While sharks may seem intimidating, they are an important part of a healthy marine ecosystem. This is especially true for tiger sharks, which have teeth to help them grip, hold, and rip their food.
While iconic sharks such as the great white have garnered a lot of scientific attention in recent years, there is one extinct shark with surprisingly recognizable teeth that has been overlooked: sand tiger sharks (Galeocerdo cuvier). Here are its characteristics.
The primary cusp
The primary cusp is the prominent notch in the top edge of a modern tiger shark tooth. This notch, with its large serial cusplets along its distal edge, is a key adaptation for puncturing and tearing open hard-shelled prey such as sea turtles. It is also the feature that allows sand tiger shark teeth to easily distinguish themselves from those of other cartilaginous fish, which do not have such a distinctive primary cusp.
It is important to remember that sand tiger sharks are at the top of the marine food chain, and these sharp, powerful teeth are an integral part of their successful predatory lifestyle. They hunt slow-moving prey by ambush, stalking their prey and then rushing in to grab them. They are able to do this efficiently thanks to their primary hunting stunt: the piercing, gripping, and crushing action of their teeth.
In order to achieve this, sand tiger shark teeth are adapted for shearing action and have a serrated blade. The curved blade has two series of serrations, one on each side. The first serrations are relatively coarse, and then the second set of serrations get finer and closer together. This is important, as it increases the tooth’s cutting power, while still allowing for the smooth shearing of soft prey.
Fossils of sand tiger shark teeth are common in marine Oligocene to Recent deposits. They can be found in sites along the entire east coast of the United States, including the Calvert Cliffs, Aurora, Yorktown and Pungo River formations in Maryland, the Aurora site in North Carolina, and Venice Beach and the Peace River in Florida.
These fossils are all Carcharias latidens, but the shapes of the lateral teeth may differ. Some have only a single cusp, while others have long and pointy cusplets. This variation is an indication that, like today’s sand tiger sharks, ancestors of these species tracked warmer waters during the Cretaceous period, moving between Massachusetts and Delaware when temperatures shifted from a warm greenhouse climate toward the colder Antarctic Peninsula.
Biomechanical studies that analyze shark tooth loading and performance in isolation oversimplify the functions of these complex chondrichthyan structures (Whitenack + Gottfried 2010). However, in silico simulations of the canonical Wnt signalling pathway demonstrate that variations in shark dental morphology are highly predictable and occur according to a strict developmental bauplan.
The serrated cusp
Tiger shark teeth were so sharp that they could cut through bone and cartilage. They also had serrated edges, which probably helped them tear meat and fish from prey. The serrations on tiger shark teeth are less complex than those of their contemporary, the extinct long-toothed mako shark (Megalodon). This suggests that tiger sharks used their teeth differently from mako sharks, relying more on cutting than tearing to kill their prey.
The tiger shark’s teeth are also more likely to be black than those of other modern sharks. This is because they have less hydroxyapatite, which is a yellow mineral that oxidizes into a dark substance called apatite over time. The apatite in sharks’ teeth is also more compact, so it is harder and more dense than human tooth enamel. This makes tiger shark teeth much more resistant to corrosion and discoloration.
Perez’s research on tiger shark teeth has led to his becoming an expert in fossil conservation and preservation, particularly in marine resins. He is now working on developing a new method for preserving shark teeth and other marine biominerals. The technique involves using resin to fill and seal the cracks in teeth and then coating the surfaces with a protective layer of oil. This prevents a brittle substance called chitin from growing inside the teeth and weakening them.
A thermionic-emission electron gun scanning electron microscope (SEM; Hitachi SU3800, Tokyo) was used to collect backscattered electron images of a sand tiger shark tooth mounted in epoxy. The resulting BSE composition images reveal the structure of the coronal section with bright regions corresponding to high atomic number elements and dark regions to low atomic number elements.
The tooth was then divided into coronal and sagittal sections. Sagittal sections were created with a Buehler Isomet slow-spinning abrasive 102 mm diamond saw at 1.3 mm spatial intervals, utilizing a 0.3 mm sawblade kerf across the tooth. Coronal sections were made by sanding the bottom of the epoxy mold, beginning with coarse grit papers and progressing to higher grits until the target layers were exposed. The top of each section was then smoothed with 5000 grit wet-dry sandpaper to remove previous tooling marks and facilitate a consistent surface for subsequent analysis.
The secondary cusp
The slender lateral cusplets on either side of the primary cusp are efficient at sawing through soft prey. This tooth is also designed to pierce and grip hard shelled marine animals such as sea turtles and clams.
Unlike the teeth of most other sharks, all tiger shark teeth have both a mesial and distal serrated cutting edge. The sharply notched distal cutting edge enables the shark to bite off portions of the animal it is hunting. This ability to bite off chunks of flesh demonstrates the shark’s evolutionary arms race with its prey and is one of the reasons why tiger sharks have such a bad reputation as aggressive predators (Compagno et al., 2005).
This feature is easily discerned in fossil tiger shark teeth. The mesial cutting edge of the tiger shark’s upper teeth are usually worn down and eroded. The lateral cusplets, however, are still intact and well preserved in most fossils. This feature is very important when attempting to determine which species a fossil tiger shark tooth came from.
The upper teeth of the extinct Longtooth Tiger Shark, Physogaleus contortus, are unmistakable. They have a long twisting crown and a raised root that gives them a distinctive look. This shape was probably derived from the fact that this species gave birth to live young rather than laying eggs like other sharks (Oldham and Cocke, 1980).
Fossils of this species date to the Oligocene and early Miocene epochs and are known from Florida in North America. This shark was a small carcharhinid that is closely related to the modern Tiger Shark, G. cuvier. Its teeth were similar in size and complexity of serrations to G. cuvier’s but it has a noticeably taller crown.
The lower teeth of this shark are much less pronounced and not as complex in their serrations. The slender lateral cusplets are not as clearly defined as those on the upper teeth and are more closely related to the modern Sand Tiger Shark, Carcharias taurus. Fossils of this shark are common in Florida and have been found at sites dating back to the Middle Archaic period. One specimen has drilled holes that suggest it was used as an implement for food preparation.
Sharks are predators that feed on a variety of animals and can eat creatures as large as whales. To do this, sharks use their teeth which are modified placoid scales with an outer layer of enamel, dentine and a central pulp cavity. The shape, size and structure of sharks’ teeth vary according to a species’ primary food source. Some teeth are designed to grasp or tear, while others are adapted to crush and grind mollusks and crustaceans. The upper and lower jaws of a shark are joined by massive muscles used for biting. This makes it important for a shark to be able to distinguish the different types of prey and select the appropriate tooth to attack it with.
Tiger sharks are a cosmopolitan species that can be found in all oceans and are among the largest of the modern carnivorous sharks. They are also one of the most feared and revered predators. The tiger shark’s ability to sense low-frequency pressure waves produced by swimming animals allows it to detect its prey in murky water. This enables the tiger shark to stalk its prey without the risk of being detected by other predators.
The tiger shark is a fierce and adaptable predator. Its inherited morphology has allowed it to extend its essentially piscivorous diet to include sea turtles, which have tough shells that are extremely difficult to penetrate.
To do this, tiger sharks have a unique feature, which is that the mesial cutting edge of their upper and lower teeth is sharper than the distal. This enables the shark to shear through the shell of its prey with relatively little force.
It’s not uncommon for a shark to lose or break one of its teeth while hunting, but a replacement is almost instantly formed. Most sharks have five rows of teeth, with the front set doing most of the work. The back sets are smaller, and when a tooth breaks or is lost it’s replaced by a tooth from the next row forward.
This is a great example of a fossil tiger shark tooth (Galeocerdo cuvier). The serrations are very prominent and the root is robust. A wonderful addition to any shark or tiger shark collector’s collection!