Steneosaurus obtusidens

"Steneosaurus" obtusidens Temporal range: 166.1–163.5 Ma PreЄ Є O S D C P T J K Pg N ↓ Callovian
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Sauropsida
Infraclass:	Archosauromorpha
(unranked):	Mesoeucrocodylia
Suborder:	Thalattosuchia
Family:	Teleosauridae
Genus:	"Steneosaurus"
Species:	S. obtusidens
Binomial name
Steneosaurus obtusidens Andrews, 1909

"Steneosaurus" obtusidens is a species of teleosaurid thalattosuchian from the Middle Jurassic Callovian of England and France. Like many other teleosaurids from Europe, it has had a convoluted taxonomic history.

Taxonomy

"Steneosaurus" obtusidens was first described from the Callovian-aged Oxford Clay Formation of Cambridgeshire, southeastern England on the basis of a partial skeleton (NHMUK R.3168).^[1] Characters cited as diagnostic for "S." obtusidens included: short rostrum (preorbital length 52 percent of total skull length); teeth blunt and rounded at the tips; armor adorned with elongate pit ornamentation.

The validity of "Steneosaurus" obtusidens was disputed in a 1987 paper reviewing the type specimens of nominal teleosaurid species from the Oxford Clay. Characters used by Charles William Andrews to distinguish "S." obtusidens from other species were dismissed as variable within specimens of Steneosaurus edwardsi, and "S." obtusidens was sunk as a junior synonym of Steneosaurus durobrivensis (=S. edwardsi).^[2] Some authors considered this taxon a probable junior synonym of Machimosaurus hughii based on a subsequently discovered specimen found in Callovian-age exposures in Calvados, Lower Normandy, France, though they stressed that a taxonomic review of blunt-snouted teleosaurids was needed.^[3][4] This synonymy was accepted in a 2009 paper regarding thalattosuchian morphometrics without comment.^[5]

In 2013, a new specimen of Machimosaurus was described from Late Jurassic (Kimmeridgian deposits in southern Germany (later named Machimosaurus buffetauti), and it became clear that variation within blunt-toothed teleosaurids was taxonomically significant enough for "Steneosaurus" obtusidens to be recognized as generically distinct from Machimosaurus.^[6] Other cladistic and comparative studies agreed with this assessment, recovering "S." obtusidens in a clade with Machimosaurus and Steneosaurus edwardsi.^[7][8][9] As it stands, "Steneosaurus" obtusidens is clearly related to Machimosaurus, but is generically distinct and in need of a new generic name.

References

1. Andrews, C.W. (1909). "On some new Steneosaurs from the Oxford Clay of Peterborough". Annals and Magazine of Natural History. 3: 299–308. doi:10.1080/00222930908692579.
2. Adams-Tresman, S. M. (1987). "The Callovian (Midde Jurassic) teleosaurid marine crocodiles from central England". Palaeontology. 30 (1): 195–206.
3. Hua, Vignaud; Pennetier; Pennetier (1994). "Un squelette de Steneosaurus obtusidens Andrews, 1909 dans le Callovien de Villers-sur-mer(Calvados, France)et le problème de la definition des Teleosauridae à dents obtuses". C.R.Acad.Sci.II. 318: 1557–1562.
4. Hua, S., 1999, Le Crocodilien Machimosaurus mosae (Thalattosuchia, Teleosauridae) du Kimmeridgien du Boulonnais (Pas de Calais, France): Palaeontographica Abt. A., v. 252, Lfg. 4-6, p. 141-170.
5. Pierce, S. E.; Angielczyk, K. D.; Rayfield, E. J. (2009). "Morphospace occupation in thalattosuchian crocodylomorphs: skull shape variation, species delineation and temporal patterns". Palaeontology. 52 (5): 1057–1097. doi:10.1111/j.1475-4983.2009.00904.x.
6. Martin, J. E.; Vincent, P. (2013). "New remains of Machimosaurus hugii von Meyer, 1837 (Crocodilia, Thalattosuchia) from the Kimmeridgian of Germany". Fossil Record. 16: 179–196. doi:10.1002/mmng.201300009.
7. Mueller-Töwe, IJ (2005). "Phylogenetic relationships of the Thalattosuchia". Zitteliana. 45: 211–213.
8. Young, M. T.; Brusatte, S. L.; De Andrade, M. B.; Desojo, J. B.; Beatty, B. L.; Steel, L.; Fernández, M. S.; Sakamoto, M.; Ruiz-Omeñaca, J. I.; Schoch, R. R. (2012). "Butler, Richard J, ed. "The Cranial Osteology and Feeding Ecology of the Metriorhynchid Crocodylomorph Genera Dakosaurus and Plesiosuchus from the Late Jurassic of Europe". PLoS ONE. 7 (9): e44985. doi:10.1371/journal.pone.0044985. PMC 3445579. PMID 23028723.
9. Young, M. T.; Hua, S.; Steel, L.; Foffa, D.; Brusatte, S. L.; Thüring, S.; Mateus, O.; Ignacio-Ruiz Omeñaca, J.; Lepage, Y.; Havilk, P.; Andrade, M. B. (2014). "Revision of the Late Jurassic teleosaurid genus Machimosaurus (Crocodylomorpha, Thalattosuchia)". Royal Society Open Science. 1 (140222): 1–42.