The evolution of crocodiles. Xinran Jin. 

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The Origin of Crocodiles. According to National Geographic, "Crocodiles today are often considered survivors of the age of dinosaurs." For now, that's true: modern crocodiles have been around for about 80 million years. But they are just a small fraction of the crocodile relatives who once roamed the earth and, in fact, once ruled the planet. The Crurotarsan (a term paleontologists use to include all crocodile relatives) emerged about 240 million years ago, usually at the same time as the dinosaurs (Source: MEL White, National Geographic magazine, November 2009).. 

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According to National Geographic, "Crocodiles today are often considered survivors of the age of dinosaurs." For now, that's true: modern crocodiles have been around for about 80 million years. But they are just a small fraction of the crocodile relatives who once roamed the earth and, in fact, once ruled the planet. The Crurotarsan (a term paleontologists use to include all crocodile relatives) emerged about 240 million years ago, usually at the same time as the dinosaurs (Source: MEL White, National Geographic magazine, November 2009).

The beginning Mesozoic period of the Triassic. 图标 描述已自动生成. 

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The beginning Mesozoic period of the Triassic

At the beginning of the Mesozoic Era, known as the Triassic Period, there were no crocodiles, just dinosaurs. This period began about 237 million years ago and lasted about 37 million years. Archosaurs, the crocodile's oldest relative, were among the many plant-eating  dinos  that thrived during this period. Archosaurs looked very much like crocodiles, except that their nostrils were positioned on the tops of their heads rather than the tips of their snouts. These reptiles subsisted on marine organisms in freshwater lakes and rivers worldwide.

Here is where your presentation begins. The Jurassic Period. 

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During the middle Mesozoic era, known as the Jurassic period, some dinosaurs evolved into new species, including birds and crocodiles. This period began about 200 million years ago. The earliest crocodiles were small, terrestrial, two-legged sprinters, and many were vegetarians.

The Cretaceous Period. The final part of the Mesozoic Era, the Cretaceous Period, began about 145 million years ago and lasted until about 65 million years ago. It was during this final epic that the modern crocodile, Crocodylidae, first appeared as a distinct species and flourished.. 

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The final part of the Mesozoic Era, the Cretaceous Period, began about 145 million years ago and lasted until about 65 million years ago. It was during this final epic that the modern   crocodile, Crocodylidae, first appeared as a distinct species and flourished.

References. 图标 描述已自动生成. 1. https:// factsanddetails.com / asian /cat68/sub434/item2435.html 2. https:// www.thoughtco.com /prehistoric-crocodile-profile-4047616. 

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1. https:// factsanddetails.com / asian /cat68/sub434/item2435.html 2.   https:// www.thoughtco.com /prehistoric-crocodile-profile-4047616