. Annals of the South African Museum = Annale van die Suid-Afrikaanse Museum. Natural history. CRETACEOUS FAUNAS FROM SOUTH AFRICA 287. Fig. 134. Gauthiericeras libertae van Hoepen, 1955. Whorl section and suture-line of holotype. x 1. (After Van Hoepen 1955, figs 24-25.) CONCLUSIONS A general reappraisal of Coniacian stratigraphy and revision of the very rich peroniceratid faunas found in Zululand provide an outline of the evolution of the group that is of some significance for interregional correlation and elucida- tion of evolutionary patterns among late Cretaceous ammonites (Fig. 135). The
. Annals of the South African Museum = Annale van die Suid-Afrikaanse Museum. Natural history. CRETACEOUS FAUNAS FROM SOUTH AFRICA 287. Fig. 134. Gauthiericeras libertae van Hoepen, 1955. Whorl section and suture-line of holotype. x 1. (After Van Hoepen 1955, figs 24-25.) CONCLUSIONS A general reappraisal of Coniacian stratigraphy and revision of the very rich peroniceratid faunas found in Zululand provide an outline of the evolution of the group that is of some significance for interregional correlation and elucida- tion of evolutionary patterns among late Cretaceous ammonites (Fig. 135). The earliest genus of the Peroniceratinae is Peroniceras itself. The appear- ance of P. (Peroniceras) (of which Fraudatoroceras van Hoepen, 1965, Cobba- noceras Matsumoto, 1965, and Gloriaceras Etayo-Serna, 1979, are synonyms) marks the base of the Middle Coniacian as that term is used here. There is a hi- atus in the record between the first appearance of Peroniceras and the Collignoniceratinae, which are believed to be the ancestral stock spanning the Lower Coniacian. Matsumoto (1965: 213) beheved that the origin of Peroniceras lay in Prionocyclus, and the Prionocyclus lineage certainly survived to give rise to Prionocycloceras, which extends to the Upper Coniacian. Matsumoto sug- gested that the lateral keels of Peroniceras arose by the elevation of the outer edges of the grooves flanking the keel of ancestral Prionocycloceras. Indepen- dent observations by Etayo-Serna (1979) and the present authors shows that the keels arise by elongation and eventual absorption of outer ventrolateral clavi into a keel, and that both lateral and siphonal keels of several Peroniceras (Per- oniceras) species show undulations at some stage in ontogeny. The suture of the type species of Peroniceras (Peroniceras), P. (P.) moureti de Grossouvre, 1894 (a synonym of P. (P.) tridorsatum (Schliiter, 1867)) is rela- tively simple, like that of ancestral Collignoniceratinae. Other species, such as P. (P.)
Size: 1691px × 1478px
Photo credit: © Library Book Collection / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1800, bookdecade1890, booksubjectnaturalhistory, booky
