Dougal Dixon "The New Dinosaurs" - The Nearctic realm
Main Site library Forum Guestbook


The Nearctic realm consists of a roughly triangular complex of continent and islands, reaching from the desert latitudes in the south to the polar ice cap in the north. At its broadest it runs along the Arctic Circle where it consists of glaciered mountains and icy islands in a frozen sea. To the south, in its more habitable zone, it is a continent 5,000 kilometres (3,000 m) broad, but this narrows rapidly to an isthmus connecting it to the Neotropical realm in the south. Much of this isthmus is desert, and provides the barrier between this realm and its Neotropical neighbour.
The continent once occupied the western part of the supercontinent of Laurasia. It was in this region that the two supercontinents, Laurasia and Gondwana, were almost permanently united in the days of the world continent of Pangaea. It did not split away from the continents that were to become the Ethiopian and the Neotropical realms until late Jurassic times. At about this time, too, it broke free from the remainder of Laurasia, as a new ocean opened up between it and the rest of the supercontinent to the east. Since then, land connections with other continents have come and gone many times. In the north-west the most westerly portion is separated from the most easterly point of the Palaearctic realm by the shallowest and narrowest of seaways. Throughout its history this seaway has dried out and flooded again, each time allowing animals to cross from one continent to another. At the moment it is flooded and forms the boundary to the realm, but that will only be a temporary state. Likewise, to the south, the isthmus between the Nearctic and Neotropical continents is a very temporary affair, breaking and re-uniting many times in the past, and each time having an effect on the migration of animals. At the moment the connection is complete, but that may not be for long.
Topographically the continent consists of new mountains in the west, old mountains in the east, and flat plains between. The western mountains are still building up, due to the movement of the oceanic plate there, and earthquakes and volcanoes are frequent. The whole of the northern portion of the continent, much of it submerged and only appearing as islands, consists of hard, old Precambrian rocks, the kind that form the nuclei of all continents. The southern half of the lowland section consists of a vast river basin draining to a gulf in the south.
The habitats range from frigid cold to searing hot climates. The far north is still in the grip of the Ice Age, with continental glaciers smothering the great north-eastern island, and pack ice choking the straits and inlets. Where the land is not ice covered it consists of tundra bleak and only habitable for a few short months of the year. Even if the land bridge between the Nearctic and Palaearctic realms were not currently broken, these conditions would prove just as impenetrable a barrier between the two areas.
Further south lies a vast belt of coniferous forest, almost a continuation of that region found in the Palaearctic realm. The animals there are similar to those in the Palaearctic forests, as there was a clear connection between the two realms until very recently.
Deciduous forests lie to the south of this and clothe the older mountain ranges found in the east. Here, the tree-living animals, particularly the arbrosaurs, are superficially similar to those that live in deciduous forests elsewhere. They have been separated from them for so long, however, that these arbrosaurs are of totally different species.
The western third of the continent consists of mountain ranges high and elongated, with desert valleys and plains between them. Both plant-eating and meat-eating dinosaurs have adapted to the sparse food supplies in the high reaches.
The central lowlands, drained by the vast river system, is a region of temperate grasses. The grass is long and lush by the rivers but becomes shorter and sparser as the land dries out and rises towards the western mountains. Hadrosaurs, evolved originally to live in lush forest, now roam these open prairies, having adapted successfully to a grazing existence. With the development of fleet-footed grazing animals, comes the evolution of carnivorous hunting animals.
Low-lying lands around the south-eastern corner of the continent, where the land has only recently risen from the sea, and the vast deltas produced as the huge river empties into the gulf to the south, have given rise to a unique series of water-living animals. Here are dinosaurs that hunt fish, and pterosaurs that strain tiny invertebrates from the shallow water. There is even a hunting dinosaur that demonstrates a cunning intelligence unparalleled in the dinosaur world, to enable it to catch swift flying creatures such as birds and pterosaurs.



The sprintosaurs evolved from the duckbilled dinosaurs of the Cretaceous period. These, in turn, evolved from completely bipedal dinosaurs (a) but began to spend more time on all four legs (b). When they evolved into the plains-living sprintosaurs, they became completely quadrupedal (c). The legs are long and lightweight, with muscles concentrated in the thighs and upper arms, and the tail, having lost its balancing function, has degenerated either to a stump or to a flagpole.
Crests vary from species to species and are used as signalling and identification devices. The shapes range from hook shapes, as in Ancorachephalus major, (d), through rows of knobs, as in Sprintosaurus quadribullus, (e), to broad blade shapes, as in S. dolabratops, (f).

Prairies and grassland


Family Sprintosauridae

The prairies the grasslands that spread out across the centre of the Nearctic continent from the great winding river on the lowland plain to the towering wall of the massive western mountains support vast herds of grazing animals. The most widespread of these are the sprintosaurs, evolved from the duckbilled hadrosaurs of the late Cretaceous. In the last 65 million years, as the forests gradually gave way to the grasslands, the hadrosaurs evolved to adapt to the changing habitats. Like the hadrosaurs before them, there are two main groups of sprintosaur, the crested, and the non-crested.
The crested sprintosaurs tend to inhabit the western high prairies, grazing the short grasses and undergrowth of prickly pear cactus in the dry shadow of the mountains. In the long evenings of the mating season the thin upland air resonates to the shrill trumpeting sounds as the sprintosaurs call to one another, using the hollow crests as sounding tubes. The crests are formed from the bones of the nose. They probably evolved to extend the nasal passage and allow dry air to pass over moist membranes before reaching the lungs. They successfully perform this function, because the air of the high prairie is very dry. Distinctively shaped crests are found in different species of crested sprintosaur and serve to distinguish members of one species from another, as they roam the sparse grasslands below the mountain ramparts. Both male and female sprintosaurs possess the crest.
The non-crested sprintosaurs, like their slightly larger crested cousins, evolved from the hadrosaurs. However, while the crested forms evolved from such crested hadrosaurs as Corythosaurus and Parasaurolophus, the non-crested forms evolved from the flat-headed line of the hadrosaur group that included Hadrosaurus and Anatosaurus. Since Cretaceous times, their evolution into a grassland animal was parallel to that of the crested sprintosaurs. The cropping beak and the huge battery of constantly replaced grinding teeth needed little modification to suit a diet of tough, silica-rich grasses. As their faces were permanently in the grass, eating, the animal adopted a four-footed posture. On the open plains danger can be seen from a long way off and so the legs became spindly and lightweight to enable the animal to run swiftly from harm. The face became long to keep the eyes above the level of the grass so that a lookout could be kept for predators while grazing.
The main difference between the non-crested and crested sprintosaurs, apart from the crest, is the presence of the tail. Having lost its function as a counterbalance, necessary when its ancestors went about on two legs, the tail has become a tall, stiff flagpost. The males have a fin of skin supported by bony struts at the tip, and this is used for signalling. Different species have different sizes and patterns of fin. The non-crested sprintosaurs live mainly on the long-grass, lowland prairie where the adaptations of the particularly long face and the tail flag are of most use. The sprintosaurs, both crested and non-crested types, travel over the plains in closely knit herds.

Vexillosaurus levipes is a non-crested sprintosaur from the floodplains of the great central river. It moves about in tight herds often only seen as a bunch of tails waving above the long grasses. When a predator such as the northclaw Monuncus attacks, the herd breaks up in a confusing flurry of flags and poles, leaving the attacker bewildered.


The northclaw is a coelurosaur, one of the more lightly built theropod dinosaurs and, apart from its large head and furry coat, it differs little from its Jurassic and Cretaceous ancestors. The main difference is the massive single claw, the killing organ on its right forelimb.

Prairie and grassland


Monocornus occidentalis

The lightly built sprintosaurs are not the only grazing animals that roam across the vast prairies. Huge slowly-moving grass-eaters also exist here, cropping the grasses down to their roots and moving on in black dusty herds. The huge monocorn is one of several species of ceratopsian that still inhabit the Nearctic continent. It differs in appearance from the members of its ancestral stock, such as Triceratops and Styracosaurus, but the differences are not really profound, and they are a reflection of the life that the animal now leads. The herds of monocorn need to be on the move constantly, for once all the grass in one area is eaten up they have to move on to fresh areas. The legs are therefore longer and more slender then we would expect in such a large animal. The feet are digitigrade, that is they support the weight of the body on the toes rather than on the flat of the foot the plantigrade condition of the monocorns ancestors. In common with the ancient ceratopsians the neck and shoulders are protected by a bony frill, and a horn on the nose is used as a weapon.
The ceratopsians are now no longer confined to the Nearctic continent. Several species are now found in the Palaearctic realm where they spread via the land bridge between the Nearctic and Palaearctic continents before the Ice Age.

Prairie and grassland


Monuncus cursus

Puma-like, the northclaw slinks through the grasses of the prairie, its tawny stripes blending it into the dry yellows and browns of the vegetation. Its reptilian eye is fixed on an unconcerned grazing group of crested sprintosaurs, its instinctive cunning guiding it towards the most effective attack. For long hours its sleek body moves, slowly but surely towards the unsuspecting herd. Suddenly a male sprintosaur, looking round, notes something in the grass that does not quite fit. He trumpets out a warning blast and the herd scatters in a cloud of dust. With an instant reflex the northclaw darts up from its place of hiding and arrows down on the slowest of its prey. Its powerful hind legs thrust the horizontal body forward, balanced by the stiff rod of a tail. Then, when almost upon the young sprintosaur, which is still deciding which way to run, the single long claw springs out, hooks into the skin and pulls the animal over, kicking and struggling in the dust and the grass. Another blow of the claw and the prey is disembowelled, and the northclaw settles down to feast.

The bony frill of the monocorn is very long, covering the length of the neck to the high shoulders. It is used when males spar with one another for herd leadership. The contestants push harmlessly against one another until one tires and gives way.

The horn of the monocorn is a formidable weapon when turned on an attacking carnivore like a northclaw. Monocorn herds usually travel with big males on the outside protecting the females and hornless young.




Tundra and alpine


Nivesaurus yetiforme

The tangle of braided mountain chains in the western third of the continent is relatively new, thrust up to its present height only in Cretaceous times. The open river plains of the Jurassic and the steamy forests of the Cretaceous period the habitats of the most prolific dinosaur communities in the past are now craggy mountains, clothed in glaciers and snow. A few dinosaurs adapted to this new environment, moving in from the regions round about and adopting a lifestyle that would support them there. One such is the 2 metre (6 1/2 ft) long balaclav, one of the specialized modern hypsilophodonts. It evolved insulating layers of fat and fur, an ability to eat the alpine plants and mosses, and a compact shape to preserve its body heat.

When not hunting the male mountain leapers stand as motionless sentinels, guarding the females and the young of the pack. On bright days the pack may sun itself on the open slopes, at which time it is vulnerable to attack by birds of prey and mountain pterosaurs.


Tundra and alpine


Montanus saltus

The intelligence that gradually developed among the coelurosaurs enabled them to adapt to all kinds of harsh conditions. The large brain of the mountain leaper coordinates its movements, and enables it to make swift judgements as it springs and leaps between the spires and crags of the mountain peaks, hunting the birds and small mountain mammals on which it feeds. It has developed a high degree of endothermy warm-bloodedness to help it to cope with the icy climates, and the thick shiny fur is indicative of this, providing the insulation that keeps the animals body at a constant temperature. The head and body reach a length of about 1 metre (3 ft), but the flowing hair, the long legs and long balancing tail with its spectacular plume make it look much larger. Mountain leapers live in small packs, with the males undertaking all the hunting, and protection of the females and the young.

The balaclav lives in small family groups in the highest mountains. It can often be seen trekking across snowfields and glaciers from one lichenous rock or mossy hollow to another. It can subsist on a very poor diet.

Layers of fat insulate the balaclav, and the hairs on the tail and feet help it to grip icy surfaces. Its broad beak and the spade-like nails on the three middle fingers enable it to scrape up lichens and moss, while the longer claws are used for digging up alpine plants.

Mountain leapers are agile and swift when traversing the mountain peaks and crags. With surefooted springs and leaps they move rapidly, maintaining balance with the long tail.


The springe is the most cunning of the hunting dinosaurs. Its Cretaceous ancestors were the most intelligent animals of the time, and this trait has continued through evolution. The intelligence has evolved for a simple purpose to find food more efficiently.



The hunting strategy of the springe is one of ambush. It lies on a tidal mudbank, in an attitude of rigor mortis, with its head and tail thrown back and its hind leg pulled into a stiff pose. It inflates its belly, showing off the death-like mottling, and emits a smell like that of putrefaction (1). This performance is irresistible to the carrion birds and scavenging pterosaurs of the swamps who flock to the site. A swift dart of the killing claw (2) and a victim is impaled.

Mixed woodland wetlands


Necrosimulacrum avilaqueum

In the midst of the southern deltas of the Nearctic continent there lives one of the most cunning of the dinosaur hunters. Descended from the saurornithoids, such as Stenonychosaurus and Saurorinithoides, the springe, measuring about 3 metres (10 ft) long, has a similar size and proportion to its ancestors. Its head, however, has expanded and now contains a larger brain, and the killing claw is carried on a particularly long second toe. With its naked skin mottled a deathly white and pink, and the matted, dark patterned fur, the springe has a derelict, morbid appearance.

Mixed woodland wetlands


Pterocolum nibicundum

A great tract of land on the southern and south-western shore of the Nearctic continent consists of deltas, swamps and backwaters. Since Cretaceous times it has gradually been rising above sea level, and it is now covered in marshy vegetation, comprising vast areas of reed beds and mangroves with stands of conifers, evergreen oaks and magnolias on the drier banks. The available moisture and warm climate mean that several varieties of plants and animals live here. Bird and pterosaur life is particularly abundant, as the birds have adapted well to this pleasant environment. Ducks graze the water weed, divers plunge into the waters after fish, and waders peck after small creatures in the mud and shallows. However, the pterosaurs live side-by-side with the various species of birds and reveal similar adaptations to the same conditions.
The sift is built to the general pterosaur design, with a small lightweight body stiffened for flight, wings of membrane supported by the arms and extended fourth finger, and a very flexible neck. However, in appearance the sift is more like a wading bird, with its long-shanked legs and its tapering beak-like jaws. The sift congregates in flocks out in the shallows. The folded wings, larger in proportion than those of birds, catch the sun and provide an everchanging pattern of light as the flock moves about filtering the tiny insects and crustaceans from the muddy water. The long, thin jaws are armed with a multitude of tiny, comb-like teeth which are used to trap the water-borne food.


The open skies above the swamps and lakes are usually filled with wheeling flocks of birds and pterosaurs, particularly at dawn and at dusk in the evening. At a distance, pterosaurs like the sift can be distinguished from birds in flight by their comparatively larger wings.


The sift feeds on the tiny plants and animals that abound in the shallow waters of the deltas. Shrimps, worms and little fish are stirred up by the long-toed feet and caught with the narrow jaws. Floating algae and weeds are strained from the water by the fine teeth.


The second finger of the nauger is remarkable, being about as long as the forearm. It is used for poking down burrows and winkling out the larvae of the wood beetles on which the arbrosaur feeds. A hooked claw at the end secures the catch.

The skull of the nauger is perfectly adapted to its purpose of drilling into solid wood. The teeth grow only at the front of the jaw and are directed forward, each one lending support to the one before. Those at the very front bear the brunt of the pecking force. When they wear out or break, they are replaced by more teeth growing in from behind. The neck joint is very strong, protecting the back of the skull and the brain and giving support to the heavy neck muscles needed for the constant rapid pecking.

Deciduous and mixed woodland


Raminsidius jacksoni

As on all the other continents, the arbrosaurs fill the trees of the Nearctic realm. Some eat insects, others consume fruit and berries, and some prey upon other arbrosaurs. The treepounce is one such carnivore. With a head and body reaching 70 centimetres (2 ft) it is larger than most of the arbrosaurs, and so it tends to be less agile. However, what it lacks in agility it makes up for in stealth. Lying along a branch on a sunny day its spotted coat makes it almost invisible in dappled sunlight. With infinite patience it waits until an unsuspecting nauger, or smaller arbrosaur scrambles close, and then pounces, making a quick kill.

The treepounce relies mainly on its hearing for hunting, and so its ears are highly developed. Tufts of hairs around the ear-opening funnel the sounds into the ear canal. In appearance the tufts resemble the fleshy external ears found on some smaller mammals. The colouring of the coat conceals the treepounce in the trees.

Deciduous and mixed woodland


Picusaurus terebradens

In the deciduous forests of the Nearctic realm live a vast variety of different arbrosaurs, each one specifically adapted to a particular way of life. One of the most highly specialized is the nauger, with its wood-boring jaws and its long thin finger. It feeds almost exclusively on the grubs of wood-burrowing beetles that it hunts in the living wood of the trunks and branches. The strong hind legs and the stiff bristles on the tail give it a firm grasp on the tree while it listens for movement beneath the bark and drills into the wood after the larvae.
If there were no dinosaurs living, it is possible that some of the ecological niches now occupied by tree-living arbrosaurs would have been occupied by birds. It seems entirely probable that a bird could have evolved to fill the niche of the pecking arbrosaur, with a strong bill taking the place of the powerful teeth, and possibly a specialized tongue doing the work of the long finger.

The long legs enable the footle to leap nimbly through the treetops. The three fingers and four toes, all long and thin, can perch on, and grasp, the thinnest of twigs while the long jaws can root around under the leaves to catch insects hidden there. Many species of footle live in the forests of the Nearctic realm.

Deciduous and mixed woodland


Currerus elegans

The trees are alive with myriads of tiny insectivorous arbrosaurs, each one differing from the next by the different colours of the pelt, by different display tufts on the head and tail, and by slight differences in the shape and size of the head. The arrangement of the skull and jaws depends upon the diet. Feeding both in the trees and on the ground, the tiny arbrosaurs have short, thick jaws to crunch up beetles, or long thin jaws to dig for buried larvae and worms. All the arbrosaurs have the same light build, long, springing legs and thin toes. The body is small and balanced for running and jumping by the long, stiff tail.
The footle is a typical narrow-jawed arbrosaur. It is about 50 centimetres (1 l/2 ft) long but most of this is made up of the long tufted tail. The body weighs only a few grams. It is a very agile little creature, scampering along boughs and leaping from branch to branch with ease.








Hosted by uCoz