Weapons of Attack

The offensive weapons of predatory dinosaurs, including the so-called carno-saurs (Sects. 11.1,11.3.2),were primarily their sharp, inwardly curved, and serrated teeth (Fig. 85). Especially in the case of bipedal forms,however,the action of these teeth was often supplemented by forelimbs which grabbed the prey while it was being bitten. In numerous cases, curved jaws helped to hold the struggling prey securely. Many predators also had formidable claws that were used to slash the bodies of their prey. For instance, the Early Cretaceous thero-pod Deinonychus ('terrible claw'; Figs. 86,87) from North America, like other members of the family Dromaeosauridae, was equipped with vicious claws on its hind legs with which it could easily disembowel other dinosaurs. So, too, was Velociraptor (Sect. 9.2.2).

■ Fig. 85a-c. Carnivorous dinosaur heads (not to scale). a Teratosaurus (Upper Triassic), b Allo-saurus (Upper Jurassic), c Tyrannosaurus (Upper Cretaceous).The apparent similarity is the result of convergence in diet and mode of life

The use of weapons by extant animals is invariably supplemented by numerous behavioural and ecological attributes. Similar attributes can only be inferred among fossil forms. For instance, cryptic coloration not only enables potential prey to avoid the attention of predatory enemies, but may also make it possible for the latter to creep upon their victims, unnoticed until the final attack is delivered. By living together in herds, potential prey animals may be relatively safe from attack by predators and also protect their young. Again, by

■ Fig. 86. Deinonychus (Dromaeosauridae; Lower Cretaceous; length ca. 3.5 m). (Cloudsley-Thompson 1999 after Halstead and Halstead 1981)
Ankylo Fossil Fighters
■ Fig. 87. Deinonychus attacking a herbivorous sauropod. (Adapted from a drawing by Steve Kirk in Brochu et al. 2000)

hunting in packs, smaller predators are able to overcome prey that they could not possibly subdue on their own. Consideration of these and other such matters will be deferred until subsequent chapters, but they must always be taken into account.

Defensive Weapons

The first line of defence among animals that have been detected by a formidable enemy is usually to react by flight. This tactic was undoubtedly employed by most, if not all, of the smaller and more speedy dinosaurs.

Animals that are less agile and cannot move quickly, however, often rely on their armour for defence. This was the case with Mesozoic Testudines, as it is with extant turtles and tortoises. It was also true of the placodonts, the ankylo-saurids, nodosaurids and other armoured dinosaurs, as well, to a lesser extent, of the crocodilians which then, as now, had thickened dorsal plates.

Dinosaurs had thick, tough, scaly skin. Their scales were rounded or took the form of tubercles. Large, flat tubercles covered the under surface of the body while, in some ceratopsians and hadrosaurs, the back was coated with rows or clusters of pointed tubercles. Bony plates lay beneath the armoured skin of the ankylosaurs (Ornithischia; Fig. 88) and of the titanosaurid sauropodomorphs in the Cretaceous period.

Anatomical structures that may well have been weapons have been found in the fossils of many species of dinosaurs, but the ways in which they were used remain a mystery. Alexander (1997a) pointed out that no modern animals have weapons like the half-metre spikes on the tail of Stegosaurus (Fig. 71), or the heavy bony clubs on the tails of some ankylosaurs (see below).Were these used in defence against predators, in fights between rival males, or both? Probably both!

■ Fig. 88. Scelidosaurus (Scelidosauridae; Lower Jurassic; length ca. 4 m) being inspected by an early carnosaur

Four-legged ornithischians evolved increasingly effective body armour during the Mesozoic Era. Scelidosaurus (Fig. 89), one of the earliest and most primitive members of the group, had a small head and toothless beak. However, its massive body was well armoured. The back was covered in parallel rows of bony, spike-studded plates that resembled those of the ankylosaurs, to which it may have been related, and that ran from the neck to the tip of the tail. The stegosaurs (Fig. 71) not only had bony plates or spines on the back, but spines also on the shoulder and tail (see below). We have already seen that the dorsal spines probably had an important thermoregulatory function (Sect. 7.5.2). It is not yet known for certain whether these were covered with horn, which would indicate that they were also defensive weapons, or more probably were covered with a thin layer of vascular skin. The bodies of the ankylosaurids (Fig. 89) were undoubtedly sheathed in bony plates and spines covered with horn, while the nodosaurid

■ Fig. 89. Dyoplosaurus (Ankylosauridae; Upper Cretaceous; length ca. 7.5 m). (Cloudsley-Thompson 1994)

ankylosaurs had long spines on their flanks as well. Finally, many ceratopsians (Fig. 72) bore horns on their nose and brows, while their necks were covered with horny, protective frills.

Claws were used in defence as well as offensively. Diplodocus (Fig. 66), for instance, had enlarged thumb claws with which no doubt it could defend itself from the attacks of predatory carnosaurs. These claws were used in addition to its whip-like tail (see below). The claws of predatory dinosaurs would not only have been used for the capture of prey but also in defence against larger enemies.

The tails of dinosaurs were usually held above the ground when the animals moved about. Long, stiffened tails balanced the necks and heads of the bipedal dinosaurs as they ran. Elongated tails also balanced the necks and heads of the four-legged prosauropods and sauropods. Many modern reptiles, especially monitor lizards (Varanidae) and crocodiles, use their tails as weapons. Dinosaurs undoubtedly did the same. The fossilised tail bones of apatosaurs, in particular, often show signs of fracture, doubtless engendered by their use as gigantic whips in defence against predatory theropods. Short, thick tails characterised the four-legged, horned dinosaurs. Like the long tails of the sauropods, these would not only have served as props when their owners reared up to browse, but were also useful as weapons: Stegosaurus (Fig. 71) probably jabbed its tail spikes at predatory carnosaurs. Its tail could swing freely because it lacked the bony tendons that stiffened the tails of most ornithischians. Dyoplosaurus (Fig. 89) would also have swung its tail sideways at the enemy. Bony outgrowths at the tip of the tail converted this into a formidable club or mace, an adaptation first seen in the sauropod Shunosaurus, but better developed among the armoured ankylosaurs (Figs. 90,116). In these, bones embedded in skin were fused with the tail vertebrae (Lambert 1992).

Some of the most striking developments in defensive weapons evolved among the horned Ceratopsia (Dodson 1996). Of these, the best known species is probably Triceratops horridus (Fig. 72). In addition to its heavily armoured collar, it bore three sharp horns on its head. Over a dozen species in the genus Triceratops have already been described. Other genera of horned dinosaurs include Psittaco-saurus (Psittacosauridae), Protoceratops and Breviceratops (Protoceratopsidae) as well as Centrosaurus, Brachyceratops, Chasmosaurus (Fig. 95b), Anchicera-tops, Torosaurus (Figs. 91,95d) and Pachyrhinosaurus (Fig. 95f) - which was unusual in having a thick pad of bone above the eyes where horns are usually found - to mention but a few of the Ceratopsidae.

■ Fig. 90a-d. Examples of ankylosaur tail club (not to scale). a Talarurus, b Euoplocephalus, c Ankylosaurus, d Sarchania (Upper Cretaceous)

■ Fig. 90a-d. Examples of ankylosaur tail club (not to scale). a Talarurus, b Euoplocephalus, c Ankylosaurus, d Sarchania (Upper Cretaceous)

The Length Talarurus Picture

■ Fig. 92. Reconstruction of a struggle to the death between a small Protoceratops (Ceratopsia; length up to ca. 2.7 m) and a Velociraptor (Oviraptoridae; length ca. 1.8 m; Upper Cretaceous). Seen from above; the Velociraptor is lying on its side, as found in the fossil record


■ Fig. 93. Anchiceratops (length ca. 6 m) confronting Albertosaurus (length ca. 8 m; Upper Cretaceous). (After Dodson 1996)

Cretaceous Ecology
■ Fig. 94. Triceratops (length ca. 9 m) defeats Tyrannosaurus (length ca. 15 m; Upper Cretaceous). (After Dodson 1996)

Ceratopsian weapons may have served not only for interspecific defence but also in intraspecific display and combat (Sect. 9.3.1) - as is seen today among deer and antelope. Nevertheless, not only is there considerable indirect evidence of their use against predatory enemies, but also direct fossil evidence. A life and death struggle between a predatory Velociraptor and a small plant-eating Protoceratops during the Upper Cretaceous has been preserved for 80 my in the sandstone of the Gobi Desert, Mongolia. The two dinosaurs died while the Protoceratops was biting the right arm of the Velociraptor which had jammed its left hind killing claw beneath the frill of its prey (Fig. 92). This huge claw had probably penetrated to the base of the neck of the Protoceratops where the most important blood vessels were situated. The fight might have been ended by a sandstorm or when a large sand dune, saturated with rainwater, slid onto the struggling animals and smothered them before the Protoceratops had been completely overwhelmed. Alternatively, it is possible that the Protoceratops was defending its eggs from the Velociraptor.

Although ceratopsians have been portrayed as taking up a defensive circle like musk oxen (Ovibos moschatus) to protect themselves and their offspring against a large predator, there is as yet no scientific evidence in favour of this hypothesis (Dodson 1996). A dramatic imaginary drawing by Robert Walters (in Dodson 1996) illustrates an Anchiceratops confronting the carnosaur Al-bertosaurus in Alberta, Canada, some 70 mya (Fig. 93), while a painting by Wayne D. Barlowe in the same book illustrates the possible consequence of an encounter between Triceratops horridus and Tyrannosaurus rex (Fig. 94), in which the giant carnosaur is killed by the herbivore (Dodson 1996). Predators did not always come off best in Mesozoic times - any more than they do today! Of course, if T.rex was only a scavenger, which might have been the case in view of its diminutive front legs, then it would not have attacked a Triceratops in the first place (Chap. 11).

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