Biomedical subjects

Michael J Benton

Publications and source records attributed to Michael J Benton.

7 recordsLinked to original sources

PubMed2006

Paleontological evidence to date the tree of life.

The role of fossils in dating the tree of life has been misunderstood. Fossils can provide good "minimum" age estimates for branches in the tree, but "maximum" constraints on those ages are poorer. Current debates about which are the "best" fossil dates for calibration move to consideration of the most appropriate constraints on the ages of tree nodes. Because fossil-based dates are constraints, and because molecular evolution is not perfectly clock-like, analysts should use more rather than fewer dates, but there has to be a balance between many genes and few dates versus many dates and few genes. We provide "hard" minimum and "soft" maximum age constraints for 30 divergences among key genome model organisms; these should contribute to better understanding of the dating of the animal tree of life.

Animals↗

PubMed2005

The quality of the fossil record of Mesozoic birds.

The Mesozoic fossil record has proved critical for understanding the early evolution and subsequent radiation of birds. Little is known, however, about its relative completeness: just how 'good' is the fossil record of birds from the Mesozoic? This question has come to prominence recently in the debate over differences in estimated dates of origin of major clades of birds from molecular and palaeontological data. Using a dataset comprising all known fossil taxa, we present analyses that go some way towards answering this question. Whereas avian diversity remains poorly represented in the Mesozoic, many relatively complete bird specimens have been discovered. New taxa have been added to the phylogenetic tree of basal birds, but its overall shape remains constant, suggesting that the broad outlines of early avian evolution are consistently represented: no stage in the Mesozoic is characterized by an overabundance of scrappy fossils compared with more complete specimens. Examples of Neornithes (modern orders) are known from later stages in the Cretaceous, but their fossils are rarer and scrappier than those of basal bird groups, which we suggest is a biological, rather than a geological, signal.

Animals↗

PubMed2004

The evolution of large size: how does Cope's Rule work?

Cope's Rule is the tendency for organisms in evolving lineages to increase in size over time. The concept is detailed in many textbooks, but has rarely been demonstrated. Many suggestions of the benefits of large body size exist, but none has yet been confirmed empirically. Using a large-scale analysis of recent studies, Kingsolver and Pfennig have now shown how size benefits survival, mating success and fecundity, and they provide convincing arguments for a mechanism that is capable of driving Cope's Rule.

Journal Article↗

PubMed2003

Taxonomic level as a determinant of the shape of the Phanerozoic marine biodiversity curve.

Key aims of recent paleobiological research have been the construction of Phanerozoic global biodiversity patterns and the formulation of models and mechanisms of diversification describing such patterns. Two conflicting theories of global diversification have been equilibrium versus expansionist growth of taxonomic diversity. These models, however, rely on accurate empirical data curves, and it is not clear to what extent the taxonomic level at which the data are analyzed controls the resulting pattern. Global Phanerozoic marine diversity curves are constructed at ordinal, familial, and generic levels using several fossil-range data sets. The fit of a single logistic model reduces from ordinal through familial to generic level, while conversely, that of an exponential growth model increases. Three sequential logistic equations, fitted to three time periods during which diversity appears to approach or reach an equilibrium state, provide the best description of the data at familial and generic levels. However, an exponential growth curve describes the diversification of marine life since the end-Permian extinction equally as well as a logistic. A species-level model of global Phanerozoic marine diversification, constructed by extrapolation of the trends from familial to generic level, suggests growth in numbers of marine species was broadly exponential. When smaller subsets of the data are analyzed, the effect of taxonomic level on the shape of the diversity curve becomes more pronounced. In the absence of species data, a consistent signal at more than one higher taxonomic level is required to predict a species-level pattern.

Ecosystem↗

PubMed2003

Dating the tree of life.

The relative merits of molecular and paleontological dates of major branching points in the tree of life are currently debated. In some cases, molecular date estimates are up to twice as old as paleontological dates. However, although it is true that paleontological dates are often too young (missing fossils), molecular dates are often too old (statistical bias). Intense study of the dating of major splits in the tree of mammals has shown rapprochement as fossil dates become older and molecular dates become younger.

Amino Acid Sequence↗

PubMed2002

A genus-level supertree of the Dinosauria.

One of the ultimate aims of systematics is the reconstruction of the tree of life. This is a huge undertaking that is inhibited by the existence of a computational limit to the inclusiveness of phylogenetic analyses. Supertree methods have been developed to overcome, or at least to go around this problem by combining smaller, partially overlapping cladograms. Here, we present a very inclusive generic-level supertree of Dinosauria (covering a total of 277 genera), which is remarkably well resolved and provides some clarity in many contentious areas of dinosaur systematics.

Animals↗

PubMed2002

Genetic effects of mercury contamination on aquatic snail populations: allozyme genotypes and DNA strand breakage.

Allozyme data and DNA strand break frequencies were compared among populations of Pleurocera canaliculatum from five sites with varying mercury contamination on the North Fork Holston River (NFHR) in southwestern Virginia, USA. Allozyme genotype frequencies for four loci were significantly different between populations from the three most highly contaminated sites and those from two lesser contaminated sites. In addition, heterozygosity at three of these loci was significantly lower in the populations from the most highly contaminated sites. The DNA strand break frequency was significantly correlated to whole-body total mercury concentration in snails from three sites. These data add to the evidence supporting the use of DNA strand breakage as an indicator of chemical contamination and the use of allozyme analysis as a marker of contamination and possible selection for pollution resistance. However, the relationship between contaminant-induced changes in the genetic variation of enzymes of central metabolism and the functionalities upon which selection for resistance may act remain unclear, and mechanisms other than selection for resistance must be considered. Use of enzymes from other biochemical pathways may be appropriate for other species or for those under other chemical pollution pressures.

Adaptation, Physiological↗