The monospecific ichnogenus Scoyenia White is characterized by longitudinally striat- ed wall linings surrounding meniscate burrow fills. Ancorichnus Heinberg is similar but has an unornamented exterior. Ichnospecies of Ancorichnus are based upon fabricational differences in menisci; those of A. coronus (n. ichnosp.) are continuous with the wall lining, whereas those of A. ancorichnus Heinberg are not. Scoyenia and Ancorichnus are interpreted as feeding structures, although certain details of the feeding-burrowing mechanism remain conjectural. The Scoyenia organism is thought to be an arthropod (other than insects or decapods); Ancorichnus ancorichnus may have been produced by priapulids, sipunculids, or ethologically equivalent worms, whereas A. coronus seems to have been made by arthropods somewhat akin to the Scoyenia animal. These last two forms also may have more or less similar environmental significance. By definition, Scoyenia gracilis is diagnostic of the Scoyenia ichnofacies. However, various different interpretations or applications of this ichnofacies concept have rendered it virtually mean- ingless beyond a general nonmarine connotation. Recent work suggests that 1) nonmarine ichno- facies are equally as numerous and different as marine ichnofacies, 2) the Scoyenia ichnofacies is only one among many nonmarine assemblages, and yet 3) even the Scoyenia ichnofacies remains largely undefined and poorly understood. As a test of the distinctiveness and validity of the concept, we suggest that future designations of this ichnofacies be restricted to trace fossil assemblages in which Scoyenia gracilis, Ancorichnus coronus, or ethologically and ecologically equivalent burrows predominate. Known occurrences of such trace fossils indicate that the tracemakers preferred moist or wet nonmarine substrates, whether shallow aquatic deposits periodically exposed to air or low- lying subaerial deposits periodically inundated by water.

Morphological, ethological, and environmental significance of the ichnogenera Scoyenia and Ancorichnus

More than 20 trace fossil species occur in marine facies of the Cretaceous Star Point and Blackhawk formations in the Book Cliffs and Wasatch Plateau provinces of Utah. Major genera include Ancoric...

Characteristic trace fossils in nearshore to offshore sequences, Upper Cretaceous of east-central Utah

Portrait of a Gondwanan ecosystem: A new late Permian fossil locality from KwaZulu-Natal, South Africa

ABSTRAcr-In Coal Creek Canyon, Utah, the Spring Canyon Member of the Blackhawk Formation is divisible into four regressive hemicycles of deposition, each representing the downdip part of a nearshore-to-offshore sequence. The first and fourth hemicycles are best developed. Individual bedding units span middle-shoreface to lower-offshore lithofacies, the latter corresponding to a thin intertongue of Mancos Shale. Trace fossil assemblages include ~22 ichnospecies and 17 ichnogenera: Ancorichnus, Aulichnites, Chondrites, Cylindrichnus, Ophiomorpha, Palaeophycus, Phoebichnus, Planolites, Rosselia, Schaubcylindrichnus, Scolicia, Skolithos, Taenidium, Teichichnus, Terebellina, Thalassinoides, and Uchirites. Diversity and abundance of ichnospecies are greater in nearshore than in offshore lithofacies. Distal deposits are typified by obscure bioturbate textures: Cylindrichnus concentricus, Palaeophycus heberti, and Rosselia socialis are prevalent through the remainder of the lithofacies suite. Ophiomorpha irregulaire and Schaubcylindrichnus coronus are most common in middle-shoreface beds and Chondrites ichnosp. in upper-offshore beds; Ophiomorpha nodosa and O. annulata also are common in this part of the sequence.

Ordovician sphinctozoan sponges of alaska and yukon territory

A global synthesis of gymnosperm families, fossil and extant, provides a new and distinctive perspective on the macroevolutionary biodiversity trends within this group through their 375 million-year history. The total diversity recognised here amounts to 84 families in 37 orders and 10 classes, of which 13 families in 4 orders and 4 classes are extant and 71 families in 37 orders and 10 classes are extinct. The 71 extinct families are based on reference wholeplant genera with the focus on ovulate fruit, an approach dictated by the highly varying availability and grade of data on affiliated organs. The stratigraphic ranges of the 84 gymnosperm families are plotted according to their first and last appearances—at the resolution of the geological stage—in the fossil record. The biodiversity histogram based on these data clearly reveals four broad phases in the history of the gymnosperms: three periods of radiation and extinction from the latest Devonian to latest Cretaceous, followed by an interval of stasis through the Tertiary to present. The ‘Secondary Radiation’ through the Triassic, following the end-Permian extinction, is clearly the most explosive and leads to the putative diversity heyday of the gymnosperms in the Carnian—with 30 families (23 orders, 10 classes). A series of 30 full-page colour charts provide the holistic context in which to interpret gymnosperm history. The first group of 10 charts are plotted to matching geological time scales and follow the interdependent histories of the most pertinent physical phenomena (plate tectonics, climate, extinction events) and the major terrestrial biological groups (plants, insects, tetrapods). A second set of 10 charts, again to the same scale, correlates the megaplant-bearing formations globally: it is the floras from these strata that provide the basis for the history outlined here. The third set of 10 charts constitute two pictorial essays, on the phytohistory of the Araucariaceae and on the comparative morphology of the extant gymnosperm families. In a chapter devoted to the ‘macroevolutionary life cycle of the gymnosperms’, a systematic coverage of floral kingdoms, biodiversity patterns, insect associations and other fields is traced period by period from the Devonian to Quaternary. Here is included an elaboration of the four major ‘phases’ (youth, adolescence, maturity, old age) and the lesser ‘pulses’ punctuating the life cycle. In a final chapter we touch on gymnosperm biodiversity trends at the microevolutionary (genera and species) level. This is done through documenting the known biodiversity at a selection of some 13 important formations (or localities) scattered globally and through the geological column. Though quite incomplete, the trends witnessed tend to parallel those plotted for macroevolutionary diversity.

Brief history of the gymnosperms: classification, biodiversity, phytogeography and ecology

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Karel Bořiwog Presl

Papers

Versuch Einer Geognostisch-Botanischen Darstellung Der Flora Der Vorwelt