4 South 1.06
1994: PhD, University of Bristol
Smithsonian Postdoctoral Fellow
Postdoctoral work at the University of Bristol
Assistant Curator of the Oxford University Museum
2000-2008: Lecturer in Evolutionary Biology, University of Bath
2008-present: Senior Lecturer in Evolutionary Biology, University of Bath
BB10012 Ecology and evolution
BB20040 Concepts in evolution
BB20041 Easter field course
BB20153 Biological data interpretation
BB30131 Evolution in deep time
BB50165 Biology/biochemistry for mathematical biologists
Why study fossils?
Biologists studying extant organisms have a huge battery of methods at their disposal. Morphology can be observed and dissected in great detail, physiology and biochemistry can be made the subject of experiment, behaviour can be observed, and heritable changes within populations can be studied from generation to generation. Information is available at tremendously high temporal resolution (the “ecological” time scale). But life has a history spanning something in the region of 3.5 billion years, with Metazoa originating at least 540 million years ago. The extant biota is just one time slice of this history. However great our understanding of living animals, we could never have predicted the existence of dinosaurs from looking at today???s birds and reptiles, or giant 5m long sea “scorpions” (eurypterids) from studying spiders and mites. Fossils provide us with less detailed morphological and palaeobiogeographical information, but over vastly longer (geological) time scales.
Should we use fossils to reconstruct the ?Tree of Life??
Evolutionary biologists try to reconstruct rapid and deep evolutionary branching events that happened many tens or hundreds of millions of years ago. Unlike living species, fossils offer ancient snapshots of life forms that were around at the time those branching events occurred. Moreover, living species have millions of years ?worth? of change piled on top of this, which can often bury the important signals we need to understand. Detractors have claimed that because fossil data are often less complete, usually just bones, shells and other hard parts, they are likely to muddy the water and make it difficult to find a robust evolutionary tree. Work on groups as diverse as plants, insects and vertebrates demonstrate that this is not the case. We are also documenting cases where adding just one fossil to an analysis can result in a radically different picture of that group’s evolutionary history. The trees constructed without fossils may be oversimplifications, and far from the truth.
Why is the evolution of arthropods so difficult to reconstruct?
Arthropods are the most abundant and diverse of all the multicelled animal phyla. From their rapid radiation in the Cambrian they evolved to fill virtually every habitat and exploit almost all imaginable lifestyles. Their radiation has been the focus of debates concerning the overall pattern of the diversification of life, and their internal relationships remain problematic despite a century of study. Data from molecules, morphology and the fossil record frequently suggest conflicting patterns in arthropod evolution. Controversy now centres on the relative merits of these different sources of data, appropriate methods of analysis, and how to reconcile conflicts. The Malacostraca (shrimps, crabs, woodlice and their relatives) are my primary focus at present.
Do phylogeny and the temporal sequence of fossils agree?
Biologists routinely compare inferences about the order of evolutionary branching (phylogeny) with the order in which groups appear in the fossil record (stratigraphy). Where they conflict, ghost ranges are inferred: intervals of geological time where a fossil lineage should exist, but for which there is no direct evidence. The presence of very numerous and/or extensive ghost ranges is often believed to imply spurious phylogenies or a misleadingly patchy fossil record, or both. Some major taxa have cladograms with a better fit to the fossil record than others. Arthropods appear to be especially bad, whereas mammals and dinosaurs are especially good, for example. There are also trends through time. It has usually be assumed that the frequency of ghost ranges should increase with the age of rocks. While this is true, there is also a marked increase in ghost range frequency from the late Mesozoic to the present day.
Jenner RA, Ni Dhubhghaill C, Ferla MP, Wills MA. (2009) Eumalacostracan phylogeny and total evidence: limitations of the usual suspects. BMC Evolutionary Biology DOI: 10.1186/1471-2148-9-21
Wills MA, Barrett PM, Heathcote JF. (2008) The modified gap excess ratio (GER*) and the stratigraphic congruence of dinosaur phylogenies. Systematic Biology 57: 891-904.
Adamowicz SJ, Purvis A, Wills MA. (2008) Increasing morphological complexity as a major evolutionary trend in the Crustacea. Proceedings of the National Academy of Sciences of the United States of America. 105: 4786-4791
Jenner R & Wills MA. (2007) The choice of model organisms in evo-devo. Nature Reviews Genetics 8, 311-319.
Wills MA. (2007) Fossil ghost ranges are most common in some of the oldest and some of the youngest strata. Proceedings of the Royal Society of London B, Biological Sciences 74, 2421-7.
Cobbett A, Wilkinson M & Wills MA. (2007) Fossils impact as hard as living taxa in parsimony analyses of morphology. Systematic Biology 56, 753-66.
Pollitt JR, Fortey RA, Wills MA. (2005). Systematics of the trilobite families Lichidae Hawle & Corda, 1847 and Lichakephalidae Tripp, 1957: The application of Bayesian inference to morphological data. Journal of Systematic Palaeontology 3, 225-241.
Buckling A, Wills MA, Colegrave N. (2003). Adaptation limits diversification of experimental bacterial populations. Science 302, 2107-2109.
Wills MA. (2002) The tree of life and the rock of ages: are we getting better at estimating phylogeny? Bioessays 24, 203-207.
Wills MA (2001). How good is the fossil record of arthropods? An assessment using the stratigraphic congruence of cladograms. Geological Journal 36, 187-210.
Benton MJ, Wills MA, Hitchin R. (2000) Quality of the fossil record through time. Nature 403, 534-537
Download my program Ghosts, and e-mail me at email@example.com for the password
Wills MA (1998) Congruence between phylogeny and stratigraphy: randomization tests and the gap excess ratio. Systematic Biology 48, 559-580
[DelBat] Program for first order jackknife as described in Cobbett et al. (2007)