166
R. R. DELL
about 2 million years ago. Hays believes that on this evidence glaciation
began about 4.5 million years ago, and that there have been two periods
of rapid cooling since then, one at about 2.5 million years ago, the other
at 700 000 years ago. From a study of Radiolaria in sea bottom deposits,
Hays (1965) concluded that the Antarctic Convergence could have
shifted north by about 5' of latitude during glacial maxima.
It seems certain therefore that gradual cooling set in about midTertiary, and that the Antarctic Continent has not been free of ice since
this period of refrigeration set in. The general hydrological conditions
existing today would probably be initiated once ice shelves dominated
the edges of the Continent, and began to produce the cold Antarctic
Bottom Water.
Adie (1963) considered that problems connected with the distribution of faunas and floras of the Southern Hemisphere fell into two clearcut periods, the first before the Cretaceous, and the second, after the
Cretaceous. Although there may well have been suitable connections
between South America and Antarctica through the Andean geosyncline
in the Carboniferous, this connection does not appear likely to have
influenced the existing fauna.
However, since the early Tertiary there appears to have been some
form of connection between South America and Antarctica through the
Scotia Arc (Adie, 1963).
Some Antarctic groups appear to be of relatively ancient origin.
The ophiuroid genera differ markedly from genera in other parts of the
world. The evidence points to a long evolution in comparative isolation
during the Tertiary (Fell, 1961). The cidarid ecninoids originating in
the Palaeozoic have shown slow rates of evolution throughout their
history. However, the subfamily Ctenocidarinae has developed in the
Antarctic.
Pawson (1969a) considered that the only close relationship of the
Antarctic holothurian fauna with any Subantarctic area was with
southern South America. The generic composition lends credence to the
belief that the Antarctic fauna has been built up by those forms which
could tolerate low temperatures, and which could enter the area from
South America. Some of these elements may have been derived ultimately from the Indo-Pacific or even the New Zealand area with the
assistance of the West Wind Drift.
Two opposing views have been advanced regarding the origin of the
Antarctic crinoids. Marr (1963) suggested that the high Antarctic
forms probably originated on the shelf, the evidence being largely based
upon the circumpolar distribution of such endemic species as Promachocrinus kerguelensis. On the other hand, John (1938) believed that
R. R. DELL
about 2 million years ago. Hays believes that on this evidence glaciation
began about 4.5 million years ago, and that there have been two periods
of rapid cooling since then, one at about 2.5 million years ago, the other
at 700 000 years ago. From a study of Radiolaria in sea bottom deposits,
Hays (1965) concluded that the Antarctic Convergence could have
shifted north by about 5' of latitude during glacial maxima.
It seems certain therefore that gradual cooling set in about midTertiary, and that the Antarctic Continent has not been free of ice since
this period of refrigeration set in. The general hydrological conditions
existing today would probably be initiated once ice shelves dominated
the edges of the Continent, and began to produce the cold Antarctic
Bottom Water.
Adie (1963) considered that problems connected with the distribution of faunas and floras of the Southern Hemisphere fell into two clearcut periods, the first before the Cretaceous, and the second, after the
Cretaceous. Although there may well have been suitable connections
between South America and Antarctica through the Andean geosyncline
in the Carboniferous, this connection does not appear likely to have
influenced the existing fauna.
However, since the early Tertiary there appears to have been some
form of connection between South America and Antarctica through the
Scotia Arc (Adie, 1963).
Some Antarctic groups appear to be of relatively ancient origin.
The ophiuroid genera differ markedly from genera in other parts of the
world. The evidence points to a long evolution in comparative isolation
during the Tertiary (Fell, 1961). The cidarid ecninoids originating in
the Palaeozoic have shown slow rates of evolution throughout their
history. However, the subfamily Ctenocidarinae has developed in the
Antarctic.
Pawson (1969a) considered that the only close relationship of the
Antarctic holothurian fauna with any Subantarctic area was with
southern South America. The generic composition lends credence to the
belief that the Antarctic fauna has been built up by those forms which
could tolerate low temperatures, and which could enter the area from
South America. Some of these elements may have been derived ultimately from the Indo-Pacific or even the New Zealand area with the
assistance of the West Wind Drift.
Two opposing views have been advanced regarding the origin of the
Antarctic crinoids. Marr (1963) suggested that the high Antarctic
forms probably originated on the shelf, the evidence being largely based
upon the circumpolar distribution of such endemic species as Promachocrinus kerguelensis. On the other hand, John (1938) believed that