This is a fossilised barnacle, or, to look at it from another perspective, the travel diary of a long dead whale.
Researchers led by Larry Taylor of the University of California, Berkeley, in the US, have discovered that the ancient barnacles – when alive, anchored on the back of a grey or humpback whale – record the changing oxygen isotope ratios of the oceans through which they travel.
This data is retained after death. In a paper published in the journal Proceedings of the National Academy of Sciences, Taylor and colleagues reveal that the stored isotope data represents a proxy for when and where the host whale travelled.
“We want to understand how malleable migratory behaviour has been through time, how rapidly whales have adapted to previous climate changes, and see if this can give us some clues as to how they might respond to the current changes in Earth’s climate,” says Taylor.