A quick and dirty guide to the general identification of fossil shark teeth
This will be a quick guide to the identification of most teeth down to the level of order. Below this, at the family, genus and species level, there are many published guides both in book form and on the internet that will help in this area. This will cover most of the larger types which are most likely to be collected. I will omit (for space reasons) the smaller types such as Orectolobiformes (Nurse and Carpet Sharks), Heterodontiformes (Port Jackson Sharks), Pristiophorifomes (Saw Sharks), Squaliformes (Dogfish), Squatiniformes (Angel Sharks) and older, more primitive sharks such as Hybodontiformes. Most of these omitted types are small, rare, and/or confined to specific areas or ages and thus somewhat less likely to be collected.
Note: For sharks, Order names end in ‘iformes’, Family names end in ‘idae’. Genus names often end in ‘us’ but don’t have to. Species names vary widely. Genus and species names are italicized. Genus is capitalized, species is not.
We will briefly cover the Orders of Carcharhiniformes (Grey Sharks), Hexanchiformes (6 and 7 Gill Sharks), and Lamniformes (Giant Sharks, Makos and their relatives, and Sand Tiger Sharks). The teeth of these various animals are usually fairly large and most often collected.
The first question to ask is what age is the tooth? Genera and species are usually confined to a certain age frame. Knowing that age range limits the possible identifications.
KEY ROOT FEATURES
When one collects a specimen, they usually focus on the enamel blade. As this is harder and more durable than the root, it usually survives damage and wear better than the root. However, the root often contains details that can narrow the identification down to genus and/or species level.
Details to look for on the root are: Is there a nutritive groove in the center of the root? This would be found on Carcharhiniformes, as with the Sandbar shark, Carcharhinus (Figure 1) and some Lamniform sharks such as the Sand Tiger Sharks here illustrated by Carcharias (Figure 2) and their relatives, along with the Porbeagle Sharks.
Figure 1. Carcharhinus tooth displaying nutritive root
Figure 2. Carcharias tooth displaying nutritive root
Are there central pore(s) as with Makos, Isurus (Figure 3); and Great Whites, Carcharodon (Figure 4)?
|Figure 3. Isurus tooth displaying central pore||Figure 4. Carcharodon tooth displaying central pore|
Are there scattered pores across the root as found in Crow Sharks, Squalicorax (Figure 5.); Giant Sharks, i.e. Carcharocles (Figure 6) and its ancestors; the Hexanchiform sharks, such as the Six Gill, Hexanchus (Figure 7); and the Seven Gill Shark, Notorynchus (Figure 8)?
Other important features can be found on the shoulders of the root. Are there lateral cusplets as with the aforementioned Sand Tigers, or as seen here in Otodus (megalodon ancestor, Figure 9)?
Figure 9. Otodus tooth displaying lateral cusplets.
Note: There is no nutritive groove in the root.
Are there serrations on the shoulders as seen here in a tiger shark, Galeocerdo?
Figure 10. Galeocerdo tooth displaying serrated shoulders.
Note: a shallow nutritive groove is present which helps put it in the order Carcharhiniformes.
All these various shoulder features are easily damaged which is why it is important to have excellent quality specimens for positive identification.
KEY BLADE FEATURES
Moving on to the main cusp or blade, we can further narrow down the identification. Keep in mind that the flat side of the tooth faces the outside of the mouth (labial) while the curved, more attractive side faces the inside of the mouth (lingual).
The first question, is it serrated or smooth edged? There are various serrated teeth existing at different times. In the Cretaceous, if the tooth is serrated it usually a species of Squalicorax (Figure 11), or more rarely, Pseudocorax.
Figure 11. Squalicorax tooth displaying a serrated blade.
In the Palaeocene, the only serrated tooth is Palaeocarcharodon (Figure 12).
|Figure 12. Palaeocarcharodon tooth displaying a serrated blade.|
In later epochs, we add the various Carcharhiniformes, including the family of Hemigaleidae, such as Hemipristis (Figure 13), along with some of the aforementioned Laminformes, Carcharodon* (Great White) and Carcharocles (Giant Shark). There are a few others, but they are rare.
Figure 13. Hemipristis tooth displaying a serrated blade.
*Note: Most fossil species of Carcharodon are not serrated.
Once you have narrowed down the order that the tooth is found in, you can then begin getting the identification down to family and then genus and species. Published guides can help you here. In addition I have been slowly publishing identification guides in the Group -Shocking Shark Teeth- which can be found here: https://www.myfossil.org/groups/shocking-shark-teeth/
You may have to dig down to older posts to find all of them. Perhaps in the future these posts can be consolidated into a single guide.