Gigantspinosaurus – the ‘lost’ Chinese stegosaur

As promised a second guest post, this time by Susie Maidment and on the incredibly elusive Giganspinosaurus. So few people know about this stegosaur that despite being described in 1992 it didn’t even make it into that dinosaur encyclopedia that is ‘The Dinosauria‘ in 2003:

Studying dinosaurs inevitably involves a great deal of travel. During my four years studying stegosaurs, I visited 32 institutions on three continents, adding up to a total of about five months in dark basements looking at bones. I visited China for a month in 2004 in search of a number of illusive stegosaurian specimens with names that proved almost impossible to pronounce correctly, along with a fellow PhD student. Half way through our month-long trip, we arrived in Zigong, a small (by Chinese standards) city in Sichuan Province. Zigong achieved worldwide fame, at least in palaeontology circles, in the 1970s and 80s due to the discovery of a vast collection of dinosaurian fossils from the Shaximiao Formations, dating from the lowermost Middle Jurassic to the Late Jurassic. The area was at the time a lush flood plain, but periodic floods, droughts and other natural disasters led to the accumulation of large numbers of extremely well-preserved dinosaurian fossils. The discovery of a bone bed just outside Zigong led the authorities to build the imaginatively named Zigong Dinosaur Museum over the site, and today tourists can view a large collection of dinosaurian remains still in the ground, with additional specimens on display.

I was in Zigong to study one of the most interesting ornithischian dinosaurs ever discovered: the basal stegosaur Huayangosaurus. Although clearly a stegosaur because of the parallel rows of dermal plates extending vertically from the back, it bears a number of features that link it with much more primitive armoured dinosaurs, and it has helped to elucidate the order of acquisition of certain features in the evolutionary history of these ornithischians. At Zigong, they found at least one almost entirely complete specimen of Huayangosaurus, including a complete, articulated skull. Only one other complete stegosaurian skull is known from anywhere in the world: they are incredibly rare.

The road out to the Zigong Dinosaur Museum (ZDM) is a narrow strip of tarmac with a lane of dirt either side. Enormous trucks with wheels the size of your average Toyota thunder down the road and taxis weave in and out, onto the dirt and back onto the tarmac again, gambling with your life at every corner. Car travel throughout Asia is the same: there is one simple rule – don’t look out the front. Having mystifyingly defied certain death on multiple occasions, we arrived at the ZDM and were introduced to the curator, who claimed to have no knowledge of our visit and of many of the specimens we were interested in seeing. However, a few calls back to Beijing and all was sorted out: we were assigned an English-speaking guide and taken to the collections.

Unfortunately it turned out that Huayangosaurus, the specimen that I had travelled half way around the world to study, was currently part of a touring exhibition, and was at that moment on display in the Queensland Museum, Australia. However, the beautiful complete skull, too delicate and precious to be sent out of the museum, let alone out of the country, was available for me to study, and I set to work on that. Two days later and I had looked at, photographed, drawn and described the skull from every possible angle and I was wondering what I was going to do for the next week. I decided to take a look at the exhibition hall, which turned out to be a dimly lit room (why are dinosaur halls always dimly lit? Is it supposed to make it atmospheric or something? It’s not like there wasn’t any sun in the Jurassic) featuring dioramas of various dinosaurs, one of which, in the corner, was a stegosaur. I wandered over and read the name label: Gigantspinosaurus sichuanensis. I’d heard the name before, but only on an internet mailing list. I’d been unable to uncover anything at all about the specimen, and yet here it was, mounted, and apparently reasonably complete.

I decided to take a look and make some notes for comparative purposes, and I decided to include the specimen in my cladistic analysis. Studying a specimen on display is always difficult. Not only are you unable to rotate the elements, look at and photograph them from multiple orientations, there’s never enough light, so you need to do everything by torch light (that dimly lit atmospheric thing again). Also, you get members of the public (invariably seven year old boys) asking you difficult questions about dinosaurs you’ve never heard of. Fortunately my three-week intensive Chinese language course didn’t extend much beyond the basics, so I was unable to converse with most of the visitors, who watched perplexed as I lay underneath the specimen trying to draw the pelvis.

Gigantspinosaurus proved to be a fascinating specimen. It was found sometime prior to 1986, when an article in the Asian journal Vertebrata Palasiatica announced the discovery of some stegosaurian shoulder spines. The one page article is in Chinese but there is a photograph of the specimen, with a caption in English. The specimen is not named in the article, but it is undoubtedly Gigantspinosaurus: the exhibition about the specimen in the ZDM has a plaster replica of how the specimen was found and it is identical to the photograph.

Large spines, extending at a low angle from a flat, plate-like base, are known in Kentrosaurus, and there has always been some discussion about where on the body these spines would have been located. It was originally thought that they were located over the hips – and they were described as parasacral spines. However, the discovery of Gigantspinosaurus proved this to be incorrect: the specimen was recovered with both spines lying adjacent to the scapulae, and the spines have been renamed parascapular spines. Gigantspinosaurus certainly lives up to its name: the parascapular spines, which are comma-shaped, are nearly twice the length of the scapulae and extend either side of the body: they are absolutely massive. I cannot imagine how this animal turned around: if it swung its shoulders one way or the other it would have stabbed itself in the hips! If they were covered in a keratin sheath, as has been proposed for stegosaurian dermal armour, they would have been even bigger – maybe two or three inches longer that currently preserved.

The specimen was named and briefly described by Ouyang in 1992 in an obscure conference proceedings volume, completely in Chinese, and it has been on display since 1996 at the ZDM. Some aspects of the anatomy of Gigantspinosaurus are reminiscent of Huayangosaurus; for example the morphology of the lower jaw and the vertebrae are similar. Most stegosaurs, like Stegosaurus and Kentrosaurus, have dorsal vertebrae that are greatly elongated above the neural canal: they look like they have been stretched from above and below. However, those of Gigantspinosaurus, like those of Huayangosaurus, are not ‘stretched’ but are similar to the dorsal vertebrae of basal thyreophorans (the early armoured dinosaurs) like Scelidosaurus. Another fascinating feature of the vertebrae of Gigantspinosaurus is the presence of ossified tendons extending down the dorsal vertebral column. Until I noticed these features in Gigantspinosaurus and also in Huayangosaurus, they were thought to be absent from all stegosaurs. They are not seen in any of the well-known specimens of Stegosaurus, and have not been identified in Dacentrurus or Kentrosaurus either. Despite similarities to Huayangosaurus, there are also a number of differences. The pelvic area of Gigantspinosaurus is more similar in morphology to that of other stegosaurs such as Stegosaurus and Kentrosaurus, whose anterior processes project both forwards and laterally, and differs markedly from the pelvis of Huayangosaurus, in which these processes project more anteriorly.

The specimen of Gigantspinosaurus on display at the ZDM also has an interesting pathology: its left upper leg bone, the femur, was broken about midway down the shaft during life. The bone was badly broken: not just cracked but the two halves were offset from each other, but had healed – new bone had grown around the fracture. This shows that the broken leg didn’t kill the animal, but I suspect it probably contributed to its death: the ZDM Gigantspinosaurus probably limped badly.

My cladistic analysis suggests that Gigantspinosaurus was the most primitive stegosaur, more primitive even than Huayangosaurus. To be honest I am not confident about that assignment: I think we need further fossils and a more detailed study of the currently known material to decide where it fits into the stegosaurian family tree. I hope that the staff at the ZDM will get a full description of this fascinating animal out soon: it is key to our understanding of stegosaurian phylogenetic relationships.