Evolutionary contingency.
Explore the source record for details and available documents.
Adaptation, Biological↗
Biomedical subjects
Douglas H Erwin
Publications and source records attributed to Douglas H Erwin.
What can we learn about ecology and evolution from the fossil record?
The increased application of abundance data embedded within a more detailed and precise environmental context is enabling paleontologists to explore more rigorously the dynamics and underlying processes of ecological and evolutionary change in deep time. Several recent findings are of special theoretical interest. Community membership is commonly more stable and persistent than expected by chance, even in the face of the extreme environmental changes of the Ice Ages, and major evolutionary novelties commonly lie dormant for tens of millions of years before the ecological explosions of the clades that possess them. As we discuss here, questions such as these cannot be adequately addressed without the use of the fossil record.
Animals↗
Gene regulatory networks and the evolution of animal body plans.
Development of the animal body plan is controlled by large gene regulatory networks (GRNs), and hence evolution of body plans must depend upon change in the architecture of developmental GRNs. However, these networks are composed of diverse components that evolve at different rates and in different ways. Because of the hierarchical organization of developmental GRNs, some kinds of change affect terminal properties of the body plan such as occur in speciation, whereas others affect major aspects of body plan morphology. A notable feature of the paleontological record of animal evolution is the establishment by the Early "Cambrian of virtually all phylum-level body plans. We identify a class of GRN component, the kernels" of the network, which, because of their developmental role and their particular internal structure, are most impervious to change. Conservation of phyletic body plans may have been due to the retention since pre-Cambrian time of GRN kernels, which underlie development of major body parts.
Adaptation, Biological↗
Macroevolution. Seeds of diversity.
Explore the source record for details and available documents.
Adaptation, Biological↗
Abrupt and gradual extinction among Late Permian land vertebrates in the Karoo basin, South Africa.
The Karoo basin of South Africa exposes a succession of Upper Permian to Lower Triassic terrestrial strata containing abundant terrestrial vertebrate fossils. Paleomagnetic/magnetostratigraphic and carbon-isotope data allow sections to be correlated across the basin. With this stratigraphy, the vertebrate fossil data show a gradual extinction in the Upper Permian punctuated by an enhanced extinction pulse at the Permian-Triassic boundary interval, particularly among the dicynodont therapsids, coinciding with negative carbon-isotope anomalies.
Animals↗
Evolution. Insights into innovation.
Explore the source record for details and available documents.
Animals↗
Dynamic response of Permian brachiopod communities to long-term environmental change.
The fossil record preserves numerous natural experiments that can shed light on the response of ecological communities to environmental change. However, directly observing the community dynamics of extinct organisms is not possible. As an alternative, neutral ecological models suggest that species abundance distributions reflect dynamical processes like migration, competition, recruitment, and extinction. Live-dead comparisons suggest that such distributions can be faithfully preserved in the rock record. Here we use a maximum-likelihood approach to show that brachiopod (lamp shell) abundance distributions from four temporally distinct ecological landscapes from the Glass Mountains, Texas (of the Permian period), exhibit significant differences. Further, all four are better fitted by zero-sum multinomial distributions, characteristic of Hubbell's neutral model, than by log-normal distributions, as predicted by the traditional ecological null hypothesis. Using the neutral model as a guide, we suggest that sea level fluctuations spanning about 10 Myr altered the degrees of isolation and exchange among local communities within these ecological landscapes. Neither these long-term environmental changes nor higher-frequency sea level fluctuations resulted in wholesale extinction or major innovation within evolutionary lineages.
Animals↗
Impact at the Permo-Triassic boundary: a critical evaluation.
The recognition in 1980 of a signature of an extraterrestrial impact at the Cretaceous-Tertiary boundary and its apparent involvement with the mass extinction generated considerable enthusiasm for impacts at other mass extinctions. Numerous claims of impact evidence for the Permo-Triassic mass extinction (251.6 Ma), the largest of the Phanerozoic mass extinctions, have generally been rejected, found wanting, or been difficult to reproduce. Despite this lack of repeatable support, considerable available evidence is consistent with an impact, including the rapidity of extinction, coincident carbon shift, and evident correlation between terrestrial and marine extinctions. However attractive the hypothesis, the coincidence with the Siberian flood basalts and the complex nature of the carbon shift are in conflict with an impact. The most intriguing possibility is that the greatest mass extinction of the Phanerozoic left signals very similar to the end-Cretaceous mass extinction but was produced by entirely Earth-bound processes. If true, this would tell us far more about the nature of ecosystems and how they fail than would identification of another impact.
Carbon↗
Recovery after mass extinction: evolutionary assembly in large-scale biosphere dynamics.
Biotic recoveries following mass extinctions are characterized by a process in which whole ecologies are reconstructed from low-diversity systems, often characterized by opportunistic groups. The recovery process provides an unexpected window to ecosystem dynamics. In many aspects, recovery is very similar to ecological succession, but important differences are also apparently linked to the innovative patterns of niche construction observed in the fossil record. In this paper, we analyse the similarities and differences between ecological succession and evolutionary recovery to provide a preliminary ecological theory of recoveries. A simple evolutionary model with three trophic levels is presented, and its properties (closely resembling those observed in the fossil record) are compared with characteristic patterns of ecological response to disturbances in continuous models of three-level ecosystems.
Animals↗
The last common bilaterian ancestor.
Many regulatory genes appear to be utilized in at least superficially similar ways in the development of particular body parts in Drosophila and in chordates. These similarities have been widely interpreted as functional homologies, producing the conventional view of the last common protostome-deuterostome ancestor (PDA) as a complex organism that possessed some of the same body parts as modern bilaterians. Here we discuss an alternative view, in which the last common PDA had a less complex body plan than is frequently conceived. This reconstruction alters expectations for Neoproterozoic fossil remains that could illustrate the pathways of bilaterian evolution.
Animals↗