White Ribbed Ammonite

Description

Another cretaceous ammonite fossil. This is a whole ammonite that has exceptionally preserved ribbing on the surface. This intricate pattern marks the division between each gas filled chamber inside.  These chambers are thought to be for buoyancy and new chambers were added throughout its life, suggesting that they got bigger with age.

The climate during this period was warmer than what it is now, with the average global temperature at around 18°C. There was no ice at the poles and sea levels were around 200m higher than they are today. Drivers of past climate change include tectonic plate movement and Milankovic cycles, which took between 10’s of thousands and millions of years to happen. The major climate catastrophe of the cretaceous period was the asteroid impact, which led to the extinction of 70% of known ammonite species. Ammonites fed on plankton, which without the ability to photosynthesise after the meteorite impact, led to a collapse in the ocean food chain. Ammonites are useful as index fossils to help date other fossils.

This specimen is from Madagascar.