Friday, August 30, 2013

Photography experiment with fur seal crania

Ewan was pretty excited because today we received in the mail two LED photo floods that can be used for fossil photography. I decided to try one out, as I needed to photograph some NZ fur seal skulls, mandibles, and teeth which Carolina Loch recently prepared from fleshy, stinky heads. We use a sheet of somewhat opaque plexiglass that can be backlit with a small floodlight, which burns out the background making photo and figure editing quite a bit easier, in addition to giving photos a nice "glowy" or luminescent feel to them. Aside from this, we also use two large floodlights and a set of diffusers to create soft lighting. Ewan is an expert in fossil photography and there are hundreds of small tips he has, and all sorts of home-built tools and gadgets to prop specimens of any shape up in just the right position.

The juvenile NZ fur seal (Arctocephalus forsteri) mandible under normal photographic conditions, with the dentition removed.

The nice thing about a small LED photo flood is that it can go directly under the plexiglass plate, directly backlighting the specimen you're going to photograph. When I placed a fur seal mandible directly over the LED, it actually shone right through thin parts of the bone - and this actually allowed me to see the outline of the tooth sockets (alveoli). This is pretty interesting, because normally to get an image like this in lateral view you need to take an X-ray; unfortunately, since fossils are filled up with all sorts of other crap like sediment and calcite, this method won't work on fossils. In fact it won't even work for some modern specimens, and it is likely only useful for very thin bones. In a way, it is somewhat analogous to an X-ray: the photograph is capturing radiation that is able to pass through thinner (and presumably lower density) parts of the bone. In this case, it's not strictly following bone density as it is following bone thickness - but that's a minor point I concede, as it still results in a similar looking (and informative) image for my purposes.

 Right mandible of juvenile NZ fur seal (Arctocephalus forsteri), showing the alveoli; 
lower photograph is slower shutter speed.

Then I got to thinking, what else can I show with this? I took one of the two skulls and turned on the LED light, and found that it would indeed show some of the brain surface topography that is imprinted on the endocast of the skull. I've got some more photos, and it turned out quite well I think. Now, I'm not sure what sort of practical application this could have other than being a cheap alternative to X-rays in somewhat rare cases like this, but maybe somebody will think of some useful way to use this for delicate osteological specimens.

 Illuminated braincase showing some impressions of sulci and gyri.


Bewildermunster said...

The brain case looks wild! Neat images.

Daniela Sanfelice said...

Great work, I loved the blog!