We have produced computer simulations of multiramous graptoloids with the intention of defining the rules governing branching strategies and colony form. Close matches between such simulations and real graptolites show that complex rhabdosomes may be produced by the permutation of relatively simple sets of rules. Those designs found in nature produce an efficient and regular distribution of zooids through the area included by an essentially planar rhabdosome. Strikingly geometrical arrays of stipes, such as the Goniograptus and yin/yang patterns, closely approach paradigmatic harvesting arrays. For dichotomously branching anisograptids the evolutionary trend in reduction of “primary stipes” can be explained by the production of larger spreading colonies. Multiramous graptoloids fed during vertical movement through the water column. Changes in a single branching decision may produce considerable changes in rhabdosome morphology, but these are not necessarily of high taxonomic importance; this is proved by a specimen which is a morphological combination of two “genera.” Although primarily under genetic control, certain modifications to colony form were probably the result of inhibitory interaction between adjacent stipes.

Astogenetic trajectories have constrained evolutionary changes in bryozoans. Rates and timing of astogenetic differentiation have been modified for characters defining the morphology of zooids, subcolonies, and colonies. This paper catalogs 46 examples of bryozoan heterochrony, representing all five skeletonized orders. Heterochrony is inferred to have been a pervasive phenomenon in the evolution of Paleozoic stenolaemates, illustrated by 40 examples, 19 of which produced paedomorphosis and 21 peramorphosis. As a consequence, a restricted range of morphologic states has reappeared repetitively as homeomorphies and evolutionary reversals. Large-scale patterns developed across both geologic time and geographic space reflect variation in heterochronic products irrespective of the developmental processes by which they were achieved. Available evidence indicates that smaller, paedomorphic, and more plastic species inhabited onshore, low-diversity areas. Nonheritable plasticity is inferred to be a correlate of early growth stages and paedomorphosis. Taller, generally peramorphic species with damped plasticity are found in higher diversity, offshore regions. Seven key innovations, which first appeared during the early diversification of bryozoan clades, are peramorphic, and recapitulation was a predominant pattern during their Ordovician radiation. Trends in later phylogeny, on the other hand, have favored paedomorphic derived morphologies, as illustrated by 19 of the 32 examples. Recurrent reverse recapitulation suggests that offshore ancestors frequently gave rise to onshore paedomorphs.

The known Cretaceous formicoids are better interpreted from morphological evidence as forming a single subfamily, the Sphecomyrminae, and even a single genus, Sphecomyrma, rather than multiple families and genera. The females appear to have been differentiated as queen and worker castes belonging to the same colonial species instead of winged and wingless solitary females belonging to different species. The former conclusion is supported by the fact that the abdomens of workers of modern ant species and extinct Miocene ant species are smaller relative to the rest of the body than is the case for modern wingless solitary wasps. The wingless Cretaceous formicoids conform to the proportions of ant workers rather than to those of wasps (Figs. 1–2) and hence are reasonably interpreted to have lived in colonies.

The Cretaceous formicoids are nevertheless anatomically primitive with reference to modern ants and share some key traits with nonsocial aculeate wasps. They were distributed widely over Laurasia and appear to have been much less abundant than modern ants.

The origin of endothermic homeothermy and of high metabolic rate in mammals is currently believed to be the result of early (Mesozoic) selection in advanced cynodont therapsids and/or early mammals for either (1) enhanced thermoregulatory capacity or (2) increased powers of endurance and stamina. Selective factors underlying the origin of specialized respiration/ventilation-support systems in mammals are possible indices of the validity of these two hypotheses. One such support structure is the diaphragm, a specialized muscle that facilitates lung ventilation. We tested capacity for maintenance of resting metabolic rate, thermoregulation, and for extended, intense exercise in laboratory rats (Rattus rattus) in which diaphragm function had been completely ablated. The results were virtual elimination of aeroboic scope (active metabolic rate — resting metabolic rate) but resting metabolic rate was unaffected. Thermoregulatory capacity was unimpaired to at least 8° below lower critical temperature. These and other data suggest that the origin of the mammalian diaphragm, as well as mammalian metabolic rates, may have been related to selection for greater levels of sustainable activity rather than for functions associated with thermoregulation.

Like living herbivorous lizards, chelonians, birds, and mammals, plant-eating dinosaurs probably relied on a symbiotic gut microflora, housed in a hindgut fermentation chamber, to break down plant cell wall constituents. Large body sizes in most herbivorous dinosaurs resulted in low mass-specific metabolic rates and low rates of digesta passage through the gut; the effects of large body size were probably enhanced by the low metabolic rates of large dinosaurs as compared with large mammals. The long residence time of digesta in the gut permitted long exposure of refractory plant materials to the microflora, probably enabling even those dinosaurs with unsophisticated dentitions to survive on fodder with high fiber content. Large herbivorous dinosaurs probably fed on plants whose allelochemical defenses were geared more toward reducing digestibility than attacking the herbivore's metabolism directly, obviating the need for a foregut fermentation chamber and permitting these large herbivores to take advantage of the energetic benefits of hindgut fermentation for digestion of low-quality fodder. Differences in dentitions among the groups of herbivorous dinosaurs may correlate with differences in standard metabolic rate, activity level, body size, or food quality, or combinations of these factors, but the relative importance of each is difficult to assess. Because the mass of the fermentation contents was probably large in big herbivorous dinosaurs, the heat of fermentation may have been a significant source of thermoregulatory heat for these reptiles.

Cretaceous floras in Alaska, when compared to those at mid-latitudes, generally indicate later appearances in Alaska of major clades and major leaf morphologies. Compared to mid-latitude floras, Alaskan Late Cretaceous floras contain few major clades. The Alaskan clades diversified but at a low taxonomic level. Migrational pathways into high latitudes were probably along streams. Similar patterns characterized the Alaskan Tertiary, although some southward migrations of lineages occurred during the Neogene.

Review of other Arctic paleontological data from Ellesmere Island, previously used to suggest that the Arctic was a major center of origin during the Late Cretaceous, indicates that the ages of supposedly substantiating dinoflagellate floras were misinterpreted. When the dinoflagellate data are interpreted according to standard methodology, first occurrences of genera and species groups on Ellesmere are, like the Alaskan occurrences, later than first occurrences at middle latitudes.

Extinctions at the top of the Sunwaptan Stage (=“Ptychaspid Biomere”) near the Cambrian-Ordovician boundary eliminated about half of North American trilobite families. The families that extend from the shelf into the upper slope show significantly higher survival than those confined to the shelf. Biofacies and lithofacies distribution patterns indicate that the extinctions cannot be attributed to a shelfwide physical environmental perturbation, such as a fall in water temperature or the spread of anoxic waters. We develop a simple biogeographic model which suggests that diversity of a faunal province is influenced profoundly by changes in the number of component biofacies. This model is tested with an analysis of biofacies distribution patterns across the upper boundary of the Sunwaptan Stage. The extinctions correspond closely to lithofacies shifts in the outer shelf that indicate the initiation of major paleogeographic changes, possibly in response to a sea-level rise. The effects of these changes cascade across the entire shelf by the shoreward migration of off-shelf and shelf-margin taxa. Biofacies become reduced in number through telescoping and their environmental ranges expand during the extinction interval, suggesting an increase in the proportion of eurytopic taxa. Selective survival of wide-ranging eurytopes may have influenced the dynamics of faunal replacement by lowering speciation rates of shelf taxa. Consequently, the proportion of shelf endemics will decline and biofacies will be dominated by immigrant taxa. There are sufficient similarities in extinction patterns across the upper boundary of the Sunwaptan Stage and those at other Upper Cambrian stage boundaries to suggest that the biogeographic model developed here may have broader application.

Few paleontological studies of species distribution in time and space have adequately considered the effects of sample size. Most species occur very infrequently, and therefore sample size effects may be large relative to the faunal patterns reported. Examination of 10 carefully compiled large data sets (each more than 1,000 occurrences) reveals that the species-occurrence frequency distribution of each fits the log series distribution well and therefore sample size effects can be predicted. Results show that, if the materials used in assembling a large data set are resampled, as many as 25% of the species will not be found a second time even if both samples are of the same size. If the two samples are of unequal size, then the larger sample may have as many as 70% unique species and the smaller sample no unique species. The implications of these values are important to studies of species richness, origination, and extinction patterns, and biogeographic phenomena such as endemism or province boundaries. I provide graphs showing the predicted sample size effects for a range of data set size, species richness, and relative data size. For data sets that do not fit the log series distribution well, I provide example calculations and equations which are usable without a large computer. If these graphs or equations are not used, then I suggest that species which occur infrequently be eliminated from consideration. Studies in which sample size effects are not considered should include sample size information in sufficient detail that other workers might make their own evaluation of observed faunal patterns.