Way Back Wednesday: Marine Life

A few members of our team went into the archive annex this morning to do some housekeeping: checking on and changing silica gel packets in the boxes of small finds. We have indicator strips that show when a box is no longer dry due to ambient humidity. Lauren grabbed a random box of environmental archaeology small finds to have a nose around, and, much to her surprise, it was mostly material she herself had found and recorded while managing environmental processing in 2013: stycas, glass and ceramic beads, and some flint flakes. In an amongst those bits from nearly a decade ago, two examples of local marine life appeared.

First, another St. Cuthbert bead! This one was found in 2010 in a burnt context from Trench 3. It seems to be associated with the stables phase of the trench, around 10th century. We hope to do a deep-dive post (pun intended) on crinoids in the future, as they have been on our mind after the large one we found earlier this season.

The second was something that struck Lauren and the finds team as odd years ago: it looked like a tiny cowrie shell. True cowrie shells (family Cypraeidae) were often found historically in Indian Ocean trade networks, so this miniature version was separated out as a small find because it seemed non-native to the area. The sample was taken in Trench 1, associated with an early medieval linear feature. Further research shortly after the dig in 2013, however, revealed more information about this tiny mollusc.

This shell is from the family Triviidae which has a two species local to the North Atlantic and North Sea, but the species are often called the “European cowrie” and “northern cowrie.”

The European or spotted cowrie is used to refer to trivia monacha (da Costa 1778), a carnivorous snail that lives at the low tide of the shore. They usually have dark spots on the pinkish upper shell, which our specimen does not have.

The “northern cowrie” is trivia arctica (Pulteney, 1799) which has an unspotted shell. These species were actually thought to be one and the same until 1925. Both species prey on sea squirts, and they are in turn food for fish like Atlantic cod, who also occasionally turn up in our animal bone. Our shell is also a bit chalky to the touch, but it’s not immediately clear if ours is a proper fossil and thus old at the time it was deposited in the sample or if it was alive contemporary to the occupation of the context from which the sample came.

Living t. arctica specimen, image by Frans Slieker (NHMR).

Why do we care so much about tiny molluscs? Why does it matter that this was found here? Molluscs are extremely useful when studying the environment in the past. Some snails have very specific habitable ranges that can help us infer climate information, and today is especially valuable in understanding periods of climate stability and instability in the past. Others are fantastic to chemically profile to understand the water and plant life signatures for a particular region, which was a methodology we used in our interpretation of the Bowl Hole burial ground skeletal material.

This particular shell was saved because it looked different from the mollusc shells we had been finding previously. It turns out it was local, but it was probably not being collected for food unlike the winkles we find en masse, so we don’t have examples of it in the record.

For more information and more images:

Gallery of the Family Triviidae via National History Museum Rotterdam

Differentiating the species

T. monacha, European cowrie: entry for Encyclopedia of Life, entry in World Register of Marine Species

T. arctica, Northern cowrie: entry for Encyclopedia of Life, entry in World Register of Marine Species

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