Ceratosaurs

Whereas the Herrerasauridae (Sect. 9.1) are known only from the Late Triassic of South America, the Ceratosauria was a much larger group that persisted from the Late Triassic to the Upper Cretaceous period. Possibly, the oldest ceratosaur genus known so far is Coelophysis (Fig. 117; family Podokesauri-dae) of which many well-preserved specimens have been found in Connecticut and New Mexico. They are of all ages - from newly hatched babies to full-grown adults. However, the latter only measured ca. 3 m in length and about 1 m in height, which is small for a dinosaur. Built for speed with light, hollow bones, they probably weighed little more than 20 kg. They were highly active

■ Fig. 117. Coelophysis (Podokesauridae; Upper Triassic; length ca. 3 m)

predators with pointed heads and sharp, serrated teeth. Their long, slender hind legs had bird-like feet and three toes, each with sharp claws. There were four fingers on the hands, but only three of these were strong enough to grasp prey (Charig 1979). These ceratosaurs probably chased almost anything that moved, including the early shrew-like mammals, as they roamed the upland forests hunting in packs close to streams and lakes. Two of the adult skeletons from New Mexico contained the bones of tiny Coelophysis in their bodies. This was initially thought to indicate that the animals were ovoviviparous, but their hip bones were too narrow for this to have been the case. The only explanation is that these dinosaurs were cannibalistic. Since cannibalism is widespread among animals of all kinds, it is not surprising that it should have been practised by at least some theropods (Currie 1997a).

Another member of the Podokesauridae, Procompsognathus (length ca. 1.2 m) was a rapacious little theropod which inhabited the deserts of northern Europe during the Upper Triassic. It would have chased its prey, consisting of insects, lizards and the like, on its long legs. It ran with only three of its four toes touching the ground. Each hand had five fingers. This is a primitive feature, since the evolutionary trend was toward fewer fingers and toes (Palmer 1999). Its diminutive relative Saltopus was only ca. 60 cm in length and probably weighed as little at 1 kg. Saltopus still retained five digits on each hand, although the fourth and fifth were reduced. It was more advanced, too, in its skeletal structure. Only a single specimen has been found, however, and it is possible that this animal was not a dinosaur but a non-dinosurian archosaur (see Benton 2004).

Maniraptora

The remaining families of ceratosaurs (Division Maniraptora) shared a number of characteristics with birds. As the name suggests, these are especially evident in the fore limbs, and the class Aves is actually included within the Maniraptora (Sect. 11.5). The family Coeluridae flourished from the Upper Jurassic to the Lower Cretaceous. Coelurus ('hollow tail') from the Upper Jurassic (length ca. 2 m) was an active, highly cursorial predator that inhabited the forests and swamps of North America. Its long arms and hands with three clawed fingers could have grasped small animal prey and the eggs of other dinosaurs.

Compsognathus (Fig. 118; family Compsognathidae) from Europe was a contemporary of the coelurids and resembled them closely. It had typical hollow bones, a long neck and tail, two forceps-like fingers on its short arms, and long, slender legs with three long clawed toes pointing forwards and a small fourth toe projecting backwards. Measuring only ca. 60-90 cm in length - not much larger than a chicken - it probably weighed only about 3.6 kg. Its long skull was unusually large in relation to the size of its body. The first specimen to be discovered was found in a lithographic limestone quarry in Germany, in 1861. The fossil was very well preserved in fine-grained sediment. Compsognathus may have lived on insects, scorpions and small reptiles as well as vegetable matter. Part of the skeleton of a lizard (Bavarisaurus) can be seen in the gut region of the

■ Fig. 118. Compsognathus (Compsognathidae; Upper Triassic; length ca. 60 cm)

holotype of Compsognathus longipes (Chin 1997). Judging by the proportions of the limbs and its long tail, John Ostrom in 1978 deduced that Bavarisaurus must have been an agile and speedy ground-living lizard. In order to catch prey such as this, Compsognathus would of necessity have possessed keen sight, speed, manoeuverability and rapid reactions (Norman 1985).

Sinosauropteryx (Fig. 126a; Compsognathidae), one of the first of the feathered dinosaurs to be discovered, was found in the same region of China as Pro-tarchaeopteryx, which was also a 'dino-bird' (Sect. 11.5). Although very similar to Compsognathus, Sinosauropteryx was slightly larger (ca. 1.2 m long) and an equally effective predator. Fossilised stomach contents included a lizard and a small mammal.

The Oviraptoridae, a small family of toothless therapods, lived in eastern Asia during the Upper Cretaceous. Oviraptor (Fig. 104) was a typical mani-raptoran ceratosaurian. As we have seen (Sect. 9.3.3),it has probably been misnamed and could even have been a herbivore (Sect. 10.1). Its short parrot-like beak and powerful jaws might have been adapted for shearing fibrous plant tissues, as well as cracking thick-shelled dinosaur eggs (Norman 1991) and crushing the shells of molluscs. However, Currie (1997a) argued that although they were clearly adapted to produce powerful bites, the beaks were hollow and filled with air. They would not have been suitable for crushing thick molluscan shells and, in any case, oviraptorids were most common in semi-arid and arid environments. The sharper claws and body proportions of Oviraptor suggest that it would have preyed on smaller animals such as lizards and mammals, these to be swallowed whole. The most likely possibility seems to be that, as with members of the ostrich-like Ornithomimidae, Oviraptor was omnivorous, feeding upon anything, animal or vegetable small enough to be swallowed without being chewed.

The Ornithomimidae was a specialised dinosaur family that evolved from the coelurosaurs at the end of the Jurassic period. Their toothless jaws were long and slender - quite unable to produce enough power to tear carcasses apart or kill anything but the smallest animals. It has long been assumed that they were omnivorous and fed on invertebrates, small vertebrates, eggs and easily digested vegetable matter, including fruit, berries and seeds. The best-known genera are Ornithomimus and Struthiomimus from the Upper Cretaceous of North America,both of which were ca. 3.5 m in length. Ornithomimus inhabited dense cypress swamps and forests. It would have sprinted with its body parallel to the ground and balanced by its long, stiff, outstretched tail. Its neck would have curved upward in an S-shape - as would the necks of most bipedal dinosaurs - so that it could see ahead, while its arms dangled in front ready to grasp any potential food item. Struthiomimus existed slightly earlier than Ornithomimus. Its arms were longer and it probably hunted along river banks in more open country (Palmer 1999).

The largest of the ornithomimids was Gallimimus (Fig. 119) from Mongolia, which measured ca. 4 m in length. All the 'ostrich' dinosaurs appear to have been extremely fast, with big eyes and large brains. Those of Dromiceiomimus

■ Fig. 119. Gallimimus (Ornithomimidae; Upper Cretaceous; length ca. 4 m)

were proportionately larger than the brains of any modern land mammals other than primates. There is still no consensus as to the feeding habits of the ornithomimids. Some authors consider them to have been predators, others have argued that they might have been herbivorous. I think this to have been far less likely. Barsbold and Osmolska (1990) considered that some of them were moderately fast, wading animals, moving about on spongy substrates and feeding upon fishes and molluscs. Dromiceiomimus probably hunted after dark, chasing lizards and small mammals through the deciduous woodlands in which it lived (Palmer 1999). In a review of the theropods, Currie (1997b) suggested that the ornithomimids were the fastest of all the dinosaurs. Like ostriches (Struthio camelus), they could probably run at speeds up to 80 km/h, according to Currie (1997a), though this figure has been disputed.

Dromaeosaurids

The family Dromaeosauridae comprised some of the most ferocious predatory dinosaurs of the Cretaceous period. Not only did they have the lightweight bodies and speed of the early coelurosaurs, from which they probably evolved, but they possessed much larger brains and huge sickle-shaped killing claws on the second toe of each hind leg (Sect. 9.12). As early as 1964, J.H. Ostrom suggested that they might well have hunted in packs, rather as Cape hunting dogs

(Lycaon pictus) do today. Deinonychus (Figs. 86,87) and Velociraptor (Fig. 92) have already been mentioned in this context.

When dromaeosaurs were running, their killing claws were flicked upwards and held clear of the ground while the body was poised horizontally and balanced by the outstretched tail. This was kept rigid by bundles of bony rods growing from the vertebrae. It is essential to maintain balance when standing on one leg and striking the prey with the other, and this is assisted by having a stiffened tail (Sect. 7.3).

The discovery in Manitoba of five complete skeletons of Deinonychus beside that of a Tenontosaurus (Fig. 111) may well be those of a pack of these predators, killed by some chance event whilst attacking the large herbivore. Alternatively, of course, the assemblage of bodies might have been accidentally brought together after death, perhaps washed down by a flood into a hollow or river basin (Palmer 1999). The possible predatory attack has been superbly reconstructed in a drawing by John Sibbick in Norman (1985). Sibbick also illustrated, in a sequence of drawings, how an individual Deinonychus might have hunted fleet-footed prey, such as Hypsilophodon (Fig. 111), by leaping onto their backs, subduing them with arms and teeth and administering the coup de grâce with the killing claws.

Troodontids

Although smaller and lighter in build than dromaeosaurs, the Troodontidae (= Sauronithoididae) were also fast, intelligent predators. Sauronithoides (Fig. 120) from Mongolia is credited with having been one of the most intelligent of the dinosaurs. (Another is Stenonychosaurus, a member of the same

■ Fig. 120. Sauronithoides (Troodontidae; Upper Cretaceous; length ca. 2 m). (After Cloudsley-Thompson 1977 after Russell 1971)

family.) The bird-like skull of the troodontids, long, low and light in weight, contained a relatively enormous brain. Sauronithoides evidently had fast reflexes and well-developed senses. Its eyes were huge (ca. 15 mm diameter) judging from the size of the sockets. This indicates that the animal was probably a crepuscular or nocturnal predator, as were the other members of the family. Moreover, the position of the eyes on the skull suggests the possession of binocular vision (Sect. 9.3.1) and all that this implies. The troodontids had sharp teeth, serrated on the posterior edges, and a slightly enlarged claw on the second toe, which was normally folded back. This would have been used in defence, and also to slash potential prey such as lizards and small mammals.

Therizinosaurids - Segnosaurs

The known remains of these enigmatic dinosaurs from Mongolia and China consist of the incomplete skeletons of at least four genera. The therizinosaurids ('scythe lizards') or segnosaurs were most unusual theropods, ca. 3-7 m long with a massive pelvis and short tail. They had long hind legs with four-toed feet while the arms, which were shorter, bore hands with three elongated fingers and enormous sickle-like claws. The best fossil of Therizinosaurus consists of a huge arm, 2.5 m in length with claws 0.7 m long. This does not include the horny part of the claw, which would have made it even longer. The neck was powerful, but the skull was small, with weak, peg-shaped cheek teeth and a toothless beak in front.

■ Fig. 121. Alxasaurus (Therizinosauridae; Upper Cretaceous; length ca. 7 m)

Because many of the fossils were associated with aquatic environments, the segnosaurs were at one time thought to have been piscivorous. The suggestion has also been made that the claws were formidable weapons for slashing through the skin of their prey, or even for tearing termitaria apart like the claws of anteaters (Myrmecophagidae). The discovery of Alxasaurus (Fig. 121) in China, however, provided information suggesting that the therizinosaurids were more probably leaf eaters like giant ground sloths (Megatherium). Perhaps they sat, balanced tripedally on their rear limbs and tail, raking tree branches with their claws and passing them to their toothless beaks (Maryanska 1997). This is how they are illustrated in Fig. 121 (see Blount and Crowley 2001).

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