The tiger shark is one of the largest predatory sharks known today. Its highly serrated teeth allow it to cut and tear through the flesh of its prey — from sea turtles, to eels, rays, dolphins, squid, and fishes.
Fossil tiger shark teeth have an immense fossil potential for shedding light on the evolutionary history of these predators. They have also been used to determine changes in oceanography and paleoecology over time.
Eocene
The Eocene was a period of intense tectonic activity that caused continental plates to move closer to their current positions, altering ocean circulation and air flow. It also saw a major shift in climate from warm to cold. The resulting ice sheets in Antarctica and Greenland contributed to the global cooling trend that began at about 49 million years ago and is known as the Eocene-Oligocene extinction event (also called the Grande Coupure).
Early in the Eocene, the world’s oceans were teeming with fish and other marine life. This provided abundant food for sharks, early whales, and other large marine mammals that evolved at this time.
One of the earliest carcharinid sharks, Basilosaurus, emerged during this period and was a significant part of the marine fauna of the Eocene. Moreover, early marine mammals like mesonychids and hoofed predators like Mesonyx developed.
Fossils of a variety of large, extinct sea creatures are commonly found in Eocene sediments. These include the ancestors of modern elephants, hyrax, monkeys and strange forms such as rhinoceros-like Embrithopods.
A number of species of sand tiger sharks are also well represented in Eocene fossils from North Africa, Europe, Asia and South America. These fossils are interpreted as belonging to a group of odontaspidids that spread widely during the early Palaeogene and eventually diversified into Brachycarcharias, which includes several different species.
Some of these species are also represented in fossils from the middle Eocene of China. This suggests a link between the evolution of sand tiger sharks and the evolutionary lineage that led to the evolution of modern tarsiers and strepsirrhines.
Another interesting aspect of the Eocene is that many of the bird orders first appear during this period, including eagles, pelicans, quail and vultures. These animals resemble their modern ancestors, but they remained flightless, with giant hooked beaks that suggested that they were carnivorous.
In addition, the Eocene was a period in which the first large terrestrial mammal types, including elephants and hyrax, evolved. These mammal types resembled their ancestors, but were larger and more efficient hunters.
Oligocene
The Oligocene period (33 to 23 million years ago) is a geologic epoch which covers the final part of the Paleogene Period. It is preceded by the Eocene and Miocene epochs, and is a time when many major changes took place on Earth.
During this time, the world experienced a gradual decrease in average temperatures. The Earth also experienced a reduction in average sea levels. Antarctica drifted slowly south, became more isolated from South America and Australia, and developed the polar ice cap that it still retains today.
On land, mammals continued to increase in size and prominence throughout this epoch. Elephants and other large land animals, such as amphicyonids, canids, camels, and protoceratids, began to dominate on land in Asia, Africa, and North America. The earliest forms of rhinoceroses, which reach great heights, and caprimulgiformes, birds that possess gaping mouths for catching insects, appeared as well.
In the oceans, bivalves and molluscs characteristic of this period appeared in abundance. Sharks and other predatory marine animals appeared as well, such as the baleen and toothed cetaceans (whales) that are ancestors of modern whales.
There were also some species of turtles and crocodiles that appeared in this epoch, as well as the ancestor of pinnipeds, which are sea wolves or otter-like reptiles. This epoch also saw the extinction of the Choristodera, a group of semi-aquatic, crocodile-like reptiles that were thought to have originated in the Jurassic.
This epoch also witnessed the appearance of new types of sharks, including longtooth tiger sharks, which have unique teeth with a twisted crown and a raised root. These sharks are very common along the Calvert Cliffs of Maryland.
A number of reposited tiger shark tooth specimens from this epoch are housed in museums around the world, including the Smithsonian Institution’s National Museum of Natural History and the San Diego Natural History Museum. These fossils are extremely valuable for study and can be used as a tool to understand how sharks have changed over time.
Miocene
The Miocene was a time when many animals were evolving. In fact, the mammals that we know today originated in this period. These animals grew bigger and more advanced than they are today. Some of these animals also migrated from one place to another.
Some of the most common fossils that we see in this period include birds and fish. Some of these fishes are very large. They weighed up to 50 pounds.
Birds were very diverse, with some of them being as big as penguins! They had their own unique flight patterns and specialized in different kinds of hunting. Some of them had wingspans of 25 feet!
Other animals that appeared in this period included horses, bears, and otters. This epoch was also the time when mammals first started traveling into northern latitudes.
During the Miocene, oceanic upwelling and deep water currents helped to bring more sediment to the surface. This made it easier for marine organisms to survive and develop.
These sediments accumulated in places like the Bakersfield region of California where they formed a deposit known as “Sharktooth Hill.” Shark teeth from this site are among the most valuable in the world.
The Miocene period is notable for its high sea-levels, which are associated with glaciations in Antarctica. These climatic changes were tied to the evolution of the circum-Antarctic current, which separated Antarctica from Australia.
In addition, the Miocene period saw a biotic transition in stable carbon isotopes that is commonly known as the “C3/C4 transition.” This shift was caused by an increase in CO2 levels in the atmosphere.
This transition was accompanied by a change in the vegetation that was present at the time. Studies have shown that the vegetation in this region was much like modern woodland savannas.
Pliocene
About 17 million years ago, a warm, shallow sea covered southern Maryland. Luxuriant growths of marine algae and succulent aquatic plants flourished here, providing plentiful food for the sharks that bred there. Among the vertebrate inhabitants were seacows, whales, turtles, porpoises, and rays.
The warm, shallow waters of the Miocene were a great breeding ground for numerous species of sea mammals. Fossil teeth of these animals are the most common type of fossil found in the Sharktooth Hill bone bed, as well as many other similar sites.
This bone bed was deposited during the Middle Miocene, about 15.9 to 15.2 million years ago. This is when the climate was at its optimum and the sharks were most active in the region, and they were likely a major food source for many sea mammal species.
One of the most striking features of this bone bed is the large number of teeth, most of them belonging to extinct sharks. This is especially true of the Galeocerdo triqueter (Tiger Sharks) and Hemipristis serra (Requiem Sharks), but it also includes teeth of several other extinct shark species, including Oxyrhina desorii (Mackerel Sharks), Sphyrma prisca (Hammer-head Sharks), and Odontaspis elegans (Sand Sharks).
Another interesting feature of this fossil deposit is that it shows evidence of damage to some whale bones, indicating that sharks were feeding on these animals in the area. This damage was not evident on the fossil seals from the same area, indicating that these were probably postmortem bites rather than injuries inflicted during the animals’ lifetimes.
These findings are very important for understanding the ecology of the Sharktooth Hill fauna and its relationship to other marine mammals in the area. In addition to the abundance of shark teeth, these fossils indicate that the area had warm water and a rich invertebrate community.
The shark teeth drilled from this bone bed and other similar sites almost certainly represented implements for hunting, helping these prehistoric marine creatures survive. They were also used for ornamentation and religious purposes, and may have been hafted onto war clubs for use in battle.