Polacanthus Reconstruction: Part 10 ‘Splate’

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.

Polacanthus Reconstruction: Part 9 ‘Tall Spines’

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’.

Polacanthus Reconstruction: Part 6 'Cervical Spines'

With the first pair of Cervical (neck) spines done, I decided to base the next pair of (slightly bigger than half scale spines) on a plaster cast of a fossil Polacanthus spine rather than some small black and white photographs.

With the outline of the template marked out on the foam, I cut out one of the spines and started carving. A couple of hours later I had finished the left spine.

Before starting the opposite spine I thought it would be a good idea to mount the spine on the Minimi model to see how it looks. I temporarily attached the foam spine to the fibreglass model with a small piece of modelling putty

So far so good. Next I added the first cervical (neck) spine to check the effect of both spines together.

Obviously to finish the model they will need to be blended to fit when finally mounting them but the overall impression seems great.

An hour later I had carved the opposite spine.

So I mounted the pair of spines on the model.

Not too bad for a few hours work! Next I will look at a reconstruction of the Polacanthid Gastonia and sculpt a pair of  ‘solid-based’ scapula-coracoid spines.

Polacanthus Reconstruction: Part 5 ‘First Blood….’

With everything to hand I was finally in a position to actually do something. Before putting scalpel to foam I needed to create some templates to base the sculpted spines on.

The Minmi model is approximately half the size of an adult Polacanthus. Assuming the spines discovered to date are from adults (which is quite likely) then I would need to scale the spine to half actual size.

However there was another aspect to this reconstruction. The spines would be fine in their original condition for a skeletal reconstruction. However this was going to be a life-like, fleshed reconstruction. In life the spines would have been covered in keratin, like a crocodile scute.

So the spines would actually need to be slightly bigger than half size to take into account the keratin surface. With this in mind I selected the pre-sacral (neck to hip) spines images and set about drawing slightly bigger than half scale outlines.

Once left and right Cervical Spine templates were cut out I drew their outlines on the foam. (Note the ‘keel’ on the bottom of Spine 1 below was deliberately omitted on the foam as it would be embedded in the skin in life and would not be visible on the finished model).

I selected the first Spine and cut around the outline.

A few hours later I had sculpted both Left and Right Spines, but not before the scalpel blade caught the tip of my left index finger!!! So after a quick rumage through my first aid kit for a plaster, I donned a latex glove and a rubber glove to finish the sculpts.

With the light level dropping I decide to call it a day. My sacrifice had not been in vain!