The continent containing the Neotropical realm is almost an island, connected to the Nearctic continent by only the narrowest necks of land in the north-west. For 8,000 kilometres (5,000 m) the continent stretches north-south, from the tropics of the northern hemisphere almost to the Antarctic circle. At its widest it reaches 5,500 kilometres (3,500 m) from coast to coast just south of the equator. The realm also includes the northern land bridge last established about five million years ago, and the southernmost tail of the Nearctic continent proper. It is the barren desert conditions found here that define the barrier between the two realms. In the very south a compact string of islands connects the continent to the vast frozen continent that lies over the south pole. This continent has so little life on it that it does not constitute a zoogeographical realm.
The Neotropical realm was once the western part of the supercontinent Gondwana. This is obvious from the shape of the eastern coastline, which follows the shape of the western coastline of the Ethiopian continent exactly, showing where the two became separated in the middle Cretaceous period. Its separation from the Nearctic continent in the north was not so complete nor so final. Both the Neotropical and Nearctic continents have been moving continuously towards the west, overriding the oceanic plates there. The relative plate movements along the western coast of the two continents has meant that there has been a continual steady build-up of fold mountain chains and volcanoes along the western coasts. This build-up has continued in the ill-defined region between the continents as well, and over the millenia island chains and land bridges have been created across the sea channel, and then destroyed again. At the moment, the connection is present in the form of the land bridge in the west and a loop of volcanic islands in the east.
As with the other continents, the physical geography reflects the geological history. There are old mountains in the east, representing one edge of the old rift-valley along which the Ethiopian continent tore away during the Cretaceous period. Along the entire western coast there is a new mountain range, constantly being enlarged by the reaction between the continent and the plates of the nearby ocean. Volcanoes bubble and stream along the length of this mountain range. The isthmus that connects this continent to the Nearctic continent can be thought of as the northward continuation of this range. Two main river basins are found in the lowlands. The central one measuring 5,827,500 square kilometres (2,250,000 sq m), represents the greatest river system in the world.
Most of the northern reaches of the realm, being within the tropics, are clothed in tropical rainforest. The huge river basin found in the broadest section of the continent is feel by the daily rain that falls here. As in most tropical forests, the favourable growing conditions mean that thousands of species of trees grow here, supporting many different kinds of tree-living animal, from the insects to the tree-living dinosaurs that feed on them. The forest floor has its own fauna of insects and insectivorous dinosaurs.
To the south, the largest areas of the lowlands are occupied by grasslands, that range from tropical in the north through temperate and then cold in the south. On these pampas live grass-eating animals – huge long-necked grazing dinosaurs like those that have existed on the continent throughout its life as an island realm. These dinosaurs are becoming rare and even extinct now, and are being replaced by other creatures that are evolving from animals that have migrated south from the Nearctic realm.
As the western mountains provide the land connection between the Neotropical and the Nearctic realms, it is hardly surprising that many of the immigrants to the realm have evolved from Nearctic mountain animals. Many of those coming south have developed into forest-living and pampas-living types. Some, however, have remained mountain creatures. Some of the largest pterosaurs in the world soar above these wild mountain chains.
There are deserts here too. The grasslands in the very south are extremely dry. They are in the rain-shadow zone of the mountains, where the prevailing winds drop all their rain on the other side of the ranges. Coastal deserts are found in a narrow strip between the mountains and the sea. Here, the cold ocean currents cause the air to cool and descend so that no rain falls. Further south on this coastal strip, however, there are moister, more fertile conditions where the wet winds blowing from the ocean have more influence on the climate than the cooling by the ocean currents.

Tropical rainforest

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PANGALOON

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Filarmura tuburostra

An interesting example of the re-evolution of features once lost, arises in the case of the pangaloon. Its body is covered in scales, but these are not the conventional reptilian scales that were possessed by its archosaurian ancestors 200 million years ago. These scales are actually plates of fused hairs. The original scales were retained as the archosaur evolved into the primitive coelurosaur dinosaur. Then, as the coelurosaur developed and evolved into the warm-blooded arbrosaur, the scales evolved into insulating fur.
The pangaloon, which is evolved from an arbrosaur that has reverted to a ground-dwelling way of life, has redeveloped a scaly armour from masses of fur fused together. Its ground-dwelling habit evolved as the ants flourished and became widespread in the early part of the Tertiary period. As the ants evolved then so did the ant-eating adaptations of animals like the pangaloon. The typical, long toothy jaws of the arbrosaur have been replaced, in the pangaloon, by a tubular snout, along which lies a long sticky tongue that can be thrust out to a distance greater than the length of the head. It can push its snout down ant burrows and lap up the ants that adhere to the tongue’s stickiness. The middle claw of the forelimb has developed into a strong hook that can tear into ants’ nests to expose their tunnels and chambers. The nostrils are high up on the face and can be closed for protection.

Tropical rainforest – swamps

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WATERGULP

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Fluvisaurus hauristus

The waters of the vast network of channels and tributaries that pour into the great river flowing eastwards along the equator are alive with aquatic animals of one kind or another. The forest reaches over the quiet bayous and backwaters, steeping them in a murky green gloom. Water plants root in the deep mud, reach upwards through the turbid waters and spread their leaves out over the placid surface. The undersides of the floating leaves support colonies of water snails and other aquatic invertebrates, and these are eaten both by fish, and by lightly built animals that crawl over the tops of the leaves and probe downwards. The floating leaves themselves are eaten by huge, placid, slow-moving water beasts that swim lazily in the shallows and engulf huge mouthfuls of the vegetation.
The largest of these river browsers is the watergulp, evolved from the swift-footed hypsilophodonts that were so successful in Cretaceous times. The powerful hind legs have since evolved into paddles, as have the versatile five-fingered forelimbs. These are used mainly for stabilizing the animal's great bulk, and the two claws on the forepaddles are useful for grubbing around the muddy roots. Most of the swimming action is achieved by the tail. The stiff rod-like tail of the ancestral hypsilophodont has become more flexible, and a tall leathery fin along the upper surface can produce powerful swimming strokes.

The evolution of the legs and tail of the watergulp mean that it can move only in water. Its eyes and nostrils are high on the head, allowing it to see above the water surface when submerged. The mouth is broad, and the sharp-edged horny beak can cut through the stems and leaves of the toughest water plants. At about 2.5 metres (8 ft) long it is one of the largest river animals. Each watergulp also supports a large colony of parasites and other companions that feed on algae growing on its flanks, and on small creatures disturbed from the mud by its passage.

 

As in many aquatic vertebrates, the watergulp’s ribs are very heavy, giving it enough weight to keep it submerged. It also swallows stones from time to time to adjust its buoyancy.

The pangaloon has a long sticky tongue (a) which it extends into ant burrows. The dense scaly armour of the pangaloon is not a protection against ants but guards against attacks by predatory reptiles that live on the tropical forest floor. The pangaloon is a slow-moving animal and unlike its relatives, it cannot take refuge in trees. When it is threatened, the pangaloon can curl the paddle-shaped tail (b) beneath its body to protect its soft underparts from the stings and biting jaws of the large ants.

The nectar-eating gimp feeds rather like moths and bees, pushing its snout down into the base of long flowers to reach the nectar. As a result, the snout emerges covered with pollen which the gimp then unwittingly transfers to another flower, thus fertilizing it. The animal’s shape is similar to that of the small arbrosaurs but it is not as fast-moving. Its forelimbs can grasp flower stems. Its body is very small, since nectar needs very little digestion and requires only a small gut.

Many species of gimp exist in the Neotropical forest. Each one eats the nectar of a particular species of flower and has a correspondingly different shaped snout. A more obvious difference between species is the pattern on the back. This can range from spots, to stripes, or large patches of colour.

 

The scaly glider has a set of paddle-like scales, growing horizontally from each side of the body and spreading out to form gliding wings. Muscles in the flanks and attached to the ribs give the scales some limited mobility, allowing the bright undersides to be exposed or hidden at will.

Tropical rainforest

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SCALY GLIDER

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Pennasaurus volans

Bright flashes of colour appear in the heights, up among the branches, creepers and trunks of the Neotropical canopy. To and fro, the colours dart, like large butterflies, swooping and wheeling in the breezes, then flopping onto a branch and blending instantly with the mottled bark in the dappled sunshine. These are not butterflies, however, but some of the smallest dinosaurs that have ever existed. Descended from the same coelurosaur stock as the arbrosaurs, the scaly gliders adapted to a gliding life with the evolution of the flowering plants and hence, the butterflies. The latter represent the gliders’ principal food. A controlled dive and glide through the air can bring a scaly glider close to a butterfly at rest on a flower, and, with a quick snatch of pointed jaws, the insect is caught and the glider sails on to rest and digest.
Flying and gliding animals frequently evolve in tropical forests. With the network of massive boughs and close-growing branches, animals can easily jump from one tree to another. The more aerodynamic the animal’s shape, the further it can jump. The conditions are perfect for the evolution of gliding structures that can carry an animal over even longer spaces. In the case of the scaly glider, these structures consist of broad scales projecting sideways from the body. In flight, they turn the animal into an aerodynamic skimmer, while at rest, they help to camouflage it against the tree-bark. They are brightly hued beneath, but drab when seen from above.

Tropical rainforest

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GIMP

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Melexsorbius parvus

As in tropical forests all round the equator, the trees of the Neotropical realm are full of numerous kinds of animals. They support many more different types of animal than the trees of the forests in the temperate or cold zones. With the constant high temperatures and the daily rainfall, vegetation flourishes and several hundred different species of tree thrive in a very small area. A thick canopy consisting of intermeshed boughs of the tallest trees spreads out to catch the sunlight. Epiphytes and dangling creepers festoon these high branches. As a result, there are many different kinds of leaves, flowers and fruits available above the gloom and roots of the forest floor. Many varieties of animals have evolved to exploit these potential foodstuffs. Generally, the tree-living animals of the Neotropical realm are smaller than those of the tropical forests in the rest of the world. The airy canopy is alive with little arbrosaurs adapted to feed on the thousands upon thousands of different types of insects that make their homes there.
Some of the arbrosaurs, however, have abandoned their insectivorous way of life and have evolved into totally new forms. The nectar-sucking gimp, for instance, is a tiny animal, no more than 20 centimetres (8 in) long including the slender delicate head, and eats nothing but nectar. Its snout has evolved into a long tube which acts as a rigid sheath for an extendable nectar-gathering tongue. These features are similar to those of the ant-eating adaptation of the pangaloon (page 68), and it is likely that both animals evolved from the same group of arbrosaurs that crossed from the Nearctic realm early in the Tertiary period. The tubular snout may be seen as an example of pre-adaptation where a feature evolves spontaneously and is then retained because it is perfectly suited for a particular purpose.

With a total length of only 30 centimetres (12 in), including the whip-like tail, and a ‘wing’ span of 25 centimetres (10 in), the scaly glider is the smallest and most lightweight of all the dinosaurs.

Grassland – pampas

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TURTOSAUR

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Turotosaurus armatus

The Neotropical continent has had an interesting history. After it had broken away from the ancestral supercontinent it remained an island continent for most of its life. It connected only occasionally to the continent of the Nearctic realm in the north, as it is today. At the end of the Cretaceous period the duckbilled dinosaurs spread over most of the continents and established themselves as the principal large herbivores, replacing the great four-footed sauropods. The sauropods still exist, but mostly in places where the duckbills never gained a foothold, such as the Neotropical continent. Isolated from the influences of migration from other continents, the sauropods evolved in their own way.
The titanosaur family – the only surviving family of sauropod – had begun to develop armour as early as the late Cretaceous period. They continued to do so in the Neotropical continent and, in the late Tertiary, with the arrival of the new meat-eaters, the armour developed into very flamboyant and spectacular forms. The turtosaur has a solid shield of armour over its back and flanks. The tail and neck are also shielded, the tail by overlapping rings of horn, and the neck by jointed horn sections. The head is covered with a continuous horny shield. The jaws have no teeth, but the mouth edges of the horn shield are sharp and are ideal for cropping grass.

The armour of the turtosaur is formed from bone masses that grow in the skin and are covered by a layer of horn. The back armour is a solid mosaic of small skin bones, with much larger bones spread between them. These larger bones provide the bases for a series of conical spikes. Huge hip bones and shoulder bones support the weight. There is no armour on the legs or the underside of the tail. When danger threatens the animal flops down on its belly and presents an impenetrable shield of bone and horn to its enemy.

The long neck and the trunk of the lumber enable it to graze over a large area without moving far. The neck is quite stiff but can be swung from side to side at the shoulders. Towards the head it becomes more flexible. The teeth are confined to the front of its mouth (a) and are adapted for cropping grass. The muscles of the short trunk are anchored on broad plates of bone at each side of the enormous nostril openings in the skull (b). The trunk is a feeding organ used to grasp and uproot large bunches of grass. It is also a breathing organ, but the position of the external nostrils do not interfere with its feeding action (c).

Grassland – pampas

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LUMBER

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Elephasaurus giganteus

Isolated from the influences of migration from other continents, the sauropods of the Neotropical continent evolved in their own way to cope with such changing conditions as the spread of the grasslands. The lumber is a grassland-living sauropod that has evolved from a tree browser into a grass-grazer. During the Tertiary period many strange grassland-dwelling sauropods developed to live in the newly evolved pampas, including a number of long-legged, running forms. These were very vulnerable to the swift-footed carnivorous dinosaurs (pages 74–5) that spread across the continent about four million years ago, when the present land bridge was established to the Nearctic continent to the north. The long-legged sauropods were fast runners, but they were nowhere near as fast as the meat-eaters and were eventually made extinct.
The sauropods that survived did so because they evolved defensive strategies. The turtosaur, for instance, evolved armour. Others, such as the lumber, took refuge in mere size. The lumber is the largest land animal alive today, with a length of 25 metres (80 ft) and a weight of 70 tonnes. It cannot raise its neck far above its shoulders, but it can sweep round and reach vast areas of grass without moving its feet. Its teeth are confined to the front of its mouth and are hard-wearing, adapted for cropping grass. The trunk helps to pull bunches of grass towards the mouth, where they are torn off and swallowed. The skin is thick and leathery, quite resistant to meat-eaters’ claws and teeth, and most carnivores leave the huge creature well alone.

Grassland – pampas

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CUTLASSTOOTH

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Caedosaurus gladiadens

Many animals flooded into the Neotropical continent about four million years ago, when the string of volcanic islands linking with the Nearctic continent to the north, fused to form a land bridge. The animals quickly evolved and developed to fill the ecological niches they found. In most instances the animals that came south were more successful and began to replace the indigenous animals that had dominated the continent for the previous 50 million years. The reason for this may be that the indigenous animals had evolved few variations in that period of time. The continent itself had not shifted substantially and there had been little change in the environment and the climate except for the spread of the grasslands. There was no necessity then, for the animals to evolve, and they had settled into a long period of decadence.
The animals from the north, on the other hand, had suffered millions of years of change, with changes in climate and interchanges of animals with the Palaearctic realm, and had been evolving vigorously. When they reached the Neotropical continent they were more able to adapt to the conditions found there and, as a result, the native animals suffered. The most noticeable instance is found among the meat-eaters. The first of the northern animals to reach the continent were the mountain-leapers (page 61). Being skilled at traversing high mountain ranges, they were well able to cross the mountainous neck of land that connected the two continents and spread into many of the ecological niches. Large meat-eaters quickly developed from this stock and preyed on the swift-footed sauropods of the plains. Even larger types developed, some with their heavy heads and small arms, looking as if they had evolved from the great carnosaurs of the Cretaceous period rather than the small agile coelurosaurs.
One such is the cutlasstooth which has evolved huge cutting teeth that enable it to prey on the large sauropods like the lumber (page 73). Hunting in packs, cutlasstooths can set upon a lumber and slash it until it bleeds to death.

Grassland – pampas

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GOURMAND

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Ganeosaurus tarchis

During the last four million years, many of the meat-eating dinosaurs that were unique to the Neotropical continent were destroyed during the invasion of the more versatile creatures from the north. The tyrannosaur family of carnosaurs that developed in late Cretaceous times were the largest of the meat-eating dinosaurs, although some of the spinosaurs approached them in size. As they became larger their heads became heavier and their forelimbs became increasingly smaller. They spread through the areas that now constitute the Nearctic and Palaearctic realms but they have long been extinct in these regions.
A group of tyrannosaurs did manage to filter into the Neotropical continent when the land bridge was temporarily in place about 55 million years ago, and there they survived while their relatives died out elsewhere. The line of their evolution continued and they increased in size. The gourmand is a massive creature, 17 metres (60 ft) long and weighing 15 tonnes. The forelimbs have atrophied entirely, with no trace of either limb bones or shoulder girdle in the skeleton. As the tyrannosaurs grew huge, they became too heavy and slow to hunt. They developed a scavenging mode of life, a life now led by the gourmand.
The small forelimbs of the ancestral tyrannosaurs were used to steady the animal as it arose from its belly after resting on the ground. In the gourmand this is unnecessary since the hips have moved forward to balance the body perfectly. The legs are jointed in such a way that they lift the body straight upwards off the ground. The animal is a scavenger, moving slowly across the pampas and swallowing whole the carcass of any dead animal it discovers. The skull is very flexible and the jaws can unhinge to enable it to engulf its prey. Once it has eaten, the gourmand rests for several days while it digests its meal. It does this while lying motionless in the grass. The armour protects it from predators during this period.

The slow-moving gourmand is protected from other meat-eaters by a back armour of bony plates sheathed in horn. Its scavenging lifestyle is very different from that of its ancestors.

The dip is a patient animal and sits by the pools of mountain waterfalls waiting for fish. It is able to judge its distance from its target despite the distorting effect of the water, and darts its long head downwards, cleaving the water and pinning the slippery fish between its many sharp teeth.

The harridan has a wingspan of over 5 metres (17 ft). In addition to the wing membranes it possesses membranes on its hind legs. Each of these is supported by a very long first toe, and is used to control the animal in flight.

The harridan is a mountain pterosaur, evolved to soar in the mountain air currents. It is equally at home on the ground, however. The wings and leg membranes can fold away when it is at rest, and the harridan can walk about the crags and ledges like any other biped.

With its keen stereoscopic vision, the harridan can accurately swoop down and snatch unsuspecting small animals living on the ledges far below the mountain peaks.

Barren land – mountains

DIP

Harundosaurus montanus

The western mountain range that forms the backbone of the Neotropical continent traps moist air blowing in from the ocean and is always drenched in rain. The precipitation produces streams that cascade steeply back to the ocean on the western side, or form small rivers that develop into the tributaries of the huge rivers that meander across the lowlands to the east. These streams are full of different types of fish and invertebrates. The fish are eaten by various animals including birds, pterosaurs and specialized hunting dinosaurs.
One of the most interesting animals is the dip, a fish-eating dinosaur evolved from the coelurosaurs. Like many of the hunting dinosaurs of the Neotropical continent, the dip is descended from the mountain leaper (page 61) that migrated southwards when the land bridge to the Nearctic continent was established about four million years ago. It retains the long silky fur of its ancestors that is necessary to protect it from the harsh mountain climates. The head has evolved the shape that has developed in many groups of fish-eating animals. The jaws are long and narrow and furnished with many fine-pointed teeth. The eyes are set so that they are directed forward and give stereoscopic vision. Like the mountain leaper, the dip is very fleet of foot and can run acrobatically along the sides of crags to escape the predatory birds and pterosaurs that abound in the region.

Barren land – mountains

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HARRIDAN

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Harpyia latala

Between the mountain peaks and above the valleys of the western mountain range soar a number of large birds and pterosaurs. They circle in the winds rising from the valley heads and the updraughts from warm hill slopes. One of the largest of these soaring creatures is the harridan, a pterosaur. It can manoeuvre expertly while in flight. The air sweeping over its broad wings is controlled by additional membranes attached to the second and third fingers of the hand. These two fingers are elongated but not as much as the fourth finger that in all pterosaurs, supports the main flying membrane. The first finger carries a claw which is used when the animal is crawling on cliff faces. Its head is almost mammal-like, with an elongated snout and sharp teeth at the front. The eyes are directed forward and give a good stereoscopic vision.
This pterosaur is a solitary animal. It mates for life and nests on high pinnacles in the mountains, rearing no more than two young each year. With its warm-blooded physiology, and its carnivorous hunting habits, it is very similar to the predatory birds that are found in the mountainous areas of other realms.
The harridan has very keen eyesight and can spot small animals scampering about on the ledges hundreds of metres below. It then swoops out of the sky and pounces accurately on its food. Its prey usually consists of the small mammals that have adopted a mountain habitat.