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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.

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