Fossil fish coprolite discoveries on Wardie fossil hunt
Figure 1. On the afternoon of Wednesday 23rd September, I took part in a socially distanced fossil hunt to Wardie shore SSSI, Edinburgh led by Dr Tom Challands, University of Edinburgh (see above).
Previous Discoveries at Wardie Shore SSSI
Figure 2. Part of a fish body fossil brought by Dr Tom Challands to show participants (Scale 10p)
Figure 3. Life reconstruction of the Wardie shark Trystichius arcuatus. © Kristen Tietjen, University of Chicago.
Wardie Shore is a well-renowned Carboniferous fish locality with numerous fish beds discovered by the late fossil collector, Stan Wood. The rocks exposed at Wardie belong to the Lower Oil Shale Group and consist of dark grey-black, laminated organic rich mudstones with a reasonably high Total Organic Carbon (TOC) content of around ~4%. They were deposited in a deep lacustrine (lake) environment that covered most of the Lothian area during the Carboniferous Period known as Lake Cadell. This lake was occasionally connected to the sea, allowing marine faunas such as sharks (see above) to be found in these deposits (McAdam and Clarkson. 1996). My aim was to hunt for loose fossil material along the shoreline, this time with greater success than previously at Joppa shore. NOTE: Wardie Shore is a Site of Special Scientific Interest (SSSI) so please do not hammer the bedrock. Fossil material can be found by splitting open loose red siderite nodules found along the foreshore.
Discoveries made on the Wardie Shore fossil hunt
Figure 4. Dr Tom Challands pointing out to the group a rare example of a large, sandstone dyke which has been emplaced into the surrounding bedrock (NT 24228 77098).
The presence of a large sandstone dyke (see Figure 4.) which was subsequently injected from either above or below the surrounding shale could represent soft sediment deformation from earthquake activity or pressure overbearing from the weight of the water column above the lake bed.
The occurrence of a large, Stigmaria root in situ at (NT 24356 77110) (see Figure 5.) suggests it was once part of a larger root system of a lycopod tree. Such trees must have grew along the shoreline of Lake Cadell during the Carboniferous Period.
As you will read below, by far the most common fossil found at Wardie are those of fish coprolites (fossilised fish feces or poo!) (see Figure 6.).
Figure 5. Large, fossil tree root (Stigmaria) exposed on bedding plane at (NT 24356 77110) (Scale 10p).
Figure 6. Small, ellipsoid coprolites preserved on a bedding plane at (NT 24369 77100) (Scale 10p).
Personal fossil discoveries at Wardie Shore
Figure 7. (left) and 8. (right) exhibiting carbonaceous fossil plant fragments with the dark grey-black shale (NT 24310 77100) (Scale 10p).
Figure 9. Example of a typical loose red rounded siderite nodule which occasionally contains fossil material (NT 24277 77103) (Scale 10p).
Figure 10. Ellipsoid coprolite preserved within a siderite nodule at (NT 24491 77095).
Figure 11. Two halves of an ellipsoid coprolite preserved within a siderite nodule at (NT 24501 77086) *Note the concentric layering of this coprolite is still preserved.
Carbonaceous fossil plant material was found within some loose shale flags (see Figures 7. and 8.), suggesting plant material occasionally was washed into Lake Cadell. *This also supports the evidence and statements made regarding (Figure 5.).
As already stated, the most common fossils found at Wardie shore are those of fish coprolites (see Figure 6.).
To collect coprolites in loose material, the fossil collector should target rounded nodules (which form concentric shapes around the fossil during the fossilisation process) and those of red colour which represent the mineral siderite (see Figure 9.). Siderite precipitated here when the original organic matter began to decompose and react with the chemistry of the ancient lake environment.
Splitting this material with either a rock hammer or off a larger loose boulder on the shore will occasionally reveal coprolites like those seen in (Figures 10. and 11.). These small, ellipsoid feces were likely produced by fish that inhabited the lake e.g. (see Figure 3.). Although coprolites are usually seen as 'fossil poo' that is nothing more than a source of entertainment to young children, they are in fact of great importance to the palaeoecologist. The analysis of coprolites like those found at Wardie can increase our understanding of fossil foodwebs and about 'who ate who', which is essential in understanding how ecosystems have changed and operated over deep time.