Dinosaur expert William T. Blows sets the record straight

In 2022 William T. Blows read about a dermal plate dinosaur fossil with a deep ventral cavity on display in Stroud Museum. The fossil had always been regarded as a stegosaur back plate, but deep ventral cavities do not normally occur in stegosaur plates. They do, however, occur in ankylosaurs such as Polacanthus. So was the Stroud fossil really a stegosaur? And was it really a back plate? Blows set off for Stroud to investigate. Here he recounts the history of the fossil - and a supposedly similar find now in the Natural History Museum – and draws his conclusions.

You can read more about his research in Cotswold Dinosaurs by William T. Blows and Alexia Clark, available from the Museum in the Park bookshop for £5.

---

History

Two dinosaur bones designated as ‘Stegosaurus dermal plates’ were collected around 1935 from New Park Quarry (Figure 1), an exposure of Middle Jurassic Chipping Norton Formation in Gloucestershire, England. They were the only stegosaur fossils found along with numerous other Cetiosaurus, Megalosaurus and crocodilian remains (Clark and Blows 2023). New Park Quarry is a site of special scientific interest (SSSI) because of the important Middle Jurassic reptilian fauna it preserves.

Figure 1. New Park Quarry, also called Stow Quarry, where the bones were found, showing the Chipping Norton Formation of the Middle Jurassic, about 167 million years old. Photograph dated 1939, from the collection at Museum in the Park, Stroud.

Mr Charles Irving Gardiner MA, FGS (Figure 2), a geologist and the curator of Stroud Museum, Gloucestershire, from 1929 to 1940, was probably the original collector of the fossils.

Figure 2 (left, above) Mr Charles Irving Gardiner MA, FGS. Photograph from the Museum in the Park, Stroud.

Figure 3 (right, above) Professor S. H. Reynolds of Bristol University. Photograph courtesy of Special Collections, University of Bristol.

Most of the collection was sent to the London Natural History Museum for preparation by Mr Barlow, a geological assistant at the museum. Barlow reunited two large fragments and suggested these made up an almost complete dinosaur dermal plate, similar to those seen in Stegosaurus. Sir Arthur Smith Woodward, director of the Natural History Museum geological department at that time, agreed with this. Professor S. H. Reynolds of Bristol University (Figure 3), the author of the first papers to describe the bone collection (Reynolds 1937, 1939) also agreed with the dermal plate designation. The “Stegosaurus dermal plate” repaired by Mr Barlow, became the London specimen (NHMUK R5938). A second specimen in the collection was also thought to be a stegosaur plate and became the Stroud specimen (STGCM 1944.41).

In the 1930s, duplicate fossils were shared between several museums so that each museum had specimens for display, rather than keeping all the bones that are found together in one museum for research purposes. Duplicate New Park Quarry fossils were shared between Stroud Museum and the London Natural History Museum including two Megalosaurus femora and the two “Stegosaurus dermal plates”. There is no record of how closely associated these “plates” were in situ in the same quarry, information required to determine if they were both from the same animal.  

Galton and Powell (1983) removed the designation of Stegosaurus, an Upper Jurassic North American dinosaur, and tentatively reassigned both bones to the British stegosaur Lexovisaurus. Both “plates” are much older than Stegosaurus, being some of the oldest stegosaur remains ever found in the UK (Galton 2017).

Recent developments

I visited both specimens during the Autumn of 2022. The reason for the Stroud visit was to examine the ventral groove which had been reported by Galton and Powell (1983) to be 80mm deep into the specimen. Ventral grooves this deep are seen in proximal caudal plates of Lower Cretaceous polacanthid dinosaurs. The chance that the Stroud specimen could be a very rare UK Middle Jurassic polacanthid dinosaur had to be tested.

On examination it became clear that the Stroud specimen is not a dermal plate, but is a posterior section of the right ilium (the upper bone of the pelvis) with the head of the right ischium (the rear bone of the pelvis) attached (Figure 4 A and B).

Figure 4: A. B. STGCM 1944.41 stegosaur right ilium, shown in A. dorsal view, B, ventral view showing attached head of ischium. C. D. NHMUK R5938 two views of a dermal plate. Both from the middle Jurassic of New Park Quarry, Gloucestershire.

The “ventral groove” was created by the head of the ischium overlying the acetabulum, the socket for the femur (thigh bone). Unlike dermal plates which are quite thin, the Stroud specimen is thick. Sacral rib attachments along the medial edge indicates its pelvic origin. The smaller overall size, compared with other stegosaur pelvic remains, and the unfused nature of the sacral rib sites indicate that it may have been an immature animal. The correct assignment of the Stroud specimen as a pelvic fragment had been overlooked since the 1930s. It appears that the correct designation of the London specimen as a dermal plate had perhaps influenced the designation given to the Stroud specimen.

The London specimen is undoubtably a dermal plate, possibly from the pelvis or anterior tail. Both specimens may have been from the same stegosaurian animal, with Stroud Museum having part of the pelvis, and the London Natural History Museum having the dermal plate that was possibly mounted over that pelvis.

Institutions

NHMUK Natural History Museum, London, UK; STGCM Stroud Gloucester Cowle Museum, Stroud, UK.

Acknowledgements

The author thanks Mr Kevin Ward of Stroud Museum, Ms Alexia Clark, previously of Stroud Museum, and Dr Susannah Maidment of the London Natural History Museum, for allowing full access to the specimens in their care, for permission to use photographs, and for providing important historical information surrounding the early history of these fossils.

References

CLARK, A. and BLOWS, W. T. 2023, Cotswold Dinosaurs, the history and science of two quarries, two museums and one collection of bones. Stroud District (Cowle) Museum Trust.

GALTON, P. M.  2017 Purported earliest bones of a plated dinosaur (Ornithischia; Stegosauria): A “dermal tail spine” and a centrum from the Aalenian-Bajocian (Middle Jurassic) of England, with comments on other early thyreophorans. Neues Jahrbuch für Geologie und Paläontologie - Abhandlungen 285 (1), 1-10.

GALTON, P. M. & POWELL, H. P. 1983 Stegosaurian dinosaurs from the Bathonian (Middle Jurassic) of England, the earliest record of the family Stegosauridae, Geobios 16 (2) 219-229.

REYNOLDS, S. H. 1937 Fossil reptiles of Gloucestershire. Proceedings of the Cotteswold Nat. Field Club, Gloucester, 26 (1): 51-65.

REYNOLDS, S. H. 1939 On a collection of reptilian bones from the Oolite of Stow-on-the-Wold, Gloucestershire. The Geological Magazine 76 (5): 193-241.

Further Reading

Cotswold Dinosaurs, available from the Museum in the Park Shop