Patrick R. Racheboeuf

TRACE FOSSILS FROM NEARSHORE TO OFFSHORE ENVIRONMENTS: LOWER DEVONIAN OF BOLIVIA

Abstract Abundant and diverse trace fossils occur in deposits, recording an Early Devonian transgression in Bolivia. The very well-exposed Presto-El Peral section is located in the Interandean Belt 50 km northeast of Sucre. Trace fossils can be assigned to five associations from nearshore to offshore environments (namely Skolithos, Diplocraterion, Altichnus, Palaeophycus, and Zoophycos associations). They clearly illustrate the different colonization phases of the benthos with increasing marine influence. A deeper-water Helminthopsis association occurs in other complementary sections on the Eastern Cordillera. Variation of bioturbation intensity, ichnodiversity, and preservation potential is evaluated. The morphology of traces, mainly deep burrows, shows a significant gradient related to the behavior of tracemakers and the environmental changes. Main trends are consistent with the Seilacherian bathymetric model which is detailed here and/or emended with a well-exposed field example. A precise correlation is proposed with fossil benthic associations dominated by brachiopods. The whole gives an accurate model for benthos colonization and benthic marine zonation.

Les Brachiopodes chonetacés dans les assemblages benthiques siluriens et devoniens

Abstract The distribution of chonetacean branchiopods within Siluro-Devonian benthic assemblages demonstrates clear relationships between morphology and paleoenvironments. Silurian chonetaceans may be assigned to five morphoogical types. The subsequent diversification of environments following Early Devonian transgression was translated into a radiational expansion. Shell shape, particularly the development and distribution of hinge spines, reflected environmental conditions (e.g. substrate grain size, hydrodynamics) enabling a bathymetric zonation of the chonetaceans along a gradient of benthic assemblages. These results led to a reconsideration of the function of the chonetid spines, interpreted as attachment structures, and to other paleobiologic, paleogeographic and phylogenetic implications.

Trilobites et Ostracodes du Dévonien inférieur de la zone d’Ossa-Morena (Espagne)

Resume Les Trilobites et Ostracodes provenant de trois unites paleozoiques de la Zone d’Ossa-Morena (Sud de l’Espagne) apportent des precisions sur la stratigraphie du Devonien inferieur (Praguien-Emsien inferieur) de cette region. La repartition geographique de ces fossiles confirme les affinites (au niveau specifique) existant entre les faunes benthiques du Sud de l’Europe et du Nord de l’Afrique; en outre elle illustre l’uniformisation des faunes entre les regions nord-gondwaniennes et celles qui constituent la bordure sud du Continent des Vieux Gres Rouges. Les moules externes et internes des Ostracodes sont decrits. Ils montrent des relations avec les faunes neritiques de meme âge en Europe; Cornikloedenina? meridiana nov. sp. se distingue par un lobe adductorial epineux. Des Ostracodes presentent l’ornementation en empreinte digitale caracteristique des Entomozoacea et deux groupes d’epines, l’un antero-median, l’autre antero-ventral, ont ete trouves pour la premiere fois; ils sont decrits comme Morenozoe racheboeufi nov. gen., nov. sp. et leur position systematique est discutee.

New Hyolitha from the Devonian of Bolivia

Abstract New finds of Hyolitha in the Devonian of Bolivia consist of the hyolithid Bolithes crasquinae new genus and species, which is the first well-preserved hyolithid from strata of this age in the region. In addition, specimens of the orthothecids Bolitheca steinmanni (Knod, 1908) and Neobactrotheca pharetra Marek and Isaacson, 1992 serve to increase knowledge concerning the range of morphologic variability within those taxa. Incompletely preserved hyoliths include Hyolithes sp. indet.? which would be the first definitive representative of that genus from South America. Two polyclaviculate hyolithid opercula, and an unusually large hyolithid conch are left in open nomenclature. The large conch is noteworthy because of signs of failed predation, making this only the second hyolithid on record on which the effects of predation can be recognized, and the first from the Devonian of South America. Hyolithes dorbignyi Kozlowski, 1923 is transferred to ‘Hyolithes’ owing to poor preservation.

Spine asymmetry in chonetoidean brachiopods: an example of reiterated heterochronies linked to intra-Devonian events

Abstract From the Early Devonian, the distribution of spines along the posterior margin of the ventral valve of chonetoidean brachiopods, previously symmetrical on each side of the beak during the Silurian, exhibits asymmetrical examples. The asymmetry of spines affects mainly two families which are widely distributed in the Old World Realm during the Devonian: strophochonetids and anopliids. The detailed vertical range of asymmetrical forms, compared with conodont zones, suggests close relationships with Lower and Middle intra-Devonian events. The geographic distribution of the asymmetrical taxa indicates that they mainly characterize the intertropical zones. The development of spine asymmetry is interpreted herein as an innovation and a progenetic heterochrony linked to the onset of a pioneer strategy with an epiplanktonic mode of life. The spine asymmetry is repetitive and a consequence of the intra-Devonian events which contributed to the expression of diversity among chonetoidean brachiopods.

Paulinella nov. gen., new Devonian terebratuloid (Brachiopoda) from Europe

Abstract A new genus is erected to include some European,Early Devonian terebratuloid species traditionally assigned to Trigeria Bayle , 1878 . Paulinella guerangeri ( Verneuil ) and P. gaudryi ( Oehlert ) are redescribed and lectotypes designated (the former is the type species of the new genus). The mutationellid origins of Paulinella nov. gen. are pointed out.

Devonian (Givetian) Hyolitha from the Kersadiou Formation, Massif Amoricain, France

Abstract Among hyoliths from the Givetian Kersadiou Formation in northwestern France one form is assigned to Hyolithes triliratus Hall, 1879, which is used as the basis for Brittanella new genus. The occurrence of this species in France supports affinity for fauna in that region to the Eastern Americas Realm. Other hyoliths from this unit include one species of Hyolithes Eichwald, which is left in open nomenclature, and one conch and one platyclaviculate operculum that cannot be identified to genus. The occurrence of these fossils in concretions in an oxygen-stressed dark gray shale supports the notion that this environment served as a refuge for taxa that were less efficient competitors with other normal marine benthos in the Devonian.

Sensory structures of Archaeostraca (Phyllocaridida, Crustacea)

SUMMARY The carapace of some Archaeostraca exhibits two kinds of structures that are best interpreted as corresponding to sensory organs. Dorsal ones are located either along the dorsal margin of the valves of the carapace, or on the median dorsal plate. Anterolateral ones are located in the anterior region of both valves. Both structures are respectively homologous of the anterior and posterior sensory organs known from extant Leptostraca and other Crustacea. These structures are described in adult Archaeostraca from the Ordovician to the Carboniferous. It is expected that they could have baroreceptor, mechanoreceptor, and/or chemoreceptor functions in some cases, and a function in osmotic regulation in others.

THE DEVONIAN OF THE HODH AREA (ISLAMIC REPUBLIC OF MAURITANIA): PALEONTOLOGY AND STRATIGRAPHY

Abstract Paleontological study of 16 samples from four sections through the Silurian-Devonian marine deposits of the Hodh region establishes the development of the Middle Devonian and adds to our knowledge of the Paleozoic sequence in the West African platform. Above Silurian deposits locally dated by graptolites from the Llandovery, Devonian shales yield an abundant although low diversity benthic fauna, which is assigned to a Givetian age. The brachiopod fauna shows strong affinity with the NE Americas Realm. Two new species are described, Arcuaminetes deynouxi and Eleutherokomma monodi. The revision of the Devonian fauna of the Hodh area supports: 1) the apparent lack of Lower Devonian deposits; 2) the Givetian age of the Devonian succession; and 3) the strong eastern Americas Realm affinity of the fauna, as previously established for the Mauritanian Adrar area.

Reclassification of Semenewia concentrica (De Koninck, 1847) (Brachiopoda, Lower Carboniferous)

Abstract Reinvestigation of Semenewia concentrica ( De Koninck , 1847), previously considered to be a chonetoidean, reveals that it belongs amongst the strophalosioid productida. Futhermore Semenewia turns out to be a synonym of some specimens of Palmerhytis Brunton & Mundy , 1986, so the remaining specimens of the latter are renamed Parmephrix nov. gen., with the new type species P. eileeni nov. sp.