Euan N. K. Clarkson

Autofluorescence imaging, an excellent tool for comparative morphology

Here we present a set of methods for documenting (exo‐)morphology by applying autofluorescence imaging. For arthropods, but also for other taxa, autofluorescence imaging combined with composite imaging is a fast documentation method with high‐resolution capacities. Compared to conventional micro‐ and macrophotography, the illumination is much more homogenous, and structures are often better contrasted. Applying different wavelengths to the same object can additionally be used to enhance distinct structures. Autofluorescence imaging can be applied to dried and embedded specimens, but also directly on specimens within their storage liquid. This has an enormous potential for the documentation of rare specimens and especially type specimens without the need of preparation. Also for various fossils, autofluorescence can be used to enhance the contrast between the fossil and the matrix significantly, making even smallest details visible. ‘Life‐colour’ fluorescence especially is identified as a technique with great potential. It provides additional information for which otherwise more complex methods would have to be applied. The complete range of differences and variations between fluorescence macrophotography and different types of fluorescence microscopy techniques are here explored and evaluated in detail. Also future improvements are suggested. In summary, autofluorescence imaging is a powerful, easy and fast‐to‐apply tool for morphological studies.

Faunal dynamics and microevolutionary investigations in the Upper Cambrian Olenus Zone at Andrarum, Skåne, Sweden

Abstract The Upper Cambrian Homagnostus obesus/Olenus Biozone is well exposed in the old quarries at Andrarum, and is typically represented by unfossiliferous black shales with fossiliferous carbonate concretions. Near the north end of the “Great Quarry”, however, the shales themselves are replete with fossils, and in these a 1.8 m section has been logged to establish how trilobite populations fluctuated through time. Successive bedding planes were examined, at 1-cm intervals where possible, and for each surface trilobite exuviae, with rare complete specimens, were counted within a 5×5 cm quadrat. Olenus and Homagnostus are very common, but their abundance fluctuates dramatically; they co-occur in the upper part of the sequence but are otherwise almost mutually exclusive. This suggests that they had different ecological requirements. The rare Glyptagnostus and the bradoriid “ostracode” Cyclotron are confined to particular levels; the latter genus is found where no other fossils are present and may have be...

Structure, ontogeny, and moulting of the olenid trilobite Ctenopyge (Eoctenopyge) angusta Westergård, 1922 from the upper Cambrian of Västergötland, Sweden

The genus Ctenopyge is known mainly from disarticulated sclerites and from rare complete specimens flattened in shales. Hitherto, very few specimens have been found preserved intact and in three dimensions. In a recently discovered fauna, however, in the Peltura minor Subzone in Vastergotland, central Sweden, there occur several species of Ctenopyge, of which many are complete and superbly preserved; moreover they occur at all stages of growth. Of these the abundant Ctenopyge (Eoctenopyge) angusta Westergard, 1922 is described and reconstructed here as an adult, and the entire ontogeny is documented for all post–protaspid growth stages. Many characters typical of the adult, such as the long genal spines and the caudal spine, develop very early in ontogeny, and the relative dimensions of the cranidium do not greatly change during growth. Macropleural spines, however, develop later. The transitory pygidium, relatively large and shield–shaped in the early meraspid, later becomes very small as the ten thoracic segments are liberated; a median spine develops on the last thoracic segment only at the holaspid stage. Instar groupings can be clearly distinguished for the early stages. Recurrent associations of sclerites are interpreted as moulting configurations. As reconstructed, the genal spines are horizontal and parallel with the extended thorax; an adaptation which presumably allowed the trilobite to rest on the sea floor.

Ontogeny of the carboniferous trilobite Paladin eichwaldi shunnerensis (King 1914)

The Carboniferous trilobite Paladin eichwaldi shunnerensis (King 1914), at its type locality in northern England is exceptionally well-preserved, and shows all stages of growth from the degree 0 meraspis onwards. The post-protaspid ontogenyis described here with particular reference to the development of cuticular sculpture. On the dorsal surface of the smallest specimens a polygonal network of raised ridges (cell polygons) is apparent. With size increase, granules progressively appear amongst the polygons, which in turn change into large tubercles as the polygonal network fades. As the trilobite grows into an adult, the tubercles become relatively smaller, and pits, the openings of cuticular canals, appear amongst them. Marginal terrace lines become pronounced. On the hypostome, however, terrace lines become effaced centrally, while large pits develop. In the early meraspis the eyes are “schizochroal”, but the lenses rapidly become closely packed and contiguous and the eye is soon of “holochroal” type. The meraspid phase is passed through very rapidly. Whereas the earlymeraspis could not enroll, its pygidium could be bent down vertically, and this facility might have allowed the larva an escape reaction.

Image formation by bifocal lenses in a trilobite eye

In this work we report on a unique and ancient type of eye, in which the lower surface of the upper calcite lens units possessed an enigmatic central bulge making the dioptric apparatus similar to a bifocal lens. This eye belonged to the trilobite Dalmanitina socialis, which became extinct several hundred million years ago. As far as we know, image formation by bifocal lenses of this kind did/does not occur in any other ancient or modern animal visual system. We suggest that the function of these bifocal lenses may be to enable the trilobite to see simultaneously both very near (e.g. floating food particles and tiny preys) and far (e.g. sea floor, conspecifics, or approaching enemies) in the optical environment through the central and peripheral lens region, respectively. This was the only reasonable function we could find to explain the puzzling lens shape. We admit that it is not clear whether bifocality was necessary for the animal studied. We show that the misleading and accidental resemblance of an erroneous correcting lens surface (designed by René DesCartes in 1637 [DesCartes, R. (1637). Oeuvres de DesCartes. La Géometrie. Livre 2. pp. 134. J. Maire, Leyden] to the correcting interface in the compound Dalmanitina lens may be the reason why the earlier students of the Dalmanitina lens did not recognize its possible bifocality.

Ontogeny and structure of a new, miniaturised and spiny olenid trilobite from Southern Sweden

Several hundred specimens of a tiny olenid trilobite, Ctenopyge ceciliae sp. nov., have been found in stinkstone nodules in the upper Cambrian Peltura scarabaeoides Zone in southern Sweden. This exceptionally spinose form is known only from disarticulated specimens, but is quite well preserved, and all growth stages are represented. The early ontogenetic stages are exceptionally small, the protaspis being only half the size of that of the associated Peltura species. There may have been no more than three thoracic segments. Thus the whole ontogeny was compressed, and this together with the very small size of the adult indicates a true miniaturisation. Whereas the likely control of the origin of the tiny C. ceciliae was basically progenesis, the extreme spinosity had a different origin; allometric growth or possibly peramorphosis. C. ceciliae is small enough for the spines to have appreciably retarded sinking through frictional effects, and this small trilobite is interpreted as a free-swimming or floating form.

Geochemistry of a Silurian metabentonite and associated apatite from the North Esk Inlier, Pentland Hills

Synopsis Geochemical data are presented for an important metabentonite horizon within the Upper Llandovery and early Wenlock succession of the North Esk Inlier of the Pentland Hills. The metabentonite marks a horizon of rapid faunal change, with a rich assemblage below and an impoverished assemblage above. Characterizing the metabentonite and its constituent apatite crystals on the basis of rare earth and other trace elements has allowed two separate outcrops to be correlated locally and the source magma type identified. In addition, these apatite data provide a chemical fingerprint with which to correlate this horizon with similar occurrences elsewhere in northern Europe.

Palaeoecology of the Viséan of East Kirkton, West Lothian, Scotland

The Visean sequence at East Kirkton was deposited in a shallow lake, set within a richly vegetated landscape formed of volcanic cones a few hundred metres high. There was little volcanic activity, however, while the lake existed, and the many tuff horizons within the sequence were washed in during weathering. The lake may have been generally cool, though of unusual water chemistry, as a result of which the spherulitic East Kirkton Limestone precipitated. At times, however, water temperatures may have risen sharply through localised hot-spring activity; both factors deterred «normal» aquatic life. The bulk of the preserved biota consists of plants (permineralisations and compressions) and dominantly land-living animals, including the oldest terrestrial tetrapods (amphibians and reptiliomorphs), large terrestrial-aquatic eurypterids, the first harvestman and rate millipedes

A new Lower Ordovician conodont faunule from the Northern Belt of the Southern Uplands

Synopsis A deep water Periodon—Prioniodus—Protopanderodus assemblage has been isolated from red cherts and mudstones in the Hawkwood Burn, a tributary of the Wandel Burn. Constraints provided by associated graptolites and the absence of Pygodus and Arenig taxa known to occur in the Southern Uplands suggest this part of the sequence is Llanvirn in age.

Furongian (upper Cambrian) biostratigraphy and trilobites of the Haslov-1 drill core, Scania, S. Sweden

Abstract A drilling made in 1972 at Håslöv, Scania, southern Sweden, penetrated a 2572 m thick succession of Phanerozoic strata. The only cored parts of the succession derive from the Upper Ordovician and the Furongian (upper Cambrian) series. Merely the uppermost part of the Furongian was recovered, comprising eight metres of Alum Shale with limestone concretions. Nine species and subspecies of trilobites are identified and their succession is used for subdividing the core into the Peltura scarabaeoides Zone, comprising the Parabolina lobata and the Peltura paradoxa subzones, and the Acerocare Zone, comprising the Peltura transiens Subzone. The conodont Cordylodus proavus? was found in the uppermost part of the core. The faunal succession is interrupted by conspicuous unfossiliferous intervals; the most extensive one measuring 3.39 m. Approximately coeval barren intervals have been recorded from other localities in Scania. Although the ecological significance of these intervals remains to be evaluated, it can be concluded that they are a regional feature in the Furongian of Scania.