crocodiles

Why Have Crocodiles Changed So Little Over Time? | Earth Wise

February 9, 2021 By EarthWise Leave a Comment

Crocodiles today look very similar to ones from the Jurassic period some 200 million years ago. In fact, there are very few species of crocodilians alive today – approximately two dozen to be exact. Many other species have achieved a diversity of many thousands of species in the same amount of time.

During prehistoric times, many more types of crocodiles roamed the earth, including some as big as dinosaurs and other serpentine forms that lived in the sea.

According to findings by scientists at the University of Bristol in the U.K., a stop-start pattern of evolution could explain why crocodiles have changed so little over time. In the study, which was recently published in the journal Nature Communications Biology, researchers describe how crocodiles follow a pattern of evolution known as “punctuated equilibrium.” In other words, crocodiles’ rate of evolution is generally slow, but occasionally picks up because the environment has changed.

According to the research team, this slow rate of evolution is how crocodile diversity became so limited. It appears crocodiles arrived at a body that was efficient and versatile. They didn’t need to continue to change in order to survive.

This efficiency and versatility could be an explanation for why crocodiles survived the meteor impact that wiped out the dinosaurs. Since crocodiles can’t control their body temperature and rely on the environment for warmth, they generally fare better in warm conditions. During the age of dinosaurs, the climate was warmer than it is today, which could explain why crocodile diversity was higher.

The scientists next step is to try to figure out why some prehistoric crocodiles died out while others did not.

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Why crocodiles have changed so little since the age of the dinosaurs

Photo, posted December 26, 2012, courtesy of Nicholas Smith via Flickr.

Earth Wise is a production of WAMC Northeast Public Radio.

The Decline Of Earth’s Largest Freshwater Creatures

September 23, 2019 By EarthWise Leave a Comment

While nearly 70% of the globe is covered by water, only 2.5% of it is freshwater. The rest is saline and ocean-based. And only 1% of our freshwater is easily accessible, with much of it locked away in snowfields and glaciers.

Despite freshwater only making up a small fraction of all water on the planet, it’s home to one third of all vertebrate species. Some have survived hundreds of millions of years, but many of the world’s largest freshwater creatures – including fish, reptiles, amphibians, and mammals – may soon find themselves on the brink of extinction.

According to a study recently published in the journal Global Change Biology, scientists from the Leibniz-Institute of Freshwater Ecology and Inland Fisheries and international colleagues have quantified the global decline of freshwater megafauna for the first time. In four decades since 1970, the global populations of these freshwater giants have declined 88% – twice as much as the loss of vertebrate populations on land or in the oceans.

Freshwater megafauna include all freshwater animals that weigh 30 kilograms (about 66 pounds) or more, such as certain dolphins, beavers, crocodiles, turtles and sturgeons.

Overexploitation is one of the main threats to freshwater megafauna. (These animals are often targeted for their meat, eggs, and skin). The other main threat is the loss of free-flowing rivers. Many of the world’s large rivers are already highly fragmented, which impacts access to spawning and feeding grounds. The research team says another 3700 large dams are planned or under construction, including 800 in habitats rich with freshwater megafauna, including the Amazon, Congo, and Ganges river basins.

Current conservation measures are clearly failing our freshwater creatures.

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