Scientists are using archaeological techniques to examine how sea otters use large rocks on the shoreline as "anvils" to break open shells – offering a distinction between human and animal coastal settlement evidence.
Sea otters are the only marine mammal which is known to use stone tools, breaking open shells using both small rocks while floating on their backs and large stationary rocks on the shoreline.
When they use shoreline rocks, they leave behind mounds of abandoned shells – creating valuable archaeological evidence of where their habitat has stretched to.
Now, an interdisciplinary study published in the journal Scientific Reports has combined a decade of sea otter observation with archaeological methods to identify otters’ use of so-called anvil stones.
It found that in taking a random sample from the piles of shells around anvil stones, there was a particular style of damage which could be attributed to sea otters.
The shell breakage patterns provide a novel way to distinguish mussels broken by sea otters pounding on emergent anvils from those broken by humans or other animals, explained Dr Natalie Uomini of the Max Planck Institute.
For archaeologists who excavate past human behaviour, it is crucial to be able to distinguish the evidence of sea otter food consumption from that of humans.
Jessica Fujii of the Monterey Bay Aquarium, said: Our study suggests that stationary anvil use can be detected in locations previously inhabited by sea otters.
This information could help to document past sea otter presence and diet in locations where they are currently extirpated.
More broadly, the recovery of past animal behavioural traces helps us to understand the evolution of behaviours like stone anvil use, which is rare in the animal kingdom and is extremely rare in marine animals.
We hope that this study establishes a new path for the growing field of animal archaeology.