Author: Publisher:
ISBN:
Category :
Languages : en
Pages :
Book Description
Intraspecific Variation Through Ontogeny in Late Cretaceous Ammonites
Author: Intraspecific Variation Through Ontogeny in Late Cretaceous Ammonites
Author: Carina KleinPublisher:
ISBN:
Category : Ammonoidea
Languages : en
Pages : 25
Book Description
This project assesses intraspecific variation through the ontogeny of the ammonite Scaphites whitfieldi Cobban, 1951, from the Upper Cretaceous of the U.S. Western Interior. Our sample consists of 103 dorsoventral cross sections from nine localities that represent two lithofacies (shale and siltstone). We measured four shell parameters (ww/dm, ww/wh, uw/dm, and WER) to describe the ontogenetic changes in shell morphology. We investigated the variation at three growth stages: immediately after hatching (dm = 1 mm), the neanoconch (dm = 4 mm), and the submature stage (defined as at or near the base of the mature hooklike body chamber). In general, the shell becomes more discoidal through ontogeny with a narrower umbilicus and a more compressed whorl section. The results of the univariate analysis indicate that the variation is statistically significantly higher in the neanoconch than in either the hatchling or submature stage. This pattern is also apparent in the multivariate analysis in which the disparity increases markedly from the hatchling to the neanoconch and then decreases again at the submature stage. These results are consistent with the hypothesis that the neanoconch represents a transition in the life history of the animal to a more demersal mode of life followed by a canalization of morphology toward maturity. However, because the neanic transition occurs over a range of sizes, it is possible that some individuals may have already undergone these changes at dm = 4 mm, whereas others may not have, thus inflating the degree of variation. To resolve this issue in the future, it is critical to examine each ontogenetic trajectory individually to pinpoint the exact size at which the morphological changes occur. We also compared the values of ww/dm, ww/wh, uw/dm, and WER of the three growth stages for the sample from siltstone versus the sample from shale. The comparison reveals that the specimens from siltstone occupy lower regions of the morphospace, implying that these specimens are generally more compressed than those from shale. This difference may be related to selection pressures for improved hydrodynamic efficiency in the higher energy environment represented by siltstone.
Intraspecific Variation In, and Ontogeny Of, Prionotropis Woollgari and Prionocyclus Wyomingensis
Author: Otto HaasAmmonoid Paleobiology: From anatomy to ecology
Author: Christian KlugPublisher: Springer
ISBN: 9401796300
Category : Science
Languages : en
Pages : 943
Book Description
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.
Ontogeny of Upper Cretaceous (Turonian-Santonian) Scaphitid Ammonites from the Western Interior of North America
Author: Neil H. LandmanPublisher:
ISBN:
Category : Ammonoidea
Languages : en
Pages : 136
Book Description
"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
Evolution of the Ammonoids
Author: Kate LoMedico MarriottPublisher: CRC Press
ISBN: 1000814874
Category : Nature
Languages : en
Pages : 311
Book Description
Ammonites are an extinct and charismatic lineage that persisted for over 300 million years. They were used, with other fossils, to corroborate the principle of faunal succession and launch the field of biostratigraphy. Despite intense research, many important questions remain unanswered. Furthermore, outdated hypotheses persist. Many new findings include a better understanding of their appearance in life, their locomotion, and their role in long-gone ecosystems. And, of course, there are still controversies; e.g. why did shell complexity increase during evolutionary history. This richly illustrated book describes the full range of ammonoids and their fascinating evolutionary history. Key Features Documents the early history of paleontology and the role played by ammonoids Describes the basic anatomy of a diverse and long-persisting lineage Summarizes the classification and diversity of ammonoids Lavishly illustrated with beautiful reconstructions Highlights recent findings and outstanding controversies Related Titles Ponder, W. F. D. R. Lindberg and J. M. Ponder. Biology and Evolution of the Mollusca (Vol 1. ISBN 978-1-0321-7660-4, Vol 2. ISBN 9781032173542) Mente, E., eds. Reproductive Biology of Crustaceans: Case Studies of Decapod Crustaceans (ISBN 978-0-3674-5277-3) Koenemann, S. & R. Jenner, eds. Crustacea and Arthropod Relationships (ISBN 978-0-3673-9294-9) Schierwater, B. & R. DeSalle, eds. Invertebrate Zoology: A Tree of Life Approach (ISBN 978-0-3676-8567-6)
LATE CRETACEOUS (CENOMANIAN-CAMPANIAN) AMMONITE SYSTEMATIC PALEONTOLOGY AND BIOSTRATIGRAPHY, SOUTHEASTERN SAN JUAN BASIN, SANDOVAL COUNTY, NEW MEXICO
Author: PAUL L. SEALEYPublisher: New Mexico Museum of Natural History and Science
ISBN:
Category : Nature
Languages : en
Pages : 245
Book Description
Ammonites and Some Characteristic Bivalves from the Upper Cretaceous Frontier Formation, Natrona County, Wyoming
Author: William A. CobbanPublisher:
ISBN:
Category : Ammonoidea
Languages : en
Pages : 48
Book Description
Evolutionary patterns in Late Cretaceous ammonites
Author: William J. KennedyHigh-Resolution Approaches in Stratigraphic Paleontology
Author: P.J. HarriesPublisher: Springer Science & Business Media
ISBN: 1402090536
Category : Science
Languages : en
Pages : 480
Book Description
This volume delves into a spectrum of theoretical as well as applied aspects of high-resolution stratigraphic approaches in paleontology. It explores how increasingly detailed knowledge of the fossil record can enhance our understanding of the evolution of life on Earth and also allows geoscientists to address a broad range of important evolutionary and environmental questions in this arena. A 'zipped' version of the program CONOP9 2007 along with read-me files, sample files, and other documentation are available via a web site (see below). An earlier version of CONOP9 was initially supplied with 'High-Resolution Approaches in Stratigraphic Paleontology' (PJ Harries, editor) and described in Chapter 13 of that volume. This is an updated version of the program, and the documentation supplied with this version supersedes the information supplied in that chapter. To view the CONOP9 Programs, click on the link CONOP9 Programs on the right side of this page under Related links.