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Author : William Aubrey Cobban,William James Kennedy
Publisher : Unknown
Page : 52 pages
File Size : 53,6 Mb
Release : 1993
Category : Menuites oralensis
ISBN : ERDC:35925002595590
Descriptions and illustrations of two important species of Menuites.
Author : William Aubrey Cobban
Publisher : Unknown
Page : 84 pages
File Size : 52,8 Mb
Release : 1971
Category : Ammonoidea
ISBN : ERDC:35925000231909
A species each of Anisoceras, Desmoceras, Tragodesmoceras, Calycoceras, Nigericeras, and Paracompsoceras (new genus) is described and illustrated.
Author : Neil H. Landman
Publisher : Unknown
Page : 136 pages
File Size : 49,7 Mb
Release : 1987
Category : Ammonoidea
ISBN : IND:30000121325900
"Scaphites are a group of late Cretaceous heteromorphic ammonites in which the final body chamber partially uncoils, thereby marking the attainment of the adult stage. This distinctive change in shape permits unequivocal separation of variation due to developmental stage from phenotypic variation among adults. In the Western Interior of North America, scaphites are represented by a wide diversity of endemic species. Many of these species are abundant and well preserved and, therefore, are especially suitable for a detailed investigation of ontogenetic development. I studied the ontogeny of several species of Turonian-Santonian scaphites in the genera Scaphites, Clioscaphites and Pteroscaphites, utilizing both whole fossils and polished sections. The study of their ontogeny bears on the questions of scaphite systematics and morphological development, and ammonite life history in general. The initial whorls of scaphites, as in other ammonites, consist of a bulbous protoconch and part of a planispiral whorl (referred to as the ammonitella). The ammonitella displays a uniform tuberculate micro-ornamentation extending 0.75 whorls to a depression (primary constriction) after which growth lines appear. The shell wall is prismatic in microstructure and nacre first appears at the constriction where it forms an internal pad (primary varix). These morphological observations support a scheme of direct development in which the constriction marks the aperture of the embryonic shell. Preserved ammonitellas of Scaphites ferronensis and Baculites cf. B. asper, B. codyensis suggest that hatching may have occurred after the development of the Proseptum. In scaphites, the proseptum displays a unique necklike attachment that appears as a superimposed saddle on the prosuture. The caecum and its prosiphonal attachment are similar among all the species studied. The diameter of the embryonic shell averages 700 [micrometers] and ranges from approximately 600 to 800 [micrometers]. The ammonitella angle averages 270ð, which is similar to the angular length of the juvenile body chamber. Unlike modern Nautilus, the embryonic shell is comparable in size to the young of many Recent dibranchiate cephalopods and may have followed a planktonic mode of life immediately after hatching. The juvenile shell conforms to a logarithmic spiral but exhibits a conspicuous change in morphology at approximately 3-4 mm diameter corresponding to two whorls from the primary constriction. The change involves modifications in the growth patterns of the umbilical diameter and spiral radius and coincides with the first appearance of macro-ornamentation. It also corresponds to a minimum in septal spacing and the attainment of a stable, ventral position of the siphuncle. These changes may indicate a transition from a passive planktonic to a more active mode of life. Similar morphometric changes occur in many other ammonites at this approximate size and whorl number and may represent a common developmental pattern. In micromorph scaphites of the genus Pteroscaphites, this whorl size coincides with the initiation of an accelerated maturity. As in modern Nautilus, the period of septal secretion in scaphites and other ammonites was probably dependent on the rate of apertural growth and buoyancy requirements rather than external astronomical rhythms. The period may also have displayed an increase over ontogeny, although the absolute rate of growth is unknown. Maturity is expressed by the development of an uncoiled body chamber, although the degree of uncoiling varies widely among species. Interspecific comparisons are therefore facilitated by examination of the more similarly shaped phragmocones. Within species, histograms of adult phragmocone diameter form unimodal distributions although a well-marked sexual dimorphism appears in many species. The ratio of maximum to minimum phragmocone diameter ranges from 1.7 in S. preventricosus to 4.6 in S. carlilensis. The diameter of the adult phragmocone and the number of postembryonic whorls exhibit a positive correlation within and among species. The adult size and the extent to which the mature body chamber uncoils also covary within and among species. Evolutionary changes in size, with concomitant changes in the timing of sexual maturation, may thus explain interspecific variation in the degree of mature uncoiling"--Page 119
Author : William Aubrey Cobban
Publisher : Unknown
Page : 64 pages
File Size : 52,6 Mb
Release : 1969
Category : Ammonoidea
ISBN : ERDC:35925000206885
Additional title page description: Three chronological forms each of Scaphites leei and Scaphites hippocrepis occur in dimorphic pairs and provide a means of correlating thin units of strata.
Author : William Aubrey Cobban
Publisher : Unknown
Page : 15 pages
File Size : 48,8 Mb
Release : 1988
Category : Paleontology
ISBN : LCCN:87600203
Author : William Aubrey Cobban
Publisher : Unknown
Page : 15 pages
File Size : 52,5 Mb
Release : 1987
Category : Paleontology
ISBN : LCCN:87600272
Author : William Aubrey Cobban
Publisher : Unknown
Page : 28 pages
File Size : 49,5 Mb
Release : 1987
Category : Acanthoceratidae
ISBN : OCLC:896811399
Author : Neil H. Landman
Publisher : Unknown
Page : 31 pages
File Size : 47,6 Mb
Release : 1999
Category : Ammonoidea
ISBN : OCLC:247848763
Author : William Aubrey Cobban,William James Kennedy,Geological Survey (U.S.)
Publisher : Unknown
Page : 32 pages
File Size : 52,7 Mb
Release : 1989
Category : Frontier Formation
ISBN : UOM:39015095165661
A multidisciplinary approach to research studies of sedimentary rocks and their constituents and the evolution of sedimentary basins, both ancient and modern.
Author : William Aubrey Cobban,Geological Survey (U.S.)
Publisher : Unknown
Page : 48 pages
File Size : 46,5 Mb
Release : 1990
Category : Ammonoidea
ISBN : UOM:39015095166198
Author : Neal L. Larson
Publisher : Unknown
Page : 168 pages
File Size : 45,9 Mb
Release : 1997
Category : Nature
ISBN : UOM:39015049683371
Ammonites are extinct marine animals related to present day squid, octopi, and chambered nautilus. Contains descriptions of more than 90 species that lived for 12 million years in the Pierre Seaway, which extended through the interior of North America, connecting the Arctic Ocean with the Gulf of Mexico.
Author : Lucy E. Edwards
Publisher : Unknown
Page : 264 pages
File Size : 43,6 Mb
Release : 2001
Category : Geology
ISBN : OSU:32435085210029
Author : Neil H. Landman,Richard Arnold Davis,Royal H. Mapes
Publisher : Springer Science & Business Media
Page : 493 pages
File Size : 54,7 Mb
Release : 2007-09-09
Category : Science
ISBN : 9781402068065
This book brings together international scientists who focus on present-day and fossil cephalopods, ranging broadly from Paleozoic ammonoids to today's octopods. It covers systematics and evolution; hard- and soft part morphology; and ecology, biogeography, and taphonomy. The book also includes new evidence for the existence of an ink sac in fossil ammonoids and features the first record of an in-depth study of octopus ecology in Alaska.
Author : Christian Klug,Dieter Korn,Kenneth De Baets,Isabelle Kruta,Royal H. Mapes
Publisher : Unknown
Page : 128 pages
File Size : 40,5 Mb
Release : 2015
Category : Electronic
ISBN : 9401796319
This two-volume work is a testament to the abiding interest and human fascination with ammonites. We offer a new model to explain the morphogenesis of septa and the shell, we explore their habitats by the content of stable isotopes in their shells, we discuss the origin and later evolution of this important clade, and we deliver hypotheses on its demise. The Ammonoidea produced a great number of species that can be used in biostratigraphy and possibly, this is the macrofossil group, which has been used the most for that purpose. Nevertheless, many aspects of their anatomy, mode of life, development or paleobiogeographic distribution are still poorly known. Themes treated are biostratigraphy, paleoecology, paleoenvironment, paleobiogeography, evolution, phylogeny, and ontogeny. Advances such as an explosion of new information about ammonites, new technologies such as isotopic analysis, tomography and virtual paleontology in general, as well as continuous discovery of new fossil finds have given us the opportunity to present a comprehensive and timely "state of the art" compilation. Moreover, it also points the way for future studies to further enhance our understanding of this endlessly fascinating group of organisms.
Author : Sreepat Jain
Publisher : Springer Nature
Page : 335 pages
File Size : 48,7 Mb
Release : 2019-12-12
Category : Science
ISBN : 9788132239628
This book provides practical morphological information, together with detailed illustrations and brief explanatory texts. Each chapter starts with a brief introduction, and goes on to describe the respective organism’s morphology in detail through numerous illustrations. This is followed by a brief note on its classification, and concludes with illustrated examples of stratigraphically important organisms through time with their major distinguishing characteristics. Featuring over 2500 clearly labelled, hand-drawn and classroom-friendly illustrations, the book offers a fundamental resource for budding palaeontologists, petroleum geologists and palaeobiologists.