Luis O’Dogherty

Ammonite faunal turnover tracing sea-level changes during the Jurassic (Betic Cordillera, southern Spain)

Ammonite faunal turnover has been used to trace changes in sea level during the Jurassic in the Betic Cordillera, southern Spain (i.e. westernmost Tethys). Major turnovers recorded in the Jurassic succession are interpreted as extinction phenomena, and as appearance, diversification and radiation bioevents of the various ammonite associations. They are explained as being due to falls and rises in sea level, respectively. The ten most abrupt diversification and radiation bioevents have been detected in the ammonite associations associated with pelagic Jurassic sedimentary rocks. All of these bioevents can be linked with sea-level rises, most coinciding with the eustatic increases of the same age expressed in the eustatic curves of Hallam and Haq et al. The relative sea-level falls, including eustatic ones coinciding with extinctions, are recorded as stratigraphic breaks and stratigraphic condensation phenomena in the Betic Jurassic succession. The seven most significant extinction events recognized in the Betic Jurassic are also largely attributable to eustatic falls. We conclude that the proposed faunal turnover curve is predominantly the expression of global changes in sea-level and it can be considered as a basis for plotting a Jurassic eustatic curve.

A morphogenetic explanation of Buckman's law of covariation

In this paper, we demonstrate that Buckmans law of covariation, describing the cases of extreme variability observed in ammonoids, can be explained in a simple way by analysing the internal shell geometry. This geometry can be characterized by the amount of lateral and ventral curvature of the shell which controls the thickness of the mantle and the concentration of morphogens present in the shell-secreting epithelium. The most salient ornamentation is present where the whorls are most curved, shells with slight angular bulges often being spinose or carinate and flat ones being almost smooth. These observations agree with a morphogenetic model based on Meinhardts reaction -- diffusion mechanisms [Meinhardt 1995].

Diversity of radiolarian families through time

The examination of radiolarian biodiversity at the family level through Phanerozoic time reveals some general trends known in other groups of organisms, especially among plankton, while some other trends seem to be quite peculiar. The Permian /Triassic crisis that is one of the most important in the evolution of marine organisms, is marked in radiolarian assemblages by the extinction of two orders (Albaillellaria and Latentifistularia) towards the end of the Permian, and mostly by the tremendous diversification of Spumellaria and Nassellaria in the early-mid Triassic. Radiolarian diversity increased from Cambrian to Jurassic, remained quite stable during the Cretaceous and has decreased slightly since then.

Sea-level changes and ammonite faunal turnover during the Lias/Dogger transition in the western Tethys

The aim of this paper was to investigate the possible connections between ammonite faunal turnover and the eustatic events recorded in Tethyan sequences during the middle Toarcian/early Bajocian time interval. For this we have analysed the biostratigraphic ranges, at the subzone level, of approximately 600 ammonite species belonging to 160 genera from several selected sections of the western Tethys (Mediterranean and Submediterranean provinces). The analysis of taxon ranges enabled us to plot curves for ammonite faunal turnovers, inter-subzonal distance, and diversity. Comparing the mentioned curves with Tethyan sequences [Hardenbol et al., 1998], we find that sea-level changes correlate well with origination and extinction events and faunal diversity. Most of the faunal turnovers correlate with stratigraphic events. Extinction events with their corresponding decrease in diversity correlate with regressive intervals and with major or minor sequence boundaries. Origination events and their corresponding increase in diversity were clearly connected with transgressions in Tethyan sequences. In several cases, the major sequence boundary and the subsequent transgressive phase correlate with major ammonite faunal turnover, whereas minor or medium sequence boundaries generally gave rise to minor or medium turnovers.

New data on Lower Carboniferous stratigraphy and palaeogeography of the Malaguide Complex (Betic Cordillera, Southern Spain)

Abstract The Malaguide basement is formed by a thick, strongly deformed but weakly metamorphosed sedimentary succession of ?Ordovician–Carboniferous age, mainly made of basinal mudstones and turbidites, which includes a thin but conspicuous Lower Carboniferous chert–limestone interval (Falcona formation). The chert member (ribbon radiolarites) yielded, for the first time in Southern Spain, Tournaisian radiolarians. The Visean age of the limestone member is refined by conodonts. This formation is related to a period of generalized pelagic sedimentation, caused by relatively high sea level, low clastic input and high equatorial productivity, which preceded the closure of the Palaeotethys basins due to the Variscan orogeny.

Middle and Late Jurassic radiolarians from the Neotethys suture in the Eastern Alps

Abstract. Cherty limestones, marls and radiolarites are widespread in the Hallstatt Mélange of the Northern Calcareous Alps. The mélange was formed during the Neotethyan orogeny in a series of deep-water basins that progressively developed in front of the advancing nappe front. The low thermal overprint of these rocks favors the good preservation of radiolarians (polycystines) that have been used for dating and reconstructing the Jurassic tectonostratigraphy of the area. This paper describes rich Middle—Late Jurassic radiolarian faunas from four localities in the Hallstatt Mélange near Bad Mitterndorf in Austria. Two different successions, both spanning from the Bathonian to the Oxfordian, are dated. In the first succession, the radiolarites are intercalated between or occur as matrix in mass-flow deposits originating from the accretionary wedge. The second succession is nearly 100m thick but is devoid of mass-flow deposits and documents a continuous radiolarite deposition in greater distance from the nappe stack. Both successions are ascribed to the Sandlingalm Basin, which evolved on a relatively distal continental margin during early stages of the orogeny. The highly diverse and well-preserved radiolarian assemblages have been used for a detailed taxonomic study. Two new families are described: Minocapsidae n. fam. and Xitomitridae n. fam.; six new genera are described Doliocapsa n. gen., Crococapsa n. gen., Parvimitrella n. gen., Xitomitra n. gen., Campanomitra n. gen., and Mizukidella n. gen. In addition, one new replacement name, Takemuraella (pro Triversus), is introduced, the diagnoses of 6 genera are emended, and two new species are described: Hemicryptocapsa nonaginta n. sp. and Mizukidella mokaensis n. sp.

The plankton turnover at the Permo-Triassic boundary, emphasis on radiolarians

The examination of plankton biodiversity through Permian-Triassic period seems to display different patterns of evolution depending of the scale of study (taxonomy stratigraphy or biogeography). In this paper we present the state of the art of the plankton turnover at the Permo-Triassic and we review more precisely the pattern of extinction and recovery of radiolarians during such period, because at that time, plankton was essentially represented by radiolarians. At a global scale the end-Permian to early Triassic period is marked by several strong extinctions in the marine realm, and in the radiolarians they occur progressively as exemplified by two orders of radiolarians: Albaillelaria and Latentifistularia. Nevertheless, this period is marked by a tremendous post-crisis diversification in both at family and generic level, more than extinction; an actualized revision of the diversity at the family level is also offered in our review. At a moderate scale (i.e. genera and in a region) the modifications appear impressive while at specific and regional domain the message is not so clear, one can wonder if some crisis manifestation results from a taxonomic accident or from preservative conditions. In fact, strangely enough more the number of studies is, more the diversity is high, and oppositely less they are, more the provincialism is evoked.

Pentaspongoreta, nomen novum for the genus Anachoreta O’Dogherty, 1994 (Radiolaria), non Gistel, 1848 (Hymenoptera)

In 1994, O’Dogherty (p. 137) erected the genus Anachoreta for a distinctive multicyrtid radiolarian having pentagonal post-abdominal segments in cross-section, a feature hitherto unknown among Cretaceous nassellarians. This monospecific taxon is a useful stratigraphical marker, ranging from the latest Albian to Middle–Late Cenomanian times. Recently, it was discovered that Gistel (1848) first gave the same name Anachoreta to an insect of the suborder Symphyta (Hymenoptera) as replacement name pro Lophyrus Latreille, 1802, previously preoccupied. Therefore, in accordance with the International Code of Zoological Nomenclature (1999) (Article 60), the name Pentaspongoreta is herein proposed as a replacement (type species Anachoreta sagitta O’Dogherty, 1994, p. 138, by original designation) for the preoccupied homonym Anachoreta O’Dogherty, 1994, non Gistel, 1848. Pentaspongoreta is named for its pentahedrical-shaped test and spongy meshwork; feminine gender.