Priodontognathus

Priodontognathus Temporal range: ?Upper Jurassic
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Sauropsida
Superorder:	Dinosauria
Order:	Ornithischia
Suborder:	Thyreophora
Infraorder:	Ankylosauria
Family:	uncertain
Genus:	Priodontognathus Seeley, 1875
Species:	P. phillipsii (Seeley, 1869 [originally Iguanodon])
Binomial name
Priodontognathus phillipsii Seeley, 1875

Priodontognathus (meaning "saw tooth jaw") was a genus of ankylosaurian dinosaur possibly from the Oxfordian-age Upper Jurassic Lower Calcareous Grit of Yorkshire, England. It is a dubious genus based on a maxilla, and has been erroneously mixed up with iguanodonts and stegosaurs.

History and Taxonomy

English paleontologist Harry Govier Seeley, who described the genus, first mentioned the holotype (SMC B53408), a maxilla or upper jaw bone, in 1869.^[1] Seeley was at the time compiling a catalogue of the fossils of the Woodwardian Museum. Part of these formed the Forbes Collection that after the death of James Forbes-Young had in 1862 been donated to the University of Cambridge by his sons Charles Young and Henry Young. The provenance of this particular bone from that collection was unknown; first believed to be found near Tilgate from a Lower Cretaceous stratum, it was later thought to have been discovered somewhere near the coast of Yorkshire in a Jurassic layer.^[2] Seeley initially assumed that it was referable to Iguanodon, and named it Iguanodon Phillipsii. The specific name honoured geology professor John Phillips. The five inch long fragment lacked the teeth, only seventeen empty tooth sockets being visible. By 1875, after subsequent preparation had uncovered the replacement teeth within the jaw bone, Seeley had recognized that it was different, and so gave it the generic name Priodontognathus. The name is derived from Greek prion, "saw", odous, "tooth" and gnathos, "jaw", in recognition of the form of its teeth.^[3] Because the replacement teeth had not yet erupted, their serrations had not been worn down and many sharp denticula could be seen, shaped as the points of a saw.

Because armored dinosaurs were very poorly known at the time, he had little to compare it to, and in light of this it is not too surprising that he later, in 1893, had it mixed up with the stegosaurian Omosaurus (now Dacentrurus);^[2] stegosaurs are most closely related to the ankylosaurs within the Thyreophora. At this time, he confusingly named a species Omosaurus phillipsii based on a femur (YM 498), and seems to have tentatively assigned this species to Priodontognathus despite their having the same specific name (see at the bottom), and despite the two species being based on non-comparable material.^[2] This led to a later misunderstanding by some authors, assuming Omosaurus phillipsii was nothing but Priodontognathus phillipsii reassigned to Omosaurus. However, this is precluded by the mere fact that both species have been based on different type specimens.

After this time, it was generally considered to be a stegosaurid,^[4][5] although at least one author, Baron Franz Nopcsa, recognized that it was not, and assigned it to "Acanthopholididae", which we would recognize as Nodosauridae.^[6] Alfred Sherwood Romer also recognized that it was an ankylosaurian, although he synonymized it with Hylaeosaurus.^[7]

Peter Galton reassessed the genus in 1980 and established that it was a distinct genus, which he compared to Priconodon and Sauropelta and assigned to Nodosauridae.^[8] While his assessment of it as a type of ankylosaurian has been accepted, his belief that it was valid was not, and it has been usually considered a dubious genus of uncertain ankylosaurian affinities since then.^{[9][10][11][12]}

Paleobiology

As an ankylosaurian, Priodontognathus would have been a slow quadrupedal herbivore, built low to the ground, and possessing armor as a protective feature against theropods and other carnivores.^[12] It was a rather small animal, a few metres long; if the Oxfordian date is correct this might be seen as a feature shared with all early nodosaurids.

"Omosaurus" phillipsii

As mentioned, Seeley named a femur Omosaurus phillipsii in 1893, which has become confused with this animal, due to being discussed in the same article (and considered to possibly be the same genus), and due to them having the same species name. Omosaurus phillipsii, now known as "Dacentrurus" phillipsii or "Omosaurus" phillipsii (depending on how an author denotes dubious species), is a dubious species of stegosaurian from the Malton Oolite Member of the Coralline Oolite Formation, Slingsby, North Yorkshire.^[2] Galton (1983) found it to have no diagnostic features, and that its major significance was of being the only record then known of Oxfordian stegosaurians.^[13] The femur, which is in three pieces, is that of a juvenile.^[13]

Miscellany

The double "i" at the end of the species name for both Priodontognathus and "Omosaurus" phillipsii is an old formulation and is today not done. The extra "i" has not been formally removed, but authors sometimes leave it off. For that matter, as mentioned above regarding the name of "Omosaurus" phillipsi, Priodontognathus will sometimes be referred to as "Iguanodon" phillipsii.^[9][11][12] Seeley's original use of a capital to write Phillipsii is now no longer conventional, lower case being used for the beginning of all specific epithets even if they were derived from personal names, resulting in this case in a phillipsi.

References

1. ^ Seeley, H.G. (1869). Index to the fossil remains of Aves, Ornithosauria, and Reptilia from the Secondary Strata. Cambridge University Press:Cambridge, 143 p.
2. ^ ^{a b c d} Seeley, H.G. (1893). On Omosaurus phillipsii. Annual Report, Yorkshire Philosophical Society, 1892. 52-57.
3. ^ Seeley, H.G. (1875). On the maxillary bone of a new dinosaur (Priodontognathus phillipsii), contained in the Woodwardian Museum of the University of Cambridge. Quarterly Journal of the Geological Society of London 31:439-443.
4. ^ von Huene, F. (1909). Skizze zu einer Systematik und Stammesgeschichte der Dinosaurier. Centralblatt für Mineralogie, Geologie und Paläontologie 1909:12-22. [German]
5. ^ von Zittel, K.A.. (1911). Grundzüge der Paläontologie (Paläozoologie). II. Abteilung. Vertebrata. Druck und Verlag von R. Oldenbourg:München, 1-598. [German]
6. ^ Nopcsa, F. (1902). Notizen über cretacische Dinosaurier. Sitzungsberichte der Mathematisch-Naturwissenschaftlichen Classe der Kaiserlichen Akademie der Wissenschaften 111(1):93-114. [German]
7. ^ Romer, A.S. (1956). Osteology of the Reptiles. University of Chicago Press:Chicago, 1-772. ISBN 0-89464985-X
8. ^ Galton, P.M. 1980. Priodontognathus phillipsii (Seeley), an ankylosaurian dinosaur from the Upper Jurassic (or possibly Lower Cretaceous) of England. Neues Jahrbuch für Geologie und Paläontologie Monatshefte 1980(8):477-489.
9. ^ ^{a b} Coombs, Jr., W.P., and Maryańska, T. (1990). Ankylosauria. In: Weishampel, D.B., Dodson, P., and Osmólska, H. (eds.). The Dinosauria (first edition). University of California Press:Berkeley, 456-483. ISBN 0-520-06727-4
10. ^ Ford, T.L. (2000). A review of ankylosaur osteoderms from New Mexico and a preliminary review of ankylosaur armor. In: Lucas, S.G., and Heckert, A.B. (eds.). Dinosaurs of New Mexico. New Mexico Museum of Natural History and Science Bulletin 17:157-176.
11. ^ ^{a b} Carpenter, K. (2001). Phylogenetic analysis of the Ankylosauria. In: Carpenter, K. (ed.). The Armored Dinosaurs. Indiana University Press:Bloomington, 455-483. ISBN 0-253-33964-2
12. ^ ^{a b c} Vickaryous, M.K., Maryańska, T., and Weishampel, D.B. (2004). Ankylosauria. In: Weishampel, D.B., Dodson, P., and Osmólska, H. (eds.). The Dinosauria (second edition). University of California Press:Berkeley, 363-392. ISBN 0-520-24209-2
13. ^ ^{a b} A juvenile stegosaurian dinosaur, Omosaurus phillipsii Seeley from the Oxfordian (Upper Jurassic) of England. Géobios 16:95-101.

External links

• A Dinosaur Mailing List post mentioning the confusing taxonomy (scroll to the bottom)

Dinosaurs portal