The Triassic Period was the first period of the Mesozoic Era, and ran from 248 to 200 million years ago. A lot happened to Earth and its life-forms during the Triassic but the most celebrated event was the evolution of dinosaurs. These remarkable creatures emerged around 230 MYA and dominated the planet throughout the Mesozoic Era.
One world, one continent
Planet Earth looked very different at the beginning of the Triassic Period. There was just one landmass, a huge continent known as Pangaea. It stretched from pole to pole and included a vast desert at its centre. There was no grass, although ferns and mosses provided ground-cover in less arid areas. Pangaea began to break up in the mid-Triassic.
Just before the beginning of the Triassic, Earth experienced its largest mass extinction - more than 90% of the planet's life-forms at sea and on land were extinguished.
Geologists are divided over the cause of this momentous crisis, but possible explanations include glaciation, climatic fluctuation and large-scale volcanic activity. Whatever the reason, it seems likely that the drastic reduction in the diversity of animal life consequently contributed to the rise of the dinosaurs.
During the first half of the Triassic, however, dinosaurs were still a long way from ruling the Earth. They had a variety of competitors, including close relatives from the same animal group that dinosaurs themselves belonged to, the archosaurs ("ruling reptiles"). Crocodile-like terrestrial predators were among the most successful of these archosaur rivals but they had died out by the end of the Triassic.
One of the oddest creatures that shared the planet with early dinosaurs was placerias. It must have looked like a cross between a hog, a cow and a turtle. Placerias was a large, herding herbivore with a horny beak and a pair of downward-pointing tusks. It was a dicynodont ("two dog-teeth") - a group of animals that shared common ancestors (the synapsids) with modern mammals. Palaeontologists believe placerias ate low-growing plants, as well as using its tusks and beak to grub for roots and tubers.
The dicynodonts were very successful before they died out. Early Triassic dicynodont remains have been found in South Africa, India, China, Russia, Australia and Antarctica.
Slim and dangerous
One of the first true dinosaurs was coelophysis ("hollow form"), a carnivorous, bipedal predator that emerged in the late Triassic, between 225 and 220 MYA. Hollow-boned coelophysis grew up to 3 metres in length, weighed around 27kg and probably fed on smaller reptiles and amphibians. It had curved claws on its hands and a slim head crammed full of very sharp teeth.
Some experts have suggested that coelophysis could bring down bigger animals by taking slashing bites out of their legs or sides. Fossil coelophysis skeletons have been found in the same locations, so it's possible that these dinosaurs may have herded, although there's no firm evidence that they hunted in packs. It is also believed that coelophysis was a cannibal that preyed upon its own young during lean times.
First of the giants
Around 210 MYA, a new type of dinosaur emerged - the giant herbivore, plateosaurus ("flat lizard"). Weighing around 3 tonnes and growing up to 7 metres, plateosarus was a forerunner of the huge Jurassic dinosaurs. It had a long, powerful tail and a set of coarsely serrated teeth for chewing tough vegetation. plateosaurus also had a large, curved claw on its thumb. We're not sure whether this was used for food collection or defence.
Large numbers of plateosaurus skeletons have been found in the same location, suggesting they may have herded. Alternatively, instinct drew them to the same place to die.
Waiting in the wings
Dinosaurs were the big success story of the Triassic but another group of animals was beginning to emerge, too. These were the cynodonts, small, mammal-like creatures that lived in burrows. They probably laid eggs may have been warm-blooded.
An extinction event just before the Triassic began had given dinosaurs a leg-up on to the evolutionary ladder. As the period came to a close, another extinction event occurred. Geologists don't know what caused it but, once again, large numbers of sea and land animals were wiped out - although the effects are not believed to have been as severe as the extinction event just before the Triassic Period opened. In any event, dinosaurs came through the crisis stronger than ever, setting the stage for an explosion in numbers and diversity.