As the Madre de Dios River flows through Peru toward the Amazon, it eats away at the landscape, slowly turning rock into mud.

The ratios of strontium isotopes in fossil shark teeth can be used to better understand ... scientists could estimate the age of the sites based only on mammal fossils. The sites were thought ...

MacFadden, University of Florida (THE CONVERSATION) The ratios of strontium isotopes in fossil shark teeth can be used to ... age of the sites based only on mammal fossils. The sites were thought ...

More information: Stephanie R. Killingsworth et al, Marine strontium isotopes preserved in fossil shark teeth calibrate Neogene land mammal evolution, Palaeogeography, Palaeoclimatology ...

Remarkably, fossil shark teeth are also incredibly abundant. Sharks ruled the earth’s oceans for 400 million years, and every individual grows and sheds thousands of teeth in their lifetime.