UPPER CRETACEOUS AMMONITE 
Suture patterns are of the typically simple type characteristic 
of Vascoceras. 
Barber (1957), Meister (1989) and Courville (1992) separated 
forms of V. globosum costatum with subtriangular to triangular 
whorl sections as Paravascoceras costatum tectiforme Barber, P. 
tectiforme Barber and Vascoceras tectiforme (Barber). In unit O 
t Ashaka there is a complete intergradation of forms with 
ounded and triangular whorl sections. The latter themselves 
how rounded venters in their early growth stages. This shape 
ariation is attributed no taxonomic significance here. 
Of greater interest is the fact that V. globosum costatum shows 
gradation into Thomasites at the same stratigraphical level at 
shaka. A variation series is shown in Figs 41-44, 50. This 
sncompasses more or less smooth forms with ovoid to 
subtriangular whorls (Figs 41, 50) through forms with weak but 
efinite ventral tubercles and incipient carinae (Figs 42, 43), into 
strongly ornamented individuals (Fig. 44) occurring in the upper 
part of the unit and well within the morphological range of 
Thomasites gongilensis (Woods) (see faunas described by Barber 
1957, Meister 1989). The Neoptychites cephalotus (Courtiller) of 
Meister (1989: 12, pl. 4, fig. 4) and Thomasites sp. nov.? of 
ourville (1992: 420, pl. 10, fig. 4; pl. 12, fig. 1) are further 
2xamples of early Thomasites. V. globosum costatum seems to 
2ontain the ancestors of 7: gongilensis, a species which reaches 
ts acme in unit R at Ashaka where it forms the bulk of the 
mmonite fauna. 
The Paravascoceras aff. chevalieri (Furon) of Reyment (1955: 
53, pl. 14, figs 1a, b) from southern Nigeria also shows three rows 
of ventral tubercles and resembles the early Thomasites from 
Ashaka. The same can be said of the material of Discovascoceras 
tesselitense described by Collignon (1965: 181, pl. G, figs la, b) 
which shows three ventral carinae, subtriangular whorls and a 
eep, fairly narrow umbilicus. Hirano (1983) and Berthou et al. 
(1985) compared this material with Pseudotissotia, but it 
ppears closer to the Nigerian forms transitional from 
Pascoceras to Thomasites described here. 
Vascoceras globosum globosum (Reyment, 1954b) 
igs ol yo2 
Pachyvascoceras globosum Reyment: 259, pl. 3, fig. 3; 
pl. 4, fig. 4; text-figs 3e, 7. 
| 1957  Vascoceras globosum globosum (Reyment) Barber: 21 
(pars). 
1957 —- Vascoceras globosum carteri Barber: 25, pl. 8, fig. 2; pl. 
28, figs 8, 9. 
| 1965 Vascoceras carteri Barber; Reyment: pl. 3, fig. 12. 
30 
number 
of 
individuals 
20.6 23.4 
U/D(%) 
globosum globosum (Reyment) (see also Fig. 12). 
ee 
79 
1976 Paravascoceras carteri (Barber) Offodile & Reyment: 
55, figs 27, 28. 
1989  Paravascoceras carteri (Barber); Meister: 21 (pars), pl. 
9, fig. 3 (only); pl. 10, figs 1, 2; text-fig. 14. 
1992 Vascoceras tectiforme (Barber) sensu 
Courville: pl. 7, fig. 3 (only). 
1992  Vascoceras gr. globosum (Reyment) ou Fagesia sp. 
Courville: pl. 8, figs 1, 2. 
Vascoceras sp. aff. obscurum Barber; Courville: pl. 10, 
fig. 3 (only). 
Meister; 
71992 
MATERIAL AND OCCURRENCE. Three specimens, C.93544-6, 
Pindiga Formation, unit R, Ashaka. The form also occurs in 
unit O at Ashaka and unit O at Pindiga. 
DIMENSIONS. See Figs 12, 48. 
REMARKS. V. globosum globosum is characterized by its highly 
depressed whorls which are at least twice as broad as high. 
Although such forms occur throughout the range of V. globosum 
in north-eastern Nigeria there are morphological and 
stratigraphical reasons for considering the earlier individuals as 
a separate subspecies. In unit O at Ashaka highly depressed 
examples of V. globosum are rare but those that occur fall well 
outside the morphological range of V. globosum costatum (see 
Figs 12, 48). In both unit R at Ashaka and unit O at Pindiga V. 
globosum globosum is the only member of the species that has 
been found. It is fairly frequent at these levels where the more 
compressed part of the morphological spectrum is occupied by 
large numbers of Thomasites gongilensis. 
The juvenile whorls in V. globosum globosum show sharper 
ribbing than in V. globosum costatum. The ribs cross the flank, 
unlike in V. globosum proprium in which they are largely confined 
to the venter and outer flanks. Specimen C.93544 (Fig. 51) is a 
very close match for the holotype of Pachyvascoceras globosum 
(C.47408, see Reyment 19545: pl. 3, fig. 3; pl. 5, fig. 4) which is 
also a juvenile. 
Since details of the inner whorls are useful in identification it 
is difficult to determine which of the specimens described by 
Barber (1957: 21) as V. globosum globosum should be referred to 
that subspecies and which are depressed examples of V. 
globosum proprium (see below). His material appears to include 
both. 
The sutures in V. globosum globosum are deeply incised; this 
appears to be a general feature of highly depressed Vascoceras 
which is shared with V. harttii (see below). Courville (1992: 421) 
drew attention to the suture pattern in V. globosum globosum and 
suggested that it may be better referred to Fagesia Pervinquiete. 
30 
1.31 1.89 2.47 
Wb/Wh 
ig. 48 Shell proportions in Vascoceras globosum (Reyment) occurring in unit O at Ashaka. Forms with a high Wb/Wh ratio are here assigned to V. 
