Laboratory experiments on regular echinoids indicate that low water temperatures retard organic decomposition far more effectively than anoxia, and that the primary role of anoxia in the preservation of articulated multi-element calcareous skeletons may be in excluding scavenging organisms. When tumbled at 20 rpm, specimens that were first allowed to decay for two days in warm seawater (30°C) disintegrated more than six times faster than specimens treated at room temperature (23°C) and more than an order of magnitude faster than specimens treated in cool water (11°C). In contrast, the effects of aerobic versus anerobic decay on disintegration rates were insignificant. The longer the period that specimens were allowed to decay before tumbling, the greater the rate at which specimens disintegrated, until a threshold time that appears to mark the decomposition of collagenous ligaments. This required a few days at 30°C, about two weeks at 23°C, and more than 4 weeks at 11°C for Strongylocentrotus. Up until this threshold, coronas disintegrate by a combination of cross-plate fractures and separation along plate sutures; cross-plate fractures thus can be taphonomic in origin and are not necessarily related to predation. Specimens decayed for longer-than-threshold periods of time disintegrate virtually instantaneously upon tumbling by sutural separation only. Undisturbed coronas can remain intact for months, sufficient time for epibiont occupation. Rates of disintegration were documented semi-quantitatively by recognizing seven stages of test disarticulation, and quantitatively by tensometer measures of test strength and toughness. The effects of temperature and oxygen on decay and the existence of a decay threshold in disintegration should apply at least in a qualitative sense to many other animals whose skeletons consist of multiple, collagen-bound elements.

Regular echinoids should still be perceived as taphonomically fragile organisms, but our results suggest the potential for latitudinal as well as bathymetric gradients in the preservation of fossil echinoid faunas. Echinoid preservation under any given set of conditions should also be a function of taxonomic differences in test construction (particularly stereom interlocking along plate sutures) as suggested by previous workers, although our experiments indicate that these effects should only be significant among post-threshold specimens. A survey of regular echinoids from Upper Cretaceous white chalk facies of Britain substantiates the basic experimental patterns, yielding examples of all disarticulation stages and significant taxonomic differences in quality of preservation. A diverse array of borers and encrusters on fossil coronas also corroborates the post-mortem persistence of some tests on mid-latitude seafloors.

Organic preservation of non-mineralizing animals constitutes an important part of the paleontological record, yet the processes involved have not been investigated in detail. Organic-walled fossils are generally explicable as a coincidence of original, relatively recalcitrant, extra-cellular materials and more or less anti-biotic depositional circumstances. One of the most pervasive natural inhibitors of biodegradation results from substrate and enzyme adsorption onto, and within, clay minerals; such interactions are likely responsible for many of the organic-walled fossils preserved in clastic sediments. Close examination of the fossil Lagerstätte of the Burgess Shale (Middle Cambrian, British Columbia) reveals that most of its so-called soft-bodied fossils are composed of primary (although kerogenized) organic carbon. Their preservation can be attributed to pervasive clay-organic interactions as the organisms were transported in a moving sediment cloud and buried with all cavities and spaces permeated with fine grained clays. The organic-walled Burgess Shale fossils were studied both in petrographic thin section and isolated from the rock matrix, following careful acid maceration. Isotopic analysis of bulk organic and carbonate carbon yielded values consistent with a normal marine paleoenvironment. Anatomical and histological consideration of the enigmatic Burgess worm Amiskwia suggest that it may in fact be a chaetognath, while the putative chordate Pikaia appears not to be related to modern cephalochordates.

The enigmatic fossil Wiwaxia corrugata is organically preserved in the Burgess Shale (Middle Cambrian, British Columbia) and is therefore extractable by careful acid maceration of the mineralic matrix. High magnification transmitted light microscopy and SEM of macerated Wiwaxia sclerites reveal a substantial amount of previously undescribed structural and microstructural detail. Anatomical and histological comparison with modern organisms indicates that Wiwaxia sclerites are polychaete paleae (flattened setae) and that Wiwaxia was a jawed annelid broadly related to the extant polychaete families Chrysopetalidae and/or Aprhoditidae (Palmyra). Canadia spinosa, an uncontested fossil polychaete from the same beds, shows a paleal microstructure identical to that of Wiwaxia, as well as a closely comparable gross anatomy and taphonomic grade. The unique combination of taxonomically significant characters shared by Wiwaxia and Canadia suggest that they are more closely related to each other than either is to any other fossil or extant polychaete. Thus they constitute a separate superfamily, Canadiacea superfam. nov., in the order Phyllodocida.

Differences in zooid skeletal ontogeny are strongly linked to the distribution of bryozoan species, even along such large-scale environmental gradients as depth and latitude. Three growth patterns broadly characterize zooid formation for encrusting cheilostome bryozoans: zooidal and intrazooidal budding, which facilitate growth in two dimensions at colony margins; and frontal budding, which also permits upward growth in the third dimension. Analyses of skeletal growth patterns of encrusting species present in 230 Recent assemblages from the North Atlantic, Mediterranean, North Sea, and Gulf of Mexico show that species with zooidal budding dominate overwhelmingly at lower latitudes and in shallower water, as assessed by percentages of species within assemblages. In contrast, patterns within moderately diverse fossil assemblages from North America indicate that within the geographic and environmental limits sampled, species with intrazooidal budding once dominated and probably originated in shallow, warm water environments. Intrazooidal budding now occurs with greater relative frequency among species from deeper and higher latitude assemblages. Patterns for frontal budding suggest a slight decrease with increasing depth, but no consistent relationship with latitude. These paleoenvironmental trends occur withn a putatively monophyletic clade and are markedly similar to onshore/offshore trends recognized in other groups of marine benthos, based on patterns of occurrence of supra-specific taxa and novel morphotypes. Results presented here are based on relative dominance of species within assemblages and thus provide a novel comparative test of these previously reported trends.

Six compilations of fossil tetrapod families, spanning 100 years, each contain a broadly similar diversity pattern since the Upper Devonian. Comparison of four recent data bases, one of which is derived from a strict cladistic treatment, reveals widespread taxonomic and stratigraphic inaccuracies in three earlier data bases. Improvement of our interpretation of the tetrapod fossil record will come through continued taxonomic and stratigraphic revision as well as discovery of new fossils.

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 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.

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.

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.

The first lower molar length, width, and posterior loop width were analyzed for ten Cosomys primus populations from horizontal deposits ranging in elevation from 3,000 to 3,295 feet. Sedimentation rates based on radiometric dates for two ashes and rates derived in previous studies suggest that these sediments span an interval of time that ranges from 45,000 to 164,000 years ago. Nonmetric data included the presence of enamel pits, prism folds, and crenulations; the number of triangles; and relative dentine tract heights. Coefficients of variation for the metrics were low, 4 to 7, and a one-way ANOVA revealed no significant differences between any of the populations. Changes in the mean phenotype were less than two phenotypic standard deviations and were not correlated with elevation. The presence of enamel pits, prism folds, and crenulations correlated only with less occlusal wear.

Thus, these microtine rodent populations appear to exhibit stasis over a time period of at least 45,000 and possibly as much as 164,000 years, unless the deposits accumulated more rapidly than previously estimated.