14
J.T. Eastman and A. Clarke
accumulating slowly. In the Southern Ocean the only evidence for rapid
changes in temperature comes from the late Palaeocene where Kennett and
Stott [63] have demonstrated a possible short-term warm event.
Although significant changes in circulation patterns clearly have the
potential to influence distribution and evolutionary process through
regional or wider-scale extinction, there is as yet no evidence that these
processes have been important in the evolution of the Southern Ocean
marine fauna.
The Evolution of the Antarctic Fish Fauna
The broad features of the evolution of the Southern Ocean fish fauna are
now well established [1] and so will only be summarized here.
The vast ice-sheets of Antarctica limit the exposure of rock, and so our
knowledge of the fossil history of the Southern Ocean fish fauna is
frustratingly incomplete. Mesozoic fossils confirm the suggestion from
tectonic reconstructions that the shallow waters around Gondwana were
populated by faunas typical of the period [1]. Early Cenozoic fossils from
Seymour Island indicate that prior to the oceanographic isolation of
Antarctica, the fish fauna of Gondwana was diverse and contained
representatives of many cosmopolitan taxa. The fauna appears to have been
typical of the temperate seas of the time.
Unfortunately there are few postEocene fossil fish known from
Antarctica and the modem fauna thus has no fossil record. We are
therefore left with the intriguing observation that at some time between the
Eocene and today, early Tertiary fish fauna of Antarctica largely
disappeared. There was then a substantial radiation of notothenioid and
liparid fish to produce the fauna we see today.
What Caused the Demise of the Early Tertiary Fish Fauna?
In the absence of a fossil record, we can only speculate on the causes of the
extinction of the early Tertiary fish fauna of Antarctica. Nevertheless it is
tempting to assume that a major factor must have been the severe reduction
in the amount of shallow water and the loss of many habitats traditionally
rich in fish consequent upon the major glaciation of Antarctica. This
working hypothesis would then put the extinction event (if needed it can
be regarded as a single event) around the late Eocene/early Oligocene (4035 Ma BP). An explanation based on habitat loss also implies that the
associated cooling was not necessarily the primary cause of extinction, but
in truth there is no evidence to allow us to distinguish the two causes
(which may have acted together).
J.T. Eastman and A. Clarke
accumulating slowly. In the Southern Ocean the only evidence for rapid
changes in temperature comes from the late Palaeocene where Kennett and
Stott [63] have demonstrated a possible short-term warm event.
Although significant changes in circulation patterns clearly have the
potential to influence distribution and evolutionary process through
regional or wider-scale extinction, there is as yet no evidence that these
processes have been important in the evolution of the Southern Ocean
marine fauna.
The Evolution of the Antarctic Fish Fauna
The broad features of the evolution of the Southern Ocean fish fauna are
now well established [1] and so will only be summarized here.
The vast ice-sheets of Antarctica limit the exposure of rock, and so our
knowledge of the fossil history of the Southern Ocean fish fauna is
frustratingly incomplete. Mesozoic fossils confirm the suggestion from
tectonic reconstructions that the shallow waters around Gondwana were
populated by faunas typical of the period [1]. Early Cenozoic fossils from
Seymour Island indicate that prior to the oceanographic isolation of
Antarctica, the fish fauna of Gondwana was diverse and contained
representatives of many cosmopolitan taxa. The fauna appears to have been
typical of the temperate seas of the time.
Unfortunately there are few postEocene fossil fish known from
Antarctica and the modem fauna thus has no fossil record. We are
therefore left with the intriguing observation that at some time between the
Eocene and today, early Tertiary fish fauna of Antarctica largely
disappeared. There was then a substantial radiation of notothenioid and
liparid fish to produce the fauna we see today.
What Caused the Demise of the Early Tertiary Fish Fauna?
In the absence of a fossil record, we can only speculate on the causes of the
extinction of the early Tertiary fish fauna of Antarctica. Nevertheless it is
tempting to assume that a major factor must have been the severe reduction
in the amount of shallow water and the loss of many habitats traditionally
rich in fish consequent upon the major glaciation of Antarctica. This
working hypothesis would then put the extinction event (if needed it can
be regarded as a single event) around the late Eocene/early Oligocene (4035 Ma BP). An explanation based on habitat loss also implies that the
associated cooling was not necessarily the primary cause of extinction, but
in truth there is no evidence to allow us to distinguish the two causes
(which may have acted together).