Proceratosaurus, , Huene, 1926

Rauhut, Oliver W. M., Milner, Angela C. & Moore-Fay, Scott, 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 158 (1), pp. 155-195 : 185

PROCERATOSAURUS

Assessing the ontogenetic stage of the type specimen of Proceratosaurus on the basis of the skull alone is difficult, as most indicators used in assessing the ontogenetic stage of fossil archosaurs depend either on the fusion or ossification patterns of the enchondral skeletal elements (e.g. Brochu, 1996; Tykoski, 2005; Irmis, 2007), or on long-bone histology (e.g. Chinsamy, 1993; Curry, 1999; Sander, 1999; Erickson & Tumanova, 2000; Sander & Tückmantel, 2003). However, a few comments concerning this question are offered.

Firstly, although no extensive fusion of skull elements is present, sutures are generally firmly closed. Unfortunately, though, most of the sutures that frequently fuse in adult theropods (e.g. sutures of the braincase and the interparietal suture) are not preserved or cannot be studied in Proceratosaurus . None of the exposed bone surface shows a pitted or striated appearance, as is often found in juvenile dinosaurs ( Britt & Naylor, 1994), including the surface of the quadrate – the only enchondral ossification that could be studied in detail. This indicates that the type specimen of Proceratosaurus represents at least a subadult individual.

Most juvenile dinosaurs, including theropods, show skull proportions typical for juvenile vertebrates in general, with short snouts and large orbits (e.g. Colbert, 1989; Carpenter, 1994; Horner & Currie, 1994; Rauhut & Fechner, 2005; Salgado, Coria & Chiappe, 2005). Thus, the rather low and elongate shape of the skull of Proceratosaurus and the long snout are consistent with the interpretation of this specimen as a subadult individual. It might be noted, however, that Carr (1999) found relative elongation of the snout in juvenile tyrannosaurids, when compared with adult individuals, so it cannot be completely ruled out that the type of Proceratosaurus might be a late juvenile.

Although estimating the body size from the skull size is somewhat problematic in theropods, because of the varying proportions between different groups, skull length in general correlates well with both body length and body mass ( Therrien & Henderson, 2007). Thus, an approximate size range can be given for Proceratosaurus . With an estimated total skull length of 280–300 mm, applying the formulae given by Therrien & Henderson (2007: 110) results in a size range of 2.98–3.16 m in body length, and a body mass of 28–36 kg, which indicates a rather small and gracile animal. Thus, Proceratosaurus is comparable with its closest relative, Guanlong , which is approximately 3-m long ( Xu et al., 2006: 715), and represents an adult individual according to its long-bone histology. Note, however, that the formula of Therrien & Henderson seems to overestimate the length of Guanlong ( Therrien & Henderson, 2007: table 2), indicating that this animal had a rather large skull in proportion to body length. If the same was true for Proceratosaurus , the size range given above should be regarded as a maximum estimate.