All erect, branching (ramose) organisms adhere to the same fundamental geometric growth law: the rate of distal growth decreases away from the branch axis. Regardless of the phylogenetic history of an organism, the formation of cylindrical branches requires adherence to this law. In colonial ramose organisms such as trees, corals, and bryozoans, this law poses a problem. How do colonies coordinate the growth rates of the individual modules to produce an integrated branch? This question is addressed in the context of three Ordovician and three Devonian species of ramose trepostome bryozoans. Using remnant growing tips in the endozone as isochronous surfaces, relative rates of skeletal secretion among zooids were measured. Measurements of skeletal and void spaces across a colony branch enabled calculation of the volume of skeletal material secreted by zooids between successive remnant growing tips. Results indicate that rate of skeletal secretion systematically decreases from the branch axis outward into the exozone. This suggests that zooid morphogenesis is controlled to a certain degree by the colony. Colonial control over zooidal growth rates in turn regulates the shape of the colony.

Morphological gradients in graptoloid colonies are explained by the production and diffusion of a morphogen from the sicula distalwards. Size of the thecae is inversely related to the amount of morphogen present. The graduate decrease of morphogen is given by a set of algebraic equations, and its effect on zooid growth is described by a modified Michaelis-Menten relationship. Changes in size of thecae computed on the basis of these equations fit the changes observed in graptolite colonies. Sets of differential equations are also given to describe the rate of morphogen diffusion and some other processes possibly involved in the development of uniaxiate graptoloid colonies. The suggested basic model of these colonies can be completed by a number of additional assumptions; however, computer experiments reveal that such assumptions do not affect the main properties of the model, namely the appearance of graded series of thecae. New evidence for regeneration of the sicular portion of the broken rhabdosome is presented, providing arguments that morphogen was produced by the siculozooid as a single bolus of secretion. Some local exclusions from the regular size gradient are discussed, and tentative explanations are suggested.

In Baculites, a straight shelled ammonite, the constructional limits on shell shape resulting from the limited strength of nacre in tension are circumvented by a system of vaults in the phragmocone. Vaults bridge between regions of the phragmocone supported by the complex ammonite septal suture, and maintain the shell wall in compression when hydrostatic load induces bending moments. To determine how these vaults interact in the phragmocone to resist hydrostatic loading, measurements were made on a suite of Baculites specimens. In Baculites there is a statistically significant inverse relationship between circumferential curvature (radius of curvature) of the vaulted shell surface and the size of vaults spanning between sutural elements supporting the phragmocone. The inverse relationship between radius of curvature and the sizes of spans in this system of vaults results in the generation of comparable reactive forces at the ends of the vault spans where adjacent vaults interact. The equivalence of these reactive forces prevents the lateral displacement of the vault ends. Consequently, compressive stresses from adjacent vaults are superimposed on, and reduce, the tensional stress component of bending. Limiting tensile stress is of utmost importance in a lightweight shell composed of a brittle material such as nacre, which is strong in compression but weak in tension.

Baculites is particularly appropriate for this study because its straight shell is curved only in the circumferential direction, thus simplifying the problem. However, sutural patterns in coiled ammonites appear to be similarly constrained to produce vaults in the phragmocone which vary inversely in curvature and span size.

The exceptionally preserved Triassic (Anisian) Grès à Voltzia fauna from the Vosges of northeastern France is compared with four major Carboniferous Konservat-Lagerstätten. The problem of comparing faunas with different types of preservation and degrees of taxonomic determination is addressed with a newly devised similarity coefficient. This coefficient quantifies and combines data from different levels in the taxonomic hierarchy and allows comparisons between biotas in a consistent direction regardless of relative diversity. The rank order of similarity between the four Carboniferous Konservat-Lagerstätten and the Grès à Voltzia is as follows: 1. Mazon Creek (Westphalian D) of Illinois; 2. Glencartholm (Visean) of southern Scotland; 3. Bear Gulch (Namurian) of Montana; and 4. Blanzy-Montceau (Stephanian) of France. These occurrences represent conditions transitional between nearshore fully marine and fresh water. The Grès à Voltzia fauna is significantly closer to the Mazon Creek fauna than to the others; the taxonomic overlap with Blanzy-Montceau and Bear Gulch is limited.

Stratigraphic age has an insignificant influence on the result; indeed, the fauna closest in age to the Grès à Voltzia, that of Blanzy-Montceau, is least similar. Taphonomic factors are important in determining the range of organisms preserved. The Glencartholm fauna is represented only by forms with either mineralized or robust chitinous skeletons, implying a greater degree of decay prior to the onset of diagenetic mineralization than in the other Konservat-Lagerstätten. Environment, however, is the major control on similarity. The Mazon Creek biota, like that of Grès à Voltzia, represents settings transitional between terrestrial and marine-influenced delta. Groups common to both Konservat-Lagerstätten include medusae, brachiopods, polychaetes, bivalve and gastropod molluscs, limulids, scorpions, spiders, branchiopods, ostracodes, malacostracans, cycloids, euthycarcinoid and myriapod uniramians, insects, fish, and tetrapods. There is a striking continuity between the faunas of Carboniferous and Triassic transitional sedimentary environments. Groups that were adapted to fluctuating conditions (e.g., shifting salinity) show strong congruence at the family and lower levels and were little affected by Permian extinctions. The major taxonomic contrasts are in the eumalacostracans and insects: many of the groups represented in the Grès à Voltzia appeared in the Permian and radiated across the Permo-Triassic boundary as Paleozoic forms became extinct.

The origin of ammonite sutures is one of the most interesting open problems in paleontology. Present theories of suture formation deal with function rather than morphogenesis. Here we present a study showing that sutures are scale-invariant. In each of ten different ammonite genera, the ontogenetic sequence of the suture can be characterized by the same fractal dimension. We propose a morphogenetic theory for ammonite sutures that is based on the similarity between sutures and the Saffman-Taylor instability in both fractal characters and physical mechanism.

The Paratethyan basins of eastern Europe and western Asia became isolated from marine influence in the Late Miocene, and were the sites of several remarkable endemic radiations of brackish and freshwater organisms. Here I describe the patterns of tempo and mode before and during the radiation of the gastropod Melanopsis in the Pannonian basin of eastern and central Europe, and I explore the underlying mechanisms of evolutionary change.

The most ancient melanopsid species in this area, M. impressa, was present in freshwater areas marginal to the basin well before the radiation. Widely spaced samples of M. impressa indicate that this species underwent a period of stasis lasting at least 7 m.y. The end of stasis corresponded with the extinction of the last of the normal marine fauna in the basin, suggesting that the lack of other fauna and/or reduced salinity in the basin permitted expansion of the melanopsids from the basin margins into the basin proper. Stasis ended with the onset of changes in size, shouldering, and ontogeny, which led eventually to M. fossilis. Change occurred over a 2-m.y. interval; a series of intermediates is present for all three characters. Within-sample correlations provide no evidence that the three characters are constructionally linked; instead they appear to be changing independently. The mode of change in the M. impressa–M. fossilis lineage appears to have been anagenetic. Alterations in the rate and direction of selection (and/or genetic links between characters) are probably required to explain the overall slowness of the change.

Most Pannonian basin melanopsid species arose by rapid cladogenesis in the Middle Pannonian Stage. Physical factors in the basin probably influenced the timing of this diversification; contrasting patterns of variation and diversity between two melanopsid clades suggest that intrinsic factors influenced the extent of diversification.

The miniaturization of shells, often observed in Mesozoic brachiopods, is analyzed in two species of the well-known genus Homoeorhynchia. We investigated shell development in the context of recent works that consider growth as a function of size, shape, and age. The miniaturization results from heterochronic disturbances during development. Although these shells exhibit a large morphological plasticity, architectural constraints limit their morphogenesis, so that small adult specimens are not exactly reduced replicas of large ones. Adult morphology depends largely on the pattern of rib formation, with miniaturization arising by two different processes affecting this pattern: predisplacement of the appearance of ribs in H. meridionalis and acceleration in H. cynocephala. The first case seems to be a reversible process without evolutionary consequences, but the second occurs within an evolutionary trend. In both cases, the miniaturization seems to be related to environmental influences. Study of the growth pathway of these species allows recognition of basic characters in the morphological variation of populations.

Amino acid analyses of undecalcified samples of fossil crocodile and rhinoceros enamel and dentin from mature teeth revealed that the total protein content of these mineralized fossil tissues varied from ~0.01–0.007% by weight. Except in one instance, amino acid analyses of the enamel proteins revealed them to be free of collagen and to have an amino acid composition similar to the proteins obtained from the enamel of mature modern vertebrates. Molecular sieving of the acid soluble enamel proteins demonstrated that the components consisted principally of small peptides and free amino acids, as in the enamel of modern vertebrates.

Based on the presence of hydroxyproline (hyp) and hydroxylysine (hyl), collagen was detected in undecalcified mature dentin of fossil rhinoceros, but not in undecalcified crocodile dentin. It was only by sequential extraction procedures that the presence of collagen in the dentin of fossil crocodile was established, emphasizing the utility and importance of analyzing the soluble components in specific extracts of the fossil. Based on these data and the concentrations of hyp and hyl in the material solubilized by the various solvents, the dentin of fossil rhinoceros contained considerably more collagen per weight and as a percentage of the total protein in the dentin than did the dentin of fossil crocodile.

As with modern dentin, EDTA and dilute acid solubilize the noncollagenous proteins and peptides found in fossil enamel and dentin, some of which contain O-phosphoserine [Ser(P)], an amino acid unique to mineralized connective tissues. Similar to recent reported findings from fossil bone, less of the original content of the noncollagenous proteins, including those phosphorylated, is degraded and removed from the enamel and dentin during fossilization than the percentage of dentinal collagen and the nonphosphorylated domains of the enamel proteins which are removed. This selective resistance to degradation and removal of the noncollagenous proteins, including phosphoproteins, may reflect the strong interaction of these proteins with the mineral phase of fossilized tissues. The amount and close packing of the inorganic crystals may also inhibit the interaction of the proteins in the interior of the enamel and dentin with the geochemical environment.

Both fossil preservation and sampling methods affect perceived patterns of biotic diversity. Artificial range truncations, for example, may lead to incongruences between apparent- and actual-diversity curves. Thus, a catastrophic extinction event may appear gradual. Recent advances in biostratigraphic-gap analysis provide models for the distribution of gap lengths between fossil occurrence horizons and provide methods to place confidence intervals on local taxon ranges and remove the biases caused by artificial range truncations. Confidence intervals for a set of local taxon ranges may then be evaluated collectively to test a hypothesis of co-extinction/co-emigration or co-origination/co-immigration. In the case of terminal Cretaceous ammonites from Seymour Island, range-chart data are compatible with an abrupt extinction event, although the test statistic is not minimized at the stratigraphic horizon that was suggested by Macellari (1986).

Vertebrates and cephalochordates generate significant quantities of lactic acid during intense exercise. This is associated with heavy reliance on anaerobic metabolism for intramuscular ATP formation. We report here exercise-related generation of lactate in the appendicularian Oiko-pleura longicauda (Tunicata: Appendicularia) and in the brittle star Ophioderma panamensis (Echinodermata: Ophiuroidea). The chordate-wide distribution of this pattern of activity metabolism suggests its presence in Early Paleozoic prochordates. The presence of the chordate pattern of activity physiology in Ophioderma suggests that very early (Ediacarian?) deuterostomes may also have generated lactate during intense exercise. Further investigation of activity physiology in other echinoderms is warranted.

This short contribution clarifies similarities and differences between the findings of Gilinsky and Bambach (1986) and Gilinsky and Good (1989) regarding the shapes of clades. The methods developed in the latter contribution are preferred.

Fossil leaves and palynomorphs represent different phases of the plant life cycle, are studied as systematically independent entities, and are subject to different taphonomic, sampling, and recognition biases in the paleobotanical record. They thus provide parallel, and largely independent, documentation of long-term trends in land plant diversity, and the palynological record may be used as a comparative test of floristic trends inferred from macrofossil evidence. Analyses of relative “species” richness in 91 macrofossil and 860 palynomorph Cretaceous “floras” (assemblages) from between 25° and 65° N paleolatitude show a major mid-Cretaceous increase in the within-flora diversity of angiosperms, from near 0% prior to the Aptian (120 Ma) to 50–80% by the end of the Maastrichtian (65 Ma). This level of diversity is attained rapidly in macrofloras, but more slowly in palynofloras. In the latest Cretaceous, macrofloras and palynofloras both indicate that “pteridophytes,” conifers, and other “gymnosperms” are generally less diverse than angiosperms. In both data sets, “pteridophyte” diversity shows a clear decline through the Cretaceous, whereas conifer diversity shows no marked temporal trend. Broad congruence of these patterns, in spite of different biases in the macrofossil and palynomorph records, indicates that they provide a robust reflection of floristic trends through the Cretaceous. Nevertheless, discrepancies between the patterns do occur and underline the importance of complementary macrofossil and palynological analyses for accurate resolution of long-term vegetational change.

The earliest fossil record of animals has long been an enigma. For nearly a century after the appearance of The Origin of Species, mineralized trilobites were thought to be among the first organisms to appear as fossils, and as they were considered to be complex life forms, a long previous episode of animal evolution seemed to be indicated. Discovery and description of Tommotian and Vendian faunas, with their small shelly and Ediacaran fossils respectively, provided us with an idea of the nature of organisms in strata that are progressively older than the trilobite-bearing beds. Yet in these older assemblages we do not find the sorts of organisms that might be expected to be precursors to the well-known Phanerozoic clades. The puzzle remains.

Genera of montane conifers first appeared in the fossil record in large numbers in the Middle Eocene (47-45 Ma) as widespread volcanism in the Cordilleran region provided scattered, cold upland tracts suited for them. Higher subalpine environments, generally above 2,000 m, probably were confined then to upper slopes of scattered strato-volcanos and basement highs covered with thick pyroclastic deposits. As relief increased in the middle Tertiary, and especially during the Pliocene-Quaternary, the area suited for a subalpine forest zone increased significantly, enabling montane conifers to spread into that higher, colder environment and form a new major forest zone. During glaciations the subalpine zone was much larger and probably from 900-1,000 m lower than at present. Spreading post-glacial warmth and drought account for its retreat to higher levels and for the discontinuous distribution of the forest and its species today. Recency of the subalpine adaptive zone is implied also by the close relations of its varieties and subspecies of herbaceous perennials, a few annuals, and pines to those in vegetation zones below it.

Digitizing the third upper molars of Microtus pennsylvanicus reveals evolutionary change in some traits but stability in others during the last 30,000 years. Fossils from Strait Canyon, Virginia (radiocarbon dated between 29,870 + 1,800/-1,400 and 17,880 ± 150 yr B.P.) were compared with modern samples from the margin of the species' conterminous geographic range: Virginia, Colorado, Alaska, and Hudson Bay. Since the late Pleistocene a modification from narrow to wide teeth took place in the eastern populations but not in the western ones, and populations in Virginia apparently evolved wider confluence between triangles 1 and 2. Traits that remained stable through time in the Virginia area, but not necessarily elsewhere, include the numerical shape factors of the occlusal surface and the posterior loop. Potentially widespread stability is evident in the perimeter of the posterior loop relative to total tooth perimeter. Tooth length forms a geographic cline, in which both the fossil and modern populations from Virginia occupy the same position. A peripheral population from southern Colorado shows the most derived dental morphology. These morphological relationships suggest that mosaic evolution operates in arvicoline lineages and provide testable paradigms for future studies.