Wits Evolutionary Studies Institute (ESI)
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Item Late Triassic traversodont cynodonts from Nova Scotia and southern Africa(Bernard Price Institute for Palaeontological Research, 1984) Hopson, James A.The first gomphodont cynodont from North America is described from the Upper Triassic Wolfville Formation, Fundy Group, Newark Supergroup, of Burntcoat, Minas Basin, Nova Scotia, Canada. Known material consists of a large mandible, edentulous but for two incisors, a probably associated canine, and two small dentaries; an isolated multicusped tooth may belong to this species. This gomphodont closely resembles the large traversodont Scalenodontoides macrodontes from the lower Elliot Formation (= Red Beds) of Lesotho; it is provisionally placed in this genus but is a distinct species, ?Scaleno- dontoides plemmyridon sp. nov. It differs from S. macrodontes primarily in its more massive symphyseal region and much larger mental foramen from which a prominent groove extends posterodorsally. The large, posteriorly-located mental foramen is believed to be a well-developed oral vestibule and cheek. The isolated tooth, provisionally interpreted as a traversodont lower postcanine, is anteroposteriorly compressed, with a high anterior blade formed by three transversely-aligned cusps and a short heel; it does not resemble postcanines of S. macrodontes and so reference to ?S. plemmyridon is questionable. Scalenodontoides is the sister genus of Exaeretodon from the Late Triassic of Argentina, Brazil, and India; they are allied on the basis of: upper incisors reduced from 4 to 3, all incisors greatly enlarged, and internarial bar incomplete. These resemblances to tritylodontids are convergent. Scalenodontoides and Exaeretodon share with Gomphodontosuchus the enlargement of the anterolabial cusp of the lower postcanines and posterior inclination of the anterolingual cusp. The Wolfville and basal Elliot faunas are considered to be Late Carnian or Carno-Norian in age. Faunas containing Exaeretodon are older Carnian, though the Santa Maria Formation of Brazil may be Late Ladinian.Item A REVISED CLASSIFICATION OF CYNODONTS (REPTILIA; THERAPSIDA)(BERNARD PRICE INSTITUTE FOR PALAEONTOLOGICAL RESEARCH, 1972) Hopson, James A.; Kitching, James W.Cynodonts are very advanced mammal-like reptiles of the Permian-Triassic which are of special interest to evolutionists because they gave rise to the Class Mammalia during Middle or Late Triassic time. Cynodonts have been known from strata of Early Triassic age in South Africa for over one hundred years, and numerous specimens have been collected and described. In recent years the record of cynodonts has been extended into earlier and later time zones, not only in southern Africa but in East Africa, South America, Russia , China, and, most recently, in North America. Much of the material from outside of Africa has not yet been fully described.Item A juvenile gomphodont cynodont specimen from the Cynognathus Assemblage Zone of South Africa: implications for the origin of gomphodont postcanine morphology(BERNARD PRICE INSTITUTE FOR PALAEONTOLOGICAL RESEARCH, 2005) Hopson, James A.The partial skull and lower jaws of a small gomphodont cynodont from the Cynognathus Assemblage Zone of South Africa has a well-preserved postcanine dentition distinctly different from that of contemporaneous adult Diademodon and Trirachodon. On the basis of its small size and great amount of tooth replacement it is interpreted to be a juvenile individual. The postcanines are compared with those of adults and juveniles of Diademodon and traversodontids and is seen to differ from them. Comparison with adults of Trirachodon shows some unique postcanine resemblances, such as well-developed anterior and posterior many-cusped cingula and three transverse cusps joined by a prominent ridge. Thus it is identified as a probable juvenile Trirachodon of uncertain species. Unlike in Trirachodon adults, tall central and internal cusps of the upper postcanines lie close together on the medial side of the crown, separated from the tall external cusp by a deep valley. In these features it shows a striking resemblance to the traversodontid Scalenodon angustifrons, but not to more primitive traversodontids. The lower postcanines superficially resemble those of traversodontids in that two cusps (central and internal) are very tall and the posterior basin is elongated, but, unlike in traversodontids, the external cusp is present, though relatively small. Evidence of tooth replacement occurs in the incisors, canines, and postcanines. At least two replacement waves of gomphodont teeth are indicated, as well as replacement of small, possibly sectorial teeth at the rear of the tooth row. Probable homology of (at least) the external and internal cusps in the three gomphodont families suggests that the common ancestor also possessed transversely-expanded crowns developed from an external sectorial position (homologous with the ancestral blade-like tooth) and a hypertrophied internal cingulum.