The early evolution and palaeobiogeography of Mesozoic
planktonic foraminifera
MALCOLM B. HART, MELISSA J. OXFORD & WENDY HUDSON
Department of Geological Sciences & Plymouth Environmental Research Centre,
University of Plymouth, Drake Circus, Plymouth PL4 8A A, UK
(e-mail: [email protected])
Abstract: The planktonic foraminifera almost certainly evolved from benthonic ancestors
in the early Jurassic. The meroplanktonic genus Conoglobigerina, known from south-
central and eastern Europe, appears in the Bajocian and is probably derived from the even
more geographically restricted Praegubkinella. This genus was represented by a single
taxon in the earliest Toarcian but diversified after the Toarcian anoxic event. At the same
level Oberhauserella quadrilobata Fuchs, 1967 became more inflated and there is some evi-
dence to suggest that the 'anoxic event' was the environmental perturbation that began the
transition to a planktonic mode of life. In the Callovian-Oxfordian interval, the planktonic
foraminifera are still restricted to a relatively limited area bounded by the North Atlantic
Ocean, NW Europe and Eastern Europe and this remained the case even in the earliest
Cretaceous. It was only in the Aptian-Albian that the palaeogeographical distribution
changed dramatically, probably as a response to the elevated sea levels caused by the
increased rate of ocean crust production which began in the Early Aptian. The principal
diversification events in the Jurassic (Toarcian, Bajocian, Callovian-Oxfordian) also appear
to be related to sea level highstands.The planktonic foraminifera are a distinctive
and abundant part of the modern oceanic fauna.
Together with the other planktonic groups
(coccolithophorids, diatoms, radiolarians, dino-
flagellates, etc), they assist in the chemical/
nutrient cycling of the ocean system. While the
oceanic plankton, in general, impact on the
levels of atmospheric CO2 in the Mesozoic and
Cenozoic, the contribution of the planktonic
foraminifera is probably difficult to quantify
although, as we will demonstrate, the develop-
ment of the group was rather limited until the
mid-Cretaceous. During the Mesozoic it is
known that the planktonic foraminifera:
- evolved from benthonic ancestors;
- diversified;
- expanded to attain an almost global distri-
bution;
- suffered during several major 'events'
(including possible bolide impacts and
methane escapes from gas hydrates); and
- were reduced to two or three species by the
terminal Cretaceous 'events' or 'event'
(bolide impact(s), sea-level change, tem-
perature rise/fall, volcanic fall-out, etc.).
Most micropalaeontologists (e.g. Caron 1983;
Hart 1999; Premoli Silva & Sliter 1999) have
treated the planktonic foraminifera as though
they were a single evolutionary plexus, although
those working on DNA sequencing of the
modern fauna have questioned this basic
assumption (e.g. Darling et al. 1996, I999a,b)
and suggested that the evolution of the plank-
tonic foraminifera may be polyphyletic. It is
certainly true that one cannot claim that the
Jurassic record of the group (Fig.l) provides
anything other than a disjointed set of relation-
ships. While preservation and/or collection
failure is probably a contributing factor, there
are several problems:
- the Praegubkinella - Conoglobigerina link:
- the disjointed distribution of Conoglobige-
rina; and
- the origins of Globuligerina and other taxa
in the mid- to late Jurassic.
Higher, in the Cretaceous succession, we have
little evidence for the origin of the Praehed-
bergella lineage or the heterohelicids (Fig. 2)
and it is clear that the new evidence from the
work on DNA must be taken into account and a
polyphyletic history considered alongside other
suggestions.
From: CRAME, J. A. & OWEN, A. W. (eds) 2002. Palaeobiogeography and Biodiversity Change: the Ordovician
and Mesoioic-Cenoioic Radiations. Geological Society, London, Special Publications, 194,115-125.
0305-8719/02/$15.00 © The Geological Society of London 2002.