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Middle Years Science Program
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"Dinosaurs
Show" Return to Science Shows  Program: St John's (2005). Presentation: Equipment:
Notes: Topics:
Demonstrations:
Dinosaurs Late Triassic Period Featured here are some of the dinosaurs that lived 220 million years ago.
When dinosaurs first appeared about 230 million years ago the world was very different to as we know it. There were very few representatives of any animal groups alive today - no mammals, birds or lizards (although there were some lizard-like reptiles). No grass The difference was also apparent in the plant kingdom. There were no flowering plants, which includes most of the common trees and shrubs today. The trees would not look very familiar to us today, although some were relatives of modern day ferns and podocarps. Plant life would have seemed very drab, just green and brown in colour. There was no grass, instead, low ground cover would have been ferns and mosses.
The Triassic world was unusual for another reason. About 20 million years before the appearance of the first dinosaurs, the biggest extinction the world had ever known had occurred. Over 90% of all plant and animal species then alive on land and in the sea had died out at this time. Even in the Late Triassic the world was still recovering and there was not the usual variety of life normally found on earth. Desert The continents were configured differently to today. All the land masses of the earth were joined together into one huge continent called Pangaea. This stretched from pole to pole and its central region was a vast inhospitable desert.
We can tell this, as the type of rocks that were deposited at this time have sedimentary features characteristic of a dry harsh climate. As all the continents were connected, the animals and plants found in the fossil record from that time are very similar all over the world. It took more than 10 million years before ecosystems recovered and complex systems and larger animals took even longer. Most of the dominant land animals that were around when dinosaurs evolved were products of long and established lines of descent. New life The Late Triassic was an innovative time in the animal kingdom. By the end of the period not only the dinosaurs had appeared but also pterosaurs (flying reptiles), various kinds of marine reptiles, the first crocodiles, turtles and the earliest true mammals. Towards the end of the Triassic, 220 million years ago, there was another extinction, which wiped out many of the non-dinosaurs including the dicynodonts such as Placerias and primitive archosaurs such as Postosuchus. It was after this that dinosaurs really started to radiate and diversify. Dinosaurs
gain the edge It
is likely that dinosaurs did not out-compete other animals as has often been assumed,
due to their superior speed and agility, but that they were fortunate in that
they were not hit as hard by the extinctions. Another extinction at the very end
of the Triassic, wiped out the remaining primitive archosaurs and the dinosaurs
were the only large land animals left. Late Jurassic Period Featured here are some of the dinosaurs that lived 152 million years ago.
The earliest dinosaurs were pretty small. Eoraptor was about 1 m long, its contemporary Herrerasaurus grew no more than 4 m long and Coelophysis was about 3 m long. And in all cases the length was mostly tail. However the plant-eating prosauropod, Plateosaurus, that appeared at the end of the Triassic period, was a harbinger of things to come. At up to 9 m long it was the first really big dinosaur. Prosauropods could walk either on all fours or just on their hind legs, leaving their hands free, perhaps to grasp branches and bring them within reach of their mouths. They disappeared at the end of the Early Jurassic period and their role was taken by the sauropods which thrived during from the Middle Jurassic to the Early Cretaceous period. Sauropods had huge elephantine bodies coupled with very long necks and tails. They walked only on all fours. Some such as Diplodocus could probably have reared up on their hind legs using their tails as props. Diplodocus skeletons show a number of features that support this: it has high vertebral spines over its hip region showing it had strong muscles and ligaments there and it has skid-like bones underneath its tail which would have protected the delicate nerves and blood vessels there when its tail was resting on the ground. The Morrison Formation The dinosaurs featured in this episode were all found in the Morrison Formation, except Anurognathus. The Morrison Formation was deposited approximately 155-145 million years ago and covers a large area of the western US, from Montana to Arizona and Utah to Colorado. In different areas and through time Morrison environments were diverse ranging from arid deserts in the southwest through rivers and flood plains to swamps in the north. Fossil plants indicate a rather wetter environment than the rock record and this may mean that the climate was seasonal. Growth In
the Early Jurassic the maximum size of both herbiviores and carnivores increased,
and this trend continued throughout the Jurassic culminating in the staggeringly
large sauropods such as Apatosaurus and Brachiosaurus. Carnivores had also increased
in size, although not by as much and the 12m long Allosaurus was dwarfed by its
sauropod prey. They would have had to pick on the young or weak or maybe they
hunted in packs. Evidence based on growth rings and bone texture indicates that sauropods reached their adult size in 10-20 years. Also if, as has been suggested, sauropods took 70 years to reach maturity, it would be unlikley that many would survive to reproduce. The data indicating that they grew quickly also fits that from the bones of theropods and ornithopods, who were thought to reach maturity quickly. Plates Stegosaurus was an early armoured dinosaur and its defences were formidable. Later armoured dinosaurs were veritable living tanks, some even had armoured eyelids! There
are two main types of dinosaurs, named from the configuration of their pelvic
bones: bird-hipped and lizard-hipped. Sauropods and theropods are lizard-hipped
dinosaurs; Stegosaurus is a bird-hipped dinosaur, an early member of a group which
became much more common and diverse in the Cretaceous period. | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
