Thirty-six years ago, I made a fossil-collecting trip to southwest Alabama in order to collect fossil (middle Eocene) gastropods and bivalves. At one locality, however, I came across an unexpected find: namely, well-preserved shark teeth. They were in a weakly cemented, glauconite sandstone bed that was directly underneath the deposit rich in mollusks. At that time, I was unable to identify most of the teeth I found because I could not find any pertinent literature about them. Thirty-six years later, thanks to having the internet available, I have come across some information that pertains to Alabama Eocene shark teeth. I can now, at least, identify [as discussed below] some of the material I collected to the genus level, but, I mostly have too few specimens. Also, most of the teeth have less than perfect preservation, which is critical in order to confidently identify shark teeth to the species level. The black color of these teeth is the result of being buried for about 40 million years.
Carcharias sp. (Sand-tiger shark)
The name Carcharias is an ancient Greek work that means “shark.”
The geologic time Range of genus Carcharias is early Eocene to Recent. Sharks belonging to this genus live today in warm shallow seas on most continents. Individuals can be up to 3.2 m (10.5 feet) in length. They have a long streamlined body and sharp teeth for feeding on other fishes.
Classification
Kingdom Animalia
Phylum Chordata
Class Chondrichthyes
Subclass Elasmobranchii
Order Lamniformes
Family Odontaspididae = so-called “sand sharks” [this family is extinct]
Genus Carcharias
Type Species C. taurus Rafinesque, 1810
Carcharias has narrow, stout, long, sharp-pointed teeth with a slight curve. They also have a tiny cusplet on each side of a tooth. All these features [especially the cusplets] helped me confirm identification of these teeth as belonging to genus Carcharias. On modern-day sand tiger sharks, these cusplets can be larger, but, keep in mind, that during the Eocene the morphology of sand tiger sharks would have been slightly different than those of today because of slight changes, most likely related to evolutionary processes. Also, one must consider that the cusplets on the specimens I collected have been somewhat worn down by erosion.
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Figure 1. Three views of the same tooth of the sand-tiger shark Carcharias sp., from upper middle Eocene rock in southwestern Alabama. Image on the left is a front view, with tiny cusplets indicated by the arrows. Image in the middle is the back view. Image on the right is a right-side view. Tooth length of tooth: 45 mm, width 15 mm, thickness 9 mm.
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The name Galeocerdo is from the Greek words “Galeos” and “Kerdo,” which mean “shark” and “fox.” The geologic time range of genus Galeocerdo is Cretaceous? to Recent.
Figure 2: On the left: frontal views, and on the right: back views of the same two teeth of the tiger shark Galeocerdo sp., from upper middle Eocene rock southwestern. Alabama. Smaller tooth 16 mm width, 9 mm height; larger tooth 19 mm width, 12 mm height.
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Figure 3. A modern-day myliobatid (sting ray) swimming in very shallow water; a public domain image (picryl.com).
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Figure 5. Top and side views of a shark vertebra [diameter 2 cm, thickness 1 cm] showing the characteristic circular growth rings. This specimen is from the same upper middle Eocene fossil bed, where the Carcharias, Galeodea, and Myliobatis teeth were collected.
References
Ebersole, J.A., D. Cicimurri, and G. L. Stringer. 2019. Taxonomy and biostratigraphy of the elasmobranch and bony fishes (Chondrichthyes and Osteichtyes) of the lower-to-middle Eocene (Ypresian to Bartonian) Group in Alabama, USA, including Claiborne and analysis of otoliths. European Journal of Taxonomy 585, pp. 1-274.
fossilera.com
Wikipedia
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