View - Kowalewski, M. - Virginia Tech

PALEONTOLOGICAL SOCIETY PAPERS, V. 8, 2002FIGURE 3—Stratigraphic ranges and time duration of the carnivorous groups of non-mammaliansynapsids (modified from Kemp, 1982, fig. 115). A star indicates the presence of a saber-toothed formwithin the lineage.lay at 90 o to each other and were equipped withwell-developed pterygoid teeth. These structuresmay have functioned as intraoral ‘guillotine blades’(IJ, pers. obs.) and allowed the enhanced triturationof ingested food. The canines are very large andextremely robust, but the huge, caniniform incisorsare similar in size to the canines (Romer and Price,1941). There is a pronounced step at the maxilla–premaxilla junction of the upper jaw. The caninesand incisors are situated on opposite sides of thisstep, allowing the equally large lower canines tointerpose between the upper canines and incisors,creating a tight grip on prey. Sphenacodonts werehighly successful predators as shown by a long fossilrecord (about 40 million years) that extends fromthe Late Carboniferous to the Guadalupian (earlyLate Permian) (Benton, 1993). The skull designremained unchanged throughout this long period.Mid-Late Permian (approximately 275–260Ma): Dinocephalians.—The first of three therapsiddynasties belongs to the dinocephalians—large,often gigantic, synapsids from the early LatePermian of South Africa and Russia (Fig. 2.2). Overtheir evolutionary history, they increased in size;their skull bones thickened; the adductor(temporalis) chamber became more vertical inorientation; and they developed reniform (kidneyshaped)palatal tooth bosses of considerable size,robust canines, and very large, procumbent incisorsthat interlaced in a precise manner (Kemp, 1982).Dinocephalians were the largest of all synapsidsand rivaled some dinosaurs in size. The carnivorousmembers belong to the anteosaur clade (Hopson,1991; Hopson and Barghusen, 1986) and includethe South African form Anteosaurus, and thesomewhat smaller Russian forms Titanophoneus(Fig. 2.2), Syodon, Archaeosyodon, Doliosaurus,and Doliosauriscus.Anteosaurus from South Africa had a high,deep skull almost a meter long (Kemp, 1982)equipped with mighty canine teeth, as did theRussian forms Archaeosyodon, Doliosaurus, andDoliosauriscus (Orlov, 1958; Tatarinov, 1974;Chudinov, 1983; Battail and Surkov, 2000). The272