Tuesday, August 25, 2015

Another Triassic tooth, Paleosaurus fraserianus

Today is the last day of my three week vacation, during which I got a lot accomplished.  This included adding four ex-saurischians to the Theropod Database, which will each get their own post this week before I upload this month's updates to the website.  The first of these ex-saurischians is one whose identity was solved a century ago, but continues to be misunderstood by dinosaur workers.

Clepsysaurus? fraserianus (Cope, 1878a) Hay, 1930
= Paleosaurus fraserianus Cope, 1878a (as Palaeosaurus fraserianus)
= Thecodontosaurus fraserianus (Cope, 1878a) Hay, 1902
= Palaeosauriscus fraserianus (Cope, 1878a) Kuhn, 1965
Norian, Late Triassic
New Oxford Formation, Pennsylvania, US
- (AMNH 1861) tooth (20x6.5x? mm)

Holotype of Paleosaurus fraserianus (AMNH 1861) at center with section (after Huene, 1921) compared to from left to right- holotype of Paleosaurus cylindrodon (BRSMG Ca7449/4) with section (after Huxley, 1870 and Huene, 1908 respectively); right fourth premaxillary tooth of Nicrosaurus kapffi (SMNS 13078) with sections (after Hungerbuhler, 2000); eighth and ninth dentary teeth of Thecodontosaurus antiquus neotype (BRSMG Ca4529/2) (after Galton, 2007); third dentary tooth of Anchisaurus polyzelus (YPM 209) with drawing (after Fedak and Galton, 2007).

Comments- Cope (1878a) described this tooth (which was first presented the year prior) as a new species of Palaeosaurus, at the time a common misspelling of Paleosaurus. Olshevsky (2000) was the first to correct the genus' spelling in this binomial. Note there is a valid genus Palaeosaurus (Geoffroy Sant-Hillaire, 1836; which is currently a junior synonym of the teleosaurid Steneosaurus) however, which caused Kuhn (1965) to incorrectly think Paleosaurus was preoccupied since its spelling is so similar. Thus he referred all Paleosaurus species to his new genus Palaeosauriscus, but this is unnecessary according to the ICZN. Paleosaurus itself is based on P. cylindrodon, an archosauriform tooth of uncertain affinities from the Norian of England which differs from fraserianus in having elongate and oblique serrations, being less recurved, and having a more tapered distal edge in section (far left in figure above).

fraserianus a dinosaur? Nopsca (1901) was the first to assign the species explicitly to Dinosauria or Theropoda, assigning it to a subfamily Anchisauridae [sic] within Megalosauridae, but his anchisaurids consisted largely of basal sauropodomorphs and Triassic carnivorous archosauriform teeth. Hay (1902) had a similar concept for Anchisauridae within his Theropoda, similarly placing fraserianus there though assigning it to Thecodontosaurus, as he synonymized the genus with Paleosaurus. Note Colbert and Chaffee (1941) wrongly cited Cope (1878b) as using the combination Thecodontosaurus fraserianus, but that work only uses Thecodontosaurus for T. gibbidens. Hay (1930) retained fraserianus in Anchisauridae and Theropoda, but now placed it in the genus Clepsysaurus (a parasuchian), perhaps based on the similarity noted by Huene (see below). Steel (1970) referred it to his theropodan Ornithosuchidae, which besides Ornithosuchus contained Teratosaurus, Triassic carnivorous archosauriform teeth, and basal sauropodomorph remains incorrectly associated with the latter. The most confusing generic assignment has been that of Olshevsky (1991, 2000), who made fraserianus a junior synonym of Anchisaurus polyzelus, which is from the much later (Pliensbachian) Portland Formation of Connecticut. fraserianus is quite unlike sauropodomorph teeth (including Thecodontosaurus and Anchisaurus; pictured at right in figure above) in being highly recurved, with an unconstricted base, little labiolingual compression, and small serrations which are perpendicular to the tooth axis. The connection was maintained through history largely via ignorance of fraserianus' actual morphology in addition to continued confusion of Paleosaurus with Thecodontosaurus and Efraasia.

fraserianus a parasuchian? Lesley (1889) may be the first author to suggest fraserianus is parasuchian, albeit without evidence. Huene (1921) has been the only author to illustrate fraserianus, and briefly described the specimen as well. Huene convincingly illustrated the similarity with other New Oxford parasuchian teeth. He suggested fraserianus was synonymous with Clepsysaurus? veatleianus and/or Rutiodon carolinensis from the same formation. Colbert and Chaffee (1941) made fraserianus a junior synonym of Clepsysaurus pennsylvanicus, based on geography. Of Norian archosauriforms which have recurved teeth with small serrations, only some proterochampsids and phytosaurid parasuchians are reported to have reduced labiolingual compression as in fraserianus (80% of FABL). While proterochampsid teeth remain largely undescribed, they are exclusively South American, so are an unlikely identification for fraserianus. Indeed, phytosaurid material is common in the New Oxford Formation, with Rutiodon carolinensis the only currently recognized valid taxon. It's therefore possible Huene was correct and that fraserianus is synonymous with Rutiodon, but the most recent review also suggested the presence of a larger, poorly characterized form (e.g. SMP VP-36; YPM-PU 11544). The tooth of fraserianus is much smaller than these latter elements, but could be ontogenetically young as well. Unfortunately, heterodonty is so great among phytosaurid dentitions, few of which have been described in detail, that it is not currently possible to assign isolated teeth to particular genera or species. Thus fraserianus remains Phytosauridae indet., and is here placed questionably in Clepsysaurus as that is the only phytosaurid genus prior authors have referred the species to.  Based on the variation in Nicrosaurus, fraserianus may be based on a premaxillary or anterior maxillary tooth.

References- Huxley, 1870. On the classification of the Dinosauria, with observations on the Dinosauria of the Trias. Quarterly Journal of the Geological Society of London. 26, 32-51.

Cope, 1878a. On some saurians found in the Triassic of Pennsylvania, by C. M. Wheatley. Proceedings of the American Philosophical Society. 17(100), 231-232.

Cope, 1878b. Triassic saurians from Pennsylvania. The American Naturalist. 12, 58.

Lesley, 1889. A Dictionary of the Fossils of Pennsylvania and Neighboring States Named in the Reports and Catalogues of the Survey. Volume 2. The Board of Commissioners for the Geological Survey, Harrisburg. 914 pp.

Nopcsa, 1901. A dinosaurusok atnezete es szarmazasa. Földtani Közlöny. 31, 193-224.

Hay, 1902. Bibliography and catalogue of the fossil Vertebrata of North America. United States Geological Survey Bulletin. 179, 868 pp.

Huene, 1908. Die Dinosaurier der europäischen Triasformation mit Berücksichtiging der aussereuropäischen Vorkommnisse. Geologische und Paläontologische Abhandlungen Supplement-Band. 1, 419 pp.

Huene, 1921. Reptilian and stegocephalian remains from the Triassic of Pennsylvania in the Cope collection. Bulletin American Museum of Natural History. 44(19), 561-574.

Hay, 1930. Second Bibliography and Catalogue of the Fossil Vertebrata of North America. Carnegie Institution of Washington. 390(II), 1-1074.

Colbert and Chaffee, 1941. The type of Clepsysaurus pennsylvanicus and its bearing upon the genus Rutiodon.

Kuhn, 1965. Saurischia (Supplementum 1). In Fossilium Catalogus 1. Animalia. 109, 94 pp.

Olshevsky, 1991. A Revision of the Parainfraclass Archosauria Cope, 1869, Excluding the Advanced Crocodylia. Mesozoic Meanderings. 2, 196 pp.

Hungerbuhler, 2000. Heterodonty in the European phytosaur Nicrosaurus kapffi and its implications for the taxonomic utility and functional morphology of phytosaur dentitions. Journal of Vertebrate Paleontology. 20(1), 31-48.

Olshevsky, 2000. An annotated checklist of dinosaur species by continent. Mesozoic Meanderings. 3, 1-157.

Fedak and Galton, 2007. New information on the braincase and skull of Anchisaurus polyzelus (Lower Jurassic, Connecticut, USA; Saurischia: Sauropodomorpha): Implications for sauropodomorph systematics. In Barrett and Batten (eds.). Evolution and Palaeobiology of Early Sauropodomorph Dinosaurs. Special Papers in Palaeontology. 77, 245-260.

Galton, 2007. Notes on the remains of archosaurian reptiles, mostly basal sauropodomorph dinosaurs, from the 1834 fissure fill (Rhaetian, Upper Triassic) at Clifton in Bristol, southwest England. Revue de Paléobiologie. 26(2), 505-591.