Thermal potentiation and mineralogical evolution in the Bivalvia (Mollusca)

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 resistance to dissolution; resistance to chemical boring by algae and gastropods; reduced shell density in swimming and soft-bottom reclining species; enhanced flexibility in simple prismatic shell layers; and fracture localization and economy of secretion in association with certain foliated structures.Endogenous calcite in bivalve shells varies from biologically induced to weakly and strongly biologically controlled. Biologically controlled calcite generally first appears in bivalve shells as an impersistent component of the outer shell layer, only later, in some groups, expanding to include the entire outer and then part or all of the middle and inner shell layers. The initial stages of mineralogical evolution are shown by certain modern Mytilidae, Veneridae and Petricolidae. In the latter two families, the calcite occurs as conellae in the outer part of the outer shell layer. Calcitic conellae in the inner shell layer of Pliocene Mercenaria are not barnacle plates, as previously indicated, but endogenous calcite comparable in origin to other venerid conellae. Their occurrence in Mercenaria may reflect thermal potentiation of weak biological controls for calcite, as well as local detachment of the secretory mantle epithelium near the pallial and adductor musculature.

The effects of environment on <i>Arctica islandica</i> shell formation and architecture

“…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).…”

Escalation and Extinction Selectivity: Morphology Versus Isotopic Reconstruction of Bivalve Metabolism

“…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.…”

“…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.…”

Nacre in Molluscs from the Ordovician of the Midwestern United States

“…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.…”

“…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].…”