118 MALCOLM B. HART, MELISSA J. OXFORD & WENDY HUDSON
Fig. 3. Distribution of Conoglobigerina spp. in the Middle Jurassic.
Origin of the planktonic for ami niter a
In their review of this subject, Simmons et al.
(1997) dismiss the report of Pliensbachian
planktonic specimens (Gorog 1994) as probable
contamination but, more significantly, reject all
the taxa described as planktonic foraminifera by
Fuchs (1967, 1971, 1973, 1975, 1977). These
poorly preserved specimens have been exam-
ined by F. Rogl (Natural History Museum,
Vienna) and A. Gorog (Budapest, Hungary),
both of whom indicate that they are not plank-
tonic taxa. Some of this material is currently on
loan to The Natural History Museum (London)
and it is clear to the senior author that they are
benthonic taxa with flattened umbilical sides
and a complete lack of the inflated chambers
normally associated with a planktonic mode of
life.
If the Triassic and early Jurassic records of
planktonic foraminifera are rejected then the
origins of the group must be pre-Bajocian (Fig. 1)
as the species of Conoglobigerina recorded from
the Bajocian are clearly meroplanktonic (Wernli
& Gorog 1999, 2000). In the Toarcian sediments
of the Creux de Tours section (Teysachaux,
Fribourg, Switzerland) Wernli (1995) has
described a fauna of Praegubkinella spp. that is
associated with Oberhauserella quadrilobata,
one of the original 'planktonic' taxa of Fuchs
(1967). Wernli (1995) demonstrates the possible
evolution from Praegubkinella racemosa Wernli
into Conoglobigerina (Fig.l), thereby extending
the range of the ancestral forms into the
Toarcian. The section of the 'Creux de l'ours' has
been described by several authors (e.g. Mettraux
et al. 1986, 1989) and the recent commentary
(Weidmann 1993) on the Swiss Geological Map
No.1244, Chatel-St-Denis (Weidmann et al.
1993) provides much new information. The
famous section (coordinates 565.07/154.30 on
Swiss Geological Map No.1244) was improved in
1970 when a new forestry road was constructed.
Unfortunately many of the new sections are now
degraded but one face still exists on a bend where
the road crosses the stream. Previous workers
have identified the elegantulum and exaratun
Subzones of the falciferum Zone, placing the
section within the Toarcian 'anoxic event"
(Mettraux et al. 1986, 1989, and references
therein). The senior author has found specimens
of Harpoceras and Dactylioceras in this part of
the section, together with examples of Posidonia
associated with hard, organic-rich mudstones. M.
Mettraux provided the samples for the investi-
gation by Wernli (1995), the foraminifera coming
from a sample of the dark mudstones from
stratigraphically above the 'anoxic event'. The
Praegubkinella/Oberhauserella assemblage of
Wernli (1995) is, therefore, of early Toarcian age.
Work on the Toarcian foraminifera of the UK
and NW Europe (Hylton 2000; Hylton & Hart
2000) has shown that, associated with the
Toarcian anoxic event, there is a 'bloom' of small
forms of O. quadrilobata which possess slightly
more inflated chambers than the typical forms
