Striatolamia macrota
Striatolamia macrota
Common Name: Sand Tiger Shark
Order: Lamniformes
Family: Odontaspididae
Genus: Striatolamia
Geological Age: Ypresian
Summary
Striatolamia macrota is an extinct sand tiger type shark that was widespread in warm seas during the Eocene. It was an active marine predator, probably feeding mainly on fish and other relatively small marine animals. Fossil teeth of this species are common at many Eocene shark tooth localities and can occur in large numbers.
The teeth vary considerably depending on where they were positioned in the mouth. Front teeth are typically long, narrow and sharply pointed, often with small pointed side cusplets, while teeth farther back in the jaw become shorter and broader. One of the most useful identification features is the presence of fine vertical lines or folds on the inner face of the crown, while the outer face is generally smooth.
Striatolamia macrota is particularly associated with the Early and Middle Eocene, and had a very wide geographical distribution. It is well represented within the European fossil record, including the London Clay Formation of southern England and the Isle of Sheppey, as well as Eocene deposits elsewhere in Europe, Africa, Asia and North America.
Its distinctive long front teeth can be relatively easy to recognise when complete, although tooth shape changes considerably around the jaw. The combination of a slender central point, small side cusplets and fine vertical lines on the inner surface of the crown is particularly useful when distinguishing Striatolamia macrota from other Eocene sharks.
Geological Age & Range Notes
Eocene, particularly the Early to Middle Eocene. Striatolamia macrota is well recorded from the Ypresian, Lutetian and Bartonian, with some records extending into the Late Eocene. Within the London Basin it occurs in Early Eocene deposits, including the London Clay.
Fossil Material
Vertebra
Dermal Denticle
Known Localities
Diagnostic Features
- Teeth from the front of the mouth have a very long, narrow and sharply pointed central tooth.
- The central point is usually fairly straight or gently curved backwards, rather than strongly hooked.
- There is normally a small side point on either side of the main point. On front teeth these side points can be extremely small and may sometimes appear almost absent.
- The small side points become broader and more noticeable on teeth from farther around the jaw.
- One of the most useful features is found on the inside face of the tooth. This usually has fine vertical lines or folds running upwards from the bottom of the crown.
- These lines are strongest near the base and normally fade before reaching the tip. Some teeth have much stronger lines than others.
- The outside face is normally smooth, creating a useful contrast with the lined inner face.
- The cutting edges are smooth and have no serrations.
- Teeth from the front of the mouth are long and narrow, while teeth from farther around the side become shorter, broader and more triangular.
- Side teeth usually lean slightly towards the back of the mouth rather than pointing directly upwards.
- The root is divided into two large lobes. These are long and narrow on front teeth but become shorter and broader on teeth from farther back.
- Complete teeth can become quite large, although size varies greatly depending on the tooth’s original position within the jaw.
- The combination of a long narrow point, small side points and vertical lines on the inside surface is particularly characteristic of Striatolamia macrota.
Identification Notes
Striatolamia macrota is one of the more recognisable sharks from Eocene deposits, particularly when a complete front tooth is available.
The first thing to look for is a long, narrow central point with a small side point on either side. Then turn the tooth over and examine the inside surface.
A strong Striatolamia macrota candidate should normally show:
a long narrow central point + small side points + smooth cutting edges + vertical lines on the inside surface + a two-lobed root.
Look for the lines
The vertical lines on the inside of the crown are one of the most useful identification features.
They begin at the bottom of the crown and run upwards towards the tip. They usually become weaker higher up and do not cover the entire tooth.
The amount of lining varies considerably. Some teeth have very obvious folds, while others have only faint lines. Teeth from different parts of the mouth can also show different amounts of lining.
The outside surface of the tooth should normally be comparatively smooth.
Teeth change shape around the mouth
A major complication when identifying Striatolamia macrota is that its teeth look very different depending on where they came from in the jaw.
Front teeth are generally:
- very long and narrow
- upright or only slightly curved
- equipped with very small side points
- supported by long root lobes
Side teeth become:
- shorter
- much broader
- more triangular
- increasingly tilted towards one side
- equipped with broader, more rounded side points
Teeth from the very back of the mouth can therefore look surprisingly different from the classic long front teeth.
Broken teeth
The side points and root are commonly damaged or completely lost.
Fortunately, Striatolamia macrota can sometimes still be recognised from an incomplete crown if the characteristic vertical lines remain visible on the inner surface.
However, a badly worn tooth that has lost both its side points and most of its surface detail should be identified cautiously.
Where the important features cannot be seen clearly, Striatolamia sp. or Striatolamia cf. macrota is safer than forcing a species identification.
Quick identification
Look for:
long slender tooth + small side points + no serrations + vertical lines on the inside + smooth outside surface.
For complete front teeth, this combination makes Striatolamia macrota relatively distinctive among the sharks encountered in Eocene deposits.