How To Identify Your Finds (Part 1 of 10)
There are around 30 species of shark, ray and other fish fossils plus crocodile and turtle remains. You will also find a lot of pyritised wood but it's not worth the bother as it tends to fall to bits soon after it’s collected.
The most common animal fossils are the sand tiger shark teeth of Striatolamia striata. They will make up the majority of your finds. The next commonest are teeth from another sand tiger shark, Gluekmanotodus heinzelini. The following explains how to identify these and a number of others. Note: If your fossil is incomplete or heavily worn, it may not always be possible ID it. As the shore where these fossils are found can be a pretty wild, high energy environment when the tide is in, it's hardly surprising the majority of fossils are incomplete. TerminologyIn order to tell one species from another, you need to know a little of the terminology used to identify their features. The following figure, and the list below it, summarise the commonest terms for shark teeth:
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- anterior - In or near the front of the jaw.
- apical - Top/apex end of a tooth.
- basal - Bottom/base end of a tooth.
- cutting edge - Literally the tooth's cutting edge. Found on either side of crown.
- crown or cusp - The enamelled part a tooth.
- cusplet - Small projection from the side of a tooth (aka 'denticle').
- distal - The side of a tooth furthest away from the midline of the jaw.
- foramen - An opening or hole into the root.
- labial - Side of a tooth facing the lips.
- lateral - Side or flank e.g. lateral tooth.
- lingual - Side of a tooth facing the tongue.
- mesial - The side of a tooth closest the midline of the jaw.
- nutrient groove - A notch or groove separating root lobes which contains the central foramen.
- protuberance - A prominent bulge in the middle of the root either side of the nutrient groove.
- recurved - Curves backwards.
- root - Root of a tooth.
- shoulder - Where the enamel extends out onto the root lobe.
- subulate - Slender and tapering to a point.
Position in the Jaw
A really detailed explanation of all the ins-and-outs is a bit beyond the scope of this website but this paper will show you how to go about it. It compares the teeth of a living species of Sand Tiger shark called Carcharias Taurus with those of Striatolamia macrota, which is thought to be the ancestor of our own Striatolamia striata. You can apply the same principles to most of the teeth you find at Beltinge.
For general guidance though, most of the shark teeth at Beltinge fall into 2 basic shapes: Front teeth (Anterior); and side teeth (lateral). [Note: There are also back teeth (posterior) which look like small laterals with disproportionately large roots, but let's not over-complicate things). Examples of these two shapes are shown in figure 2 to the right (Anterior on the left, lateral on the right). In anterior teeth the crown is relatively long, upright and slender. Lateral crowns are more squat, triangular, blade-like, and lean towards the back of the jaw The crowns of both anterior and lateral teeth are noticeably flatter on the labial side. Anterior teeth are often strongly sigmoidal ('S' shaped) when viewed from the side. These are from the upper jaw. Anteriors from the lower jaw are less sigmoidal and have stronger protuberances than the upper jaw. As you move away from the mid jaw, the anterior teeth get less symmetrical. The root lobes also get less symmetrical with the mesial lobe getting longer. The angle formed by the root lobes also increases the further they are from the mid-jaw. Laterals: Get smaller towards the rear of the jaw; If you lay an upper lateral down on a flat surface, the tip of the crown will be touching the surface, whilst a lower lateral's crown-tip will curve away. Also, the labial surface of an upper lateral is flatter whilst that of a lower is more rounded. How To Identify Your Finds (Part 2 of 10) |