Lenses within the schizochroal eyes of phacopine trilobites are made principally of calcite, and characterization of them using light microscopy and high‐resolution electron imaging and diffraction ...has revealed an array of microstructural arrangements that suggest a common original pattern across the suborder. The low convexity lenses of Odontochile hausmanni and Dalmanites sp. contain calcite fibres termed trabeculae. The c axis of trabecular calcite lies parallel to the lens axis, and adjacent trabeculae are distinguished by small differences in their a axis orientations. Despite the common alignment, the boundaries between trabeculae cross‐cut the c axis as they fan out towards the lens base. Trabeculae are absent from the lens immediately beneath the visual surface, and instead, a radial fringe is present and is composed of micrometre‐thick sheets of calcite whose c axes are oriented at a low angle to the visual surface. High convexity lenses are more common than those of lower convexity among the species studied, and they have a much thicker radial fringe. Beneath this fringe, all of the lens calcite is oriented with its c axis parallel to the lens axis and it lacks trabeculae. We propose that both the high and low convexity lenses formed by rapid growth of calcite from a surface that migrated inwards from the cornea, and they may have had an amorphous calcium carbonate precursor. The trabeculae and radial fringes are unlikely to have had any beneficial effect on the transmission or focusing of light, but rather are the outcomes of an elegant solution to the problem of how to construct a biconvex lens from a crystalline solid.
Five cephalopod specimens from the Lower Devonian of Bohemia (Czech Republic) preserve colour patterns. They include two taxonomically undeterminable orthoceratoids and three oncocerid nautiloids ...assigned to the genus Ptenoceras. The two fragments of orthocone cephalopods from the lowest Devonian strata (Lochkovian, Monograptus uniformis Zone) display colour patterns unusual in orthoceratoids. They have irregular undulating and zigzag strips that are preserved on counterparts of adapertural regions of specimens flattened in shale, despite their original aragonitic shell having been completely dissolved. These are probably the result of the proteinous pigment inside the shell wall, being substituted during diagenesis by secondary minerals leaving only an altered trace of the original shell. Orthoceratoids from sediments unsuitable for preservation of this feature discussed here thus demonstrate an exceptional case of preservation of colour patterns, not only within Devonian cephalopods but also within other Devonian molluscs. Three specimens of Ptenoceras that preserve colour patterns come from younger Lower Devonian strata. Oblique spiral adaperturally bifurcating bands are preserved in P. alatum from the Pragian and zigzags in P. nudum from the Dalejan. Juvenile specimen of Ptenoceras? sp. from the Pragian exhibits highly undulating transversal bands—a pattern resembling colour markings in some Silurian oncocerids. Dark grey wavy lines observed on the superficially abraded adapical part of a phragmocone of nautiloid Pseudorutoceras bolli and interpreted formerly to be colour markings are here reinterpreted as secondary pigmented growth lines. Other Devonian fossils including a single brachiopod and several gastropods from the Barrandian Area with preserved colour patterns are mentioned. Variety of cephalopod colour patterns, their taxonomic significance, function and significance for palaeoecological interpretation, palaeoenvironmental conditions favouring colour pattern preservation and systematic affiliation of taxa with colour pattern preserved are discussed.
Complete exoskeletons of species of eight genera of Siluro-Devonian Scutelluinae show the morphology of the cephalon and thorax, particularly glabellar lobation, the wide inward extent of the ...doublure, and the development of fulcral processes and sockets, the latter more prominent on the external surface in stratigraphically younger species. The thorax of ten segments has axial rings with an articulating furrow and halfring as in most trilobites. The differences between the exoskeletons of Scutelluinae and Illaenidae are many, and imply anatomical differences. It is considered that Scutelluinae are related to the Ordovician Stygininae, and are to be united with them in Styginidae; a common origin for Styginidae and Illaenidae appears questionable.
Provider: - Institution: - Data provided by Europeana Collections- Höfen. Egerländer Fachwerkhaus. Eckansicht- in schwarzweiß- All metadata published by Europeana are available free of restriction ...under the Creative Commons CC0 1.0 Universal Public Domain Dedication. However, Europeana requests that you actively acknowledge and give attribution to all metadata sources including Europeana
Provider: - Institution: - Data provided by Europeana Collections- Höfen. Egerländer Fachwerkhaus. Giebelseite- in schwarzweiß- All metadata published by Europeana are available free of restriction ...under the Creative Commons CC0 1.0 Universal Public Domain Dedication. However, Europeana requests that you actively acknowledge and give attribution to all metadata sources including Europeana
PDF
