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D Jablonski

Publications and source records attributed to D Jablonski.

18 recordsLinked to original sources
PubMed2001

Effects of sampling standardization on estimates of Phanerozoic marine diversification.

Global diversity curves reflect more than just the number of taxa that have existed through time: they also mirror variation in the nature of the fossil record and the way the record is reported. These sampling effects are best quantified by assembling and analyzing large numbers of locality-specific biotic inventories. Here, we introduce a new database of this kind for the Phanerozoic fossil record of marine invertebrates. We apply four substantially distinct analytical methods that estimate taxonomic diversity by quantifying and correcting for variation through time in the number and nature of inventories. Variation introduced by the use of two dramatically different counting protocols also is explored. We present sampling-standardized diversity estimates for two long intervals that sum to 300 Myr (Middle Ordovician-Carboniferous; Late Jurassic-Paleogene). Our new curves differ considerably from traditional, synoptic curves. For example, some of them imply unexpectedly low late Cretaceous and early Tertiary diversity levels. However, such factors as the current emphasis in the database on North America and Europe still obscure our view of the global history of marine biodiversity. These limitations will be addressed as the database and methods are refined.

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PubMed2001

Lessons from the past: evolutionary impacts of mass extinctions.

Mass extinctions have played many evolutionary roles, involving differential survivorship or selectivity of taxa and traits, the disruption or preservation of evolutionary trends and ecosystem organization, and the promotion of taxonomic and morphological diversifications-often along unexpected trajectories-after the destruction or marginalization of once-dominant clades. The fossil record suggests that survivorship during mass extinctions is not strictly random, but it often fails to coincide with factors promoting survival during times of low extinction intensity. Although of very serious concern, present-day extinctions have not yet achieved the intensities seen in the Big Five mass extinctions of the geologic past, which each removed > or =50% of the subset of relatively abundant marine invertebrate genera. The best comparisons for predictive purposes therefore will involve factors such as differential extinction intensities among regions, clades, and functional groups, rules governing postextinction biotic interchanges and evolutionary dynamics, and analyses of the factors that cause taxa and evolutionary trends to continue unabated, to suffer setbacks but resume along the same trajectory, to survive only to fall into a marginal role or disappear ("dead clade walking"), or to undergo a burst of diversification. These issues need to be addressed in a spatially explicit framework, because the fossil record suggests regional differences in postextinction diversification dynamics and biotic interchanges. Postextinction diversifications lag far behind the initial taxonomic and morphological impoverishment and homogenization; they do not simply reoccupy vacated adaptive peaks, but explore opportunities as opened and constrained by intrinsic biotic factors and the ecological and evolutionary context of the radiation.

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PubMed2000

Invariant size-frequency distributions along a latitudinal gradient in marine bivalves.

In the most extensive analysis of body size in marine invertebrates to date, we show that the size-frequency distributions of northeastern Pacific bivalves at the provincial level are surprisingly invariant in modal and median size as well as size range, despite a 4-fold change in species richness from the tropics to the Arctic. The modal sizes and shapes of these size-frequency distributions are consistent with the predictions of an energetic model previously applied to terrestrial mammals and birds. However, analyses of the Miocene-Recent history of body sizes within 82 molluscan genera show little support for the expectation that the modal size is an evolutionary attractor over geological time.

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PubMed2000

Dissecting latitudinal diversity gradients: functional groups and clades of marine bivalves.

The latitudinal diversity gradient, with maximum taxonomic richness in the tropics, is widely accepted as being pervasive on land, but the existence of this pattern in the sea has been surprisingly controversial. This is partly due to Thorson's influential claim that the normal latitudinal diversity gradient occurs in marine epifauna (taxa living on the surface of the substratum) but not in infauna (burrowing or boring into the substratum), a contrast he attributed to the greater spatial and temporal environmental homogeneity of infaunal habitats. In an analysis of 930 species of north-eastern Pacific marine shelf bivalves, we found that bivalves as a whole, and both infauna and epifauna separately, show a strong latitudinal diversity gradient (measured as number of species per degree latitude) that is closely related to mean sea surface temperature (SST), even in analyses of residuals and first differences. This agrees with results for marine gastropods, but contradicts Thorson's environmental homogeneity hypothesis. The relationship between SST and diversity is consistent with a species-energy hypothesis, but the linkages from SST to diversity remain unclear. Most bivalve clades within broad functional groups conform to the general latitudinal trend, except for the deposit-feeding protobranchs. This group's non-directional pattern may be related to its mode of development, because a similar effect is seen in several other groups locked into this low-fecundity, non-feeding larval mode.

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PubMed1999

The future of the fossil record.

The fossil record provides a powerful basis for analyzing the controlling factors and impact of biological evolution over a wide range of temporal and spatial scales and in the context of an evolving Earth. An increasingly interdisciplinary paleontology has begun to formulate the next generation of questions, drawing on a wealth of new data, and on methodological advances ranging from high-resolution geochronology to simulation of morphological evolution. Key issues related to evolutionary biology include the biotic and physical factors that govern biodiversity dynamics, the developmental and ecological basis for the nonrandom introduction of evolutionary innovations in time and space, rules of biotic response to environmental perturbations, and the dynamic feedbacks between life and the Earth's surface processes. The sensitivity of evolutionary processes to rates, magnitudes, and spatial scales of change in the physical and biotic environment will be important in all these areas.

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PubMed1999

Fossils, molecules and embryos: new perspectives on the Cambrian explosion.

The Cambrian explosion is named for the geologically sudden appearance of numerous metazoan body plans (many of living phyla) between about 530 and 520 million years ago, only 1.7% of the duration of the fossil record of animals. Earlier indications of metazoans are found in the Neoproterozic; minute trails suggesting bilaterian activity date from about 600 million years ago. Larger and more elaborate fossil burrows appear near 543 million years ago, the beginning of the Cambrian Period. Evidence of metazoan activity in both trace and body fossils then increased during the 13 million years leading to the explosion. All living phyla may have originated by the end of the explosion. Molecular divergences among lineages leading to phyla record speciation events that have been earlier than the origins of the new body plans, which can arise many tens of millions of years after an initial branching. Various attempts to date those branchings by using molecular clocks have disagreed widely. While the timing of the evolution of the developmental systems of living metazoan body plans is still uncertain, the distribution of Hox and other developmental control genes among metazoans indicates that an extensive patterning system was in place prior to the Cambrian. However, it is likely that much genomic repatterning occurred during the Early Cambrian, involving both key control genes and regulators within their downstream cascades, as novel body plans evolved.

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PubMed1998

Marine latitudinal diversity gradients: tests of causal hypotheses.

Latitudinal diversity gradients are first-order expressions of diversity patterns both on land and in the oceans, although the current hypotheses that seek to explain them are based chiefly on terrestrial data. We have assembled a database of the geographic ranges of 3,916 species of marine prosobranch gastropods living on the shelves of the western Atlantic and eastern Pacific Oceans, from the tropics to the Arctic Ocean. Western Atlantic and eastern Pacific diversities are similar, and the diversity gradients are strikingly similar despite many important physical and historical differences between the oceans. This shared diversity pattern cannot be explained by: (i) latitudinal differences in species range-length (Rapoport's rule); (ii) species-area effects; or (iii) recent geologic histories. One parameter that does correlate significantly with diversity in both oceans is solar energy input, as represented by average sea surface temperature. If this correlation is causal, sea surface temperature is probably linked to diversity through some aspect of productivity. In this case, diversity is an evolutionary outcome of trophodynamic processes inherent in ecosystems, and not just a byproduct of physical geographies.

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PubMed1998

Geographic variation in the molluscan recovery from the end-cretaceous extinction

Biotic recovery patterns after the end-Cretaceous mass extinction differ among the molluscan faunas of the North American Gulf Coast, northern Europe, northern Africa, and Pakistan and northern India. In contrast to the Gulf Coast, the other three regions lack a rapid expansion and decline of "bloom taxa" and have lower proportions of invaders early in the recovery phase. The anomalous Gulf Coast patterns, distinct from extratropical Europe and the tropical regions, provide evidence for the biogeographic and macroevolutionary complexity of biotic recoveries and may have implications for present-day biotas.

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PubMed1996

Developmental evolution of metazoan bodyplans: the fossil evidence.

Evidence from the fossil record, developmental biology and metazoan phylogeny demonstrates that the rapid origination of major metazoan bodyplans during the late Neoproterozoic and earliest Cambrian was intimately associated with a series of innovations in developmental control mechanisms that included the Hox gene cluster. The interval between about 565 Ma (million years ago) and 530 Ma evidently includes the protostome-deuterostome branching, diversification of independent higher metazoan clades, diversification of important developmental control systems, and formation of higher metazoan bodyplans. Comparative paleontological and developmental studies will allow further tests of alternative models for the sequence of these events, illuminating the association between developmental and bodyplan evolution.

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PubMed1996

Paleobiology, community ecology, and scales of ecological pattern.

The fossil record provides a wealth of data on the role of regional processes and historical events in shaping biological communities over a variety of time scales. The Quaternary record with its evidence of repeated climatic change shows that both terrestrial and marine species shifted independently rather than as cohesive assemblages over scales of thousands of years. Larger scale patterns also show a strong individualistic component to taxon dynamics; assemblage stability, when it occurs, is difficult to separate from shared responses to low rates of environmental change. Nevertheless, the fossil record does suggest that some biotic interactions influence large-scale ecological and evolutionary patterns, albeit in more diffuse and protracted fashions than those generally studied by community ecologists. These include: (1) the resistance by incumbents to the establishment of new or invading taxa, with episodes of explosive diversification often appearing contingent on the removal of incumbents at extinction events; (2) steady states of within-habitat and global diversity at longer time scales (10(7)-l0(8) yr), despite enormous turnover of taxa; and (3) morphological and biogeographic responses to increased intensities of predation and substratum disturbance over similarly long time scales. The behavior of species and communities over the array of temporal and spatial scales in the fossil record takes on additional significance for framing conservation strategies, and for understanding recovery of species, lineages, and communities from environmental changes.

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PubMed1995

Selectivity of end-Cretaceous marine bivalve extinctions.

Analyses of the end-Cretaceous or Cretaceous-Tertiary mass extinction show no selectivity of marine bivalve genera by life position (burrowing versus exposed), body size, bathymetric position on the continental shelf, or relative breadth of bathymetric range. Deposit-feeders as a group have significantly lower extinction intensities than suspension-feeders, but this pattern is due entirely to low extinction in two groups (Nuculoida and Lucinoidea), which suggests that survivorship was not simply linked to feeding mode. Geographically widespread genera have significantly lower extinction intensities than narrowly distributed genera. These results corroborate earlier work suggesting that some biotic factors that enhance survivorship during times of lesser extinction intensities are ineffectual during mass extinctions.

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PubMed1994

Eastern Pacific molluscan provinces and latitudinal diversity gradient: no evidence for "Rapoport's rule".

"Rapoport's rule," which has gained wide acceptance as a potential explanation for latitudinal and other diversity gradients, holds that mean latitudinal range of species decreases toward the equator. We analyzed latitudinal ranges of 2838 eastern Pacific marine molluscan species, a subset of which figured in the original formulation of Rapoport's rule, and failed to find the predicted trends. Instead, species diversity gradients and range magnitudes appear to vary independently, with the spatial distribution of major oceanographic barriers exerting a strong influence on latitudinal ranges. Biogeographic structure should, therefore, be an important element in the assessment of diversity patterns.

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PubMed1993

Geography of end-Cretaceous marine bivalve extinctions.

Analysis of the end-Cretaceous mass extinction, based on 3514 occurrences of 340 genera of marine bivalves (Mollusca), suggests that extinction intensities were uniformly global; no latitudinal gradients or other geographic patterns are detected. Elevated extinction intensities in some tropical areas are entirely a result of the distribution of one extinct group of highly specialized bivalves, the rudists. When rudists are omitted, intensities at those localities are statistically indistinguishable from those of both the rudist-free tropics and extratropical localities.

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PubMed1989

The biology of mass extinction: a palaeontological view.

Extinctions are not biologically random: certain taxa or functional/ecological groups are more extinction-prone than others. Analysis of molluscan survivorship patterns for the end-Cretaceous mass extinctions suggests that some traits that tend to confer extinction resistance during times of normal ('background') levels of extinction are ineffectual during mass extinction. For genera, high species-richness and possession of widespread individual species imparted extinction-resistance during background times but not during the mass extinction, when overall distribution of the genus was an important factor. Reanalysis of Hoffman's (1986) data (Neues Jb. Geol. Palaont. Abh. 172, 219) on European bivalves, and preliminary analysis of a new northern European data set, reveals a similar change in survivorship rules, as do data scattered among other taxa and extinction events. Thus taxa and adaptations can be lost not because they were poorly adapted by the standards of the background processes that constitute the bulk of geological time, but because they lacked--or were not linked to--the organismic, species-level or clade-level traits favoured under mass-extinction conditions. Mass extinctions can break the hegemony of species-rich, well-adapted clades and thereby permit radiation of taxa that had previously been minor faunal elements; no net increase in the adaptation of the biota need ensue. Although some large-scale evolutionary trends transcend mass extinctions, post extinction evolutionary pathways are often channelled in directions not predictable from evolutionary patters during background times.

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PubMed1986

Mass extinctions: Sensitivity of marine larval types.

Developmental types of marine invertebrates may be divided into planktotrophs, which feed on suspended food items, and nonplanktotrophs, which do not feed but are supplied with nutrients (yolk) parentally; these may represent high mortality-fecundity and low mortality-fecundity strategies, respectively. Most versions of the bolide impact hypothesis of mass extinction propose occlusion of the sun by dust or smoke and severance of planktonic food chains for months or a few years, and this should select preferentially against planktotrophs. Yet among fossil prosobranch gastropods, planktotrophs survived the end-Cretaceous extinction equally as well as nonplanktotrophs. Indirect evidence suggests that end-Permian extinctions may have selected against planktotrophs but that the effect was prolonged over millions of years.

Journal Article↗
PubMed1978

Evidence for the presence of Thy-1 on cultured thymic epithelial cells of mice and rats.

Thymic tissue of C57BL/6 mice and DA rats was cultured. After 6--8 weeks, cultures were analyzed for their capacity to absorb anti-Thy-1 serum, and for the expression of Thy-1 on the surface of different cell types by means of the indirect peroxidase labeling method. Three main cell types were identified: epithelium-like cells, fibrocyte-like cells and macrophages, but no lymphocytes were found. The presence of Thy-1 on cultured nonlymphocytic thymus-derived cells was demonstrated by their ability to absorb the cytotoxic activity of the appropriate anti-Thy-1 sera. Electron microscopical analyses of labeling experiments revealed that Thy-1 was predominantly expressed on epithelium-like cells with preference for their cell protrusions. The possible role of Thy-1 expression, both on thymocytes and thymus epithelium for cellular interaction, is discussed.

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