No abstract

About 50% of all animal species are considered parasites. The linkage of species diversity to a parasitic lifestyle is especially evident in the insect order Hymenoptera. However, fossil evidence for host–parasitoid interactions is extremely rare, rendering hypotheses on the evolution of parasitism assumptive. Here, using high-throughput synchrotron X-ray microtomography, we examine 1510 phosphatized fly pupae from the Paleogene of France and identify 55 parasitation events by four wasp species, providing morphological and ecological data. All species developed as solitary endoparasitoids inside their hosts and exhibit different morphological adaptations for exploiting the same hosts in one habitat. Our results allow systematic and ecological placement of four distinct endoparasitoids in the Paleogene and highlight the need to investigate ecological data preserved in the fossil record.

Etter, W. 1995 11 30 Benthic diversity patterns in oxygenation gradients: an example from the Middle Jurassic of Switzerland. A high‐resolution study of the lower Opalinum Clay (Aalenian, Middle Jurassic) of northern Switzerland revealed a pattern of macrobenthic diversity and abundance which does not conform with the dysaerobic‐biofacies models currently in use. The upper dysoxic zone contains an association of moderate diversity and moderate abundance which, with increasing oxygen depletion, is replaced by an association dominated by a few peak opportunists (tiny epibenthic bivalves and presumably small annelids) at high abundances but very low diversity. In the lower dysoxic zone, abundance drops to very low levels, but diversity rises again to quite high values. The rather high diversity of the lower dysaerobic biofacies is explained in part by the presence of specialized chemosymbiontic species. The pattern documented in the lower Opalinum Clay has been calibrated by sedimentologic, taphonomic, ichnologic, and microfaunal evidence. It contradicts equilibrium models, which postulate gradual or even linear decreases in both abundance and diversity with increasing oxygen‐depletion of the bottom water. The equation of rising diversity with improved oxygenation can be misleading and can yield erroneous results in the reconstruction of ancient bottom‐water oxygenation. □Dysaerobic biofacies, high‐resolution study, diversity, chemosymbionts, equilibrium and non‐equilibrium models.

A new isopod species, Eonatatolana geisingensis gen. et sp. nov., is described from Middle Jurassic shallow-water sediments of southern Germany. It shows not only the almost completely preserved dorsal morphology but, in addition, details of the cephalic appendages, the pereiopods, pleopods and uropods. The presence of ambulatory pereiopods I-VII of a wide tridentate mandibular incisor with prominently developed posteriormost tooth and a narrow frontal lamina indicates that the new species belongs to the subfamily Conilerinae of family Cirolanidae within the suborder Cymothoida. It is closer to the species of the modern genus Natatolana Bruce than to any fossil isopod hitherto described. The isopod fossil record as well as current practices of isopod taxonomy in palaeontology are discussed, and the facies distribution and fossilization of isopods is reviewed with examples from the Jurassic.

Four species of decapod crustaceans from the Middle Jurassic Opalinus Clay (Aalenian) of Northern Switzerland are described. Of these, Mecochirus cf. eckerti is the most common one, while Eryma cf. bedelta, Glyphea sp. and Aeger sp. were present as individuals, or only a few specimens. The preservation of these crustaceans ranges from moderate to excellent, reflecting the favourable taphonomic conditions of the depositional environment. An interesting aspect of the taphocoenosis in the Opalinus Clay is that the decapod crustaceans are by far outnumbered by small peracarid crustaceans (isopods and tanaids). This is interpreted as reflecting the original differences in abundance. Yet this distribution is not frequently encountered in sedimentary sequences where decapods (although rare) are far more common than isopods and tanaids. In rare instances, this reflects the original predominance of decapods, more often it is a consequence of the differential taphonomic behaviour of these two groups. A new model relating the ecology to the taphonomic behaviour of decapod and peracarid crustaceans is proposed. According to this model, decapods dominate in settings that were deposited under extremely dysoxic (peracarids wiped out by seasonal anoxia) as well as under fully oxic conditions (peracarids destroyed by taphonomic processes). Only in muddy dysoxic depositional environments are peracarid crustaceans frequently preserved. In these settings with equal preservation potential of decapods and peracarids, the original composition of the crustacean fauna would show a predominance of peracarid crustaceans. Examples from some well known fossiliferous settings are provided to illustrate the use of the new model. ZUSAMMENFASSUNGAus dem Opalinuston (Mittlerer Jura, Aalenian) der Nordschweiz werden vier Arten von decapoden Krebsen beschrieben. Von Aeger sp., Eryma cf. bedelta und Glyphaea sp. wurden nur ganz wenige Exemplaren gefunden, während Mecochirus cf. eckerti etwas häufiger ist. Die Erhaltungsbedingungen waren während der Ablagerung des Opalinustones günstig, was sich in einer geringen Disartikulations-und Fragmentationsrate der Krebse widerspiegelt. Ein interessanter Aspekt der Taphocoenose ist die deutliche Dominanz der Kleinkrebse (Peracarida: Isopoden und Tanaidaceen). Dies dürfte die Zahlenverhältnisse der ehemaligen Lebensgemeinschaft widerspiegeln. In den meisten Ablagerungen dominieren jedoch die decapoden Krebse, wogegen Peracarida äusserst selten sind. Nur in den wenigsten Fällen entspricht dies einem ursprünglichen Überwiegen der Decapoda, viel öfter ist es eine Folge des unterschiedlichen Fossilisationspotentials der beiden Gruppen. Hier wird ein neues Modell vorgeschlagen, welches Ökologie und taphonomisches Verhalten der decapoden und peracariden Krebse miteinander verknüpft. Nach diesem Modell dominieren die Decapoda in Ablagerungen, welche in stark dysoxischem (Peracarida werden durch anoxische Ereignisse ausgelöscht) oder in vollkommen oxischem Milieu (Peracarida werden durch taphonomische Prozesse zerstör...