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Ecology of the Triassic

Introduction

Rise of the Ruling Reptiles

The Rise of the Dinosaurs

Meanwhile in The Seas

Plants of the Triassic

Further Reading

Introduction

During the Triassic period the Super continent Pangea expanded to it's maximum extent. A single tongue of ocean protruded into the continent forming the Tethys seaway situated to the East of the continent (see a map of the Triassic (outside this site)).  The increased distance from the sea dried out the interior of the continent, producing increasingly arid conditions. With the merging of  the worlds continents and the drying of inland seas animals were free to colonize the whole super continent.  It was this climate that the survivors of the end Permian extinction faced.

The huge extinctions of the End Permian event, had cleared many of the evolutionary niches for new colonizers to evolve into leading to an evolutionary race. This race led not only to the rise of the dinosaurs but also to many other important groups including, the crocodilians ( the crocodile group), the pterosuars (a group of ancient flying reptiles), the turtles, and the mammals.

The mammal like reptiles that dominated the Permian, were virtually wiped out by the Permian mass extinction. Lystrosaurus  led a recovery in the early Triassic, after 5 million years a dicynodont called Kannemeyria had evolved a 3 meter long frame, matching the size of the Late Permian species.

Cynodonts too survived the Permian, and in the Early Triassic radiated into herbivorous and carnivorous animals which achieved worldwide success.  Through the Triassic they became evermore mammal like until towards the end of the Triassic, it is hard to tell the difference between mammals and 'reptile'.  There is evidence that during the Triassic the cynodonts evolved endothermy, from nerves and blood vessels serving whiskers on the animal snouts. The argument goes that, whiskers meant the animals had hair, and the presence of fur means they wished to keep heat in. Suggesting they were warm blooded, like mammals (including ourselves) today, rather than the reptilian method of absorbing body heat from the sun.

However despite all these advances the Triassic was not the time of the Mammals, they would have to wait another  150 million years.  The Triassic saw the rise of a group which would lead to some of the largest and most terrible animals ever to walk the earth, the Dinosaurs. 

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The rise of the Ruling Reptiles

Throughout the  Triassic the mammal like reptiles (synapsids) dominated as small to medium herbivores and carnivores, but towards the end of the Triassic they virtually disappeared. Within an apparently short space of time, dinosaurs had risen from being small, ecologically unimportant organisms to occupying nearly all terrestrial niches by the end of the Triassic. (Benton 1983) They would then increase in size and rule the earth for the next 120 million years (nearly twice as long as the mammal group have been in charge so far).

The combined area of Southern Africa, and South America provides the best fossil record from the Late Permian to the Early Jurassic.  In this sequence 5 main phases of faunal replacement can be identified, each ending in major extinctions.  These phases are summerised in the diagrams below.

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Fig 1. Shows the change in species through time, found at sites around Southern Africa, South America, and related areas.

Illustrates the change from dominantly mammal like reptiles to dinosaurs through the Triassic Period.

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Fig 2. 

Similar to figure 1. Shows the relative abundance of the major groups of organisms from the Late Permian to Early Triassic.

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Fig3. 

Illustrates the evolution of the major groups of Triassic Organisms and the effects of major extinction events on this evolution.

The Triassic period opened with the Lystrosaurid Empire (see fig 1).  The dominant herbivore of the period was the medium to large herbivore Lystrosaurus. The carnivores were small to medium with the first well known thecodontian,  Proterosuchus, a 1.5 meter long carnivore.  Proterosuchus had a sprawling gait meaning it had it's legs out to the side of it's body (rather like that of a lizard today), combined with it's size the gait probably meant that Proterosuchus could not have managed more than a slow waddle in pursuit of it's prey, maybe this was all that was needed in the early Triassic.

Through the Triassic period the mammal like reptiles, continued to diversify, though by the Mid to Late Triassic the Rhynchosaurs group had  risen to equal dominance, the Thecodonts had also risen in importance (see figure 2). By the end of the Triassic the dinosaurs had become the dominant group.

There are a number of models of how the dinosaurs (diapsids) came to take over from the mammal like reptiles, many authors have generally assumed that the mammal like reptiles declined while the dinosaurs grew in  importance, the general reason behind this was that dinosaurs and thecodontids had an improved locomotory capability, or an advanced either warm blooded endothermy, or cold blooded inertial homeothermy. There is however another theory that early dinosaurs and Synapsids lived side by side, before the final take over by the dinosaur group. This theory states that the dinosaurs were opportunists who radiated into the vacant niches after an extinction event removed the mammal like reptiles.  Though it could be argued that there must have been something which helped the dinosaurs survive the extinction of the mammal likes.

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The Rise of the Dinosaurs

The Skeleton of Herrerasaurus. 

An active 2 legged flesh eater from the Upper Triassic

The dinosaurs are thought to have arisen from 3 or more thecodontian lineages (Charig 1979). It seems that the dinosaurs first became important in the North in places where rhynchosaurs and Dicroidium were absent (Germany, North America).  With the extinction of both the rhynchosaurs and Dicroidium and the expansion of the conifer woodlands so the now larger species of dinosaur where allowed to spread south, and radiate (Benton 1983).  From this evidence it seems fair to say that in their early history dinosaurs were occupying the environments which were unsuitable for the rhynchosaurs and the synapsids. It seems that the extinction of these groups and the rise of the conifers where contributing factors in the rise of the dinosaurs.

Pictured is the Skeleton of a Ceolophysis found in Ghost Ranch formation.

Ceolophysis is the best known of the early dinosaurs, and may well have been among the first.  It is thought to have been a fast bipedal active predator.

 

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Meanwhile in the Seas

As the archosaurs where conquering the land so reptiles were appearing in the seas. Several lines of fish eating reptiles with euryapsid skulls emerged. These were the nothosaurs, placodonts, and ichthyosaurs. Each of these groups has different marine adaptations and they may well have radiated from different sources.

The warm Triassic seas were populated by coiled ammonites, brachiopods, bivalves, gastropods, and sea urchins, all of which were re-radiating after the Permian crash. One of the most important events in the sea at the time was the appearance of modern reef building corals (Hexacorals or sceractinian corals) there is also some evidence for the appearance of symbiotic algae (algae that lived within the corals for mutual benefit) a hallmark of modern corals,  as they were found in deeper waters away from the influence of light. There is however conclusive evidence that symbiotic relationships had formed by the Late Triassic to Early Jurassic.

The appearance of reptiles in the seas, is not likely to be to do with anything as profound as the end Permian extinction, or a change in food source in the seas. It is more likely that it is the result of a quirk of the fossil record, and that the groups evolved in the Late Permian, but the incompleteness of the fossil record has meant that Permian specimens have not yet been found (Benton 1993)

One of the strangest animals of the Triassic seas was the Tanystropheus an early ruling reptile known from fossil localities in Germany, Switzerland and Israel. Tanystropheus grew up to 7m with a neck about 3m long, yet it contained only 10 vertebrae, each of which was highly elongate. Suggesting that the neck was not very flexible. While Tanystropheus shows no obvious adaptations for marine life, it is hard to imagine how  enough muscle could have developed to support the neck. Perhaps the animal lived on the shores and used it's long neck to catch fish rather like you or I would use a fishing rod.

The nothosaurs were flexible streamlined long necked animals with four paddle like limbs. Found from the Early to Mid Triassic.  They were thought to have lived rather like seals do today, feeding at sea and resting on land. However evidence suggests that the limbs were unlikely to have been able to support the animals on land, so they would have to drag themselves on land like seals. The front legs were generally sturdier than their rear legs, each of which had a five toed webbed foot, suggesting these were used for propulsion. Some species seem to have propelled themselves by sweeps of their long bodies.

Placodonts bodies show little adaptation for the seas, other than their heads which seem highly adapted for a diet of the rapidly radiating molluscs. The name of the group Placodontidea means 'flat-plate tooth' which it used to great effect to remove shelled organisms from their protection.  These teeth were powered by huge jaw muscles. The rest of the body of Placodonts was stocky and anything but streamlined, suggesting it was equally well adapted for life on land. It's only obvious adaptation was webs of skin between each of it's 5 toes, and a flattened tail for propulsion. These few adaptations to marine life seemed enough though as the group lasted for 35  million years, with later species developing body armour. The placodonts like the nothosaurs died out at the end of the Triassic leaving no descendants.

The great success story of the Triassic seas came in the shape of Ichthyosaurs. Ichthyosaur means fish lizard and they were exactly that. Ichthyosaurs unlike placodonts were highly adapted for the seas and would not have been able to come ashore. As a result ichthyosaurs could not move on to land to lay eggs as the other marine reptiles did, and had to evolve another means. They gave birth to live young.  We can prove this as there are fossils of Ichthyosaur mothers who died giving birth with the young still in the birthing canal. The icthhyosaurs were highly streamlined animals similar in design to sharks and dolphins today suggesting they were agile and fast predators.  The oldest examples of Icthyosaurs are found in Spitsbergen, Japan, and Canada from the early Triassic.  By the End of the Triassic some species had become huge, Schonisaurus  known from Nevada grew up to 15m long. Evidence suggests that Schonisaurus swam in schools as one deposit contains dozens of different specimens in the same alignment, in a similar way as we find beached schools of whales today. The Ichthosaur continued on through the Jurassic where it reached it's peak before declining to final extinction in the Mid Cretaceous. 

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Triassic Plants

The widespread Glossopteris flora disappeared towards the end of the Permian to be replaced by a transitional flora at the beginning of the Triassic (Anderson and Anderson 1970). During this time the horsetails and lycopods became less abundant and the seed ferns rose in their place.  The seed fern Dicroidium dominated lowland areas in the southern continents, from early to late Triassic times.  The Northern Hemisphere was dominated by conifers and ferns (non of which were seed ferns), which by the end of the Triassic period had taken over from the Seed ferns in the Southern Hemisphere.

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Further Reading

If you still want to know more about the Triassic period then try some of these or look at the useful websites page

or look at some of the references

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Go to Evidence of Extinction

Go to theories about the Triassic Mass Extinction

Return to Homepage What is an Extinction? Ways to cause an extinction

Click here for some Triassic animal pics