It is recently found that in early history of Earth, the days were slightly shorter than current; 23.5 hours were there in a day and total 372 days were there in a year.

This is at the time when dinosaurs walked the Earth.

The source of this research is ancient shells, from the Late Cretaceous period 70 million years ago.

The fossilized mollusk shell belonged to a group called rudist (it means that they have two shells) clams (also known as Torreites sanchezi), which grew quickly and their lives were recorded in daily growth rings visible in the shells.

The breakdown of days in a year and the length of a day could be ascertained through laser samplings that produced slices of shells to get an accurate count of rings.

Nowadays, an earth year is short, as days have grown longer. This is due to the moon’s gravity, which draws on ocean’s tides and slows Earth’s rate of rotation.

Meanwhile, as the moon tugs on Earth, our natural satellite distances itself about 1.5 inches per year from Earth.

According to the shell, oceans during that period were much warmer than today, reaching 104 degrees Fahrenheit in summer and above 86 degrees Fahrenheit in winter.

Rudist clams are unique looking as tall pint glasses with lids shaped like bear claw pastries.

Like oysters, the clams thrived in reef environments. And in their day, they acted like coral, building and growing together.

Rudists are quite special bivalves. There's nothing like it living today.

In the Late Cretaceous especially, worldwide most of the reef builders are these bivalves. So they really took on the ecosystem building role that the corals have nowadays.

Their shells grew faster during the day in response to sunlight. The researchers believe this means that like modern giant clams, which are covered in algae, these clams were similarly supporting a symbiotic species.

The clams were wiped out 66 million years ago, just like the dinosaurs.