Talking sharks’ teeth

Lutz Andres (Germany)

The giant-toothed ‘Megalodon’ shark (Carcharocles megalodon,) is one of the most impressive extinct creatures to have excited our imagination, and its fossilised teeth are one of the most desired objects in the fossil collecting world.

A lot of collectors and scientists believe that Megalodon is closely related to the Great White shark (Carcharodon carcharias), because of their similar teeth, which are large, triangular and serrated shape. However, that point of view is too superficial. There are a few clear differences in the tooth morphology. In addition, they had apparently different kinds of nutrition and their dental weaponry suggests different hunting strategies. A few obviously different tooth characteristics between such closely related species will be described and discussed below.

Different root shapes

The root branches of the upper and lower anterior teeth of all giant-toothed sharks (Otodontidae) are elongated to resemble a ‘V’ or ‘U’. The roots of upper anterior teeth in Great White sharks are often nearly rectangular, without well-developed root branches.

When the Great White shark attacks and bites its prey, the lower anterior teeth are the first to penetrate the body, and then the shark closes its jaws. After that, it starts immediately to shake its head in a semi-circle shape, to rip flesh out of the body, mainly with its upper anterior teeth. The pressure on these upper anterior teeth is applied laterally. Therefore, the roots have wider surfaces to absorb the laterally arising forces.

The morphological function of the roots of lower anterior teeth of the Great White shark, like in Megalodon and all other Otodontidae, is to penetrate and stop the prey from escaping. The pressure of the tearing forces comes from the inner side (lingual) outwards. The roots lobes work like supports to keep the tooth to the jaw. Like a physical lever, the longer the tooth, the less energy needs to be used and vice versa.

Cappetta (1987) described the different types of junction between root and crown in terms of “Dental characters and terminology” that “the neck (= collar or lingual furrow) [is] especially distinct on the lingual face of the tooth”. Other names for the large transitional area between the crown and root are ‘collum’ (Latin, translated: neck) and ‘bourlette’ (Kent, 1994). Welton and Farish (1993) describe a ‘dental band’ as being “a narrow, smooth, enameloid-free band at the crown-root junction on the labial or lingual surfaces or completely encircling the tooth”.

In Megalodon, like in all other giant-toothed sharks (Otodontidae), the dental band is large and chevron-shaped. It often bears a thin dark ‘enameloid’ wash and on the lingual side of the tooth only and can therefore be called ‘collum’. The teeth of a Great White shark, like its ancestor Makos (Isurus hastalis and I. praecursor), have none or, at most, a weak and narrow transitional area, which fits the description of the “dental band”.

Dental band

This ‘collum’, in Megalodon, is apparently additional collagenous tissue, and apparently helps fix the tooth to the jaw, for the same reason mentioned above (tearing forces). The higher the starting point is towards the crown (physical lever), the stronger are the retaining forces. The function of the ‘dental band’ for teeth of the Great White shark, and its ancestor, the big-toothed Mako (Isurus hastalis), is apparently of less relevance and without any different crown shapes.

The lingual face of the upper anterior teeth of all Otodontidaeis strongly convex which can clearly be seen in cross section. The tooth crowns of the Great White shark, and his ancestor the big-toothed Mako (Isurus hastalis), are not convex, but flat in cross section.

Special differences

Specialist dentition can be seen in other “super-predators”, like the flesh-eating dinosaurs Tyrannosaurus rex and Carcharodontosaurus saharicus. The first has stout, round teeth in cross section and the second much more compressed, slender ones. Erickson (2001) wrote that an animal with “much more robust teeth,” like T. rex, “was capable of smashing through flesh and bone, and delivering deeper and perhaps more instantly lethal bites”.

In contrast, animals with compressed teeth would have another feeding strategy, “inflicting rapid, slashing bites primarily to the soft tissues which meant that the prey bled to death”. These different types of teeth, and their morphological functions, are comparable with a pick and a steak knife which have different shapes of serrated cutting edges.

In both lineages of the Carcharocles and Carcharodon genera, there is a change from smooth to serrated cutting edges. Megalodon evolved from Otodus and the Great White shark from the big-toothed Mako (Isurus hastalis). Teeth of Megalodon have, in comparison with Great White sharks, a much finer and regular serration. Teeth of the Carcharodon carcharias are coarse and irregular.

Pressure distribution

In connection with T-rex teeth, Abler (1999) assumed that the “more cube-like” tips of the serration “distributed pressure uniformly” and “thus eliminated any point of concentrated force where a crack might begin” during biting the prey and hitting bones or tendon. Megalodon, like T-rex, obviously killed its prey with a crushing bite and a well-developed serration, like in Great White sharks, is obviously not much use to it.

The serration in Great White sharks first appears in the Pliocene with a more or less fine serration and became much stronger like extant animals. In contrast to Megalodon, Great White sharks kill their prey by slashing or slicing (see Klimley and Ainley, 1996). A well-developed serration, with pyramidal shaped tips, is evidently very effective for this purpose. This difference is further evidence for a different feeding strategy of predators, as a result of their own (separate) evolution.

Different tooth size

Megalodon teeth are up to 18cm long and those of the Great shark a maximum of 8cm in size. The size of the teeth is more or less in proportion to the size of the animal.

Summary

It is more than likely that the Sandtiger shark (Carcharias taurus) and the Shortfin mako (Isurus oxyrinchus), with their sharp pointed, slender and curved teeth aren’t bone crushers, but rather fish eaters. The Great White shark evidently prefers hunting smaller, up to medium-sized marine mammals, like sea lions, even devouring dead whales, as the risk of being hurt during attack is reduced. It attacks sea lions from beneath, bites a huge wound in the belly and waits for the prey is bleed to death.

Teeth of Megalodon are frequently found accompanying fossil whale bones in Miocene layers, which often have tooth marks left by serrated teeth. These marks cannot have been caused by fossil Great White sharks, because they did not exist in the Miocene (Andres, 2005). The earliest they appeared was in Early Pliocene. This fact, and the tooth characteristics in Megalodon discussed above, indicate that Megalodon was a whale hunter. Megalodon and the Great White shark may have had a similar tooth shape, but their teeth have evidently different purposes. However, the whale-hunting lifestyle and the huge size all disappeared when Megalodon became extinct in the Early Pliocene (Andres, 2000).

Graphics and images produced by Stuart Handley.

References

Abler, W.L. (1999): The teeth of the Tyrannosaurus. Scientific American, no. 9, pp. 40 – 41.

Andres, L. (2000): C. megalodon – Megatooth Shark — Carcharodon versus Carcharocles. (originally published in the magazine of the Deutsche Elasmobranchier-Gesellschaft D.E.G.: Elasmoskop, no. 1, pp. 23 – 28, 7 figs.) Internet release: www. fossilguy.com/topics/megshark/megshark.htm Andres, L. (2002): Isurus escheri (AGASSIZ, 1844). Internet release: www.elasmo.com/genera/slides/gw_evo/escheri/escheri.html.

Andres, L. (2005): The temporal and geographical distribution of the fossil Great White shark (Carcharodon carcharias LINNAEUS, 1758). Internet release: http://www.elasmo.com/genera/slides/the_gw/the_gw.html.

Bourdon, J. (2002): The evolution of a cutting-edge. Internet release: www.elasmo.com/genera/slides/gw_evo/peru/peru.html.

Bourdon, J., D.Ward and G. Grimsley (2000): The development of serrations on Otodus (Agassiz, 1843) (Selachii: Otodontidae) teeth during the Early Eocene – the transition from Otodus obliquus (Agassiz, 1843) to Carcharocles auriculatus (Blainville, 1818); Internet release: www.elasmo.com/genera/slides/o_lineage/o_sergue.html.

Cappetta, H. (1987): Chondrichthyes II /Mesozoic and Caenozoic Elasmobranchii = Handbook of Palaeoichthyology Vol. 3B, pp. 1 – 193, 148 figs.; Stuttgart.

Erickson, G.M. (1999): Breathing life into Tyrannosaurus rex. Scientific American, no. 9, pp. 32 – 39.

Erickson, G.M. (2001): The bite of Allosaurus. Nature, vol. 409, pp. 987 – 988.

Kent, B.W. (1994): Fossil Sharks of the Chesapeake Bay Region. Pp. 1 – 146, many figs.; Columbia.

Klimley, A.P. and D.G. Ainley (1996; editors): GREAT WHITE SHARKS – The Biology of Carcharodon carcharias. Pp. 1 – 517; Academic Press, San Diego. Renz, M. (2002): Megalodon – Hunting the hunter. Pp. 1 – 161; PaleoPress, Lehigh Acres.

Welton, B.J. and R.F. Farish (1993): The Collector’s Guide to Fossil Sharks and Rays from the Cretacous of Texas. Pp. 1 – 204, many pls., many figs.; Before Time, Lewisvile.