Incidental finds in the field

One of the many joys of fieldwork is the fact you have no idea what each day might bring. Apart from the main focus of your work delivering up constant surprises, the environment you are working in is often as fascinating and throws up seemingly endless delights. If you are digging in a foreign country, then this effect seems magnified and everything around you becomes a vital part of the experience. The very nature of fieldwork means you are getting up close and personal to the land and the flora and fauna you share it with for the duration of the trip. On top of all this, there seems to be a sense of heightened awareness: in the rock you are working, the weather, the lay of the land, the sounds. . . . well, you understand. The context of the physical and mental activity that is fieldwork.

So here is the first of three posts that deal not with the fieldwork itself, but the incidental finds that over the years have attracted my attention. These may seem mundane or irrelevant and of course scientifically they are, but these finds are as much a part of the field experience as the fossils we strive to discover and understand. 

Three articulated vertebra, bleached by the sun.
No idea what they belonged too, but I'm guessing artiodactyl.
Hell Creek Formation, South Dakota, USA.

The wreck of The Carbon. Compton Bay, Isle of Wight, UK.
You need a low tide to get this close too the old metal-hulled boat, which came to grief on the rocks of the Wessex Formation, Wealden. She was a 175-ton steam tug that was under tow in November 1947 when she came loose and ran aground.

Deer leg. We saw Mule deer in the area of our quarry, but this also might be a Whitetail
or Pronghorn, both of which live on the prairie and badlands. Hell Creek Formation, South Dakota, USA.

Upper jaw fragment. Once more, I have no idea what this is from, but I'll go with artiodactyl as a guess.
Potter Canyon, Dinosaur Canyon Member, Moenave Formation, Arizona, USA.

Native American microlith. In the UK, this would come home but there are understandably
very strict laws regarding the removal of Native American artifacts, so it stayed in-situ.
Moccasin Mountain, Navajo Sandstone Formation, Utah, USA.

Petroglyphs, Fort Pierce, Utah, USA. These superb petroglyphs are carved into the desert varnish
on outcrops of Shinarump Member of the Chinle Formation.
We also heard a very loud boom at this point, possible sonic, mine or other blasting.
As for what these petroglyphs actually depict, there is plenty of debate and interpretations vary.

Where possible, I always bring incidental finds home as they act as not only objects of interest in themselves but reminders of a moment in time, which often have very happy memories. Antlers, skulls, sea glass, various sub-fossil bones, teeth, hagstones, feathers, shells minerals and one day a rather fine geological hammer all enter the collection and each has a memory attached. Wonderful.

Next: Critters

Photogrammetry: Two dinosaur footprints from The Isle of Wight

The Isle of Wight, which lies off the south coast of England, has long been a good spot to find dinosaur footprints and other traces of ancient life. The rocks of the Wessex and Vectis Formations, part of the Lower Cretaceous of the Wealden of southern England, contain numerous examples of trace fossils of many kinds, from dinosaur footprints and invertebrate traces to palaeoenvironmental indicators such as ripples and mud cracks.

At least two distinct palaeoenvironments are represented in these formations. The Wessex Formation is interpreted as representing a braided river system complete with crevasse splay sandstones, ephemeral ponds and lakeside margins, all containing trace fossils (Naish and Martill, 2001). The deposits of the Vectis Formation were laid down in a coastal lagoonal environment and contain facies interpreted as mudflats and storm coquinas, both of which also preserve traces of ancient life (Radley and Barker, 2000).

On my last visit to the island I took the opportunity of recording some of these footprints using photogrammetry, and here are a couple of the meshes I was able to create. These are both from the trackway at Hanover Point, and are well-known; perhaps too well known as one print has been removed with a rock saw, and a second was in the process of being removed when the it finally dawned on the not-so-smart thieves that the rock was way too unstable to make the operation worthwhile, but not before one footprint was lost forever.

Figure 1: 3D mesh of tridactyl footprint from the Wessex Formation
of the Isle of Wight, UK.

Figure 1 shows the footprint that was in the process of being removed. This is the best preserved of the remaining prints. It's a tridactyl pes print, and has a distinct claw-mark on the leftmost digit.

Figure 2: 3D mesh of a second footprint from the same trackway as the footnoting illustrated
in figure 1.

The second print is much less well-defined and demonstrates how much variation is possible in footprint morphology within a single trackway.  The left most digit has one clearly defined node, the rest of the print indistinct; this might indicate the substrate might have variable texture and/or consistency, or the footprint was subject to alteration after being made. The line running throughout the print is a natural fault.

This trackway is well worth seeking out if you're visiting the island, although you'll need a low tide and some time to find them out on the rocks. Professionally guided tours are available from Dinosaur Isle. Please note it is illegal to remove or attempt to remove any footprint found on the south-east coast of the Island.

References:

Martill, D. and Naish, D (Eds). 2001. Dinosaurs of the Isle of Wight, 319pp. The Palaeontological Association, London.

Radley, J. and Barker, M. Paleoenvironmental significance of storm conquinas in a Lower Cretaceous lagoonal succession (Vectis Formation, Isle of Wight, England). 2000. Geological Magazine, 137. pp193-205. Cambridge University Press.

Neoichnology: bioturbation around ephemeral ponds

Randomly oriented dinosaur track assemblages occur frequently in the fossil record (Thulborn, 1990) and form under a variety of conditions. Thulborn states that these random assemblages can appear to represent a patch of ground with high dinosaur traffic that are passing through, but some sites have been interpreted as being the margins around water holes (Martill and Naish, 2001).

I went to check out a local ephemeral pond situated on farmland to see if there was evidence of bioturbation, and was able to do some photogrammetry on what I found. All images were taken between 1pm - 1.30pm on a bright, sunny day (at last!) in late May.

Ephemeral pond in grass crop grown for silage.

The pond is located in a field used for growing grass for silage, after each cutting (which occurs three times a year) cattle are allowed to graze briefly before being excluded again as the crop resumes growth. The small pond is present during the winter months and occasionally re-appears after extended wet spells over summer, however the pond gradually dries up as spring progresses. The pond appears to be fed by water draining off adjacent fields; no streams fed into the pond and it is situated in a shallow natural hollow.

I have often seen mallards at the site of this pond, and fully expected to find evidence of their presence in the form of footprints and tracks, as this site is close to where I recorded duck tracks in mud alongside a small stream; this photograph is taken from the foot of the levee which separates the stream from the field (this stream feeds into a reservoir around half a mile away and never floods into the adjacent field).

Zones of substrate consistency surrounding the pond.

As can be seen from the photo above there are three possible zones of substrate consistency. The outer margin is dry and hard, and coated with slurry applied by the farmer when wetter conditions persisted. A dried out microbial mat might also be present here. Red Deer footprints are present in this zone and these too were made when the substrate was wetter.  There was one canine trackway which was too big for a Red Fox and probably represents a pet dog. Goose and other bird droppings were present. The middle zone consists of slightly dryer area containing some deer footprints and is covered by a microbial mat which has formed over the decomposing slurry. The layer constituting the pond margin is waterlogged, and like the rest of the site consists of fine-grained sediment. There is no evidence of slurry or microbial mat in this zone. So we have a homogenous substrate with varying consistencies with a surface covered with fibrous, decomposing vegetable material and a microbial mat present in at least one zone.

3D model generated by photogrammetry.
Bioturbation in the pond margin, consisting of monotypic, randomly orientated bird footprints.

The pond margin zone was heavily bioturbated. The tridactyl tracks are randomly orientated, monotypic and all of uniform morphology. It's likely this represents a single species of bird visiting the pond to drink or feed, although no signs of probing appears present in the substrate. The term for a fossil association of tracks preserved in a single horizon is ichnocoenosis (Leonardi, 1987), I so I guess this assemblage would be termed a neoichnocoenosis.

Close-up of untextured mesh which shows the chaotic nature of the bioturbation.
Footprints and partial footprints are overlain

Textured version of the mesh. Note quality of mesh is so good the individual nodes
of each digit are clearly visible in some footprints, especially the central print.

The two images above are close-ups of the mesh, untextured and textured. The print in the middle of the image clearly shows the nodes of each digit, as well as displacement rims and is impressed deeply into the wet substrate.

The tracks are different form the duck tracks recorded in the local area. They are smaller, show no sign of interdigital webbing (as can be seen, the footprint impressions are deep) and there is a large hallux present. However, the prints are large enough to rule out many of the smaller birds to be found in the local area, and it might be that the track maker was a corvid, gull or pheasant, all of which are abundant locally. The pheasant can probably be ruled out as it has a very short hallux (see image below), and no interdigital webbing would rule out gulls as track makers. The most likely candidates are corvids and the pond lies below the route which rooks use twice daily between the local roost and the fields where they feed, and jackdaws, magpies and common crows are all present.

Of course, the prints we're looking at here are concave epireliefs, or moulds. It would be impossible to see the cast (or convex hyporelief) of these prints in the real world, but photogrammetry allows us to look underneath and view the bioturbated surface from below. The ability to look at tracks as moulds with adjustable light angles is a useful tool in footprint morphology interpretation.

The underside of the mesh, showing the tracks as casts instead of moulds.

References:

Thulborn, R.A. 1990. Dinosaur Tracks, 310pp. Chapman and Hall, London.

Martill, D. and Naish, D (Eds). 2001. Dinosaurs of the Isle of Wight, 319pp. The Palaeontological Association, London.

Leonardi, G. 1987. Glossary and Manual of Tetrapod Footprint Palaeoichnology, 43pp. Departamento Nacional de Produçao Mineral. Brazil.

Laridae vs Columbidae - guess who won.

We took a trip out yesterday to Chester and the North Wales coast. Having never visited Chester before I was looking forward to seeing the famous medieval Rows and visit the cathedral. The Rows were fascinating, the cathedral we didn't get to see as it cost 6 quid to get in if you weren't a worshipper; as we're not religious we departed.

What we did get to see was slightly less aesthetically pleasing to the eye but equally fascinating. In a nearby area hard to the city walls called the Kaleyards we spotted a Lesser Black-backed Gull attacking and eating a feral pigeon; avian dinosaur predation in an urban centre.

Feral pigeons seek respite from the weather in the lee of the city walls.
The large stones in the bottom of the image are Roman.

This area (named as the spot was where monks grew vegetables in days of yore) has an impressive coop and the area is home a large number of feral pigeons (and the odd duck, not in shot) all of whom use the city walls as shelter from the elements. When we arrived the gull had already disabled the pigeon, and whether it had attacked a healthy bird or picked on an injured or weak one we did't see.

Gull attacking still-alive pigeon.

The pigeon was still very much alive however, and the gull was pecking towards the rear of the bird. After several minutes the unfortunate pigeon gave up the ghost and the gull continued to feed, before a parking motorist scared it off. It waited a while on a nearby lamppost for a while, then flew out of sight and then returned after a few minutes and continued to feed. Lesser Black-Backed gulls have been noted as predators, and intraspecific predation in colonies of the species have been recorded by Davis et al.

The prey had been dragged a few metres away by now, and had expired.

It was a gully day. We saw Herring gulls nesting on the roof of the railway bridge, Herring gulls nesting in a window seat in a tower at Conwy castle and lotsa gulls in Llandudno, as you would expect. Here's some pics for all admirers of the Laridae out there.

Room with a view: a brooding Herring Gull at the magnificent Conwy Castle.

Adult Herring Gull on the pier at Llandudno. Ever the opportunists, these gulls are
quite bold when scavenging from the food discarded by humans.

Immature Herring Gull, also at Llandudno and keeping a close eye on the activities
of the anglers fishing of the end of the pier.

Refrences:

J.W.F. Davis, E.K. Dunn (1976). Intraspecific predation in Lesser Black-Backed Gulls Larus fuscus. International Journal of Avian Science 118, 65-77.

Neoichnology: Tracking big red ruminants

Some things send a real shiver down your spine, and for me one of these is being unexpectedly confronted with wild animals. Some years ago my wife and I were our walking in the hills near our home when we had a close encounter we've never forgotten. Our route took us past an old quarry, basically a platform delved into the hillside for the purpose of extracting the carboniferous gritstone used to pave the streets of the local towns and villages. I fancied a quick look at the exposures that were still visible despite the quarry floor having been reclaimed by nature. As we turned into the quarry we came face-to-face with a large Red Deer stag. The stag had heard us before we'd even seen it, and the movement of it looking up caught out eye. We stood a few feet away from this magnificent animal before it turned and disappeared into the scrub, leaving us with a sense of elation.

Great Britain's largest native mammal, Red Deer (Cervas elaphus) are present throughout most of Britain having migrated here around 11,000 years ago, although according to the British Deer Society website some populations represent feral animals rather than descendants of native animals. As we have extirpated all keystone predators from these islands Red Deer are thriving at present and indeed culling is necessary to ensure populations are kept in check.

Red Deer stag bellowing. You wouldn't want to bump in to this chap during the rut.
Picture by Bill Ebbesen and used under CC licence (Wikipedia).

Our local Red Deer herd spend most of their time in the surrounding hills (the area was part of a royal hunting forest) where they can be spotted grazing in fields in groups, often of over 30 individuals. They descend to lower elevation during the night and  some mornings it's possible to walk through the long grass and see where each deer spent the night. It was in the hope they had been around recently that I went looking for tracks with the intention of recording them using photogrammetry; I discussed the Mallard tracks I found during this same trip in my last post.

I was lucky this time and found and recorded two the two tracks presented here. They were both found at a small ford on a stream that runs down the hillside. This area is frequently trampled by the local dairy herd who use the ford for crossing a field boundary and drinking but as they are still inside at present the only tracks on the mud surrounding the ford were of deer and the paw prints of a small dog (the area is heavily frequented by dog walkers). The individuals that left these tracks are both relatively small, and might possibly have been left by a hind and juvenile, possibly one of last year's calves. Due to the lack of heavy trampling it seems only a few animals passed this way rather than a large group.

The first image is the smaller of the tracks. I've rendered both untextured and textured versions of each track recorded to demonstrate the morphology of the track and quality of the mesh. It has to be said that these are rather large files, and could probably be decimated without detrimental loss of information.

Red Deer track, untextured mesh. Notice organic detritus and grass blades, which have
gaps underneath where data was not recorded. Lots of detail of in this (large) mesh.

Textured version of the same print with exactly the same lighting settings.

The other track showing the mesh and track morphology.

The full render of the other track, same lighting settings as the untextured version immediately above.

As can been seen in the two sets of images above, the meshes generated by the photogrammetry software are very detailed and very accurate, capturing sub-millimetre detail. The gaps in the mesh tend to be where overhangs occur, for instance under blades of grass or underneath overhanging areas of displaced substrate. Stone and organic detritus are very well represented.

These images further demonstrate the quality of data that can be captured using photogrammetrical techniques. Hopefully there will be much more of this to come in the future!

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.

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.

Eye to eye with the fastest animal on Earth

As someone with a love of dinosaurs, it's always nice to know the fastest animal on the planet is one of them, to be specific the Peregrine falcon, Falco peregrinus. On Easter Sunday I had the good fortune to meet one face-to-face, courtesy of the Kingsley Bird and Falconry Centre, which had a stall outside the Pavilion Gardens in Buxton. We'd gone for the book fair but the highlight of the day was meeting the Peregrine, a young female who was brought by the centre as a breeding bird and who will hopefully be raising chicks this time next year.

Meeting this bird up close and personal certainly made an impression. For a start, it's fascinating to look into the forward-facing eyes of the falcon, which seem to stare you down with their intense gaze. The feet are similarly interesting, with very long talons for gripping prey caught on the wing and feet with small, unusual pads sticking out of some areas of the toes, these pads are covered with tiny, spiky scales; presumably these help the bird to grip it's feathery prey more effectively. Finally, the way the bird balances on your hand feels is quite wonderful. Apart from not being too heavy it never seems to shift it's weight, although it is obviously in constant motion as I moved my arm to look at it.

The Peregrine is found worldwide, although it is currently on the IUCN Red List, as it has been extirpated from much of it's central and eastern European range, although there are signs of a recovery. Here in the UK the species is recovering from the inevitable persecution it has suffered at the hands of gamekeepers and farmers and around 1,402 pairs are currently estimated to be breeding in the UK according to the RSPB.

Although primarily a bird of cliff and crag, here in north-west England we have some decidedly urban peregrines, helped by a successful project to encourage the birds to nest in Manchester city centre (a pair did nest a couple of miles from the city centre in 1993). Last year four chicks were raised, and all these fledged successfully. I also know of at least one nearby urban centre where the species has been sighted, and indeed I met a lady who witnessed a Peregrine take a pigeon in flight one morning the main shopping street (much to her surprise), the bird landing directly in front of her with the kill before taking off again. I think it put her off her elevenses.

Next time I'm in the city, it'll be eyes skywards to see if I can spot these magnificent birds patrolling the concrete canyons they have made their home. However, I think I'll remember this marvellous encounter for a long time to come.