Rhamphocephalus prestwichi Seeley, 1880

O’Sullivan, Michael & Martill, David M., 2018, Pterosauria of the Great Oolite Group (Bathonian, Middle Jurassic) of Oxfordshire and Gloucestershire, England, Acta Palaeontologica Polonica 63 (4), pp. 617-644 : 637

Rhamphocephalus prestwichi Seeley, 1880

Fig. 21.

1880 Rhamphocephalus prestwichi ; Seeley1880: 27–30.

1888 Rhamphocephalus prestwichi Seeley, 1880 ; Newton 1888: 534.

1888 Rhamphocephalus prestwichi Seeley, 1880 ; Lydekker 1888: 33.

1901 Rhamphocephalus prestwichi Seeley, 1880 ; Seeley 1901: 153–155.

1922 Rhamphorhynchus prestwichi ( Seeley, 1880) ; Arthaber 1922: 9.

1978 Rhamphocephalus prestwichi Seeley, 1880 ; Wellnhofer 1978: 41.

1995 Rhamphocephalus prestwichi Seeley, 1880 ; Benton and Spencer 1995: 149.

1996 Rhamphocephalus prestwichi Seeley, 1880 ; Unwin 1996: 293.

2003 Rhamphocephalus prestwichi Seeley, 1880 ; Unwin 2003: 177.

2012 Rhamphocephalus sedgwicki (sic); Buffetaut and Jeffery 2012: 1.

2013 Rhamphocephalus prestwichi Seeley, 1880 ; Witton 2013: 125–127.

Holotype: Rhamphocephalus prestwichi ( OUM J.28266) (Fig. 21A)

poorly preserved cranium presenting a dorsal view of the palate.

Type locality: Kineton Thorns Quarry, Gloucestershire, UK.

Type horizon: Bathonian, Middle Jurassic.

Remarks.— Rhamphocephalus is one of the oldest British “pterosaur” taxa re-interpreted here as a thallatosuchian based on its crocodylomorph skull morphology. The type specimen of Rhamphocephalus prestwichi OUM J. 28266 (Fig. 21A) from an unrecorded horizon in the Kineton Thorns Quarry, Stow-On-Wold, Gloucestershire ( Fig. 22 ) is a poorly preserved cranium presenting a dorsal view of the palate. It has been a contested taxon for several years due to the lack of well-supported diagnostic characters (see Introduction). Lydekker’s (1888) characters occur plesiomorphically in several other pterosaur genera ( Wellnhofer 1991) and the skull arrangement is, as noted by Seeley (1880), more crocodilian than pterosaurian. When a simplified reconstruction of OUM J.28266 is presented next to the skull of Rhamphorhynchus (Fig. 21B), the differences become apparent. Pterosaur skulls possess large, sometimes medially positioned orbits which are like the larger fenestrae of OUM J.28266 but the nares are positioned more anteriorly along the rostrum. The antorbital fenestrae are proximal to the orbits but are laterally placed and do not significantly invade the dorsal profile of the skull. The rugose striations exposed on OUM J.28266 are absent in pterosaur bone which has a smoother internal texture ( Bennett 1993). Given the lack of morphological convergence between OUM J.28266 and pterosaur skulls, it can be confidently identified as non-pterosaurian. Its cranial morphology is instead more like choristodires and thalattosuchians. Figure 23 reconstructs OUM J. 28266 in two orientations, one presenting it as a near complete medial skull and the other as an isolated squamosoparietal region. Choristodires usually have extremely broad superior temporal fenestrae and orbits more anteriorly positioned than OUM J.28266 and are therefore not a likely candidate. Thallatosuchian crocodylomorphs such as Steneosaurus Geoffroy, 1825 and Teleosaurus Geoffroy, 1825 more strongly matches OUM J. 28266 in either orientation with their large superior temporal fenestra separated by a squamosoparietal bar with a broad ventral base ( Walkden et al. 1987), small orbits proximal to the temporal fenestrae and medially position choanae corresponding with the elevated domes of OUM J.28266 ( Pierce and Benton 2006). Thus OUM J.28266 is identified as thalattosuchian but the incompleteness of the fossil limits the taxonomic resolution. With no identifiable autapomorphies, the genus Rhamphocephalus cannot be transferred to Thalattosuchia and is therefore regarded as a nomen dubium.

Stratigraphic and geographic range.—The holotype of was collected from the Stonesfield Slate of Kineton, near Stow-on-Wold prior to 1880 ( Seeley 1880). Kineton is approximately 7 miles from Stow-on-the-Wold, in Gloucestershire, near the River Windrush ( Fig. 22 ). Fossils were collected from the Kineton Thorns Quarry where exposures of the Cotswold Slate Formation and the Eyeford Member of the Fuller’s Earth Formation underlie the Taynton Limestone Formation ( Boneham and Wyatt 1993; Sumbler et al. 2002). The exact origin of OUM J.28266 is unrecorded, however, it is older than the Taynton Limestone Formation pterosaurs (~167 million years old).

Figures

Fig. 22. Maps showing location of the area of the Kineton Thorns Quarry (asterisks) within the Stow-On-Wold region, Gloucestershire, England, UK. From http://www.cotswoldphotolibrary.com.

Fig. 23. Explanatory drawings of OUM J.28266 along side the skulls of a choristodire and a thallatosuchian. A. The possible arrangement of the Rhamphocephalus prestwichi Seeley, 1880 (OUM J.28266), holotype reconstructed as a complete skull (A1) and the frontoparietal region (A2). B. Simoedosaurus Gervais, 1877, a choristodire from the Early Palaeocene of Saskatchewan, Canada; in dorsal view (from Sigogneau-Russell and Russell 1978). C. Pelagosaurus Bronn, 1841, a thallatosuchian from the Lower Jurassic of Somerset, England; in dorsal view. B, C not to scale.