Apatite fission track analyses of 21 samples from the central and eastern Pyrenees are modelled to generate time-temperature plots for the post 110±10°C cooling history over the 40-10 Ma time interval. Modelled thermal histories have been converted into exhumation plots through the application of the present-day geothermal gradient in the Pyrenees. The documented geology of the Pyrenees allows us to assume no significant extensional unroofing and subvertical exhumation trajectories, thus enabling exhumation to be translated into erosional denudation. Maps of denudation have been constructed for six, 5-Myr time intervals. Denudation varied with a 20-50-km length scale, and does not appear to have been related to the major structural zones of the mountain belt. Spatially averaged denudation rates for the six time intervals ranged from 34 to 61 mm kyr −1 assuming the present-day geothermal gradient. Maximum rates of 240 mm kyr −1 occurred in the interval 35-30 Ma, in the region of the Querigut-Millas massif.Assuming the denudation resulted primarily from erosion, the denudation maps can be used to calculate sediment discharge through time to the neighbouring foreland basins. Using a series of rectangular drainage basins with a 251 aspect ratio (based on modern linear mountain belts) and a location of the main drainage divide based on the mean present-day position, it is possible to evaluate the potential for spatial and temporal variations in sediment discharge as a function of denudation. The results show along-strike variations in sediment discharge between drainage basins of 500%, and temporal variations from individual basins of >300%. A comparison of total sediment discharge per year to the Ebro and Aquitaine basins, assuming a fixed drainage divide, shows that the discharge to the south is likely to have been between 1.5 and 2.8 times greater than to the north. sediment supply derived from erosion of the mountain

The concept of a Dirichlet tessellation has been extended to that of a 'finite body' tessellation to provide a more meaningful description of the spatial distribution of non-spherical secondary phase bodies on two-dimensional sections. A finite body tessellation consists of a network of cells constructed from the interfaces of each individual secondary phase body such that every point within a cell is closer to the corresponding body than to any other. Spatial distribution related cell characteristics derived from Dirichlet tessellations have been extended to finite body tessellations. Quantitative comparisons between the two methods indicate that finite body tessellation measurements are more physically representative as well as more sensitive to local distribution characteristics of secondary phases. To reflect the potential application of finite body tessellations, a methodology is described for analysing the effects of particle distribution and morphology on short crack behaviour in particulate reinforced metal matrix composites.

Identification of species in natural populations has recently received increased attention with a number of investigators proposing rigorous methods for species delimitation. Morphologically conservative species (or species complexes) with deep phylogenetic histories (and limited gene flow) are likely to pose particular problems when attempting to delimit species, yet this is crucial to comparative studies of the geography of speciation. We apply two methods of species delimitation to an ancient group of lizards (genus Xantusia) that occur throughout southwestern North America. Mitochondrial cytochrome b and nicotinamide adenine dinucleotide dehydrogenase subunit 4 gene sequences were generated from samples taken throughout the geographic range of Xantusia. Maximum likelihood, Bayesian, and nested cladogram analyses were used to estimate relationships among haplotypes and to infer evolutionary processes. We found multiple well-supported independent lineages within Xantusia, for which there is considerable discordance with the currently recognized taxonomy. High levels of sequence divergence (21.3%) suggest that the pattern in Xantusia may predate the vicariant events usually hypothesized for the fauna of the Baja California peninsula, and the existence of deeply divergent clades (18.8%-26.9%) elsewhere in the complex indicates the occurrence of ancient sundering events whose genetic signatures were not erased by the late Wisconsin vegetation changes. We present a revised taxonomic arrangement for this genus consistent with the distinct mtDNA lineages and discuss the phylogeographic history of this genus as a model system for studies of speciation in North American deserts.

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