THE MEDITERRANEAN LOWER CRETACEOUS

Aegocrioceras and Menuticrioceras), late Neocomitinae (Neohoploceras, Acanthodiscus,
Lyticoceras, Eleniceras, Karakaschiceras, Leopoldia and Suboosterella),
early Desmoceratidae (Eodesmoceras, Subsaynella and Valdedor sella),
early Holcodiscidae (Spitidiscus, .Plesiospitidiscus and Valdedor sella), Osterellidae
and Olcostephanidae. These genera are represented by many species in both provinces
of the area. In the Alpine Province there are some endemic taxa (Breitstrofferella).
A strong Boreal influence continued to be felt during the Hauterivian in the
northern European-Caucasian Province, this influence being particularly pronounced
in the Crimea and in North Caucasus. Boreal genera were widespread in the North-
Caucasian Hauterivian Basin, among which Speetoniceras, Simbirskites and Craspedodiscus
reached mass flourishing which guaranteed a dominating position for
them with respect to numbers and variety over the Mediterranean species (Д p yщиц,
Кудрявцев, 1960).
Some genera, e. g. Lyticoceras, Endemoceras, Distoloceras and Acanthodiscus,
which are of Mediterranean genealogy, are widespread in the northern province
of the Mediterranean Region and in the southern provinces (Northwest-European
and Volga Provinces) of the Boreal Belt. Some of them even manifest considerable
cladogenesis in the Borea! Basins (Endemoceras and Acanthodiscus).
Strong affinities exist with the Malgasian and Andean Provinces. For example,
heteromorphs are very well represented in Madagascar and Argentina, which indicates
the period of their greatest expansion in the Tethys, coinciding with the middle
of the Hauterivian.
Barremian ammonite faunas in the Mediterranean are of a more homogeneous
character, and it is difficult to distinguish the two provinces from the previous ages.
Moreover, the Boreal invasions are felt only in Northern Caucasus and partially
in the Crimea. The character of Barremian ammonite faunas is determined by the
almost general distribution of late Crioceratites, Acrioceras, Paracrioceras, Pseudothurmannia,
Hamulina, Anahamulina, Hemicrioceratites, Lepioceratoides, Toxoceratoides,
Audouliceras, Heteroceras, Hemihoplites and Matheronites, as well as
varied Barremitinae, Torcapella, Holcodiscus, Spitidiscus, Astieridiscus, Silesites,
Pseudosaynella, Heinzia, Nkklesia, Pulchellia, Subpulchellia and Abritusites.
The variety among Barremian ammonites is considerably greater than during
the previous two Ages. It is comparable only to the Berriasian, but even in comparison
with this age during the Barremian there was a considerably greater generic
differentiation, especially among heteromorphs.
There are grounds for assuming (К о т e т и ш в и л и, 1978) that bathymétrie
factors and the character of the sedimentation environments had a strong influence
on the distribution and diversity of the Barremian ammonites (and not only
Barremian), though this is most marked among them.
Characteristic Barremian ammonites, such as Colchidites, Emerites and Eristavia,
emerged in the Transcaucasian basins of Georgia, spreading from there to
the entire Mediterranean Region. In addition to Georgia, these ammonites are particularly
abundant in Northeastern Bulgaria, Romania and Southeastern France.
Barremites, Pulchellia, Nicklesia, Holcodiscus, Silesites and Hemihoplites stand
out among Barremian ammonites with their extensive distribution. Most of these
genera are known from Japan, throughout the entire Tethys Region to.Central and
South America, but they avoided Boreal waters.
Boreal immigrants: Simbirskites, Speetoniceras and Craspedodiscus, are found
in the northern part of the Mediterranean Region (mainly in the Crimea and Northern
Caucasus).
Generally speaking, the distribution of Barremian ammonites in the Mediterranean
Region manifests a decrease in generic diversity from south to north,
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