Dougal Dixon "The New Dinosaurs" - The Australasian realm
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THE AUSTRALASIAN REALM

Of all the palaeogeographic realms the Australasian must be the most isolated and self-contained. The vast proportion of its bulk is a single island continent measuring about 3,500 kilometres (2,100 m) by 3,000 kilometres (1,800 m), straddling the southern tropic. Other portions of the realm consist of several large and thousands of smaller islands scattered to the north and east. Some of the eastern islands are even more isolated than the main landmass and could be regarded as small, individual zoogeographic realms of their own. The islands to the north consist of continuous archipelagoes reaching towards the great northern continent and the Oriental realm.
The history of the Australasian realm is quite simple. Up until the late Cretaceous period the continental area was part of the southern supercontinent of Gondwana. During that time rift valleys appeared and split it away from what is now the south polar continent. Ever since then it has been moving northwards, and in the past 50 million years or so it has moved from the southern polar regions into the tropical latitudes. This represents the fastest of all the continental movements since the split-up of the supercontinents, and during this time there was no mixing of animal life from the surrounding regions. The animals present were the remains of the old Gondwana fauna a so-called relict fauna and these have had to change continually over the past 50 million years in order to adapt to the changing latitudes and climates. The animal life found in the Australasian realm is therefore quite unique. Over the past few million years, however, the continent has been approaching the offshore islands of the great northern landmass, and there has been some influx of animals from the north. There has also been a constant pressure from the oceanic plates to the east and the north, and as a result, island chains have formed, producing an offshore fringe of archipelagoes around the main continent. The movement has also given rise to the only major mountain chain on the continent itself, and this runs up the length of the eastern coast, from an island in the south to a tapering peninsula in the north. The remainder of the continent is a vast flat plateau, over half of which is more than 300 metres (1,000 ft) above sea level. The largest of the neighbouring islands consist of mixtures of old continental rocks fragments of Gondwana and new rocky material folded up from the seabed by the plate movements and forced through by new rocks emplaced as volcanoes.
The habitats of the main continent are dominated by the position of the continent across the southern desert belt of the planet. Hot air that rises and drops its rain into the rainforests at the equator spreads north and south at high altitudes and cools. At these latitudes it begins to descend and, being dry, produces arid and desert environments on any land mass that lies below. The centre of the Australasian continent is primarily desert, surrounded by dry grassland. Here live dinosaurs, relics of the old Gondwana dinosaurs, that can subsist on the poor grasses and dry scrubby bushes of the arid regions. Where an oasis of water appears, the invertebrate and fish life that thrives in it is exploited by specialized dinosaurs and pterosaurs that have evolved here and are found nowhere else in the world.
The coastal regions, particularly in the north, are more fortunate. Wet winds from the sea bring a milder and more equable climate to these areas. In the north, the forests that are produced are almost tropical jungles while, elsewhere, eucalyptus forms the characteristic woodland that clothes the eastern mountains and the coastal plains. Tree-living animals range from omnivorous arboreal dinosaurs that feed on fruits, nuts and shoots, to very specialized feeders that subsist on a diet of eucalyptus unpalatable or poisonous to most other creatures.
The islands to the north are clothed in tropical forest, being surrounded by warm ocean. The islands to the east also have a wet climate, supporting forests of various kinds, although wide areas of grassland exist supporting a unique fauna of terrestrial grazing pterosaurs. These have developed in isolation, and they parallel the grazing pterosaurs that have evolved independently in the Ethiopian realm (pages 34-5).
The more widespread oceanic islands are not technically part of the Australasian realm. They appear during volcanic eruptions and, once cooled, they represent completely fresh habitats ripe for colonization. Once vegetation is established on an island, the animal life arrives. The islands are isolated and so they are usually inhabited by descendants of flying creatures that have crossed the oceans by air. The island habitats are fully exploited by creatures like birds or pterosaurs that have given up their powers of flight.

 



 

Scrub and tall grass savanna lakes


CRIBRUM


Cribrusarus rubicundus

The rivers that drain from the eastern mountains into the arid hinterland of the Australasian continent often seep away into the desert, or else form lakes. Lakes that form in the rainy season support an explosive burst of algae and crustaceans, and the cribrum feeds on these. Coelurosaurs have been present on the Australasian continent at least since Kakuru (rainbow lizard) hunted there in early Cretaceous times. It would be from a creature such as this that the cribrum evolved. In build it is rather like a conventional 2-metre-long (6 ft) coelurosaur, but the long curved jaws are armed with thousands of tiny, needle-like teeth. These strain living creatures from the fine mud and water of the deltas and lakes. An unusual feature of the cribrum is that it changes colour depending on where it is feeding. When it is feeding in the fresh water of the streams, the colour is a light grey. When it feeds on crustaceans and algae in the salty waters of the lakes, however, its skin and hair turn pink. The red coloration in the algae is concentrated in the bodies of the crustaceans that feed on it, and thus appears in the pigmentation of the cribrum that feed on them.

Scrub and tall grass savanna rivers


POUCH


Saccosaurus spp.

Wherever fish are abundant there will be fishing animals, including, on occasion, dinosaurs. In fact, fishing dinosaurs, such as Baryonyx, existed in early Cretaceous times. The rivers of the Australasian continent, however, have a unique group of fish-catching dinosaurs called the pouches. These generally belong to the same genus, Saccosaurus, and have evolved from the coelurosaurs. They are quite amphibious, being happier sculling about on the surface of the water and diving to the river bed than waddling about on land. Their buoyant bodies, big heads and webbed feet make the adults look very ungainly and vulnerable as they tend to their nests on river banks. The nests are built of mud and sticks, above the local flood level. The eggs, hatchlings and juveniles resemble those of a totally land-living creature, suggesting that it has not been long since the pouch evolved from a terrestrial ancestor. The swimming habits of the young pouches must be learned at their parents' side while their bodies develop the aquatic adaptations of adulthood.
In the water, the adult pouch swims gracefully on the surface, with its striped tail waving as a flag. It moves steadily with powerful strokes of its webbed hind feet and dives swiftly after fish, steering with a membrane between the forelimb and the body. The catch is held in a bag of skin beneath the lower jaw until the pouch returns to land.

The cribrum stands in the shallow water, often on one leg, and feeds by sieving the water through its finely toothed jaws. It swings its head around in a wide arc to cover as much water as possible.

There are few predators on the shores of the salty lakes, but when one does appear, slinking down to the waters edge to try and trap an unwary cribrum, the herds panic and scatter in all directions. The milling surge of pink distracts and confuses the hunter, while the voluminous curtains of spray thrown up by the dash through the shallow water conceals the direction of the fleeing herd.

Fish caught by the parent pouch are stored in the bag beneath the jaw. There they are kept safe while the dinosaur waddles up to the nest and presents them to the young offspring.

Several species of pouch exist in the rivers of the Australasian continent. Many live together and the species are distinguished by the different patterns of colour on the tail.

The webbed hind feet and steering membrane of the pouch enable it to swim easily through the water. Diving swiftly beneath the surface, the pouch seizes a fish between its sharp teeth, right.

 

Desert and desert scrub


GWANNA


Gryllusaurus flavus

The interior of the Australasian continent is very dry. Almost two-thirds of its area is desert or dry grassland. It is a harsh environment for living things, but not an impossible one. Many animals exist here but the only large one is the gwanna. It is the last survivor of a once widespread plant-eating dinosaur group, the iguanodonts. These dinosaurs were closely related to the hypsilophodonts, the descendants of which are now found all over the world, but the iguanodonts tended to be much larger and had more cheek teeth. On all the other continents of the world the iguanodonts were eventually replaced by the more versatile hadrosaurs, but in the Australasian continent they survived in isolation as the hadrosaurs never reached that landmass. The larger number of cheek teeth meant that the iguanodonts were in a better position than the hypsilophodonts to evolve into grass-eaters when grassy plains developed in the mid-Tertiary period. The grasses of the region are not particularly nutritious and a large animal has to range further to find enough to eat. The gwanna lives in small family groups which can move quickly from one area to another seeking fresh pastures. The physical build of the original iguanodont was quite suitable for this way of life and it has not changed dramatically. At rest, the gwanna is on all fours, with its head near the ground. When moving, it is a bipedal animal. Its longer hind legs can bear its full weight, and its body is balanced by the heavy tail as it walks or runs across the open landscape.

The 3-metre (10 ft )-long gwanna lives in family groups of four or five adults and a number of young. The sparse grasses could not support larger herds. The gwannas sandy colour camouflages them from a distance. They move mostly by walking or running, but when faced with sudden danger, such as finding a poisonous dingum in the grass, they leap out of the way, flashing their flank patterns as a warning to others.

Desert and desert scrub


DINGUM


Velludorsum venenum

Like a big lizard, the dingum creeps through the grasses of the hot, central Australasian plains, hunting small mammals, reptiles and insects in the dry tussocks. Suddenly a dark shadow sweeps across as a hunting pterosaur hurtles down from the sky. In an immediate reaction, the dingum arches its back and dips its head. A fin of skin supported by struts of bone springs up from its curved back and presents a gaudily coloured sail to the attacker, a sudden burst of garish colour against the drab grasses. The crest on the back of the head pops up a frill of spines, each one poisonous enough to kill a large attacker. The pterosaur breaks off its attack, instinctively knowing that these colours mean danger and death, and flies away to seek easier prey.
The dingum is small for a dinosaur, measuring only about a metre (3 ft) long. It is descended from the coelurosaurs, the small meat-eaters of the Mesozoic era and, like many other Australasian animals, lives nowhere else in the world. It is a meat-eater but occasionally eats small poisonous plants. The dingum itself is immune to the poison which is then concentrated in the spines at the back of the head and used in defence. The female is quite a different animal, however, having neither poison spines nor sail. It is much larger than the male and has a more conventional coelurosaur shape. It is more secretive in its habits, avoiding predators by not being conspicuous.

The gwanna has evolved mouth parts that can deal with tough grasses. A solid horny beak at the front of the mouth crops the grass. It is then pulled by the tongue to the cheek-pouches where it is chewed thoroughly by a series of constantly replaced grinding teeth. The brightly coloured head crest is used for signalling during the mating season. The hand left, can be used for walking (two hooves), for grasping (two fingers) and for fighting (thumb spike)

The dingums complex mating and nesting ritual begins during the wet season. The male begins to build its nest from clay and the half-built nest is used as a display arena while it courts a female (1). After mating the couple continue to build (2). By the dry season, the nest is completed, with the female walled up inside incubating the eggs while the male hunts food (3). In the next wet season when the eggs have hatched, the male stands guard at a newly enlarged nest entrance while the female hunts (4).
The bright colours of the male dingums crest and sail warn would-be predators of its poisonous nature.

 

The superficial resemblance in size and shape between the Australasian crackbeak and the arbrosaurs of the northern continents (pages 1215) has come about by convergent evolution. They both evolved from lightly built running ancestors and have become lightly built tree-dwelling animals, but whereas the arbrosaurs subsist on a diet of insects and small vertebrates, the crackbeak is strictly vegetarian.

The crackbeaks bill is delicate enough to pick individual berries out of a bunch, yet powerful enough to crack open even the hardest nuts. The beak is used only for picking and cracking; the actual chewing is done by the back teeth. The horny crest on the head, along with the bright colour of the face and dewlap, are used for signalling both to mates and to enemies.

Tropical rainforest


CRACKBEAK


Fortirostrum fructiphagum

High in the luxuriant branches of the tropical forest trees in the north-east of the Australasian continent, a black and white creature throws itself from one branch to another and disappears among the foliage. At first glance it looks like an arbrosaur, one of the tree-living coelurosaurs that are found all over the world. Then it appears again, and its bright face, surmounted by a high crest, is its most obvious feature. This is a crackbeak a tree-living descendant of the successful hypsilophodonts.
Crackbeak ancestors were lightly built running animals, evolved to run swiftly across open country. Now the legs have developed into jumping legs, and the lightweight feet have evolved for perching. The small first toe has turned round to face the rear, so the foot can now be used for grasping branches. The tail is still a long, stiff balancing organ but can now be used as a third leg; pressed against a tree-trunk it gives the animal a firm anchor while feeding. As in the arbrosaurs, the crackbeak has developed a strong system of bones and muscles in the shoulder region to help it climb trees. The front feet have become dextrous hands. Crack-beaks are found in many other parts of the world, particularly in the tropical rainforests of the Ethiopian and Oriental realms, but it is only on the Australasian continent that they are so abundant and varied.

The crackbeak hand, like those of all hypsilophodonts and most of their descendants, has a full complement of five fingers. All the fingers are long and mobile. Both the first and the fifth fingers are opposable, or able to cross over the palm of the hand in order to grasp things. These are very useful to the crackbeak while climbing in the branches and selecting food from between the twigs.

The tubbs rotund shape is unique. There is no other animal like it anywhere. It probably evolved from the hypsilophodonts that were present on the Australasian continent in the Mesozoic period. The related crackbeaks must have evolved there as well, and spread to the Oriental realm along the island chains.

Temperate forest


TUBB


Pigescandens robustus

Not all tree-living animals are active jumpers. Up in the topmost branches of the eucalyptus trees of the south-eastern and south-western corners of the Australasian continent lives a silvery blob, about 70 centimetres (2 ft) long. This is the tubb, a clumsy-looking creature moving sluggishly up and down the silvery grey branches of the eucaliptus trees, feeding on nothing but the bluish foliage. At first glance it is difficult to imagine that both the tubb and the crackbeak are evolved from the same hypsilophodont ancestors, yet there are clues. The hind feet have four toes, the first of which point backwards and allow the animal to grasp branches. The hands have five fingers, the outer two of which are opposable. The deep head has powerful jaw muscles and a sharp beak, for breaking off food from the trees.
The other physical features, however, are quite different. The body is round and not suited for rapid movement. The legs are more suited for grasping trunks than for swinging along branches. The tail is short and stubby. It is the two opposable fingers on the hand that reveal the tubb to be closely related to the crackbeak. Of the hypsilophodont descendants in other parts of the world, only the taddey of the Oriental realm (page 83) possesses this feature.

The tubb is a placid animal, moving slowly and eating nothing but eucalyptus leaves and twigs. It has neither armour nor speed for defence. Its only protection from enemies, such as birds and pterosaurs, is in its distasteful flesh. Its body tissues store up the poisons that are present in the leaves and bark that it eats.

 

Temperate forest offshore islands


KLOON


Perdalus rufus

A pair of islands lies about 2,500 kilometres (1,550 m) to the south-east of the main Australasian continent. Together they are more than 1,500 kilometres (900 m) long, and so are strictly too large to be considered islands yet too small to be true continents. Geologically they contain elements of both. They consist of pieces that were once part of the main southern continent of Gondwana, yet much of their area consists of new material produced by volcanic action since Gondwana broke up.
With such a turbulent history and such an isolated position it is hardly surprising that the animal life found here is unique. Very little remains of the fauna that existed when these fragments were part of the great supercontinent. A notable exception is a group of small, primitive reptiles that lives near the north coast and has remained unchanged since Triassic times. The bulk of the animal life consists of birds and pterosaurs, many of the latter flightless. These evolved either from flightless pterosaurs that were already on the continental fragments when they broke away, and so may be related to the flightless pterosaur of the Ethiopian grasslands (pages 345), or from more conventional flying pterosaurs that flew to the islands and then abandoned their powers of flight.
The kloon, about 70 centimetres (2 1/3 ft) long, is a typical terrestrial pterosaur of these islands. It has no wings, or indeed any trace of the forelimbs that it must have possessed at one time. It is covered in thick shaggy hair and lives secretively in the undergrowth of the forests, eating low-growing plants.

Herds of wandles roam the grasslands of the southern island in leisurely moving, unconcerned herds. From an evolutionary point of view they have reached a final stage. Any influx of animals from other realms would now be a disaster for them, since they have evolved in total isolation. They are low in intelligence, are not adapted in any way for defence against predators, and could not outrun a meat-eater if they happened to meet one. Nor could they face competition from the more efficient grass-eaters that exist elsewhere.

The kloon, a vegetarian, has continually growing, gnawing teeth at the front of the jaw, and broad grinding teeth at the back. This is totally unlike the tooth pattern of the ancestral pterosaur.

In the absence of predators, the kloon has adopted a totally terrestrial way of life. The forelimbs, with the wings, have disappeared completely and the hind limbs earn1 the weight of the whole body. The original four toes of the pterosaur foot have remained.

The kloons feet are quite dextrous. While standing on one leg it can use the opposite foot to lift up awkwardly shaped food to the mouth. It is a slow-moving animal and spends much of its time deep in the undergrowth of the forests of the northern island.

Short grass savanna offshore islands


WANDLE


Pervagarus altus

If there are no ground-dwelling flesh-eaters, as is the case on the islands, many flying creatures may abandon their powers of flight and take up a ground-dwelling existence. In these areas most of the habitats on the ground may be occupied by animals whose ancestors once flew. On the southern island there are large areas of grassland to the east of the central mountain chain. These are grazed by a flightless pterosaur that is related to the kloon. This is the wandle and it is quite a large animal, being about 2 metres (6 ft) high at the hips. Like the kloon, its herbivorous diet has meant that all similarity to the carnivorous flying pterosaur ancestor has been lost. Its face has taken on the appearance of one of the sprintosaurs (pages 567) because it must accommodate a similar tooth pattern and jaw mechanism to allow it to eat the same food. Its specializations are similar to those of the terrestrial pterosaurs, such as the flarps (page 35), of the Ethiopian realm.
Many species of wandle exist at different altitudes between the mountains and the plains, and they all eat slightly different foods the tall grasses of the lowlands, or the shorter grasses of the foothills. One species lives even higher up and eats alpine vegetation. They are all slow-moving creatures. With no large meat-eating animals present they have not evolved defensive mechanisms such as armour, and have no need to be physically adapted for speed. The appearance of such an animal is always rather bizarre because it seems so unlike anything that exists under the normal environmental constraints that influence animal life over the rest of the world.

 

The coiled shell of the coconut grab is flat on the bottom, providing a skid-like surface that allows it to be dragged over the sand. There are eight tentacles. The four at the rear are broad and very muscular. They are used for pulling the animal over the ground and up coconut palms, left. The front four tentacles are long and delicate, allowing the ammonite to reach for a coconut. The eyes can focus both submerged and out of the water. Coconut grabs usually come ashore at night when it is cooler, and dawn finds the beach criss-crossed by their distinctive trails, right.

 

 

 

 

 

 

 

 

 

The shorerunner is a major predator of the coconut grab. Should one of the ammonites linger too long over its coconut so that the sudden tropical dawn finds it on dryland, it will be set upon by a flock of shorerunners and torn to pieces (a). Other prey consists of burrowing insects winkled out of tree trunks by the long jaws. The shorerunner climbs trees nimbly, balancing with its atrophied wings (b).

Tropical rainforest island shoreline


COCONUT GRAB


Nuctoceras litureperus

Scattered across the vast ocean that covers almost half the globe, is a multitude of islands. These are not fragments of any continent, but have grown completely independently of Gondwana. They have appeared mainly through volcanic action, where an underwater volcano has reached the surface and cooled. The flanks of these islands are further extended by reefs built up by corals and other sea creatures. Belonging to no recognized zoogeographic realm, this array of islands is described here as part of the Australasian realm.
At the same time as the dinosaurs developed to be the most significant animals on earth, other creatures evolved to dominate the seas. A group of animals of some importance were the ammonites, cephalopods that were encased in coiled shells. The shells consisted of empty air chambers that could be used by the animal to regulate its buoyancy. The ammonites evolved into many shapes and sizes during the Mesozoic period and are commonly found as fossils in rocks that date from that time. The coconut grab is an unusual ammonite in that it can spend much of its time out of the water crawling about on land. On many of the tropical islands of the ocean it can crawl up the beach and eat coconuts, and even climb trees to find the nuts when there are none available lying in the sand or washed up on the shore.

Tropical rainforest island shoreline


SHORERUNNER


Brevalus insularis

When new islands appear above the surface of the ocean their colonization usually follows a standard pattern. The initial living things to grow there are plants, germinating from seeds and spores borne on the wind. The first animals are always insects, again because they can be blown on the wind from distant continents. The first vertebrates to arrive are the birds and pterosaurs, winged creatures that are able to fly over the intervening ocean areas. Very often these winged creatures give up their powers of flight and take up a ground-dwelling existence, eating the plants and the insects on an island that is free from any dangerous predators.
The shorerunner is just such a pterosaur, found on one island group near the equator. It lives mainly on the beach, running here and there catching shore creatures, or pecking about in the ferny undergrowth for small reptiles and insects. It is also adept at climbing trees, using its long fingers and toes, and can run nimbly along branches using its atrophied wings for balance. The islands are no more than about five million years old, suggesting that the shorerunners ancestors must have arrived since that time. From the flying ancestor several species have developed to populate the groups of islands, all with slightly different shapes and sizes and differing eating habits.

 


CONTENTS

FOREWORD
THE GREAT EXTINCTION 6
WHAT IS A DINOSAUR? 10
THE NEW TREE OF LIFE 12
PALAEOGEOGRAPHY 16
ZOOGEOGRAPHY 18
THE HABITATS 20

THE NEW DINOSAURS 29
THE ETHIOPIAN REALM 30
THE PALAEARCTIC REALM 42
THE NEARCTIC REALM 54
THE NEOTROPICAL REALM 66
THE ORIENTAL REALM 78
THE AUSTRALASIAN REALM 88
THE OCEANS 100
CONCLUSION 108

AFTERWORD 109
GLOSSARY 113
FURTHER READING 115
INDEX 116
ACKNOWLEDGEMENTS 120


 

 

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