Dinosaur Hunter

by Steve White

  GEOGRAPHY AND ENVIRONMENT

  The Morrison Reserve is set beneath the foothills of the Front Range, a range of mountains that runs west then swings to the south-east. These mountains create rainfed waterways, including a number of large rivers that run to the north-east. Some of these actually interconnect with waterways draining off the Sundance Sea, an inland or epeiric arm running down from the polar north from the global Tethys Ocean.

  At the base of the Front Range foothills, where the Morrison FOB is based, the rivers, many of which run years long, create a lush floodplain. The rich soil of these deltas supports gallery forests of ginkgoes, podocarps and Araucarians (monkey puzzle trees), which keep their leaves all year round, and conifers not dissimilar to modern redwoods, which drop their needles at the start of the dry season. The forest understoreys are formed by tree ferns and cycads and their close relations; these are divided into slim, long-trunked types such as Williamsonia, that can grow to as high as 6–7ft; and the barrel-trunked types that look ostensibly like giant pineapples. The males of these types produce flower-like cones in the wet season. The ground covering is formed of varieties of fern and ground pine, while horsetails and scouring rushes grow densely along the edges of rivers and ponds.

  These forests support populations of mid-and high-browsing Sauropods, the most common of which is Camarasaurus; they also include the uncommon and truly giant Brachiosaurus. These are largely non-migratory, although Camarasaurs do follow the rains north-east into more open habitats.

  These well-watered floodplains give way to the Morrison Foredeep, the vast interior of the continent that is close to sea level and as such is poorly drained. The Foredeep is peppered with depressions created when the Earth’s crust warped and folded millions of years before. These depressions create large lakes and saltpans. In the wet season, many of these lakes and salt flats fill up, often preceded by violent flash flooding.

  The gallery forests of the floodplains give way to more open woodland the further you travel in to the Foredeep, much of which is covered by fern prairie, with the occasional hardy Araucarian and conifer to provide the only shade.

  During the wet season, the reddish soil turns green with thick coverings of ferns; this triggers a massive migration of herbivorous dinosaurs, including large herds of low-browsing Sauropods.

  However, the dry season leaves many watercourses parched, but some bayous and billabongs do remain watered through the year, and support local populations of hardier types, including Camptosaurus and Stegosaurus, and many smaller opportunist omnivores and herbivores such as the burrowing Drinker and Othnielia; the burrows of the latter two can be a real menace and have accounted for many a broken ankle. These herbivores survive by browsing on the few plants capable of toughing out the dry season, or by digging for the seeds and tubers left dormant in the soil.

  The big herds churn up the prairie so that once the dry season arrives, there is little left but a dust bowl; however, the herds do leave behind a rich compost of dung that provides fertilizer for the next generation of plants. By then, the herds will have dispersed and returned to the shade and cooler climes of the floodplain forests. Many species see out the dry season here, awaiting the rains that then trigger the rush to breed and fill the forests with hatchlings of many kinds and the fern prairies with crèches of young.

  LICENSED TARGETS

  You are licensed to hunt the following species in the Morrison:

  ALLOSAURUS

  A blood-soaked, fly covered Allosaurus stand ankle deep in sauropod guts.

  Length: 30ft

  Weight: 1,500–2,000lbs

  Allosaurus is the most common of the Morrison predators. This species is often ascribed to A. atrox, but confusion amongst the Allosaurus classification means that this is by no means definitive.

  By and large solitary, its body form is typical of most Carnosaurs; long tailed, shortish trunk and long, well-muscled neck. The skull is modest in length and while not as strongly constructed as in, for example, the Tyrannosaurs, the various bones of the skull are built to flex and bow, increasing the gape of the jaws (see below), and to withstand stresses imposed by struggling prey by flexing with forces exerted on it. The roof of the skull is thin (although Allosaurus generally holds its head horizontally, making a shot here problematic).

  Allosaurus is easily recognized by the lacrimal horns over the eyes; these are more pronounced in males where they function as sexual displays as well as shading the eyes, a useful function in its favoured habit – the open fern prairies and woodlands of the Foredeep. There is also a pair of raised ridges running from the tip of the snout to the lacrimal horns. These and the head in general have striking black, white and red markings in male Allosaurs; females also sport markings around the eyes and on the upper jaw, but they are not as pronounced.

  Allosaurus has large nostrils and sinuses incorporating Jacobson’s organs (vomeronasal organ or VNO); this gives the animal an excellent sense of smell. They do, however, lack the binocular vision of later Theropods, stereoscopic vision being limited to no better than that of a modern crocodile; however, this is perfectly adequate for gauging the range of prey and timing its attacks. It’s also possible that the more lateral placement of the eyes improves prey detection in the wide-open plains (a feature usually employed by herbivores to avoid predators!)

  Allosaurus’ hearing is focused on low-frequency sounds; this may help it detect the infra-sound created by Sauropods’ digestion and communication, or their heavy footfalls (Ornithopods produce similar if less pronounced noises).

  Allosaur teeth are classically modelled; large upper teeth and smaller lower ones. They are all serrated and have a blade-like construction. The jaws lack a strong bite force (less than a modern alligator) but can withstand powerful vertical forces and gape extremely widely. Although jaw muscles are generally reduced, the neck muscles are very powerfully developed. As such, while incapable of crushing bone, the jaws of Allosaurus operate very effectively as the serrated edge of a saw, cutting deep slashing wounds into prey when they are drawn violently back. Such wounds are generally not meant to kill but leave wounds that slow and disable larger prey.

  The long legs (in Carnosaur terms) make Allosaurus relatively fast – certainly faster than most of its prey items – with an average speed of around 20mph although it can perform quicker bursts of speed. The forearms are short but very well muscled and equipped with three fingers, each sporting a large, curved claw.

  All these features – the short serrated teeth, the flexing skull capable of withstanding trauma across the vertical axis, the wide gape, turn of speed, powerful forearms – make Allosaurus a very effective and active predator. Not an ambush predator as such, it stalks and chases prey, charging in and delivering slashing bites and wearing its victim down through shock and blood loss. Smaller prey such as Dryosaurs and Camptosaurs (its favoured food items) are sometimes dispatched in a single attack, the Allosaur using its superior weight and momentum to charge the prey down, then pinning it with powerful forefeet and arms. The victim is then dismantled across a vertical axis (like modern birds of prey), the head jerking upwards to pull the prey apart. The wide gape can remove huge chunks of flesh in one bite and Allosaurs consume large amounts of flesh in one sitting.

  Favouring the open fern prairies, Allosaurs are opportunist daylight hunters of smaller animals. Prey is less abundant than in the southern woodlands and gallery forests; this is especially true in the dry season when it will sometimes take on larger animals including Sauropods. Generally it favours juveniles and sub-adults but it has been known to attack full‑grown adults where it favours the smaller or lighter species such as Barosaurus, Diplodocus or Haplocanthosaurus. Such attacks are usually very long and agonizing affairs, with the Allosaur conducting a number of attacks over a period of days in the hope of eventually exhausting the Sauropod into fatal submission. Many Sauropods carry the scars of failed attempts.

  Allosaurus is also quite capable of taking on arm
oured dinosaurs. As it shares its habitat with Stegosaurus, this iconic dinosaur is regular prey for Allosaurs. However the Stegosaur’s famous ‘thagomizer’ makes it very dangerous prey and, as with larger Sauropods, attacks can be protracted and exhausting for both combatants; so adult Stegosaurs are taken only if the Allosaur is very hungry.

  Smaller Ankylosaurs such as Mymoorapelta are rare prey, living mostly in gallery forests as they do. However, some hardier species scratch out a living in the billabongs of the Foredeep. These tough little types are pugnacious and well armoured, and an Allosaur’s only hope of killing one is to flip it on its back – never an easy task at the best of times.

  Allosaurus is very territorial, with home ranges extending hundreds of square miles and usually centred on a permanent water source. Favoured territories are those that include migration routes for herds moving out into the Foredeep during the wet season. Male and female territories do overlap but they remain aggressive to one another outside of the breeding season. Intra-species battles are frequent occurrences, most often triggered by territorial intrusions but also by the contesting of kills, especially during the dry season when hungry adults are drawn to the circling pterosaurs that tend to gather over a kill. This is also the time when many juveniles and sub-adults may find themselves cannibalized by adults.

  The mating season is triggered by the arrival of the rains. Colours brighten at the season’s start in a male of breeding age; he will mate with all females who enter his range. Males roaring to attract a mate herald the start of the mating season.

  Pregnant females, especially those with overlapping territories, will gather into packs. They hunt together in a rare display of social behaviour which allows them to fatten up quickly before they dig out their nests together. Such colonial nesting allows for mutual protection from predators (including male Allosaurs). They can contain two to five females; this allows one or two to remain on guard duty while the others hunt. The eggs hatch very closely together. The chicks are precocial and leave the nest soon after hatching, the clutches forming a single crèche protected by the mothers. They stay together until the young fledge. The independent juveniles are long-legged; they are far faster than the adults and prey primarily on small, fast Ornithopods.

  While A. atrox is the one recognized species of the genus Allosaurus at this time in the Morrison, it is possible that a giant species is present, although this has yet to be verified. There have been scattered reports of huge Allosaurs in the foothill forests of the Front Range; these may be specialist giant Sauropod hunters previously described as Epanterias or Saurophaganax. However, they could be just very large specimens of A. atrox whose size has resulted in a behavioural change, allowing them to prey on the largest Sauropods that are restricted to the thick southern forests.

  TORVOSAURUS

  Portrait of a battle-scared Torvosaurus.

  Length: 30–35ft

  Weight: 2 tons

  The largest of the Morrison Theropods, Torvosaurus is also far less common than Allosaurus, being largely restricted to the deeper woodlands, gallery forests and foothills of the Front Range, although sub-adults have been seen far out in the Foredeep.

  While only slightly longer than Allosaurus, Torvosaurus is far more robust and rugged. Its head is long and narrow, with a slight kink above the nostrils. The teeth are blade-like, those in the premaxilla protruding slightly. There is a lacrimal horn but it is far less pronounced than in Allosaurus and Ceratosaurus, but does flair to horizontal, where it functions as an effective sun shade. The rest of the body is by and large typically ‘Theropod’ although the body is narrow (a feature that may help it navigate thick forest with greater ease) and the long tail is held stiff and high, acting as a counterweight to the large head. One distinctive feature of Torvosaurus is the large thumb claw carried on its short but robust forelimbs; this is not unlike the dewclaw in big cats and is used like a crampon to hook into prey or, in the case of males, to secure a hold on the female during mating. With this in mind, females also have thicker skin around their shoulders and the base of the neck. The dewclaw often leaves scars on the female Torvosaurus.

  Females are larger and more robust than the males. Both have markings across their bodies patterned in an ‘aeluroid’ style, with spots and speckles set in broad ‘clouds’ of colour to break up the animal’s silhouette when moving through the sun-dappled interior of woods and forests. The males, however have very pronounced ‘go faster’ flame-coloured markings on their heads, making them very recognizable.

  Torvosaurus is solitary except during the mating season. Its forest and woodland habitats have high prey densities year round: in the wet season, Camarasaurus and Brachiosaurus, and their young, and larger Camptosaurus species; in the dry season migratory Sauropods such as Apatosaurus and Haplocanthosaurus, the occasional Stegosaurus longispinus and even Ankylosaurs. This means that individual Torvosaur ranges aren’t as big as those of an Allosaurus out on the less prey-rich fern prairies.

  Primary prey for Torvosaurus is mid-to large-sized Sauropods, the most regularly taken being Camarasaurus, certainly the most common of the Morrison’s Sauropods. Typically an ambush predator, a Torvosaur’s primary strategy is ‘long-term pursuit and harassment’. It is mainly a daylight hunter but will use the fading light of dawn or dusk to cover attacks. Charging from cover, it will inflict long, deep wounds on its victim with its jaws and dewclaws, especially on the hind limbs, forcing the Sauropod to move more slowly and fall behind the relative safety of the herd. The Torvosaur stays close and over a period of days inflicts more and more bites, steadily weakening the prey until it is able to start feeding, usually while the shocked prey is still alive. (This is usually the best tracking strategy in finding a Torvosaurus: follow the blood trails and where possible, find the injured prey and stay with it until the Torvosaur makes another attack.)

  Torvosaurs breed in pairs that could be life-long matings although this needs further study. The female seems to live in the same broad territory that overlaps with several males; the one she chooses to breed with stays with her to raise the brood of chicks, both sharing nesting and hunting duties. The chicks are less precocial than in Allosaurus and Ceratosaurus, staying in the nest where bigger chicks will kill and cannibalize the smaller ones.

  Raising chicks sees adults broaden their menu to incorporate anything they can catch and kill; hatching is usually timed to the mass Sauropod hatchings, when small prey is abundant. Torvosaurs are opportunist scavengers, driving other predators from their kills as frequently as possible, but during the breeding season they make much greater use of their more muscular frames and aggressive temperaments.

  On leaving the nest, the chicks are attended by both parents until they fledge, at which point the adults abandon them and return to a solitary existence through the long dry season. The fledgling Torvosaurs follow the young Sauropods into the deeper forest, although they are as likely to fall prey to small Carnosaurs and to Coelurosaurs such as Ornitholestes.

  CERATOSAURUS

  Ceratosaurus, the rarest and most enigmatic of the Morrison’s Big Three.

  Length: 20ft

  Weight: 1,300lbs

  The third in the triumvirate of great Morrison predators is also perhaps the most enigmatic; it is certainly the rarest and, with its impressive head ornamentation, the most sought after.

  Generally restricted to deep forest and open woodland, Ceratosaurus could also be termed semi-aquatic, spending far more time in water than any other non-crocodilian predator, and including in its menu large fish (especially giant lungfish) and crocodylomorphs of many kinds, both terrestrial and semi‑aquatic types. It will also take large prey, such as small Sauropods, Camptosaurs and Stegosaurs.

  Ceratosaurus is easily recognizable by its distinctive flattened nose horn at the end of its snout. There is also a pair of hornlets over the eyes not unlike those in Allosaurus. These horns are not just for show and for shading the eyes. In Ceratosaurus, the horn is used in intra-speci
es battles, mainly between the males during the breeding season, following highly stylized and noisy threat displays.

  The roughly rectangular head is armed with rows of very large teeth; these can not only inflict ghastly slashing wounds in large prey but are also useful in snaring more slippery aquatic prey as well as puncturing the armoured scales of the biggest lungfish.

  Ceratosaurus is unique amongst the large predators in that it will hunt by night; as such its vision and sense of smell are acute. Its long body and longer, deep and flexible tail are ideal for weaving through thick forest but also make Ceratosaurus an excellent swimmer. The spine is marked with a line of oestoderms – raised scales that run the entire length of its body, from the base of the skull to the tip of the tail. The legs aren’t particularly long and it is not built for speed; the arms are very small and carry a reduced fourth finger.

  Sexual dimorphism in size and build is generally less exaggerated than other Theropods, but the male is strongly marked, the body a blue-black with white stripes, and white socks on the lower legs and the head. The female is a rich brown or tan and has fewer stripes.

  Mating season for Ceratosaurus takes place at the end of the dry season. The male’s sperm is retained in the female’s cloaca until the rains arrive, when the eggs are fertilized. She then builds a large nest mound, usually close to water, into which she lays the eggs then guards them until they hatch. Ceratosaur eggs gestate longer than other Theropods and the young are born precocial. They are abandoned very quickly by the female but the young can swim from an early age and will eat anything they can catch, from insects to small fish, frogs and salamanders and even other baby dinosaurs. They therefore have very large and effective teeth from a very young age.