Arkell.1956.Jurassic..

MARINE REALMS 607
head of the Gulf of California. We should say, nowadays, 'North
Cordilleran province'.
2. Mediterranean-Caucasian realm (for short, Mediterranean realm),
including on its north side the central European and south Russian province
as a 'neritic marginal zone'.
3. Himamalayan realm, combining the Himalayan and Malayan provinces
and the isolated Maorian (New Zealand) and Ethiopian provinces.
4. South Andine realm, including the Middle and South American
outcrops from Mexico to Cape Horn and, for the Neocomian, including
the Uitenhage beds of South Africa.
Innumerable facts subsequently accumulated are incompatible with
this scheme and demand extensive modifications. For instance, as was
shown above, the Kimeridgian faunas of Mexico (realm 4) show marked
affinity with those of New Zealand (realm 3) and essential elements have
also been found in Indonesia and Japan. The Bajocian faunas of southern
Alaska and western Canada (realm 1) are not boreal; they connect with
those of Western Australia (realm 3) and western Europe (realm 2). Such
instances could be multiplied at length.
It is clear that the time factor was not given sufficient weight by
Neumayr (1883) or Uhlig (1911). No map can show faunal provinces
for the whole Jurassic, for the entire situation was constantly changing.
The key to the problem is the sporadic but progressive differentiation of
marine faunas during the Jurassic. Oppel and Waagen already realized
this. Waagen wrote (1864, p. 98): 'The higher we climb in the Jurassic
series the greater become the difficulties, either of recognizing or separating
individual beds, or of correlating.' The climax is reached in the uppermost
Jurassic with the situation which still to this day requires a threefold
use of stage names—Tithonian, Volgian and Portlandian-Purbeckian,
according to the part of the world.
During the Lower Jurassic (Lias) ammonite faunas seem to have been
universal (fig. 97). The Hettangian and Sinemurian ammonites of western
Canada, northern Alaska, Indonesia and Peru agree at specific level with
those of western Europe, and European genera have been recognized in
New Zealand, New Caledonia and the Himalayas. Of European Pliensbachian
genera, Uptonia occurs in Greenland, Amaltheus, Lytoceras and
? Crucilobiceras in northern Alaska, Amaltheus and Phylloceras on the
north coast of Siberia. Recent work reviewed in this book proves that in
Japan there is a succession of Pliensbachian, Toarcian and Lower Bajocian
faunas essentially the same as that in Europe, including some genera
especially characteristic of the Mediterranean countries. In addition,
however, there are some endemic forms which have not yet been matched
elsewhere. Typical European Toarcian Pseudolioceras faunas, usually
with Dactylioceras, occur in Transbaikal, Spitsbergen, Greenland and
northern Alaska, and probably also in the Canadian Arctic Archipelago.
The Lower Bajocian faunas may have a similar distribution, for a Ludwigia
murchisonae assemblage is known near the Arctic Circle in the basin of
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