Triassic 250 to 200 Million Years Ago

At the very beginning of the Triassic period, something terrible happened. We don’t know exactly what it was – maybe a terrible asteroid impact, a series of volcanoes, or something else. But we do know that whatever happened killed two thirds of all land species and 95 percent of all ocean-dwelling species, creating the largest extinction  in Earth’s history! This means that nearly every role and habitat on the planet was left empty, just waiting for a new species to fill it.

And they did. During the rest of the Triassic period, many new groups of plants and animals evolved: big ones, small ones, predators, herbivores, and species of all shapes and sizes. But the most famous were the dinosaurs. The Triassic period was “the rise of the reptiles,” as dinosaurs and other reptiles began to rule the planet.

Adaptations

As dinosaurs began to appear on land, another creature was taking over the seas: the ichthyosaur, or “fish lizard,” a giant marine reptile that could reach more than 60 feet long!

ichthyosaur

The ichthyosaur is Nevada’s state fossil. Source: Wikipedia

The very first ichthyosaurs were shaped like eels and probably swam by slithering through the water. But as these big creatures continued to evolve , they became more compact and built for speed – later ichthyosaurs were shaped more like today’s predators of the sea, such as tuna and mackerel. But because ichthyosaurs had evolved from land animals and were reptiles – not fish – they all had lungs and breathed oxygen from the air.

Many ichthyosaurs lived in the shallow sea that once covered Nevada, so the state is rich with evidence of these ancient reptiles. In fact, the ichthyosaur is Nevada’s state fossil!

Interactions

Later on in Earth’s history, huge herbivorous dinosaurs roamed the planet. But during much of the Triassic period, the plant-eaters were relatively small, even though meat-eating dinosaurs grew large. Why might this be?

Animals can only evolve very large body sizes if they have plenty to eat. That wasn’t a problem for carnivores during the Triassic period, since there were more than enough animals to snack on. But herbivores faced a tougher challenge: during this time, the planet was hot and dry, and there weren’t as many plants to eat.

It wasn’t until millions of years later than the Earth was lush and green, and the truly gigantic plant-eating dinosaurs could evolve.

Living Fossils

http://commons.wikimedia.org/wiki/File:Tuatara.jpg

Tuataras’ relatives evolved more than 200 million years ago. Source: Wikipedia

The tuatara may look like a lizard, but it’s not – it’s a reptile whose history goes back hundreds of millions of years. In fact, tuataras haven’t changed much since they evolved way back during the Triassic period, long before T. rex , triceratops, and stegasaurus existed! Their skeletons and skulls look nearly identical to fossils dating back more than 225 million years. Their teeth are built right into their jaws – like those of ancient dinosaurs – and they even have a third eye in the middle of their forehead, which looks just like the eyes of the very first seeing organisms .

These rare reptiles, which live only in New Zealand, give scientists an idea what life looked like before the first dinosaurs roamed the planet.

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