The Evolution of Jurassic Earth
The Pangaea super-continent began to split into two during the mid-Triassic and this trend continued during the Jurassic Period. As the continents moved away from each other, the oceans began to exert more influence on Earth’s weather and the climate became far more varied.
Vegetation was becoming more sophisticated too. Palm-like plants and conifers flourished. Some experts also believe that the first flowering plants developed at the end of the Jurassic.
The late Jurassic Period is renowned for the emergence of sauropod dinosaurs. They were the classic long-necked and long-tailed dinosaurs, and the largest grew to more than 40 metres in length and probably weighed up to 100 tonnes. Much of their apparent bulk was due to internal, air-filled sacs that passed through their huge bones, allowing them to grow even bigger.
In order to process the vast amount of plant matter consumed, it is thought that sauropods may have had large stones in their stomachs, called gastroliths, to help them digest tough vegetation. Much of the evidence on the diet of dinosaurs comes from the study of their fossilised dung, called coprolites, or taking data from fossilised trackways.
Palaeontologists used to believe that sauropods were amphibious as it wasn’t thought possible that sauropods could support their vast weight without the buoyancy aid of water. Today, we are confident that sauropods had pillar-like legs that were akin to a modern elephant’s, able to support their own body weight. After studying fossil tracks and skeletal remains, it was also concluded that giant sauropods walked with their tails held aloft, not dragging along the ground as previously thought.
Thinly-necked and tailed, Diplodocus or “double beam” is probably the best-known sauropod. They were so big (over 25 metres long) that to get at their food, the Diplodocus may have uprooted saplings and pushed over trees, creating open plains. Even its eggs were a hefty 25 centimetres across.
The “arm lizard” was another well-known Jurassic giant, even featuring in the iconic first-glimpse scene in Jurassic Park. Tall rather than long, Brachiosaurus could grow up to 30 metres tall. It had a long neck that allowed it to graze among treetops and long, pillar-like legs that kept its body high off the ground. Its front shoulders were much higher than its haunches, giving it a sloped appearance rather like a giraffe.
The “roof lizard” was a medium-sized herbivore of the late Jurassic. Around 7 metres long and up to 3 tonnes in weight, Stegosaurus had a series of large, bony plates running along its spine. The plates could have been used in display or may have served as heat-regulating devices, both scenarios explaining the mat of blood vessels running through them.
The Stegosaurus had a fearsome defensive weapon in the form of a powerful, spiked tail (the spikes are known as "thagomizers", named after a Gary Larson cartoon!) that could deliver crippling blows to would-be predators.
The “other lizard” was the most common large predator of the period. Around 12 metres long, it is known to have preyed on big sauropods as well as smaller animals. There is some evidence that Allosaurus cared for its young, bringing back meat for its offspring, who lived in a protected den until they were old enough to fend for themselves.
Allosaurus didn’t have a bone-crushing bite. In fact, its curved teeth and large upper jaw would inflict deep slashing wounds on its victims when hammered down, allowing it to take one fell swoop and then stand off and wait for its victim to succumb.