Thursday, 19 April 2012

Neoichnology - whose prints are these?

I took a walk around the local area a few weeks ago with the idea of recording some traces from the local fauna, specifically tracks. Living here on the edge of the English Peak District we have quite a good range of birds and animals in the immediate vicinity, including badgers, Red Deer, Foxes and a wide variety of birdlife. There are several reservoirs in the vicinity and birds can often be spotted making their way to and from the various stretches of open water. One nearby reservoir has a heronry, and the others attract a wide variety of waterfowl including grebes, ducks, geese, moorhens and cormorants.

Riparian environments are excellent places to look for traces (and potentially analogous to many terrestrial deposits in the fossil record where tracks are found) and I found and recorded this near perfect pair of prints in the mud by a stream that flows across open farmland before entering woods and draining into a reservoir. It was a bright, sunny day (which is not ideal for photogrammetry due to hard shadows) but the images came out well, and I got good data from them and was able to generate a mesh I was very happy with. Why study untextured models? One advantage of not placing the texture is we can study morphology and other track data which might otherwise be hidden by the visual noise of the texture itself, and which can obscure details in relief. To aid the study of these details we can alter the angle of the light source for example which will enable us to see features as they cast shadows.


The image above is the mesh without any texture. The two prints are dead centre of the image, the rectangular object at the top of the image is the scale bar. The mud was quite soft and undisturbed except for these tracks. There is one other partial track at the top right margin of the mesh.


This is a close-up of the left-hand track. There is a piece of organic material that lies across the track; this was trodden on by the track maker. Notice the sub-millimetre resolution of the mesh. Also notice the displacement rims, distinct claw mark at the end of digit III (the middle one). Is that the impression of webbing or a consequence of substrate displacement when the foot was placed down? The first image shows this track from a different angle, and seems to suggest webbing was present.


The mesh with the texture applied, all other parameters unchanged. This is not a photo, but both mesh and texture were generated in Photoscan, and rendered in Cinema 4D. We can now see that the composition of the substrate has affected the morphology of the print; organic detritus and the grain size of the sediment both have some influence on the final impression. You can clearly see the hard shadows here due to the direct sun, and a bright but cloudy day with plenty of diffuse light is better for doing photogrammetry work.

Finally, here's a seamless of the mesh rotating 360 degrees, with texture.

video

So who made the tracks? The obvious candidates are a goose, duck or heron. Geese do browse on the grass in local fields, so this is a possibility. Herons are frequent fliers across the area and can often be seen hunting in the fields later in the year. In fact, digit III is 62mm in length which indicates the track maker was probably a duck, most likely a Mallard, Anas platyrhynchos, as nesting pairs do inhabit the fields surrounding the stream for some of the year. Although common, I do enjoy watching these ducks as they nest in a neighbours garden in the spring and spend their time in and out of the gardens a few doors either side of her house. There is a darker side to the mallard as many people will tell you. Darren Naish covered this subject in this post over at the excellent Tet Zoo.

Next on the subject of neoichnology: Something bigger and hairier.

2 comments:

  1. awesome!
    That's from agisoft's Photoscan? Seems I bought the right program, then ;)

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  2. Awesome stuff!

    Can rule out Heron though, considering they have minimal (if any) foot webbing and an anisodactyl foot:

    http://books.google.com/books?id=fjfDgtI7z1MC&lpg=PA9&ots=COUwRWiKaO&dq=heron%20anisodactyl&pg=PA9#v=onepage&q=heron%20anisodactyl&f=false

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