THE MEDITERRANEAN LOWER CRETACEOUS

U h 1 i g (1911) proposed the following division of the sea realms for the Late
Jurassic-Early Cretaceous (Fig. 23):
1. Boreal Realm, including also the Northern Andean Province.
2. Mediterranean-Caucasian Realm in which a northern "peripheral neritic
zone" is outlined.
3. Himalayan Realm with the following subprovinces: Himalayan, Ethiopian
and Maori.
4. Japanese Province.
5. Southern Andean Realm.
The new studies on the Early Cretaceous faunistic distribution, and especially
of ammonites, have changed U h 1 i g' s idea in many respects, although the outlines
of some of his provinces are preserved. As A г к e 1 (1956) has pointed out,
the basic shortcoming in the reconstructions of N e u m а у г (1883) and U h 1 i g
(1911) is the lack of a clear historical approach. This approach, applied in more
modern research, demonstrates a developing palaeobiogeographic panorama. It
is diversified by the emergence of different geographic barriers which isolate the populations
of the different regions, and, if these barriers are longer-lasting, they result
in a complex provincial differentiation. In such cases it may be assumed that the changes
in the faunas are the result of evolution influenced by the geographic isolation.
An example in this respect may be the isolation of the Mangislak Basin by the
emergence of a land barrier to the east of the Caucasus. This barrier played
an important palaeobiogeographic role during the Early Cretaceous and contributed
to the development of specific faunas in Mangislak and Turkmenia, with many
endemic elements and immigrants from the Boreal Basin. Consequently, geographic
isolation results in differentiation and formation of endemic faunistic associations.
The palaeobiogeographic environment develops also on the basis of the ammonite
distribution and it is possible to distinguish two main intervals: Berriasian-Barremian
and Aptian-Albian, with certain fluctuations within them.
The Barremian marks a natural boundary in the changing picture of the ammonite
distribution. Until the end of this Age the ammonite biogeography bears the
features of the model formed during the Late Jurassic, whereas essential changes
in the palaeobiogeographic panorama were imposed after the Barremian. These
changes are connected with substantial alterations in the distribution of the dry
land and shelf seas (R a w s о n, 1980).
The beginning of the Early Cretaceous indicates bipolarity in the ammonite
distribution outlined during the Late Jurassic (E n a y, 1972). The Tethys Ocean
occupied a median position in the Earth's hydrosphere, developing in subequatorial
direction between the two basic continental masses. To the north is the Boreal, to
the south — the Perigondwana Basin.
The development of the Perigondwana Basin as a palaeobiogeographic belt
(realm) is disputed by some authors, but it is supported not only and not so much
by the ammonite horology, as by the distribution of the Early Cretaceous belemnites
(Stevens, 1973), bivalvs (K a u f f m a n, 1973) and other groups of invertebrates.
The Mediterranean Region occupies the central part of the Tethys Ocean,
starting from the southern part of the North Atlantic Ocean and continuing in the
east to the Caspian Sea.
A number of authors (e. g. Wiedmann, 1982b) expand the Mediterranean
Region through the Caribbean Basin in the southwest to Peru. The Berriasian
ammonite faunas of Peru, Central Argentina and Patagonia contain many endemic
genera, which is the base for the differentiation of a common Caribbean-Andean
area with two provinces: Caribbean (Mexico, Cuba and probably California), where
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