Friday, April 6, 2012

[Paleontology • 2010] Family Proceratosauridae: [a coelurosaur, a tyrannosauroid] • hylogenetic position of the theropod dinosaur Proceratosaurus bradleyi from the Middle Jurassic of England

Figure 1. Proceratosaurus bradleyi, type skull: NHM R 4860.

The cranial osteology of the small theropod dinosaur Proceratosaurus from the Bathonian of Minchinhampton, England, is described in detail, based on new preparation and computed tomography (CT) scan images of the type, and only known, specimen. Proceratosaurus is an unusual theropod with markedly enlarged external nares and a cranial crest starting at the premaxillary–nasal junction. The skull is highly pneumatic, with pneumatized nasals, jugals, and maxillae, as well as a highly pneumatic braincase, featuring basisphenoid, anterior tympanic, basipterygoid, and carotid recesses. The dentition is unusual, with small premaxillary teeth and much larger lateral teeth, with a pronounced size difference of the serrations between the mesial and distal carina. The first dentary tooth is somewhat procumbent and flexed anteriorly. Phylogenetic analysis places Proceratosaurus in the Tyrannosauroidea, in a monophyletic clade Proceratosauridae, together with the Oxfordian Chinese taxon Guanlong. The Bathonian age of Proceratosaurus extends the origin of all clades of basal coelurosaurs back into the Middle Jurassic, and provides evidence for an early, Laurasia-wide, dispersal of the Tyrannosauroidea during the late Middle to Late Jurassic.

Keywords: Bathonian; biogeography; Coelurosauria; phylogeny; Proceratosauridae; Tyrannosauroidea

Figure 2. Proceratosaurus bradleyi, type skull: NHM R 4860. Stereophotographs

Figure 24. Stratigraphic distribution and ghost lineages in basal coelurosaurs, especially tyrannosauroids.

Figure 26. Biogeographic distribution of Jurassic tyrannosauroids. 
1, Proceratosaurus bradleyi, Great Oolite, England (Bathonian); Stokesosaurus langhami, Kimmeridge Clay, England (Tithonian); 2, Guanlong wucaii, Shishougou Formation, Xinjiang, China (Oxfordian); 3, Aviatyrannis jurassica, Guimarota Beds, Portugal (Kimmeridgian); 4, Stokesosaurus clevelandi, Morrison Formation, Utah, USA (Kimmeridgian–Tithonian).

Rauhut, O.W.M., Milner, A.C. and Moore-Fay, S. (2010). "Cranial osteology and phylogenetic position of the theropod dinosaur Proceratosaurus bradleyi (Woodward, 1910) from the Middle Jurassic of England". Zoological Journal of the Linnean Society. doi: 10.1111/j.1096-3642.2009.00591.x
Brusatte, S.L.; Norell, M.A.; Carr, T.D.; Erickson, G.M.; Hutchinson, J.R.; Balanoff, A.M.; Bever, G.S.; Choiniere, J.N.; Makovicky, P.J.; and Xu, X. (2010). "Tyrannosaur paleobiology: new research on ancient exemplar organisms". Science 329: 1481−1485. doi: 10.1126/science.1193304