Colonial organisms vary in the degree to which they are individuated at the colony level, i.e., in the degree to which the colony constitutes a unified whole, as opposed to a group of independent lower-level entities. Various arguments have been offered suggesting that evolutionary change along this continuum may be biased, that increases may be more probable than decreases. However, counterarguments can be devised, and the existing evidence is meager and inconclusive. In this paper, we demonstrate how the question can be addressed empirically by conducting a test for bias in a group of stenolaemate bryozoans, the cyclostomes. More specifically, we suggest three criteria for colony individuation: degree of connectedness among lower-level entities (in this case, zooids), degree of differentiation among lower-level entities, and number of intermediate-level parts. And we show how these criteria can be used together with a phylogeny and ancestral-state reconstruction methods to test for bias. In this case, results do not unambiguously support any single interpretation but are somewhat supportive of a null hypothesis of no bias in favor of increase.

As part of the demonstration, we also show how results can be transformed into a quantitative estimate of an upper limit on bias. Finally, we place the question of bias in a larger context, arguing that the same criteria and methods we employ here can be used to test for bias in other colonial taxa, and also at other hierarchical levels, for example, in the transitions from free-living eukaryotic cells to multicellular organisms.

Accurate estimates of predation intensity, the frequency of mortality from predation, are critical to studies of the evolution of species in response to predation, and to studies of predator-prey systems in general. Most commonly used indirect proxies for predation intensity in the fossil record have logistical or theoretical problems. Direct proxies, using actual traces of predatory activity, such as drilling and repair scars, may hold more promise. However, these direct proxies often have been used in conjunction with optimal foraging models, and in this context, the underlying assumptions and predictions of optimal foraging are examined.

Results from theoretical models using optimal foraging suggest that (1) the ratio of internal shell volume to shell thickness of prey (benefit/cost ratio) may be a questionable measurement of prey “value” to the predator, as it fails to account adequately for energetic cost to the predator during pursuit and grappling; (2) drilling and repair frequency are invalid measures of prey preference, because optimal foraging predicts that specific prey types are either always taken or always ignored; (3) pooled drilling frequency will not be a useful metric of predation intensity in systems in which the predator need not always drill; and (4) an increase in repair frequency can be a consequence of either an increase or a decrease in predation intensity.

Although drilling frequency may not indicate prey preference, it is a valid proxy for selection due to predation. An approach using size classes, in which the minimum size at which a predation refuge is achieved, is suggested for use with repair frequency.

Despite substantial advances in plate tectonic modeling in the last three decades, the postulated position of terranes in the Paleozoic has seldom been validated by faunal data. Fewer studies still have attempted a quantitative approach to distance based on explicit data sets. As a test case, we examine the position of Avalonia in the Ordovician (Arenig, Llanvirn, early Caradoc, and Ashgill) to mid-Silurian (Wenlock) with respect to Laurentia, Baltica, and West Gondwana. Using synoptic lists of 623 trilobite genera and 622 brachiopod genera for these four plates, summarized as Venn diagrams, we have devised proportional indices of mean endemism (ME, normalized by individual plate faunas to eliminate area biogeographic effects) and complementarity (C) for objective paleobiogeographic comparisons. These can discriminate the relative position of Avalonia by assessing the optimal arrangement of inter-centroid distances (measured as great circles) between relevant pairs of continental masses. The proportional indices are used to estimate the “goodness-of-fit” of the faunal data to two widely used dynamic plate tectonic models for these time slices, those of Smith and Rush (1998) and Ross and Scotese (1997). Our faunal data are more consistent with the latter model, which we use to suggest relationships between faunal indices for the five time slices and new rescaled inter-centroid distances between all six plate pairs. We have examined linear and exponential models in relation to continental separation for these indices. For our generic data, the linear model fits distinctly better overall. The fits of indices generated by using independent trilobite and brachiopod lists are mostly similar to each other at each time slice and for a given plate, reflecting a common biogeographic signal; however, the indices vary across the time slices. Combining groups into the same matrix in a “total evidence” analysis performs better still as a measure of distance for mean endemism in the “Scotese” plate model. Four-plate mean endemism performs much better than complementarity as an indicator of pairwise distance for either plate model in the test case.

Traditionally, the distinction between meraspis and holaspis among trilobites has been based on the achievement of the full adult complement of thoracic segments. Using a large sample (over 700 specimens collected from a single bed) we explore the utility of employing the ontogenetic trajectory of the cranidium as an alternative means to differentiate trilobite growth stages. This method is particularly useful for species represented solely by exuviae and disarticulated individuals. We use geometric morphometrics to examine shape change among cranidia ranging in size from 0.9 mm to 11.6 mm in cephalic length. The 114 measured specimens exhibit a rather continuous gradation in size in which no distinct instars are evident.

The meraspid and holaspid specimens exhibit allometry when partial warp scores and uniform components of shape derived from thin-plate spline analysis are regressed onto log centroid size. To describe allometric shape change, deformation vectors from the smallest to the largest specimen in both ontogenetic stages are presented in three different superimposition settings by using a new software program. We have concluded that a new superimposition method (the Sliding Baseline Registration) is a useful tool for visualizing allometry in organisms that contain an axis of symmetry. As a result, we conclude that allometry is evident in meraspides and holaspides, but the degree of allometry in holaspides is very small relative to that in meraspides. The boundary between meraspis and holaspis in Triarthrus becki appears to correspond to a large change in the rate of ontogenetic change, but neither to a change in the direction of that trajectory nor to a cessation of ontogenetic change. This boundary also corresponds to a cranidium centroid size that matches well previous determinations that holaspis begins at about 2.8 mm in cephalic length.

Major C₄ grass expansions during the late Miocene in both the Northern and Southern Hemispheres had a major impact on biological communities. We report that the diverse terrestrial fauna of Langebaanweg, South Africa, existed in a local environment that remained C₃-dominated during the late Neogene (∼5 Ma). In contrast, other Southern Hemisphere sites at similar latitudes show a clear shift to C₄ grasslands well before 5 Ma. Our results are based on stable isotope analyses of enamel carbonate from four artiodactyl and two perissodactyl families from this locality. We also provide insight into the evolution of the current Mediterranean climate system in this part of South Africa.

The Dominican Republic amber, as a data set for ecological investigation, is subject to unique biases. To understand the paleoecology of Hispaniola during the Miocene it is not sufficient only to identify the amber inclusions, the biases of entrapment also need to be elucidated. This study compares the spider (Araneae) fauna from Recent Neotropical rainforests with assemblages from Dominican Republic amber deposits. This comparison demonstrates that the site of the original resin secretion is farther removed from the ground layer than has previously been suggested. In many spider families, particularly the web weavers, mature males lead an active lifestyle as they roam in search of the more sedentary females. Male spiders are significantly more common as amber inclusions than females. When the sex ratios of preserved spiders are examined in relation to the predation strategies of their extant relatives, at family level, wandering spiders appear more susceptible to entombment than sedentary spiders. This implies that spiders, and presumably other co-occurring organisms, were trapped primarily by wandering onto sticky resin rather than by being engulfed passively by less viscous, flowing resin.

In the last decade, several statistical models have been proposed to quantify the relationships among leaf morphological characters and climate parameters. The models, based on modern plants and climate from varying geographic areas, and derived using varied statistical analyses, were intended for paleoclimatic reconstruction based on the morphological characters of fossil leaves. The goal of the research presented here is to evaluate these and newly constructed models in order to estimate past climate in tropical Africa from fossil leaves. Models found to estimate current climate most accurately using modern African leaf assemblages are used to estimate past climate from fossil leaves at three middle and late Miocene paleobotanical sites in the Tugen Hills, Kenya.

Regression models derived from predictor data having a majority of sites from higher than 25°N-S latitude consistently overestimate mean annual precipitation at modern African sites by an average of 990 mm. A pronounced cold season, as at high latitudes, has an inhibitory effect on leaf size, the primary correlate of rainfall, and may negatively affect the accuracy with which models derived from high latitudes estimate rainfall in the Tropics, which lack a cold season. Models derived from data sets consisting of samples from <25°N-S latitude yield similar and more accurate estimates for mean annual precipitation at modern African sites, expressing the predominant relationship between yearly or seasonal rainfall and leaf size at lower latitudes. Models that estimate temperature parameters, whether derived from high or low latitudes, were found to be inaccurate with modern tropical African samples. The hypothesis is proposed that non-entire margins, the primary correlate with temperature, are more likely to be present on the leaves of deciduous plants, whether they lose their leaves because of cold (at high latitudes) or seasonal drought (at low latitudes). Generally, this study indicates that modern predictor data sets from which models are drawn should be representative of the predominant climate parameters expected among fossil sites.

Four regression models are approximately equal in their ability to estimate accurately mean annual precipitation at the modern African sites. They are derived from African data or combinations of African plus other low-latitude data and provide consistent rainfall reconstructions at the three fossil sites. Estimates are 955 ± 29 to 1185 ± 96 mm/yr for Kabarsero (12.6 Ma), 490 ± 46 to 693 ± 32 mm/yr for Waril (9–10 Ma), and 730 ± 30 to 1019 ± 32 mm/yr for Kapturo. Wet-months precipitation estimates are 857 ± 30 mm/yr for Kabarsero, 437 ± 30 for Waril, and 627 ±30 for Kapturo.

These are the first quantitative estimates of climate for the Miocene of East Africa. The seasonally dry climate inferred for Waril may indicate that the Asian monsoon was established by about 9–10 Ma. Alternatively, the seasonally dry climate may reflect local topographic changes caused by rift valley development. However, the plant localities suggest that, although progressive drying may have been a trend during the Tertiary, there was not a unidirectional change from forested to open environments in the Kenya rift between 12.6 and 6.8 Ma, the time interval just prior to the origin of hominids.