evidence that the teeth named P. platyodon pertain to the taxon Rileya. Nonetheless, the type tooth of P. platyodon, from the illustration (Riley and Stutchbury, 1840:pl. 29, fig. 5), is almost certainly a posterior maxillary or dentary tooth of a heterodont phytosaur, but it lacks generic and specific diagnostic characters, and must be termed a nomen dubium. Steel (1970:25) was first to designate P. platyodon as type species of Paleosaurus, a surprising decision, since P. cylindrodon has page priority. Nonetheless, this decision makes Paleosaurus a phytosaurian taxon, albeit an invalid one. The tooth taxon Paleosaurus cylindrodon (Riley and Stutchbury, 1840:pl. 29, fig. 4) cannot be identified more precisely than Archosauria incertae sedis. Hence, the species P. cylindrodon is also a nomen dubium.
It is now assumed that all the Durdham Down dinosaur remains belong to a single species, Thecodontosaurus antiquus, and that shape variations are an expression of sexual dimorphism (i.e. one set comes from males, the other from females). In addition, most of the postcranial remains assigned by Huene (1902, 1908b) to the purported phytosaur species, Rileya platyodon, are now returned to T. antiquus.
In conclusion, the generic names Paleosaurus, Palaeosaurus, Palaeosauriscus, Rileya, Rileyasuchus, and the species P. cylindrodon and P. platyodon are invalid, being based initially on single largely non-diagnostic teeth, together with later additions of generally non-diagnostic postcranial remains.
