Occasionally individual shark teeth are found washed up on the Victorian shore, both on exposed outer coastlines and sheltered beaches of the bays. However, rarely are they from living sharks. Most of these teeth have emerged from eroding coastal cliffs where they have been locked away as fossils for many millions of years. Rich fossil deposits are found in a number of coastal locations, like the cliffs at Black Rock within Port Phillip Bay. Historically, these regions represented shallow seas that broadly covered the margin of southern Australia.
Fossil tooth of the Great White Shark, Carcharodon megaolodon
Photographer: Rodney Start. Source: Museum Victoria
Although a wide variety of shark species lived in ancient seas and are represented in fossil deposits, many did not attain a great size and their small teeth can be easily overlooked. The most frequently encountered teeth come from two of the largest sharks of early seas, the massive Fossil Great White Shark, Carcharodon megaolodon, which may have attained 12 metres or more, and the somewhat smaller Fossil Mako Isurus hastalis. Teeth of the Great White have been found measuring more than 18 cm in length.
Fossil tooth of the Mako, Isurus hastalis
Photographer: Rodney Start. Source: Museum Victoria
Teeth of these two sharks differ in shape in the same way as do those of their living relatives. The now extinct Mako most likely fed on fish and squid which they swallowed whole, as reflected in their smooth edged, rather slender teeth, some having a slightly curved profile. In contrast, most teeth of the fossil Great White are broad and triangular, and have a finely serrated edge. Like those of their living relative the White Pointer, this form of tooth is handy for cutting slabs of flesh from substantial prey. The robust structure of fossil Great White teeth was capable of withstanding tremendous forces and support the theory that these sharks ambushed
large ancestors of modern day whales, disabling them with the shock of their initial thrust. The present day White Pointer, reaching about half the size of the extinct form, feeds regularly on seals that are more easily subdued.