by Steve White
Lowland Gorgosaurs are more solitary, the dense forests offering greater success to them as ambush predators. This community of Tyrannosaurs preys primarily on sub-adult Hadrosaurs and young Ceratopsians.
The breeding season for Gorgosaurus begins at the end of the dry season (roughly equivalent to that of their Hadrosaur prey); it is usually preceded by disputes between young, territory-less males and those with established ranges. This usually results in the death and injury of many Gorgosaurs but the victors have little time to recover as they have to attract females, usually with vocalizations and, once a female is in range, a visual display of strength.
Pairs stay together for the entire breeding season, raising the brood of 10–20 pups that grow (dependent on food supply) with astonishing rapidity. Nest sites depend on environment; a more sheltered position is preferred but on the high plains, Gorgosaurs will nest in the open, especially if close to a Hadrosaur colony. While raising the young, one parent is always in attendance; at this time, they will take easier, more manageable prey that can be brought back to the nest or easily swallowed and regurgitated for the pups. Most favoured are young or sub-adult Hadrosaurs, but as the nesting season progresses and the adult duckbills become increasingly exhausted from the extended distances they are forced to travel in feeding their own litters, a single adult Gorgosaur will risk tackling an adult if it is wounded, sick or weak.
After leaving the nest, the young are long-legged, lean, downy but big-headed and, proportional to the adults, big-toothed. Though not as quick as ostrich dinosaurs, they are considerably faster than their parents and can outrun most other smaller dinosaurs, especially the young of other species that form the bulk of the pup’s diet.
The first five years of a Gorgosaur’s life are lived out as an extended childhood in the form of a small juvenile, living in forested areas and preying on insects and small vertebrates, stealing eggs and, as they are quite capable swimmers, even fishing. Few survive this early stage, but those that do suddenly transition to the non-breeding sub-adult that fulfils the ecological role between Tyrannosaur adult and the small carnivores. In this niche, they have proportionally very large teeth, but again this is a particularly tough age when they are more likely to encounter cannibalistic adults and other larger predators, as well as far more aggressive prey. Few survive this period (of roughly four years) without injury. To help them through this time of transition, the sub-adults will sometimes congregate into small packs, usually of a single sex. This is the period when they develop their hunting skills and spend a great deal of time fighting one another.
Following this growth spurt, the sub-adults fledge and become sexually mature and continue to grow but at a much slower rate until they reach full size at about 15 years of age in the females and 20 years in the males.
DASPLETOSAURUS
Length: 30ft
Weight: 3 tons
As widely distributed but not quite as common as Gorgosaurus, Daspletosaurus is by far the more rugged and robust of the two Tyrannosaur types of Dinosaur Park. Broadly similar to its more lithe counterpart in body plan, its primary differences, aside from colouration, are slightly shorter legs, but longer forearms and a more massive head with a blunt snout – if Gorgosaurus looks like a runner, Daspletosaurus looks like a brawler using strength rather than speed. It does have pronounced lacrimal horns similar to those of Gorgosaurus.
The tougher build is attributable to its primary prey item: horned dinosaurs. These rhino-to elephant-sized herbivores are well armed and have the attitude to go with their array of horns, shearing parrot-type beaks, power and speed. To hunt them requires an equally aggressive temperament and rugged build.
Daspletosaurus is perhaps the most ‘tactical’ of Tyrannosaurs. It is first and foremost an ambush predator, which does restrict its hunting ranges to areas that provide plenty of cover. It will also hunt regularly in pairs; one often acts as a decoy while the other employs classic ‘land shark’ tactics, bursting from cover to deliver a serious wound then retiring to safety to let shock and blood loss do their work. These are very simple manoeuvres – hardly the work of a pride of lions – but they are effective, if dangerous for the ‘decoy’. Unless the wound is particularly grievous or immobilizing, a wounded Ceratopsian is as likely to be enraged and charge the decoy, who may find itself in a fight for its life. Accordingly, the ambushing Daspletosaur targets the hind legs – a ‘mobility’ kill – that slows or even immobilizes the prey. The Tyrannosaur may not be as fast as a Gorgosaur but is nimble enough to duck, for instance, the horns of a wounded Styracosaurus.
As is often the case with Theropod hunts, one bite is invariably not enough and the long, arduous process of bringing down large prey begins. The pair of Daspletosaurs may also have to face not just the wounded prey but also other Daspletosaurs, alone or in pairs, attracted by the scent of blood, who contest the kill. Life is therefore extremely tough for this species; many sustain injuries not just from their particularly pugnacious prey but also from intra-species fighting.
Lowland communities of Daspletosaurus principally feed on Ceratopsians, although they will hunt duckbills and any large animal, even Ankylosaurs, should the opportunity present itself; they will also drive Gorgosaurs from their kills (another source of regular injury). On the high plains, where there is less cover, Ceratopsian hunting is restricted to riverine forests and open woodland with dense understoreys. Daspletosaurus will hunt in more open environments but in this case duckbills are the primary prey and, unlike Gorgosaurs, they are quite willing to take on fit and fully grown adults.
Some Daspletosaur communities are known as ‘transients’; these are migratory and follow those species that progress along the north–south highways, principally the highland species such as Einiosaurus; the transient Tyrannosaurs also nest alongside their prey, in the polar ranges at the start of the growing season. This occurs with the lengthening daylight at the start of the southern dry season. Further south, ‘local’ populations nest earlier, midway through the wet season when many of the less-migratory lowland Ceratopsians, such as Styracosaurus and Chasmosaurus, form into large herds and nest in colonies at the edge of the high plains and more open woods.
Sub-adult and sexually immature adults are even more migratory; they fuel their growth by staying in the lowlands at the start of the wet season to hunt around the forest-living species; this fuels a journey to the north in time for the polar breeding season. They then follow the herds back south in time for the dry season, preying on the young, the sick and the exhausted, sometimes forming loose coalitions that enable them not just to practise their hunting skills but also to defend kills from aggressive adults; males will also find themselves targets for fully grown bulls, keen to drive off or cannibalize future competition.
Pairs mate at the end of the dry season but nest later into the wet season. This allows them to hunt around the colony when the adults have often stripped away the good foliage, requiring them to travel further for food for their young. This means many nests are often left unguarded, providing easy pickings, while many adults are exhausted enough to find themselves easy kills for the Daspletosaurs.
When the Ceratopsian superherds form up once the young are old enough to leave the colony, Daspletosaurs similarly leave the nest and the family group follow the herbivores; in the lowlands, the huge numbers of horned dinosaurs, especially the young, make this a happy time for the Tyrannosaurs. For those migrating south, there is similarly a large number of young to pick off, including the sick and large numbers of strays. There are also sub-adults and old adults who make easy prey for ambushes set up by the Daspletosaurs ahead of the herd, usually in riverine forests.
At the start of the dry season, the young are abandoned, usually in the sanctuary of the deep forests. The growth rates of Daspletosaurus follow those of Gorgosaurus, with an extended juvenile phase for the first five years, followed by a rapid growth spurt to sub-adulthood then reaching sexual maturity at about 15 years old.
Sub-adult Daspletosaurs hunt smaller Ceratopsians such as Prenoceratops or Avaceratops. These are prickly customers for a young Tyrannosaur, aggressive and very tough. Some also sport small horns, but all have a powerful beak that can deliver a nasty bite. These smaller versions of the huge Ceratopsians provide the young Daspletosaur with ideal opportunities to fashion their hunting tactics, although many fail the test; a Prenoceratops beak can crush a fragile shinbone and the horns of an Avaceratops, no matter that they look paltry compared to the nasal core of a Styracosaurus, can stave ribs or crack jaws.
The Tyrannosaur, Daspletosaurus, is threatened by an angry, quiff-tailed horned dinosaur, Einosaurus.
But, alongside the sub-adult, sexually immature Gorgosaurs, these young Tyrannosaurs fulfil the ecological niche that falls between the small raptors and Troodonts, and the adult Tyrannosaur. At this stage in their life, they prey mainly on animals smaller than themselves (including juvenile Tyrannosaurs) before undergoing a major change in their body plan and lifestyle.
A HORNED DINOSAUR OF YOUR CHOICE
Dinosaur Park plays host to a large number of horned dinosaurs or Ceratopsians, both as resident populations and as migrants passing through. Species are also particular to some environments.
The horned dinosaurs are split into two families, the Centrosaurines and the Chasmosaurines. The former include Coronosaurus brinkmani, Einiosaurus, Styracosaurus, Achelousaurus and Pachyrhinosaurus lakustai; the latter is represented by Chasmosaurus irinensis, Anchiceratops and Vagaceratops.
Centrosaurines have a number of defining features; they are all, on average, 17ft long (Einiosaurus is about 14ft while Achelousaurus is about 20ft) and weigh around 2 tons. All have highly distinguishable nasal ornamentation, usually a long horn or, in the case of Achelousaurus and Pachyrhinosaurus, a boss; Einiosaurus is easily recognizable by its nasal horn, which actually curves forward over its beak. The headfrills that are one of the most recognizable characteristics of the Ceratopsians are smaller than those of the Chasmosaurines, but are lined with the epiparietal scutes seen on virtually all horned dinosaurs. However, in many Centrosaurines, these scutes have developed into an array of horns that rise from the top of the shield. Usually it is just a pair, but in the case of Coronosaurus, these hornlets are bent forward over the shield and surrounded by a cluster of smaller ornamentations. The most extravagant is, of course, Styracosaurus, whose array is a striking fan of horns. Combined with the 2ft-long nasal horn, and the bold markings on its shield and face, this particular species is the most awe-inspiring of the Dinosaur Park Ceratopsians.
Centrosaurines are also the most numerous horned dinosaurs, in some cases travelling in herds of hundreds, even thousands of animals. They are also the most visible, roaming the high plains and open woodlands, or in some cases, passing through the reserve during mass migrations to and from northern regions where some species (Pachyrhinosaurus, Einiosaurus, Achelousaurus) nest.
Chasmosaurines are rarer, with more localized populations; they live in small herds or singularly, in deep forest, marshes and coastal estuaries. These species tend to be smaller than Centrosaurines, around 14ft in length and weighing about a ton and a half. They also tend to have far more flamboyant frills that are much longer and broader, and far more colourful. They are also lined with extensive epiparietal scutes; in this family they do not develop into horns although, in Vagaceratops, they do extend forward at top edge of the frill; these features, combined with the frill itself, form a very impressive shield.
Combined with the nasal weaponry and powerful shoulders and elbows, Centrosaurines are pugnacious adversaries for Tyrannosaurs and each other; they have a slightly unusual semi-sprawled gait, the elbows at a slight angle to the body and the forefeet a little further out from the midline than the hind ones. However, this provides a lot of charging, pushing and shoving power. Centrosaurines are stabbers rather than wrestlers and many adults, especially males, carry scars from often-serious injuries on their faces, shields and flanks.
Chasmosaurines lack the large nasal horns or bosses. Instead, they tend to have small brow horns and a small nasal horn, the exception being Anchiceratops, which has a long pair of brow horns and a large nasal horn not unlike Triceratops.
Generally, though, Chasmosaurines prefer prevention rather than cure; their shields are beautifully coloured and serve to warn off rivals and predators; their environment also tends to make more affirmative action a problem; charging in swamps or marshes, or amongst densely packed trees, is not easy so they prefer to keep trouble at arm’s length, which could explain why the Chasmosaurines lost the need for impressive horns. However, their warnings are not all bluff; Chasmosaurines are just as aggressive as their Centrosaurine relatives and if it comes to a fight they will fight, although they tend to use their powerful beaks. In intra-species battles, the smaller horns are still used in battle, the fighting more a wrestling contest than the fencing ones of the Centrosaurines.
No matter the family, all the horned dinosaurs possess a powerful parrot beak that usually ends in a sharp tip; they have no teeth in the front of their jaws but at the back these form dense shearing batteries covered by cheeks. Beak size and jaw length tend to determine ecological niches; a number of Centrosaurines, including Coronosaurus, are generalists; other high plains species (Einiosaurus, Achelousaurus) are low-and mid-range browsers, while the likes of Styracosaurus are low-browsers, feeding on woodland and forest understoreys.
Chasmosaurines, with their longer jaws and delicate beaks, tend to be more refined feeders, probing deep into the forest undergrowth and grazing on water plants; they will also chop down reeds and shear off bark. All members of the family could also be classed as semi-aquatic, quite comfortable as they are in water and mud.
Local species of Centrosaurine Ceratopsians all follow the same breeding season, gathering into herds at the end of the dry season; where courtship and mating occurs. This can lead to some spectacular battles between the bulls, who are larger than the females – one of the signs of physical dimorphism between the sexes, the other being the more strident colours on the faces and shields of the males. However, these colours fade after the breeding season and telling the sexes apart can be quite difficult.
Lowland species move out of the dense forests into open woodlands and the edge of the high plains to nest at the start of wet season; reliant less on grazing and more on tougher foliage, they mainly stay close to the dense understoreys but will low-browse fern meadows when it is abundant.
Other species, such as Pachyrhinosaurus and Einiosaurus, use the abundance of the wet season to fatten up; as the season draws to a close, small herds gather in huge numbers to form ‘superherds’; these herds travel up ‘highways’ along the high plains and coastal routes along the edge of the Western Inland Seaway. As the days lengthen in the sub-polar regions, and the short growing season begins, the migrants nest.
All large Centrosaurines nest colonially. They tend to build simple nests scraped in the ground and lay about 20 eggs. Both parents tend to the young, bringing back wood pulp and vegetation for the sluggish young who put all their energy into growing quickly. Once big enough to travel, the young’s rate of growth slows down and the herds reform. The sub-adults and immature individuals stay together for mutual defence while they browse on the wet season growth. However, they join the adults and new calves to once more form superherds. These are not structured like mammalian herds but are loose aggregations, the young staying together in crèches protected by all the adults.
Chasmosaurines nest in smaller colonies, using cypress domes, meadows or sand spits. Again this is for mutual protection but unlike Centrosaurines, once the young are old enough, they head into the dense forest understoreys and marshlands. In a curious twist, the juveniles of Chasmosaurus and Vagaceratops also sprout large brow horns which then greatly reduce as they approach adulthood. These could make the young look more intimidating to smaller predators and provide more active defences that are replaced by overa
ll size once they enter their near-adult phase.
The young of both families adopt a more omnivorous diet, like small Ceratopsians, and will also scavenge.
OTHER FAUNA
SMALL CARNIVORES
There are a number of small carnivores that inhabit the Dinosaur Park Reserve, each with a more or less unique ecological niche.
The smallest is Hesperonychus. With most of its 3ft length taken up with tail, this tiny Microraptorine is arboreal, spending much of its time in the trees and shrubs. A social animal, it travels in small troops; the down of its tail is brightly marked in strips and used as a signalling device between the troop members. In many ways it fulfils the role of a small monkey, and eats a similar diet: insects, small vertebrates, the eggs and chicks of birds and small dinosaurs, and even fruit.
Bambiraptor is a common raptor frequently seen in the woods and high plains, where it functions as a generalist predator. About 4ft long and 30lbs in weight, it is well armed, with a battery of sharp teeth in strong jaws, each hand with three fingers equipped with long claws, and a well-developed sickle claw on each of its hind feet. This battery of weapons enables it to take on a broad spectrum of prey animals, from insects to small Ceratopsians and Protoceratopsids, and juvenile Hadrosaurs. It is also an opportunistic scavenger, bold enough to steal from much larger predators, and, during the wet season, will even take Tyrannosaur eggs if the opportunity presents itself.