A
large number of specimens of foraminiferan shells of Quaternary age, collected
at several localities worldwide, were found to have scars and drill-holes on
their shells, which were produced by bioeroding organisms. These traces confirm
that predation and parasitism of such minute organisms as foraminiferans living
on the seafloor are and have been widespread activities. In addition, individual
borings were also found in the shells of planktonic species of foraminiferans,
indicating the existence also of planktonic carnivores that prey on living
foraminiferans suspended in the water column. A healed boring in the shell of a
planktonic foraminiferan indicates that at least some planktonic foraminiferans
survive attack.
The geographical occurrence of one of the traces, Fossichnus solus isp. nov., suggests that its distribution is controlled by environmental parameters. This trace fossil is distinguished by a single ring-shaped groove having a circular to oval outline, and most likely represents a scar produced by an organism passively attached to the foraminiferan. Alternatively, if the central part of the ring falls out, the morphology of the trace changes dramatically to that of a drill-hole, having the trace fossil name Oichnus simplex. This might be taken to indicate that F. solus is an abandoned, incomplete O. simplex.
Other
bioerosion structures are also recorded for the first time. A sieve-like boring
is known from a single specimen, and thus does not qualify for a new formal
name. Additionally, a crescent-shaped hole and a groove-shaped hole are
extremely rare and are left in informal, open nomenclature as O. aff. asperus
and O. aff. paraboloides, respectively.
F.
solus
is quite common within its temporal and
geographic area of distribution. Therefore, this new ichnospecies has a
potential usefulness as a palaeoecological indicator, although the details of
this indicator are not yet apparent.
aff.
In a formal name, having affinity to.
Benthic.
Living at the seafloor.
Bioerosion.
The activity and results of production of borings, drill-holes, scrapings and
etchings on and within hard substrates such as shells by animals, plants, fungi
and microbes.
Borings.
Traces produced in hard substrates such as shells.
Foraminiferans.
A group of marine microorganisms classified with the Protista; single celled,
somewhat similar to Amoeba but bearing a (normally) calcite shell.
isp. nov.
New ichnospecies, established in this paper. Trace fossils are named similarly
to organisms, using genus and species names. However, trace fossil names do not
refer to the organism that produced them, which is normally unknown. They are
based on the morphology of the trace fossil.
Palaeoecology.
Ecology or life-style of organisms based on fossil material.
Planktonic.
Living suspended in the water column, unconnected with the seafloor.
Quaternary.
The latest geological stage, spanning from c. 2.5 million years ago to today.
Trace fossils.
Structures such as burrows and borings produced by life activities of organisms.