About 70 million years ago, a year had roughly 372 days, which means each day ran about half an hour shorter than yours. The figure was read from the growth layers of a single fossil clam from the mountains of Oman

A year 70 million years ago held more days than a year does now, yet it lasted essentially as long. Not from astronomy or from tracking planetary orbits, but from a single fossil clam pulled out of the mountains of Oman. The clam that kept a Cretaceous calendarThe clam is Torreites sanchezi, a reef-building rudist bivalve with no close living relative. One shell, one number, and why it holdsThe figure comes from a single individual, but not from a single layer count. The technique may be the more significant result beyond the single number it produced.