Apparent versus real biotic effects of transgressions and regressions

Abstract

In evaluating the biotic effects of transgressions and regression, care must be taken to ensure that observed patterns are not simply an artifact of the location of available stratigraphic sections along an ancient onshore-offshore gradient of adaptive types. Analysis of Recent bivalves suggests that very nearshore benthic assemblages are dominated by species that are geographically more widespread, are more eurytopic, and more often have planktotrophic larvae than species in offshore assemblages (Jackson 1974; Jablonski and Valentine 1980); this pattern may serve as a null hypothesis for paleobiogeographic analysis. Late Cretaceous bivalve and gastropod faunas of the Gulf and Atlantic Coastal Plain exhibit decreasing levels of endemism and increasing mean geographic range over the course of regression and return to high levels of endemism and low mean geographic range with the succeeding transgression. In addition, species with longer durations are more frequent at peak regression, while geologically shorter-lived species are more prevalent at peak transgression. As seen in Recent examples, the molluscan assemblages from nearshore facies have a higher proportion of species with broad environmental tolerances and planktotrophic larvae, and thus more extensive geographic and stratigraphic ranges, than do the more offshore shelf assemblages. Because late regressive phases are represented only by very nearshore facies, these directional changes in biogeographic and evolutionary characteristics are most parsimoniously interpreted as a reflection of the nature of the facies available for sampling rather than biotic effects of transgression and regression.

Geologic constraints on the macroevolutionary history of marine animals

“…3 and 6). Nevertheless, because only unconformity and rock quantity biases (9,20) are being measured here, it is possible that facies biases (9,20,35) and͞or asymmetries in environmental preservation within sedimentary sequences are causing the stronger section-genus extinction correlation.…”

Diversification, Faunal Change, and Community Replacement during the Ordovician Radiations

“…Extinction resistance: Nearshore taxa tend to have lower extinction rates and longer geologic durations than offshore taxa Lorenz, 1970, 1971;Boucot, 1975Boucot, , 1978Jablonski and Valentine, 1981). This could lead to replacement of offshore taxa during intervals of normal taxonomic turnover simply because longer-lived taxa tend to produce more daughter species than short-lived taxa (assuming, of course, that speciation rates for nearshore species are not substantially less than for offshore species, which seems not to be the case; see Jackson, 1974;Jablonski, 1980;also Stanley, 1979, p. 231ff, for low speciation rates of bivalves and gastropods in general). Alternatively, if offshore communities are more vulnerable to large-scale perturbations (as distinct from the local disturbances of the nearshore zone), then the more resistant nearshore species (or their daughter species) might move into more offshore regions during the geologic intervals following such perturbations.…”

Interdependence of specialization and biodiversity in Phanerozoic marine invertebrates

“…Furthermore, changes in sea level determine the amount of shallow water versus deeper water continental shelf area available for colonization 30 . Because the distribution of generalists and specialists in marine habitats is strongly depth related 31,32 , changes in sea level are a potential abiotic driver of changes in the degree of specialization.…”