scholarly journals MECHANICAL FEEDBACK IN SEASHELL GROWTH AND FORM

2018 ◽  
Vol 59 (4) ◽  
pp. 581-606 ◽  
Author(s):  
A. ERLICH ◽  
R. HOWELL ◽  
A. GORIELY ◽  
R. CHIRAT ◽  
D. E. MOULTON
Keyword(s):  
Fossil Record ◽  
Shell Morphology ◽  
Shell Structures ◽  
Mechanical Interaction ◽  
Modelling Framework ◽  
Local Deposition ◽  
Rigid Shell ◽  
Huge Variety ◽  
Initial Framework ◽  
Mechanical Feedback

Mollusc seashells grow through the local deposition and calcification of material at the shell opening by a soft and thin organ called the mantle. Through this process, a huge variety of shell structures are formed. Previous models have shown that these structural patterns can largely be understood by examining the mechanical interaction between the deformable mantle and the rigid shell aperture to which it adheres. In this paper we extend this modelling framework in two distinct directions. For one, we incorporate a mechanical feedback in the growth of the mollusc. Second, we develop an initial framework to couple the two primary and orthogonal modes of pattern formation in shells, which are termed antimarginal and commarginal ornamentation. In both cases we examine the change in shell morphology that occurs due to the different mechanical influences and evaluate the hypotheses in light of the fossil record.

scholarly journals A 5000-YEAR FOSSIL RECORD OF LARVAL SHELL MORPHOLOGY OF SUBMARINE CAVE MICROSHELLS

Evolution ◽  
2009 ◽  
Vol 63 (1) ◽  
pp. 295-300 ◽  
Author(s):  
Takao Ubukata ◽  
Akihisa Kitamura ◽  
Mayumi Hiramoto ◽  
Tomoki Kase
Keyword(s):  
Fossil Record ◽  
Shell Morphology ◽  
Larval Shell ◽  
Submarine Cave

Mammals: A Very Short Introduction

2017 ◽  
Author(s):  
T. S. Kemp
Keyword(s):  
Fossil Record ◽  
Evolutionary History ◽  
Homo Sapiens ◽  
Short Introduction ◽  
Large Brain ◽  
Modes Of Life ◽  
Huge Variety

Mammals: A Very Short Introduction explores the nature, evolutionary history, and modern diversity of mammals. From a little shrew-like, nocturnal, insect-eating ancestor living 200 million years ago (mya), mammals have evolved into a huge variety of different kinds of animals. This VSI explains how it is endothermy—‘warm-bloodedness’—enabling high levels of activity and the relatively large brain associated with complex, adaptable behaviour that epitomizes mammals. It describes their remarkable fossil record, revealing how and when the mammals gained their characteristics, and the tortuous course of their evolution. It reveals the adaptations mammals evolved to suit their varied modes of life, including those of mainly arboreal primates culminating in Homo sapiens.

Paleocene diversification of bucciniform gastropods on Seymour Island, Antarctica

1996 ◽  
Vol 70 (6) ◽  
pp. 923-934 ◽  
Author(s):  
Anton E. Oleinik ◽  
William J. Zinsmeister
Keyword(s):  
New Species ◽  
Mass Extinction ◽  
Fossil Record ◽  
New Genus ◽  
Shell Morphology ◽  
Geographic Isolation ◽  
Extinction Event ◽  
Early Paleocene ◽  
Mass Extinction Event ◽  
Seymour Island

Following the mass extinction event at the end of the Cretaceous, the marine molluscan faunas of the high southern latitudes underwent a marked period of diversification during the early Paleocene. The appearance of four new species belonging to the new genus Seymourosphaera, tentatively placed in the subfamily Pseudolivinae, from the lower Paleocene strata of Seymour Island, Antarctic Peninsula, clearly illustrates the post-Cretaceous extinction diversification. The abrupt radiation of the buccinids during the early Paleocene, was also apparently related to geographic isolation of Antarctica during final breakup of Gondwana. Comparative analysis of shell morphology of Seymourosphaera, new genus reveals close morphologic similarities, not only with taxa within Pseudolivinae, but also with several genera and subgenera belonging to the families Buccinidae and Nassariidae. However, incompleteness of the fossil record and a “generalized” shell morphology make difficult establishment of unequivocal phylogenetic relationships for Seymourosphaera. A taxonomic review of most closely related, and possibly ancestral genus Austrosphaera Camacho, 1949, is provided. The following new species of genus Seymourosphaera new genus are described: Seymourosphaera bulloides new species, S. subglobosa new species, S. depressa new species, and S. elevata new species.

scholarly journals A Silurian myodocope with preserved soft-parts: cautioning the interpretation of the shell-based ostracod record

2013 ◽  
Vol 280 (1752) ◽  
pp. 20122664 ◽  
Author(s):  
David J. Siveter ◽  
Derek E. G. Briggs ◽  
Derek J. Siveter ◽  
Mark D. Sutton ◽  
Sarah C. Joomun
Keyword(s):  
Fossil Record ◽  
Soft Part ◽  
Circulatory System ◽  
Shell Morphology ◽  
Fifth Limb

Ostracod crustaceans are the most abundant fossil arthropods. The Silurian Pauline avibella gen. et sp. nov., from the Herefordshire Lagerstätte, UK, is an extremely rare Palaeozoic example with soft-part preservation. Based on its soft-part morphology, especially the exceptionally preserved limbs and presence of lateral eyes, it is assigned to the myodocopid myodocopes. The ostracod is very large, with an epipod on the fifth limb pair, as well as gills implying the presence of a heart and an integrated respiratory–circulatory system as in living cylindroleberidid myodocopids. Features of its shell morphology, however, recall halocyprid myodocopes and palaeocopes, encouraging caution in classifying ostracods based on the carapace alone and querying the interpretation of their shell-based fossil record, especially for the Palaeozoic, where some 500 genera are presently assigned to the Palaeocopida.

The Silurian myodocope ostracodeEntomozoefrom the Pentland Hills, Scotland: its taxonomic, ecological and phylogenetic significance and the affinity of the bolbozoid myodocopes

1990 ◽  
Vol 81 (1) ◽  
pp. 45-67 ◽  
Author(s):  
David J. Siveter ◽  
Jean M. C. Vannier
Keyword(s):  
Fossil Record ◽  
Type Species ◽  
Soft Part ◽  
Shell Morphology ◽  
Zoological Nomenclature ◽  
Phylogenetic Significance ◽  
Taxonomic Affinity ◽  
Low Diversity ◽  
New Type ◽  
First Time

ABSTRACTThe monotypic ostracodeEntomozoe(pro Entomis) (Superorder Myodocopa) from the Silurian of Scotland, type genus of the Entomozoidae, is revised for the first time since being established in 1861. Based on the type and new collections ofEntomozoe tuberosa(Jones, 1861), the genus shows affinity to bolbozoid myodocopes rather than to forms hitherto universally considered as ‘typical’ entomozoid myodocopes. The families Entomozoidae and Bolbozoidae are considered synonymous. In the interests of stability of nomenclature, in particular to preserve the traditionally understood usage of the taxon Entomozoidae, a case must be made to the International Commission on Zoological Nomenclature to set aside any previous designations and to establish a new type-species forEntomozoe.Entomozoe, from the Llandovery Series, is the earliest known myodocope in the fossil record. It occurs as part of a low diversity, shallow water, nearshore assemblage. In contrast to other, but younger, Silurian bolbozoid myodocopes, it is probably a benthic form. The differences in the anterior shell morphology of Silurian bolbozoid taxa possibly reflect changes both in soft-part morphology and from benthic to pelagic lifestyles within the group.Both bolbozoid and ‘entomozoid’ myodocopes are assigned to the Order Myodocopida rather than to the Order Halocypridida, though the taxonomic affinity of the ‘entomozoids’ is, at best, uncertain.

New species of latest Eocene/earliest Oligocene microgastropods (Heterobranchia: Orbitestellidae and Omalogyridae) from the Gries Ranch Formation, Lewis County, Washington State, USA

Zootaxa ◽  
2021 ◽  
Vol 4981 (3) ◽  
pp. 469-480
Author(s):  
ALEXEI V. CHERNYSHEV ◽  
JAMES L. GOEDERT
Keyword(s):  
New Species ◽  
North America ◽  
Fossil Record ◽  
Washington State ◽  
Shell Morphology ◽  
Early Eocene ◽  
Western North America ◽  
Crescent Formation ◽  
Fossil Species ◽  
Latest Eocene

Continued sampling of the latest Eocene to earliest Oligocene Gries Ranch Formation in Lewis County, Washington State, has yielded new heterobranch microgastropod species. Orbitestella kieli sp. nov., is the third fossil species of this genus and family Orbitestellidae from western North America. Two new species of Ammonicera, A. rolani sp. nov. and A. danieli sp. nov., are together only the second fossil record of this genus and the family Omalogyridae from the northeastern Pacific Ocean. New specimens of two previously recorded species, O. palaiopacifica Squires & Goedert and A. benhami Squires & Goedert, from early Eocene rocks of the Crescent Formation provide new data regarding shell morphology. The fossil record of both Ammonicera and Orbitestella in western North America is restricted to early Eocene to earliest Oligocene age rocks in Washington State. 

Keys to the Shells of Bahia la Choya, Sonora, Mexico

1987 ◽  
Vol 2 ◽  
pp. 62-103
Author(s):  
Nancy Beckvar ◽  
Richard D. Norris ◽  
Sherman Suter
Keyword(s):  
Seasonal Variations ◽  
Shell Morphology ◽  
Shell Structures ◽  
Shell Material ◽  
Sand Flat ◽  
Ecological Information ◽  
Descriptive Information ◽  
External Shell ◽  
Molluscan Species ◽  
Technical Terms

These keys are intended for use on dead shell material found on the sand flat, spit and estero of Bahia la Choya. They describe one hundred seventy molluscan species, three irregular echinoids and an inarticulate brachiopod. The taxonomic list on which the keys are based was compiled from shell material collected mainly during February and March, 1985. An attempt was made to make the keys as complete as possible. However, due to seasonal variations in shell abundances, not all shell material found at Bahia la Choya may be included in the key. Additionally, not all taxa found in the Pleistocene rock exposed around the bay are described here.The keys are based on morphological similarites, not phylogenetic relationships. Descriptive terminology has been kept to a minimum, and a glossary and labeled sketches are included for those technical terms which were employed. The reader is advised to become familiar with the anatomical parts of shells before embarking on an identification.External shell morphology can be altered by physical and biological destruction. In particular, fragile shell structures may be broken off, and shell sculpturing may be worn down. The absence of these sometimes critical features may lead to an incorrect identification. Additionally, bleaching of shells can alter or destroy the original colors. Therefore, shell color is not necessarily diagnostic and is mainly used as an additional character in the description of the species.Species are described only within the keys. When the species name has been reached, phrases within the couplet contain additional descriptive information and often some ecological information.

Molluscan Development

1985 ◽  
Vol 13 ◽  
pp. 33-49 ◽  
Author(s):  
David Jablonski
Keyword(s):  
Life History ◽  
Life Cycle ◽  
Fossil Record ◽  
Early Ontogeny ◽  
Shell Morphology ◽  
Biological Research ◽  
The Past ◽  
Molluscan Development ◽  
Biological Aspects ◽  
Embryonic And Larval Development

Early ontogeny is still the least well-known part of the molluscan life cycle, despite its unarguable significance in ecology, biogeography, and evolution. The past decade has seen an acceleration in biological research on molluscan embryonic and larval development, and paleontologists have recently begun to explore this field as well. Although the very earliest phases of ontogeny are inaccessible to the paleontologist, a remarkable amount of information can be derived from the preserved details of larval shell morphology. The fossil record thus affords rich opportunities to study directly the development of extinct species, both from a phylogenetic standpoint and for tracing the evolutionary and biogeographic effects of these early stages in life history. Access to long-extinct clades and an ability to document rates and patterns of evolution allow paleontologists to test hypotheses that can be addressed only indirectly using Recent data. Here I will emphasize these paleontological aspects of molluscan development (see also Jablonski and Lutz, 1983); for the more strictly biological aspects of reproduction and embryology, see Giese and Pearse (1977, 1979), Verdonk et al. (1983) and Tompa et al. (1984).

scholarly journals Lichen preservation in amber: morphology, ultrastructure, chemofossils, and taphonomic alteration

Fossil Record ◽  
2015 ◽  
Vol 18 (2) ◽  
pp. 127-135 ◽  
Author(s):  
C. Hartl ◽  
A. R. Schmidt ◽  
J. Heinrichs ◽  
L. J. Seyfullah ◽  
N. Schäfer ◽  
...  
Keyword(s):  
Raman Spectroscopy ◽  
Fossil Record ◽  
Sem Analysis ◽  
Tissue Preservation ◽  
X Ray ◽  
Fungal Hyphae ◽  
Lichen Thallus ◽  
History Of ◽  
Huge Variety ◽  
Scanning Electron

Abstract. The fossil record of lichens is scarce and many putative fossil lichens do not show an actual physiological relationship between mycobionts and photobionts or a typical habit, and are therefore disputed. Amber has preserved a huge variety of organisms in microscopic fidelity, and so the study of amber fossils is promising for elucidating the fossil history of lichens. However, so far it has not been tested as to how amber inclusions of lichens are preserved regarding their internal characters, ultrastructure, and chemofossils. Here, we apply light microscopy, scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), and Raman spectroscopy to an amber-preserved Eocene lichen in order to gain information about the preservation of the fossil. The lichen thallus displays lifelike tissue preservation including the upper and lower cortex, medulla, photobiont layer, apothecia, and soredia. SEM analysis revealed globular photobiont cells in contact with the fungal hyphae, as well as impressions of possible former crystals of lichen compounds. EDX analysis permitted the differentiation between halite and pyrite crystals inside the lichen which were likely formed during the later diagenesis of the amber piece. Raman spectroscopy revealed the preservation of organic compounds and a difference between the composition of the cortex and the medulla of the fossil.

Phenetic discrimination of biometric simpletons: paleobiological implications of morphospecies in the lingulide brachiopod Glottidia

Paleobiology ◽  
1997 ◽  
Vol 23 (4) ◽  
pp. 444-469 ◽  
Author(s):  
Michał Kowalewski ◽  
Eric Dyreson ◽  
Jonathan D. Marcot ◽  
José A. Vargas ◽  
Karl W. Flessa ◽  
...  
Keyword(s):  
Fossil Record ◽  
Quantitative Methods ◽  
Morphological Evolution ◽  
Taxonomic Diversity ◽  
Error Rates ◽  
Shell Morphology ◽  
Taxonomic Resolution ◽  
Turnover Rates ◽  
Morphological Complexity ◽  
Extant Species

The extreme morphological simplicity of lingulide brachiopod shells makes them particularly useful for investigating the species-level taxonomic resolution of the fossil record as well as the relationships between taxonomy, morphological complexity, and evolutionary rates. Lingulides have undergone little change in shell morphology and have had low taxonomic diversity since the Paleozoic. Is this pattern an evolutionary phenomenon or an artifact of the shell's simplicity? Multivariate methods were used to establish morphogroups among seven populations of four extant species of Glottidia. Six characters (three shell dimensions and three internal septa) were measured for 162 specimens from field and museum collections. All populations follow similar allometric trajectories: internal septa display positive allometry and shell dimensions display negative allometry. The allometric pattern may reflect D'Arcy Thompson's Principle of Similitude. Principal component analysis does not reveal any distinct clusters in Glottidia morphospace but suggests that some differences independent from ontogeny exist among the populations. Size-free canonical variate analysis indicates the presence of five size-invariant groups that are statistically distinct. Bootstrap-corrected error rates indicate that four specimens are enough to classify a sample correctly at α = 0.05 and eight specimens at α = 0.01. The groups are consistent with neontological classification with the exception of two populations of G. pyramidata identified by discriminant analysis as two distinct groups. The size-free morphogroups reflect geographic separation rather than ontogenetic or substrate differences among the populations.Despite the morphological simplicity of the shell, size-free multivariate analysis of Glottidia delineates groups that offer taxonomic resolution comparable with the neontological classification. The method offers a promising tool for identifying natural morphogroups on the basis of few morphological characters. Moreover, the agreement between neontological taxonomy and the morphogroups suggests that the size-free approach can be applicable for evaluating the reality of the low diversity and turnover rates observed in the fossil record of lingulide brachiopods (= Family Lingulidae). Assuming that the neontological species of Glottidia are biologically meaningful, this study shows that morphological simplicity of lingulides does not necessarily result in taxonomic underresolution. Our analysis, as well as several previous case studies, suggests that taxonomic diversity and turnover rates do not have to be dependent on the morphological complexity of preservable parts. In many cases, when rigorous quantitative methods are employed, the differences in the rates of morphological evolution may be a real evolutionary phenomenon and not artifacts of morphological complexity.

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