A new study has revealed the reasons as to why the number of crocodylian species has continued to decline over the years. The reason is none other than the fluctuating sea levels and global cooling. The existing crocodylians that are estimated to have appeared approximately 85 million years ago include the current day species of crocodiles, caimans, alligators, gavials as well as their extinct ancestors.

However, there is a 250 million year fossil record that narrates the diverse evolution history of the extinct relatives. The relatives came in all shapes and sizes.

One of the notable sizes was that of a 12-meter giant land-based creature, Sarcosuchus, whose weight was up to eight metric tonnes.

Another species, thalattosuchian, was armed with flippers and shark-like tails which enhanced their agility in the sea.

Crocodylians depend on external heat sources from the environment the likes of the sun. Hence, declining temperatures at higher latitudes areas have such a negative influence on crocodylians and their relatives.

It is in the vast lush wetlands where crocodylians are known to do well. However, over ten million years ago the wetlands in Africa have been replaced by the formation of the Sahara desert.

On the other hand, as a result of the rise of the Andes Mountains, proto-Amazonian mega wetland habitat in South America which also hosted the crocodylians, got lost.

According to the team of researchers, the primary control over the diversity of marine species of crocodilians was the fluctuations in sea levels. There are times when the sea level could get high which on return created diversity and, in the long run, there were favorable conditions for the crocodylians to thrive.

Nevertheless, the researchers discovered that several groups did go inexistent. However, the existing ones exuded out of their natural habitations taking advantage of the desolate territories.

It was within the team’s suggestions that a warming world often triggered by global climate change may of service to crocodylian divergence. However, this may not be so because of the human activity that largely impacts on their environments.

The study was published in the journal Nature Communications.