Explore the vast range of titles available.

The concept of a sudden extinction of the dinosaurs, consequent upon the impact of some extraterrestrial object, is so dramatic that it has taken hold upon the imaginations of many scientists, as well as of the general public. The evidence for an impact, at approximately the level of the Cretaceous-Tertiary boundary, is impressive. Whether it was the cause for the iridium concentrations, so widely distributed at that level, remains disputable. The wave of extinctions, so often attributed to the impact, is equally disputable. It is now evident that no clear line can be drawn between the smaller theropod dinosaurs and the birds. In that sense, the dinosaurs are not extinct. The dating of the extinction of the larger saurischians and of the ornithischians, based as it is upon evidence from only one small corner of the globe, is equally disputable. Whenever it happened, that extinction appears to have been the product of natural causes--a slow decline, occasioned by environmental changes, and not an extraterrestrially induced catastrophe. Whether the impact had any effect at all upon the dinosaurs is questionable; if so, it appears to have been not worldwide, but confined to a limited region of the Americas.

The probable functional significance of dinoflagellate cyst morphology is considered. Ecological aspects can be inferred from living forms, even though many fewer types are present in modern than in ancient aqueous environments. Reasons are given for concluding that only incomplete versions of the phragma may be preserved. Though encystment is primarily associated with sexual reproduction, it has a secondary function as a means for surviving adverse conditions. The position of the cysts in the water column appears variable. Experimental results on cyst shape as an aid in flotation are presented and examined mathematically. Processes, except when mineralized, retard sinking significantly. Flotation may also be achieved either by cytoplasmic modification or by utilizing processes or mucus coats for attachment to suspended debris. Extreme overall elongation and process development may deter some predators. Tables and graphs portraying variations in cyst assemblages through time indicate certain evolutionary trends, including progressive increases in process length and of periblast size in cavate cysts. Noteworthy are (1) the restricted compass within which cyst size has fluctuated and (2) the extreme constancy and close comparability in size of proximate cysts, chorate central bodies and cavate endoblasts. Fossil forms having an operculum within the cyst are considered not to be abandoned cysts, but individuals that failed to excyst. Spheroidal central bodies of chorate cysts and spherical endoblasts of cavate cysts add to mechanical strength, as does parasutural ornament. Predation is considered possibly an inadvertent precursor to endoparasitism and symbiosis. Three new terms are proposed; loisthocyst, the portion of the cyst left behind after throwing off the operculum; cystoteny, the persistence of cyst characteristics into the motile stage; and mototeny, the retention in the cyst of characteristics lost from the motile stage. Reasons why some motile species develop internal skeletal elements are considered.

Maria Lejeune was by training a zoologist, working on living and fossil hexacorals. However, over a period of 16 years, she devoted her research attention to the microfossils contained in flakes of Upper Cretaceous flints, some from C. G. Ehrenberg’s classic collection, others from Belgium and the Baltic region. The results were published in 16 short papers, remarkable for the detail and precision of her descriptions and drawings. In addition, she made the first—and, so far, finest—large-scale models of fossil dinoflagellates. These were lodged in the Museum of the University of Liège, where she served as curator for 33 years (1942–1975). Eighteen years after her own micropalaeontological studies had ended, she aided W. A. S. Sarjeant in an extended restudy of her type material, reported in two joint papers.

Boris Timofeyev is a name little known to scientists outside the former U.S.S.R. However, he was a principal pioneer in the study of Late Precambrian and Early Palaeozoic micro-fossils (in particular, acritarchs). Though by no means free from error, his contributions on the microbiota of the Precambrian to Devonian are of lasting importance. An account of his life and researches is presented, along with a comprehensive listing of his scientific publications.

The style of archeopyle in the dinoflagellate cyst genus Dingodinium is reviewed on the basis of new observations of Dingodinium cerviculum. The peripyle in this species is formed by dorsal separation of the apex; the endopyle involves not only the loss of intercalary paraplates but also the opening or loss of a precingular paraplate. Revised diagnoses for this species and for the genus incorporate these new details of archeopyle and paratabulation. It is shown that these emendations may necessitate some revision of current approaches in dinoflagellate cyst taxonomy. The species ?D. albertii is rejected as a subjective junior synonym of D. cerviculum.

A taxonomic analysis of Imbatodinium with reference to morphologically similar genera has been made. It has been determined that the mechanism of excystment is more complex than supposed hitherto, as a compound archeopyle is developed by the loss of three or four opercular pieces. A revised diagnosis for the genus incorporates this new information. One new species, Imbatodinium fractum, is described and two new combinations, I. pomum (Davey) and I. radiculatum (Davey), are proposed.

A group of microfossils is described from Middle Cretaceous (Aptian) sediments of Brazil considered to have formed in a brackish-water, possibly deltaic environment. The microfossils have the form of oblate spheroids with reticulate surfaces interrupted by two bands of elongate fields and with a distinct, circular operculum; the name Mystheria oleopotrix, n. gen., n. sp., is proposed for them. Their affinity cannot be determined with precision, but it appears likely that they are insect eggs.

After a long hiatus, work on fossil dinoflagellates was revived in Germany during the 1920s and 1930s by two geologists who were namesakes, but unrelated-Walter Wetzel (1887-1978) and Otto Wetzel (1891-1971). An account is presented of their lives and geological work, their contributions to micropaleontology being emphasized and their research approaches contrasted. It is hoped this may enable a greater insight to be gained, not only into their personal academic achievements but also into the peculiar influences exerted upon them by the events which both shaped and destroyed Germany in the first half of this century. Following this article, a comprehensive bibliographical list of works published by Walter Wetzel and Otto Wetzel is presented, with translations of titles.

The first trackers of dinosaurs were probably other dinosaurs, as tracks have been found apparently showing carnivorous species following herbivores (Lockley 1991, 184). More recently, there is evidence that some early people, whose livelihood came partly from tracking, killing, and dismembering animals, sometimes observed and found significance in tracks, bones, and eggs of long-extinct species of no culinary value. Traditional knowledge of large fossils has been found to persist among aboriginal peoples on several continents. Pertinent observations have been documented, but often in sources that have not generally received the attention of paleontologists until recent decades. Dinosaur trackways in situ

Alice Evelyn Wilson (1881-1964) was the first woman to be employed in a professional capacity by the Geological Survey of Canada. Though from an academically gifted family, prolonged ill-health during youth hampered her studies; yet it brought also the interest in geology that was to determine her career. Her researches into the in vertebrate paleontology and stratigraphy of the Palaeozoic strata of eastern Canada were distinguished. Unfortunately, in a male-dominated environment, their value was slow in gaining recognition and Alice's promotions came tardily; nor did she ever gain the professional status that was her due. Only very belatedly, with post-retirement publicity and the naming after her of Alice Wilson Hall in the Geological Survey of Canada's Ottawa headquarters, was the importance of her work to be properly recognized.