. Annals of the South African Museum = Annale van die Suid-Afrikaanse Museum. Natural history. 1 12 ANNALS OF THE SOUTH AFRICAN MUSEUM the more abundant family Pristerognathidae, contemporary therocephalians with one maxillary canine. Most authors (Haughton & Brink 1955; Kermack 1956; Romer 1956; Watson & Romer 1956; Boonstra 1969) who have discussed the early Therocephalia have placed great taxonomic weight on the number of canines and consequently the concept of double-canined therocephalians is widespread in the literature. Illustrations of early therocephalians usually present the
. Annals of the South African Museum = Annale van die Suid-Afrikaanse Museum. Natural history. 1 12 ANNALS OF THE SOUTH AFRICAN MUSEUM the more abundant family Pristerognathidae, contemporary therocephalians with one maxillary canine. Most authors (Haughton & Brink 1955; Kermack 1956; Romer 1956; Watson & Romer 1956; Boonstra 1969) who have discussed the early Therocephalia have placed great taxonomic weight on the number of canines and consequently the concept of double-canined therocephalians is widespread in the literature. Illustrations of early therocephalians usually present the double-canined Lycosuchus as a general representative of the group (Du Toit 1954; Romer 1956, 1966). Kermack (1956) demonstrated in the Therocephalia and the Gorgonopsia the existence of two upper canine positions which alternate in housing a single functional canine. According to Hopson (1964) this is also the case in the cynodont Thrinaxodon liorhinus and probably most other cynodonts as well. From this it is to be expected that while the functional canine was being replaced, the animal would have two canines of different ages in each maxilla, super- ficially similar to the condition frequently observed in living mammals when the permanent canine is in the process of replacing the milk canine (Fig. 1). Kermack also described a lycosuchid Trochosaurus major with two erupted canines and states that the possession of two simultaneously functional canines was primitive for Therocephalia. This idea probably stems from the view that a similar condition was thought to typify sphenacodont pelycosaurs, the pre- sumed ancestors of therapsids. In an important paper Mendrez (1972) established the existence of an incipient crista choanalis in the pristerognathids Pristerognathus polyodon and Ptomalestes avidus, situated on the inner surface of the maxilla medial to the canines. She interpreted this structure as the first step on the way to the develop- ment of a bony secondary palate as i
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