Fossil shark teeth offer a tangible connection to prehistoric marine environments. While precise dating typically requires specialized scientific analysis, understanding visual characteristics and the geological context of a find can provide strong indicators of its age.
The Fossilization Process
When a shark sheds a tooth, it must quickly sink to the seafloor and be covered by sediment to begin the fossilization process. This rapid burial protects the tooth from decay caused by oxygen and bacteria. Over thousands to millions of years, the tooth undergoes a process called permineralization. Water carrying dissolved minerals seeps through surrounding sediments into the microscopic pores of the tooth. These minerals, such as silica and calcite, gradually fill in and replace the original organic material, transforming the tooth into a dense, stone-like fossil.
Visual Indicators of Age
The color of a fossil shark tooth, while not a direct measure of its age, provides clues about the mineral composition of the sediment where it was preserved. Minerals like manganese and iron sulfides often result in black or dark gray teeth. Iron oxides can impart shades of brown or reddish hues. In environments with fewer impurities or abundant phosphate minerals, teeth might appear lighter, ranging from gray to tan or even white. A fossilized tooth’s color is determined by the minerals absorbed during its long burial.
The tooth’s physical condition and degree of wear can also indicate its history. Teeth heavily tumbled by water currents or exposed to abrasive environments often exhibit significant erosion, breakage, or a smooth, polished appearance. Conversely, a tooth found in pristine condition, with sharp edges and intact cusps, suggests it was likely buried quickly and remained undisturbed. Adhering sediment or rock matrix on a tooth can hint at its original burial environment and sometimes correlate with specific geological formations.
Geological Context and Common Finds
Determining the age of a fossil shark tooth is most accurately achieved by understanding the geological layers or formations from which it originated. Paleontologists use geological maps to identify the age of the sediments where teeth are found. If a tooth is discovered alongside other dated fossils, such as ancient shells or bones of known age, these associated finds can help narrow down its timeframe.
Different shark species existed during distinct geological epochs, allowing for age estimation based on tooth identification. For instance, Otodus megalodon lived approximately 23 to 3.6 million years ago, spanning the Miocene and Pliocene epochs. Its teeth are large, triangular, and serrated.
Other examples include Otodus obliquus, an earlier relative that inhabited the Paleocene to Miocene epochs (66 to 5 million years ago). This species is identified by its triangular crown and distinctive cusps on the roots. The extinct Isurus hastalis, often called the broad-toothed mako, existed from the Oligocene through the Pliocene (30 to 1 million years ago), with typically slender and pointed teeth. Identifying the species of a fossil shark tooth provides a reliable age range based on known geological periods.