| mhorn | Дата: Sunday, 01.02.2015, 18:26 | Сообщение # 1 |
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| Enay R., Gallois R., Etches S. (2014) Origin of the Kimmeridgian-Tithonian Boreal perisphinctid faunas: migration and descendants of the Tethyan genera Crussoliceras and Garnierisphinctes // Revue de Paléobiologie, Genève. Vol.33. no.2. P.299-377.
http://www.ville-ge.ch/mhng/paleo/paleo-pdf/33-2/pal_33_2_01_1.pdf
http://www.ville-ge.ch/mhng/paleo/paleo-pdf/33-2/pal_33_2_01_2.pdf
Kimmeridgian perisphinctid faunas from England and eastern France have been studied in order to try to clarify the relationships between the Late Kimmeridgian perisphinctids of the Boreal Faunal Realm, whose forerunners are unknown in the Subboreal Province, and their possible ancestors in the Submediterranean Province of the Tethyan Faunal Realm. From Late Oxfordian times onward eastern France was occupied by the Western Europe Swell, a shallower water area that acted as a transitional faunal region between the Subboreal and Submediterranean Provinces. Different biozones have been developed within the provinces, and these are still imperfectly correlated. They are discussed in the present account. Here, we describe the stratigraphical and geographical distributions of the perisphinctid genera that form the basis for the study. They include the Submediterranean forms Crussoliceras and Garnierisphinctes, the Subboreal Subdichotomoceras and Pectinatites,and Tolvericerasand Pseudogravesia of the Western European Swell. Many of the English specimens studied are preserved as crushed impressions, but their positions are accurately located within a well-defined chronostratigraphical succession. In contrast, the stratigraphical relationships of much of the material from France, mostly museum specimens in solid preservation in old collections, are uncertain or have yet to be clarified. The palaeontological descriptions include 18 species or subspecies of which 8 species (Crussoliceras dubisense, lamberti, lotharingicum, petitclerci, ? Subdichotomoceras praecursor, Tolvericeras anglicum, popeyense, robertianum) and 1 subspecies (Subdichotomoceras lamplughi dorsetense) are new. The last part of the paper discusses the origin of the Subboreal perisphinctids, including the possibility that Subdichotomoceras evolved from Crussoliceras and that Pectinatites may have evolved from Subdichotomoceras. However, with the possible exception of ? S. praecursor n. sp. from the Western Europe Shelf of eastern France, there is no published description of a transitional form between Crussoliceras and Subdichotomoceras. An evolution quantum jump is needed to explain the sudden morphological differentiation of Subdichotomoceras. This probably occurred via peripatric speciation
Middle Jurassic - Lower Cretaceous ammonites & aptychi
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