Horned dinosaurs have already received considerable attention in these pages (Sect. 9.2.2). They were the last of the ornithischians to evolve before the final extinction of the dinosaurs and were extremely successful and numerous. Ad-
vanced forms had massive heads armed with a sharp parrot-like beak at the front of the jaw, a varying number of horns and great frills or sheets of bone growing from the back of the skull. These not only protected the neck and shoulders but would have engendered impressive aposematic displays. The success of the ceratopsians was almost certainly related to the ability to eat very tough vegetation thanks to the possession of efficient teeth and powerful jaws. This food probably included the newly-evolved angiosperms that thrived in Late Cretaceous times (Palmer 1999).
The family Protoceratopsidae (Fig. 92) evolved in Asia during the Upper Cretaceous. Only some genera had horns but, like the Psittacosauridae, many of them could walk upright even if they spent most of their time browsing on all fours. Microceratops (Fig. 114a) from China and Mongolia is the smallest cera-topsian so far discovered. A lightly built animal, its lifestyle probably resembled that of the hypsilophodonts (Sect. 10.5.2). Leptoceratops (length ca. 1 m) from North America was more solid but still essentially bipedal. The Mongolian Bagaceratops (Fig. 114b), although no longer than Leptoceratops, was even more heavily built and clearly quadupedal. Protoceratops (Fig. 114c) must also have spent nearly all the time on all fours, but its hind limbs were still longer than those in front so it was able to rear up and probably run bipedally. A prominent bump on its snout could have been used for ritual head-butting encounters between rival males. The North American Montanaceratops (length ca. 3 m) was generally similar in appearance,but had a definite horn on its snout. In addition, it was endowed with an unusually flexible tail, which might have been brightly coloured and used as a sexual signal during the mating reason (Palmer 1999). The Psittacosauridae were discussed in Section 9.2.2.
The great horned Ceratopsidae (Figs. 72, 93-95, 99), the third family of Ceratopsia (Benton 2004) included the most abundant herbivores of the Late Cretaceous in North America. Their long, sharp horns protruded from massive beaks with large bony frills. With their heavy build and pillar-like legs, they were without doubt exclusively quadrupedal. The number of horns varied from a single one on the nose to three in Triceratops (Fig. 72) and five in Toro-saurus (Fig. 91), Anchiceratops (Fig. 93), Chasmosaurus (Fig. 95b) and Pen-taceratops (Fig. 95a). Peter Dodson (1996) discussed the number of horns in ceratopsids in detail from a taxonomic viewpoint, simplifying the number of species in the genus Centrosaurus, suggesting that Monoclonius might actually be the female of Styracosaurus, and so on (see also Lambert 1992). Dodson, however, did not discuss any possible ecological significance in the number. It seems to be generally accepted that the variety of ceratopsid horns reflected special epigamic display functions - in addition to the deterrence of predators (Figs. 93,94: Sect. 9.2.1). Small-horned types would have tended to sway their heads sideways towards the flanks of their opponents, and to display them laterally. Genera with larger horns may have used them for head-to-head ramming, or in complicated pushing and wrestling trials of strength (Fig. 99; Sect. 9.3.1).
Farlow and Dodson (1975) had already concluded that the protoceratopsids would have behaved like small-horned antelopes and delivered sideways blows to the flanks of their opponents. Moderately large frills may have been used as display signals - the larger the frill, the more dominant the animal in its social group. Short-frilled ceratopsids with large, unpaired nose horns behaved more like rhinoceroses. Their formidable weapons might have been employed largely for bluff in agonistic situations. Possibly they were rather solitary animals and did not often need to defend their territories. Finally, the long-frilled genera would have been able to produce an impressive frontal display merely by nodding their heads and swaying them from side to side. When agonistic combat did occur, the brow horns would have been locked together in pushing and wrestling combats (Fig. 99).
Some years ago, the suggestion was made that the ceratopsians might have consumed fleshy fruits that did not require much chewing. J.H. Ostrom, however, thought it more probable that they ate vegetation such as palm and cycad fronds, which could not be exploited by reptiles that lacked the necessary dentition and powerful jaws for this purpose. There is no evidence to suggest that they used their horns to knock down small trees before shearing off and swallowing the leaves and twigs (Dodson 1996).
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