Prehistoric Sharks
Ancient sharks have patrolled Earth's oceans for over 450 million years — far outlasting the dinosaurs.
Overview
Sharks and their cartilaginous relatives have prowled the oceans for over 400 million years, surviving all five major mass extinctions. Their skeletons rarely fossilise, but their continuously replaced teeth are among the most abundant vertebrate fossils known — a record spanning bizarre forms like the buzz-saw-toothed Helicoprion to the giant Otodus megalodon.
Quick Facts
Key Characteristics
- •Skeleton of calcified cartilage rather than bone
- •Rows of replaceable teeth set in a revolvable dentition
- •Placoid (tooth-like) dermal denticles giving rough skin
- •Dorsal fin spines in many early forms
- •Megalodon reached roughly 15–20 m — the largest predatory fish known
Fossil Record
Teeth (fluorapatite) are extraordinarily abundant in marine sands, shales and phosphates. Whole-body preservation requires special conditions — the Cleveland Shale (Devonian, Ohio), Bear Gulch Limestone (Montana) and Solnhofen Limestone preserve complete sharks with cartilage, denticles and impressions.
Global Distribution
Global — rich tooth beds occur in the USA (Carolinas, Florida, California), Morocco, Belgium, England, Malta, Australia and Japan.
Evolutionary & Scientific Importance
Shark teeth are classic index fossils for many marine units and record 400 million years of predation evolution. Their long record shows repeated survival of mass extinctions, and Megalodon's story is a key case study in extinction and palaeoecology.
Classification
Sharks are not one lineage but many orders spanning 450 million years — higher relationships are frequently revised as new fossil material is found.