Strange repeating structures in a section of fossil bone

Cactusdave · Post by **Cactusdave** » Tue Mar 10, 2015 5:36 am

I recently bought a set of thin section slides of bones from the Lower Permian amphibian Eryops from a reputable eBay seller. The sections were from various bones, rib, skull, vertebral spine, radius, and one simply marked limb. These are modern ground thin sections, cemented to the slide and with no coverslip. Under the microscope they all show heavy mineralisation, with only gross bone architecture visible. In this respect they differ from sections of geologically more recent Jurassic dinosaur fossil bones which can show astonishing preservation of microscopic bone structure.
On one slide, however I saw strange arrays of regular dots, which I cannot relate either to bone structure, or to mineralisation processes. As I'm neither a Geologist, nor a Palaeontologist, I post them here in the hope than some knowledgeable person will have some idea what they are. I emphasise that they were only present on one section, the one marked 'Eryops megacephalus rib, Archer City Fm, Lower Permian Red Beds, Archer County, Texas'.

I took a look using both transmitted polarised light and incident polarised light, co-axial, and oblique. The structures were recognisable by all forms of lighting, but were much clearer and more dramatic in transmitted light.

First the transmitted polarised light images. Transmitted polarised light images were taken on a Nikon Diaphot with either a Nikon X10 Plan DIC, X20 Plan DIC, or X40 Plan DIC objective. A Canon 5D mkII was attached to the front SLR port which employs a built in X2.5 relay lens.

Because of the large amount of brightness contrast across the field, this in an HDR image derived from four separate images using the 'sum' mode in Fusion HDR, free version.

Another area at the same magnification, showing 'corn on the cob' appearance.

Image of an area with a X20 objective. HDR composite of four images.

Detail view with the X40 objective.

Incident light images to follow.

Cactusdave · Post by **Cactusdave** » Tue Mar 10, 2015 6:04 am

Just a couple of incident light images for now, to stay with the Forum posting rules. The same section was examined with incident light using an Ortholux 1 with Ultropak incident light attachment and X6.5 Ultropak objective. The photoeyepiece was a Leitz Vario-Orthomat zoom http://www.photomacrography.net/forum/v ... 294c#51190 . The camera was a Sony NEX 5N afocally coupled to the Vario-orthomat zoom with an M45 to T-mount adapter and a T-mount reversing ring screwed to the filter mount of a Minolta 45mm prime lens attached to the camera with a Minolta to Sony E-mount adapter. This setup gives minimal vignetting (< 10%) at the lowest zoom settings on the Vario-Orthomat of X5 and X6.3 which disappears at X8. Maximum zoom is X12.5.

The first image is with oblique incident light, using a single Ikea style lamp with a diffuser. Vario-orthomat zoom set to X10.

The second image is a low magnification view with the Vari-orthomat zoom set to X5 (minimum zoom) cropped by about 10% to remove vignetting. Co-axial incident polarised light with the Ultropak illuminator.

carlos.uruguay · Post by **carlos.uruguay** » Tue Mar 10, 2015 6:09 am

Very very interesting

BJ · Post by BJ » Tue Mar 10, 2015 7:11 am

Hi,

intriguing!

Way outside my area of interest and knowledge, but i think that it may be the ornamentation / structure of a squamous skin scale adpressed to the bone.

thanks for posting!

Brian

Cactusdave · Post by **Cactusdave** » Tue Mar 10, 2015 8:12 am

Interesting idea BJ, but I think the scale is wrong. These are truly microscopic structures, not visible to the naked eye. It seems a bit unlikely that a skin scale or scute would have a surface structure that could be preserved at such a minute level. I've sort of assumed that it's some kind of 'artifact' of the fossilisation process, but I'm at a loss to explain it.

piermicro · Post by **piermicro** » Tue Mar 10, 2015 9:18 am

Very interesting.

Cactusdave · Post by **Cactusdave** » Wed Mar 11, 2015 1:58 am

Thanks piermicro.

An extra incident light image. Co-axial incident polarised light, Vario-orthomat zoom at X10.

I do hope someone here has ideas about what these structures might be. Please feel free to draw the attention of friends and colleagues to them if they might have relevant expertise.

BJ · Post by BJ » Wed Mar 11, 2015 7:01 am

Hi,

i am still going to push (very gently!) for my scale hypothesis. i have just found this very extensive review article on the topic which includes some images of Eryops scales (figs 5 and 6).

http://www.palaeodiversity.org/pdf/02/P ... _gu_4c.pdf

There are structures at the same scale as in your photos. The images for some of the other amphibian scales are to my mind also supportive.

But as you say, hopefully someone familiar with this type of material will respond.

Good luck and please let us know how you get on.

Brian

Cactusdave · Post by **Cactusdave** » Wed Mar 11, 2015 7:48 am

Thanks BJ, that's very helpful. I had done some Googling, but hadn't turned up the reference you linked to. It looks very relevant, and there are certainly some structures shown in the Eryops bone section pictures that I could imagine relating to what I'm seeing. I just wish I understood the terminology better, I'm way out of my depth there. I need to print it off and try and understand it better.

carlos.uruguay · Post by **carlos.uruguay** » Wed Mar 11, 2015 7:53 pm

I do not understand anything about it. But seeing photomicrographs of fossil plants reminds me yours images
The third image:
http://thinsections.com/az_micrographs.htm
And this:
http://en.citizendium.org/wiki/File:Fos ... MacRae.jpg
Sorry if this is nonsense