Previously I wrote about sculpting a pair of the enigmatic ‘Splate’ spines. Something I will be returning to later. With a pair of Polacanthine Splates finished, the next job was to sculpt all the spines of the tail.
Based on a couple of different interpretations I needed to sculpt between 22-24 Caudal Spines, now that’s a lot of spines! Fortunately they get smaller towards the end the tail.
Unlike the ‘Splate’ I do have a cast of an (early to middle) tail spine to refer too. So I measured the spine and drew it at just over half scale to make a template.
With the outline marked on the extruded polystyrene I cut the shape out and started to carve the spine.
Once the first spine was finished I carved the other spine of the pair.
With the first pair of Caudal Spines finished I repeated the process by sculpting the second pair of spines (using the first pair as an example).
At the end of the day I took a group shot of all the pairs of spines (Cervical - Pectoral, to Caudal) sculpted to date.
Next time I will complete the process of sculpting the remaining Caudal Spines.
Stegosaurus is famous for the plates that form an alternating row from the neck to the tail. Various hypotheses have been proposed for their function: from defensive armour, thermoregulation (warming / cooling) to visual displays. Their exact function is still open for debate although current research by the Natural History Museum in London on Sophie the juvenile Stegosaurus may well conclude that all three proposals are correct. Just as feathers can be used for insulation, display and flight!
Polacanthus and it’s relatives had a diverse range of dermal osteoderms (bony armour). The ‘Splate’ or Spined-Plate is a flat plate like spine with a prominent spike in the middle. 'Splates’ have been found from Polacanthus and Hoplitosaurus. Their exact postion on the body however is a matter of debate (Shoulders, Back, Hip or Tail?) subject to future discovery of an articulated skeleton with a splate to confirm their actual placement.
Sadly I don’t have an actual fossil 'Splate’ or plaster cast so I had to base the sculpt on some line drawings and photographs with a scale bar!
Once I had a scaled drawing I traced a copy to make a template and copied this on to the Extruded Polystyrene Foam.
With the templates marked out I cut the shapes out of the blue foam and started to sculpt the first 'Splate’.
Given the narrowness of the prominent spine I took my time to sculpt the 'Splate’.
I repeated the process for the opposite spine.
With the pair of 'Splates’ finished, my next task will be to sculpt the numerous middle to late caudal tail spines for the Polacanthus model.
With the first pair of Caudal (Tail) Spines sculpted I decided to sculpt a pair of spines based on a plaster cast of an unusually tall spine.
In preparing for the reconstruction of the Polacanthus model I had made some simple line drawings of the spines I had to hand. It was a simple task to produce a just over half scale line drawing as a template. (Note the missing tip was added to the line drawing).
To check the accuracy of the template I placed it on the cast to check the curvature of the spine. So far so good, now I could mark the foam with the outline of the template.
Once the outline was marked on to the foam I carefully cut around the outline and proceeded to carve the first spine. As soon as I had finished the basic shape I compared it with the plaster cast to check the accuracy.
Now it was a case of sculpting the opposite spine of the pair.
(Note the groove on the rear and underside of the spine will be added later on but before the spine is finally mounted, when its final position has been decided).
Happy with the final result, I decided to take a photo of the spines so far!
With the first five pairs completed the next spine to be sculpted will be the spiked shield-like spine known as a ‘Splate’.
In 2010 Kai Bailey, a local Fossil Hunter, discovered a rare and unusual Polacanthus Spine at the base of the cliff.
He loaned the Spine along with some other fossils when we opened the Dinosaur Expeditions Centre in 2013. At the end of the tourism season we acquired these fossils to become a permanent part of our collection.
With only a fortnight to go until the 2013 ‘Blast from the Past’ weekend at Dinosaur Isle I had my work cut out to get the Spine prepared in time for the event. Encased in a tough sideritic concretion I spent everyday with our Paleotools ME9100 air chisel, chipping away to expose the fossil underneath.
I finished the preparation of the spine just in time for 'Blast from the Past’.
The spine is comparable to a spine discovered at Barnes High which formed the basis of a paper by Justin Delair in 1980. The spine has a keel which securely imbeds it into the body of the animal. It also has a large depression on the posterior (back) edge which suggests the position of the spine would have been an area with lateral (sideways)
movement allowing the spines to touch without damaging them.
Originally the idea was to make a silicon rubber mould and cast the spine in urethane resin, however I would still have to sculpt the other spines for the Polacanthus model. Also the missing tip would need to be sculpted, so the decision was made to sculpt all the spines for the model.
I worked out length of the spine (including the missing tip) and measured maximum width. I scaled the spine to just over half scale and drew the template on paper.
Next I cut the template out and marked the outline on the blue extruded polystyrene foam.
After I cut the shape out of the foam I started to carve the spine.
The newly sculpted spine doesn’t have a keel on the bottom because it will not be visible on the model. In addition the vertical ridges which in life would 'key’ the keratin to the spine are not shown because they would be covered-up.
With the first spine finished I started the opposite spine of the pair.
Note the prominent curve in this view of the front of the spines. This curve increased the structural integrity of the spine allowing it to withstand greater forces than if it was straight. Thereby reducing the risk of the spine snapping in half whilst being used as a weapon.
With the first pair of Caudal (Tail) spines complete, I will sculpt a pair of Polacanthus spines based on a plaster cast of an elongate Caudal spine.
I visited Dinosaur Isle Museum at Sandown on the Isle of Wight and whilst I was there I saw one of the Dorling Kindersley dinosaur models in the lab.
The Gastonia model has an original arrangement of spines.
The tall lateral (side) spines near the shoulders are quite striking compared with other reconstructions.
The model demonstrates the side row of spines from neck to the tip of the tail that formed Gastonia’s primary defense against predators.
The tail of Gastonia would have been a formidable weapon against medium to large theropods. Similar in effect to an Aztec Macuahuitl, the keratin covered tail spines would have probably caused significant lacerations to the lower body of any dinosaur unfortunate enough to be in the way of the swinging tail.
Suitable inspired, I returned to the Dinosaur Expeditions Centre at the Dinosaur Farm and decided to focus on producing a pair of dorsal (top) spines, notable for having a solid base.
I marked out the template on the foam with the keratin thickness outline added and started carving the shape out.
Once the first spine was finished I temporarily mounted it on the Minmi model to check how it looked.
I still need to blend the spine to match the body but the overall effect is imposing. So I repeated the process to make the opposite spine.
Next time I will sculpt a pair of Polacanthus spines based on a rare fossil.