. Bulletin of the Natural Histort Museum. Geology series. 62 PINDIGA ASHAKA about 56m. YOLDE Fm. Fig. 1 Stratigraphical sections through the limestone-bearing parts of the Pindiga Formation at Ashaka and Pindiga with letter codes identifying Hmestone units mentioned in the text. Approximate biostratigraphical correlations with the ammonite biozones of the western interior of the United States (after Cobban et al 1989, Hancock 1991) are also indicated. tight stratigraphical control, especially at Ashaka quarry. Furthermore, dissection of adults is frequently successful in recover
. Bulletin of the Natural Histort Museum. Geology series. 62 PINDIGA ASHAKA about 56m. YOLDE Fm. Fig. 1 Stratigraphical sections through the limestone-bearing parts of the Pindiga Formation at Ashaka and Pindiga with letter codes identifying Hmestone units mentioned in the text. Approximate biostratigraphical correlations with the ammonite biozones of the western interior of the United States (after Cobban et al 1989, Hancock 1991) are also indicated. tight stratigraphical control, especially at Ashaka quarry. Furthermore, dissection of adults is frequently successful in recovering well-preserved inner whorls which in some cases are invaluable for identification purposes, as well as for analysing ontogenetic development. These attributes have allowed a revised taxonomy to be presented here for the Nigerian faunas. The family Vascoceratidae as a whole has been discussed by Spath (1925), Furon (1935), Schneegans (1943), Reyment (19546, 1955, 1956), Barber (1957), Wiedmann (1960), Cooper (1978) and Wright & Kennedy (1981). From the time of its proposal it has been recognized that the genus Nigericeras Schneegans, 1943 is morphologically intermediate between the subfamilies Acanthoceratinae and Vascoceratinae. More recently, a number of additional genera of intermediate character have been decribed, a notable feature being the combination of a vascoceratine-type suture pattern with an acanthoceratine-type ornament. Such intermediates include Microdiphasoceras Cobban, Hook & Kennedy (1989: 53), Ruhroceras Cobban, Hook & Kennedy (1989: 54), Fikaites Zaborski (1993: 362) and Pseudovascoceras, described herein. It is believed here that the family Vascoceratidae is polyphyletic, including homeomorphic derivatives of various acanthoceratine genera. In Nigeria at least the same is true of forms previously referred to the genus Please note that these images are extracted from scanned page images that may have been digitally enhanced for r
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