Adolf Seilacher

Bathymetry of trace fossils

Abstract Trace fossil communities are mainly bathymetry-controlled. Their relative depth sequence has been established in sedimentary series of up to Cambrian age. Actual depth figures can now be added from counterparts in the present oceans. As exemplified by the spreite burrows, behavioural response to a bathymetric gradient in food suply is suggested as the main reason for the change of trace fossils with depth.

Vendobionta and Psammocorallia : lost constructions of Precambrian evolution

The non-availability of biomineralized skeletons and low levels of predation led Vendian evolution along strange avenues. The Ediacara-type Vendobionta appear to represent a kingdom, in which foliate shapes, large sizes and the necessary compartmentalization were achieved by quilting of the skin rather than by multicellularity. Psammocorallia, in contrast, are interpreted as coelenterates that constructed an internal sand skeleton. Both were immobile soft-bottom dwellers that had high population densities, and both became preserved by obrutional accidents; thus they render ‘fossil snap shots’, in which the original distributional patterns, age structures and standing biomasses of populations are accurately recorded.

Sedimentary structures tentatively attributed to seismic events

Abstract Fingerprints of earthquakes in the sedimentary record are as yet difficult to identify. This is particularly true for failure phenomena (dewatering, slumping, fault-graded and turbidite structures) that could have been triggered also by other kinds of energy input. Other promising candidates are strange biostratinomic features (convex-down stacking of shells; current-orientation in wave-ripple accumulations), as well as certain preservational features found in geosynclinal pelagic limestones. But in every case, verification of the seismic origin is still needed.

Constructional morphology of sand dollars

This paper analyzes an aberrant group of echinoids in terms of constructional morphology, i.e., as modification of an established “Bauplan” by a set of new functional and morphogenetic constraints and possibilities. The characteristics of sand dollars (flat test, spine differentiation, branched food grooves, lunules) are related to a particular combination of burrowing and sieve feeding in sandy sediments. It has independently evolved from less specialized Clypeasteroids in at least three lineages (Scutellina, Rotulidae, Arachnoididae), which have solved inherent problems differently (sutural interlocking; growth patterning of food grooves and canal systems; lunule formation; weight belts). These three groups have radiated in different degrees due to their different palegeographic histories.

The Phylum Vendobionta: a sister group of the Eumetazoa?

We offer an alternative interpretation of the Kingdom Vendobionta as a monophyletic sister group to the Eumetazoa. We hypothesize that the Vendobionta are cnidarian-like organisms that lacked cnidae. Cnidarians are held to have arisen by acquisition of cnidae by symbiosis with a microsporidian. Our analysis differs from existing interpretations of the Ediacaran fossils as ancestors of extant cnidarians in that we do not regard any of these forms as either polypoid or medusoid. This interpretation requires the erection of a new metazoan phylum, the Vendobionta.

Distinctive Features of Sandy Tempestites

Sedimentological and biological features allow to distinguish wave-generated storm sands from current-generated sandy turbidites and flood deposits. The origin of some of these features remains still uncertain.

Fossil Foraging Behavior: Computer Simulation

Meander patterns produced by ancient sediment feeders can be simulated by digital computer with x-y plotter output. Change in input constants (with a single program) produces variation comparable to genetically controlled behavioral differences between species and genera.

Ammonites as Cartesian divers

Many constructional and taphonomic incongruencies dissolve if ammonites are modeled as active Cartesian divers, whose last septum remained a rubber-like, uncalcified membrane until the next chamber cycle began. If the prochoanitic invagination of the septal mantle served as a gas gland able to produce gas at or above ambient pressure, the chamber behind could be operated like a swim bladder by sutural muscles spanning across the septal mantle. Other septal functions probably served as evolutionary stepping stones on the way to this unique design.

Mechanische Simulation und funktionelle Evolution des Ammoniten-Septums

ZusammenfassungDurch Simulation nautiloider und ammonoider Septalflächen und Lobenlinien werden die bautechnischen Lizenzen verdeutlicht, die der Evolution in Richtung auf eine druckverstrebende Gehäuse-Querwand zugrunde lagen.AbstractSimulation of nautiloid and ammonoid septa and suture lines illustrates the fabricational constraints and possibilities that controlled their evolution towards the paradigm of a pressure resistant structure.

Chapter 11 – Ordovician and Silurian Arthrophycid Ichnostratigraphy

Publisher Summary This chapter discusses that group-specific fingerprints and distinctive behavioral programs make arthrophycids more suited for ichnostratigraphic correlation than other worm burrows. Arthrophycids comprise the ichnogenera arthrophycus, daedalus, and phycodes, whose ichnospecies evolved various behavioral programs for more-efficient sediment feeding. In the Ordovician and Silurian, these trace fossils complement the scheme based on trilobite burrows and, at the same time, have a more global distribution.