UPPER CRETACEOUS AMMONITE 
83 
LL 5 mm_y 
Fig.59 Sutures in Vascoceras obscurum Barber. A, C.93910 at a diameter of 32 mm. B, C.93909 at a diameter of 45 mm. C, C.93552 at a diameter of 
30 mm. D, C.93326 at a diameter of 34 mm. All specimens from the Pindiga Formation, unit T2, Ashaka except C.93326 which is from unit X at 
the same locality. 
100, fig. 25 (with synonymy). 
Vascoceras hartti (Hyatt); Cobban, Hook & Kennedy: 
49, figs 49, 91A-D, G-K. 
1989  Fagesia superstes var. levis Renz; Meister: 37, pl. 16, fig. 
2; text-fig. 26. 
1992. Vascoceras gr. globosum (Reyment) ou Fagesia sp.; 
Courville: pl. 9, fig. 1. 
21989 
MATERIAL AND OCCURRENCE. Two specimens, C.93554-5, 
Pindiga Formation, unit X, Ashaka. 
DIMENSIONS. 
| D Wb Wh U 
| 93555 79 83 (105) 33 (42) 21 (26.5) 
C.93554 49 50 (102) 21 (43) 12 (24.5) 
| 
|REMARKS. These moderately evolute cadicones show sharp 
umbilical shoulders, which are undulating in C.93555, and 
steeply sloping umbilical walls. There are sharply rounded 
ventral ribs and occasional constrictions in C.93554 (Fig. 58) but 
they fade by a diameter of 40 mm leaving the internal mould 
| smooth but for transverse growth striae. Neither specimen shows 
| umbilical tubercles. 
Kennedy et al. (1987: 51) pointed out the difficulty in 
distinguishing V. hartti from globose V. globosum. They regarded 
a more evolute coiling and a steeply sloping umbilical wall as 
most useful in identifying the former. In these respects the 
similar V. globosum globosum. 
In the present work V. harttii has been found only in unit X at 
Ashaka. Meister (1989: 37-38) and Courville (1992: 424) also 
reported examples from unit U there which they referred to or 
compared with Fagesia superstes (Kossmat). As with V. 
globosum globosum (see above) these forms have an ontogenetic 
development characteristic of Vascoceras not Fagesia. The 
globose shape and complex suture pattern are not in themselves 
diagnostic of Fagesia. 
STRATIGRAPHICAL AND PHYLOGENETIC 
DISCUSSION 
The oldest ammonite-bearing beds in north-eastern Nigeria 
yield no vascoceratid taxa. They are characterized by 
Nigericeras gadeni, Metengonoceras dumbli (Cragin), 
Placenticeras (Karamaites) cumminsi Cragin and Metoicoceras 
geslinianum (d’Orbigny), the last species allowing correlation 
with the Geslinianum Zone in north-western Europe and the 
Gracile Zone of the western interior of the United States (see 
Kennedy 1984, Cobban 1984, Cobban ef al. 1989). This 
‘Nigericeras fauna’ is widely recognizable in West and Saharan 
Africa (see Lefranc 1978, Meister et al. 1992). 
Paravascoceras cauvini appears in unit E at Ashaka and 
becomes common in unit F there and in unit H at Pindiga. In the 
last two horizons it is associated with Burroceras? sp. (Zaborski 
1995). Although not identifiable to species level this material 
may indicate correlation with the Burroceras clydense Zone of 
New Mexico. P. cauvini ranges through units K and M at Ashaka 
wherein Vascoceras woodsi occurs. These units also contain 
Pseudaspidoceras pseudonodosoides, on which basis they can be 
correlated with the Juddii Zone in the western interior. In 
south-western New Mexico a gap exists between the Juddii Zone 
and the basal Turonian Flexuosum Zone (Cobban et al. 1989). 
Pseudaspidoceras flexuosum Powell occurs in unit T2 at Ashaka. 
Units N to T1 at Ashaka belong to the Upper Cenomanian but 
Fig.50 Vascoceras globosum costatum (Reyment). Pindiga Formation, unit O, Ashaka. C.93523, x1. 
Figs 51,52 Vascoceras globosum globosum (Reyment). Pindiga Formation, unit R, Ashaka. Fig. 51, C.93544, x1. Fig. 52a, b, C.93545, x1. 
Figs 53,54 Vascoceras obscurum Barber. Pindiga Formation, unit T2, Ashaka. Fig. 53a, b, C.93552, x1. Fig. 54, C.93553, x1. 
Figs 55-57 Vascoceras globosum proprium (Reyment). Pindiga Formation, unit T2, Ashaka. Fig. 55a, b, C.93365, x1. Fig. 56a, b, C.93549, x1. Fig. 
: material is more properly referred to V. harttii than the 
‘] 
57a, b, C.93550, x1. 
| 
Fig.58 Vascoceras harttii (Hyatt). Pindiga Formation, unit X, Ashaka. C.93554, x1. 
