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VAN VALKENBURGH AND JENKINS—HISTORY OF SYNAPSID PREDATORSbody length of Anteosaurus is estimated at morethan 5 meters (Boonstra, 1954). Large pterygoidflanges indicate a well-developed KI system inanteosaurs, and increased vertical alignment of thetemporalis muscles suggests an expanded SPcomponent of the bite cycle. Unlike later therapsids,in which the postcanine dentition was reduced,anteosaurs retained the three elements of their dentalarcade as fully functional units. Anteosaurspossessed the heaviest canines, incisors, and skullsof all carnivorous synapsids. The postcanine teethare large, trenchant, ovoid in cross section, and hencevery strong. In many anteosaur genera, the caninesare recurved, in contrast with the straighter caninesof all other carnivorous synapsid genera. Thispronounced recurvature is best seen in Syodon fromRussia. In addition to the complete functionalcomplement of marginal dental units, anteosaursalso possessed very prominent palatal tooth bosses.These reniform structures are more conspicuousthan in any other predatory synapsid andaugmented the marginal dentition considerably.Anteosaur head skeletons thus show a trend towarda remarkably expanded dental complement,comprising incisors, canines, postcanines, andpalatal teeth, all of which were large. In concert withhuge size, a powerful SP bite, and exceptionallyheavy, thick-boned skulls, anteosaur dinocephalianswere designed to prey on particularly large animalsand were among the most highly predaceous of allsynapsids (Sennikov, 1996). Potential prey includedthe bull-sized armored pareiasaurs (Lee, 1997) andenormous tapinocephalid dinocephalians (Rubidge,1995). The latter are typified by dome-headedMoschops; it and related genera such asTapinocephalus were the heaviest of all synapsids(Kemp, 1982). Despite their remarkable craniodentalweaponry, dinocephalians do not have a fossil recordas long as that of sphenacodonts and are replaced inthe early part of the Late Permian by earlytherocephalians and gorgonopsids (Anderson andCruickshank, 1977; Kemp, 1982; Rubidge, 1995;Battail and Surkov, 2000).Late Permian (approximately 260–250 Ma):Gorgonopsids.—A number of gorgonopsidecomorphs or ecotypes can be defined, based onskull construction and jaw biomechanics (Fig. 4).Cyonosaurids such as Cyonosaurus (Fig. 4.1) weresmall (skull length about 140 mm) gorgonopsidswith very long snouts, small canine ‘sabers’, slimlower jaws, and gracile skulls. These forms maybe immature or juvenile forms of other genera (IJ,pers. obs.). Cyonosaurids have a long fossil record(relative to other gorgonopsids) and seem to haveFIGURE 4—Gorgonopsid skull morphotypes that probably represented different predatory habits andniche occupation. See text for more information. 1, Cyonosaurus; 2, Gorgonops; 3, Arctops;4, Arctognathus; 5, Rubidgea; 6, Broomicephalus. Scale bar = 100 mm. Skulls not to scale.273