| Abstract: | Bien que la durée stratigraphique de la plupart des Bryozoaires crétacés ne soit pas exacterment connue, beaucoup d'espèces caractérisent assez bien les différents étages. Au Crétacé inférieur, dont la faune bryozoologique est plus pauvre que celle du Crétacé supérieur, ce sont les Cyclostomata qui dominent encore, comme au Jurassique. A l'Aptien, citons Chisma, mais aussi Ceata, Meliceritites et Laterocavea apparus au Barrémien. La faune de l'Albien, un peu appauvrie et peu connue, n'a fourni que quelques genres nouveaux encroûtants de Cheilostomata anasca (Rhammatopora, Wilbertopora).Au Cénomanien commence l'explosion des Bryozoaires. Les Cheilostomata les plus anciennes, les Cribrimorpha, les genres “Biflustra”, Cellarinidra, Quadricellaria, Onychocella, “Rhagasostoma”, Stichomicropora, Aechmella et un grand nombre de Cyclostomata (Crisisina, Heterocrisina, Fascipora, Spirentalophora, Marssoniella, Amphimarssoniella, Umbrellina, Exidmonea, Corymbopora, Desmopora, Discocytis, Supercytis, Truncatulipora, etc.) apparaissent. Le Turonien est caractérisé par les genres Cyclostomes (Reticrisina, Bicavea, Homoeosolen), les Cheilostomes (Tylopora, Euritina, Fusicellaria, Reptolunulites) et par de nombreuses Cribrimorpha.Onychocella nerei et Membranipora perincerta sont caractéristiques du Coniacien où l'on trouve aussi les Lunulites et Pavolunulites. Le Coniacien, plus riche en espéces que le Turonien, contient de très nombreux genres et espèces qui se poursuivent dans les étages plus élevés (Santonien-Maastrichtien).This paper deals with the distribution and stratigraphic value of Mid-Cretaceous Bryozoa (Aptian-Coniacian). Research on Cretaceous bryozoa has been neglected during the last decades and knowledge of the stratigraphical range of many Upper Cretaceous genera and species is based mainly on the personal experience of the present author. Accordingly, the range of most species is not exactly known, and the results of these investigations are only preliminary. Many cyclostomate genera (such as Stomatopora, Proboscina, Diastopora, Berenicea and Entalophora) lack easy identifiable specific characteristics, and all the other genera which can be recognized only by their rare ovicells (gonozoids) (such as Plagioecia, Diaperoecia, Microecia, Mecynoecia, Spiropora, Heteropora or Ceriopora, Reptomulticava, Lichenopora and many others) are not particularly suitable as guide-fossils. On the other hand, many characteristic new species have not yet been described.The bryozoa of the Lower Cretaceous are similar to those of the Jurassic. Both are characterized by the absolute predominance of the Cyclostomata and a few very rare primitive Cheilostomata belonging to the encrusting membranimorph Anasca.The Barremo-Aptian fauna, known mainly from England (Faringdon, Berkshire) and eastern and southern France, is characterized by the first Eleidae (Meliceritidae) with Meliceritites and Foricula, the first Ceidae, Clausidae and Horneridae with Siphodictyum and Laterocavea, Chisma furcillatum is known only from the Aptian. Cheilostomata are rare and are represented solely by encrusting membranimorph genera (Rhammotopora, “Membranipora”). The poor Albian bryozoan fauna, although similar to that of the Aptian, is characterized by the appearance of primitive uniserial cheilostomate genera such as (?) Pyriporopsis, Charixa and the genus Wilbertopora. Erect precenomanian Cheilostomata are not known. Albian Bryozoa are little-known and relatively rare.Within the Cenomanian (the plenus-zone included) many new cyclostomate genera Fascipora, Umbrellina, Siphoniotyphlus, Crisisina, Heterocrisina, Discofascigera, Corymbopora, Marssoniella, Amphimarssoniella, Discocytis, Discotruncatulipora, Truncatulipora, Desmepora, Exidmonea, Meliceritella and numerous cheilostomate genera besides “Membranipora” mainly Aechmella, Onychocella, Stichomicropora and several cribrimorphs appear for the first time. The Cenomanian is also characterized by the first erect cheilostomate species such as Onychocella, “Biflustra” or “Vincularia” and the oldest articulated or radicelled cheilostomes (Cellarinidra, Quadricellaria).During the Turonian (excluding the plenus-zone), which is less abundant in Bryozoa than the Cenomanian, the cheilostomes increase (common genera are Onychocella, Euritina, “Rhagasostoma”, bilamellar membranimorphs and cribrimorphs, mainly Rhabdopora) and the first primitive Lunulitidae (Reptolunulites) occur. Among the cyclostomes, represented by numerous species of Meliceritites, Semielea, Foricula, Truncatulipora, Clausa, Petalopora, Heteropora and the first representatives of Homoesolen, Reticrisina, Tervia and Bicavea appear.Within the Coniacian, rich faunas are known from France and England. Although the Cyclostomata are still dominant until the Santonian, considerable progress in the evolution of the Cheilostomata was made mainly by the development of the onychocellids, the erect membranimorphs and the radiation of the different cribrimorph families and genera. The oldest free-living Lunulitidae with Lunulites and Pavolunulites are recorded from the Coniacian. Among the Cyclostomata, the appearance of the genera Diplosolen, Clypeina, Crisina, Filicrisina, Sulcocava, Ditaxia, Pachyteichopora and Cytis is noteworthy. The Coniacian bryozoan fauna is closely related to that of the Santonian and has clearly an Upper Cretaceous character.I refer to the text for comments on single species which may be supposed to be useful as guide-fossils for the Aptian-Coniacian stages. |
