Abstract:The most important factor controlling the timing of Phanerozoic mineralogical evolution in the Bivalvia appears to be thermal potentiation of calcite deposition in colder marine and estuarine environments. Cold temperature has promoted mineralogical evolution in the Bivalvia by kinetically facilitating (potentiating) initially weak biological controls for calcite, thereby exposing their genetic basis to natural selection. Calcite has evolved in bivalve shells for a variety of selective advantages, including re… Show more
“…For instance, shell mineralogy can vary depending on water temperature (Carter, 1980). According to the thermal potentiation hypothesis, nucleation and growth of calcitic structural units is favored at low temperatures by kinetic factors (Carter et al, 1998). As a consequence, bivalve species living in cold water environments exhibit additional or thicker calcitic layers compared to the corresponding species from warm waters (Lowenstam, 1954;Taylor and Kennedy, 1969).…”
Section: Environmental Influence On Shell Microstructurementioning
Abstract. Mollusks record valuable information in their hard parts that reflect ambient environmental conditions. For this reason, shells can serve as excellent archives to reconstruct past climate and environmental variability. However, animal physiology and biomineralization, which are often poorly understood, can make the decoding of environmental signals a challenging task. Many of the routinely used shell-based proxies are sensitive to multiple different environmental and physiological variables. Therefore, the identification and interpretation of individual environmental signals (e.g., water temperature) often is particularly difficult. Additional proxies not influenced by multiple environmental variables or animal physiology would be a great asset in the field of paleoclimatology. The aim of this study is to investigate the potential use of structural properties of Arctica islandica shells as an environmental proxy. A total of 11 specimens were analyzed to study if changes of the microstructural organization of this marine bivalve are related to environmental conditions. In order to limit the interference of multiple parameters, the samples were cultured under controlled conditions. Three specimens presented here were grown at two different water temperatures (10 and 15 • C) for multiple weeks and exposed only to ambient food conditions. An additional eight specimens were reared under three different dietary regimes. Shell material was analyzed with two techniques; (1) confocal Raman microscopy (CRM) was used to quantify changes of the orientation of microstructural units and pigment distribution, and (2) scanning electron microscopy (SEM) was used to detect changes in microstructural organization. Our results indicate that A. islandica microstructure is not sensitive to changes in the food source and, likely, shell pigment are not altered by diet. However, seawater temperature had a statistically significant effect on the orientation of the biomineral. Although additional work is required, the results presented here suggest that the crystallographic orientation of biomineral units of A. islandica may serve as an alternative and independent proxy for seawater temperature.
“…For instance, shell mineralogy can vary depending on water temperature (Carter, 1980). According to the thermal potentiation hypothesis, nucleation and growth of calcitic structural units is favored at low temperatures by kinetic factors (Carter et al, 1998). As a consequence, bivalve species living in cold water environments exhibit additional or thicker calcitic layers compared to the corresponding species from warm waters (Lowenstam, 1954;Taylor and Kennedy, 1969).…”
Section: Environmental Influence On Shell Microstructurementioning
Abstract. Mollusks record valuable information in their hard parts that reflect ambient environmental conditions. For this reason, shells can serve as excellent archives to reconstruct past climate and environmental variability. However, animal physiology and biomineralization, which are often poorly understood, can make the decoding of environmental signals a challenging task. Many of the routinely used shell-based proxies are sensitive to multiple different environmental and physiological variables. Therefore, the identification and interpretation of individual environmental signals (e.g., water temperature) often is particularly difficult. Additional proxies not influenced by multiple environmental variables or animal physiology would be a great asset in the field of paleoclimatology. The aim of this study is to investigate the potential use of structural properties of Arctica islandica shells as an environmental proxy. A total of 11 specimens were analyzed to study if changes of the microstructural organization of this marine bivalve are related to environmental conditions. In order to limit the interference of multiple parameters, the samples were cultured under controlled conditions. Three specimens presented here were grown at two different water temperatures (10 and 15 • C) for multiple weeks and exposed only to ambient food conditions. An additional eight specimens were reared under three different dietary regimes. Shell material was analyzed with two techniques; (1) confocal Raman microscopy (CRM) was used to quantify changes of the orientation of microstructural units and pigment distribution, and (2) scanning electron microscopy (SEM) was used to detect changes in microstructural organization. Our results indicate that A. islandica microstructure is not sensitive to changes in the food source and, likely, shell pigment are not altered by diet. However, seawater temperature had a statistically significant effect on the orientation of the biomineral. Although additional work is required, the results presented here suggest that the crystallographic orientation of biomineral units of A. islandica may serve as an alternative and independent proxy for seawater temperature.
“…We checked initially for the presence of diagenetic (altered) calcite at the shell surface. Any surficial diagenetic calcite is readily revealed by staining the shell with Feigl's solution (Carter et al 1998), which stains aragonite black while leaving calcite white (Friedman 1959). Cross sections of shells that reveal growth banding also suggest a lack of major diagenetic recrystallization (D. Jones, pers.…”
Section: Methodsmentioning
confidence: 99%
“…comm.). An acetate peel of a cross section under microscopy easily resolves calcite (either biologic or diagenetic) from aragonite (Carter et al 1998). Finally, the presence of seasonal isotopic curves across a shell indicates the lack of diagenetic alteration (D. Jones, pers.…”
Abstract. Studies that have tested and failed to support the hypothesis that escalated species (e.g., those with predationresistant adaptations) are more susceptible to elimination during mass extinctions have concentrated on the distribution and degree of morphological defenses in molluscan species. This morphological approach to determining level of escalation in bivalves may be oversimplified because it does not account for metabolic rate, which is an important measure of escalation that is less readily accessible for fossils. Shell growth rates in living bivalves are positively correlated with metabolic rate and thus are potential indicators of level of escalation. To evaluate this approach, we used oxygen isotopes to reconstruct shell growth rates for two bivalve species (Macrocallista marylandica and Glossus markoei) from Miocene-aged sediments of Maryland. Although both species are classified as non-escalated based on morphology, the isotopic data indicate that M. marylandica was a faster-growing species with a higher metabolic rate and G. markoei was a slower-growing species with a lower metabolic rate. Based on these results, we predict that some morphologically non-escalated species in previous tests of extinction selectivity should be reclassified as escalated because of their fast shell growth rates (i.e., high metabolic rates). Studies that evaluate the level of escalation of a fauna should take into account the energetic physiology of taxa to avoid misleading results.Key words. Escalation, extinction selectivity, isotopes, metabolism, predation, shell growth rates. A fundamental question in macroevolution is whether there are long-term, predictable patterns or trends in the history of life (Gould 1985(Gould , 1990Vermeij 1987 Vermeij , 1999. Implicit in this question are two significant and related issues: the role of biotic and abiotic factors in evolution, and the effect of mass extinctions, including their selectivity, on evolution. Two end-member points of view on these questions have been articulated most forcefully by
“…This pattern reflects the change from "aragonite seas" to "calcite seas" around this time [42], although within molluscs the record does not show a tight correlation with this aspect of seawater chemistry (Table 1). Transitions from aragonite to calcite have been shown to occur in abundance during a switch to calcite seas [43], but calcite can also be favoured for other reasons like temperature and in bivalves switches to calcite often occurred during times of aragonite seas [44,45]. Thus it is still unclear to what extent these changes in seawater chemistry controlled the transitions in the mineralogy of mollusc shells at this time.…”
Section: Diversification Of Shell Microstructures In Early Palaeozoicmentioning
confidence: 99%
“…There is evidence for a strong influence on shell composition from both of these environmental factors. Thus, while West and Cohen [50] documented changes in the number of crossed-lamellar layers in snails from Lake Tanganyika correlated with intensity of predation, others documented changes in shell mineralogy correlated with changes in seawater chemistry [43,51] and temperature [44,45].…”
Section: Patterns In the Evolution Of Shell Microstructures Through Tmentioning
Nacre was previously thought to be primitive in the Mollusca, but no convincing Cambrian examples are known. This aragonitic microstructure with crystal tablets that grow within an organic framework is thought to be the strongest, most fracture-resistant type of shell microstructure. Fossils described herein from the Ordovician of Iowa, Indiana, and Ohio provide supporting evidence for the hypothesis that sometime between the middle Cambrian and late Ordovician, nacre originated in cephalopod, bivalve, and possibly gastropod lineages. The correlation of independent origins of fracture-resistant nacre with increasing shell-crushing abilities of predators during the Cambrian-Ordovician suggests an early pulse in the evolutionary arms race between predators and molluscan prey.
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