Herbivorous tetrapods make their first appearance in Upper Carboniferous fossil assemblages but only become abundant and diverse in Upper Permian ones. During the Late Carboniferous-Early Permian interval, herbivory appeared independently at least five times: in diadectids, bolosaurids, captorhinids, edaphosaurids and caseids. These animals ranged from small forms with aptitudes for collection and processing of low-fiber plant tissues (as well as terrestrial invertebrates) to giants particularly apt for utilization of high-fiber tissues. Our report focuses on the latter group since the development of high-fiber herbivory has had a critical impact on evolution of terrestrial plants and animals as well as on the organization of terrestrial ecosystems.

The low abundance and diversity of early, high-fiber herbivores reflect on one hand, sampling biases toward habitats suboptimal for herbivory, and on the other, the limited ecological capabilities of the animals themselves. Most of the Permo-Carboniferous assemblages derive from wet-land swamp and forest ecosystems where plant tissues would have been relatively rare and/or inaccessible and predation relatively intense. The likely herbivores appear apt for life in wet-land ecosystems; there they probably utilized localized patchs of productive shrub and herb along rivers and around lakes as refuges from disturbance (desiccation, temperature extremes and predation) as well as sources of food. Their low metabolic levels and growth rates minimized nutritional requirements but along with large size provided adequately for adult maintenance and for reproduction. High adult survivorship and production of a large number of eggs through a long adult lifespan would have offset high egg and juvenile mortality.

Only a few Late Carboniferous and Early Permian assemblages sample drier woodland and shrub habitats where conditions would have been more favorable for high-fiber herbivory, but by Late Permian such assemblages occur in much greater numbers and diversity. The high-fiber herbivores in these dry-land ecosystems had ecological aptitudes comparable to wet-land forms but were relatively more abundant and diverse, reflecting both a greater abundance and extent of shrubby vegetation and a lower incidence of predation.

The Siwalik fluvial deposits of Pakistan are characterized by varying proportions of red to brown silts, fine sands, and minor clays representing overbank deposition. In the Chinji Formation (~15–10.5 Ma), floodplain facies consist of overlapping packages of: 1) well-bedded siltstones and occasional sheet sands or small channel sands, 2) an overlying transitional zone with increased bioturbation and minor pedogenesis, 3) a capping paleosol. These packages are 5–6 m thick and pinch out laterally over 1–2 km; they appear to represent crevasse-splay lobes that aggraded rapidly into low-lying wet areas and then became stable land surfaces. The cycle was repeated as aggradation of the major rivers and/or local subsidence transformed the topographic highs into lows where sedimentation again buried soil surfaces. Floodplains in the Nagri Formation (~10.5–9 Ma) were associated with a larger channel system and were less complex, and those of the Dhok Pathan Formation (~9–6 Ma) were influenced by several contemporaneous river systems and again became more complex.

Paleosols are superimposed on all lithofacies and occur every 4–10 m thoughout the 3500 m sequence where overbank deposits are dominant. Paleomagnetic calibration of the Siwalik sequence indicates that paleosols represent 10–50K yrs, on average. Individual paleosols are red-orange or red-brown, 1.6–4.8 m thick, have abundant evidence of bioturbation, ped structure, clay cutans and a zone depleted in matrix carbonate above a lower zone with carbonate precipitates. A long-term record of Siwalik vegetation in Pakistan is contained in the carbon isotope ratios of paleosol carbonate. There is no evidence that paleosols varied in maturity with distance from the major channels; instead vertical and lateral facies relationships were controlled by shifting crevasse-splay lobes and overbank channels.

The processes of overbank sedimentation in the Siwalik sequence have important consequences for preservation of vertebrate faunas. Most of the 800+ fossil localities occur in channel fills within overbank facies; relatively few are associated with paleosols or the coarse deposits of major channels. The frequency of overbank channel fills varies through the different formations, resulting in uneven sampling of the vertebrate faunas. Most skeletal remains are attritrional, and bones are disassociated and fragmentary but otherwise well-preserved. This is partly a consequence of bioturbation and minor transport followed by rapid burial within the abandoned channels. The ecological setting of the Siwalik biota was controlled by a mosaic of floodplain environments that changed in complexity through time. In contrast to the Eocene Bighorn Basin floodplains, there was no simple lateral relationship of habitat types with distance from the major channels.

Suspect terranes in western North America and northeastern Siberia contain Permian taxa which were endemic to the Tethyan region. According to one hypothesis, the rocks containing these faunas were transported across the Paleopacific Ocean by plate motion during the Mesozoic. An alternative explanation is that the Tethyan species crossed the Paleopacific Ocean in much the same way as modern Indo-Pacific corals migrated into central America. A third hypothesis attributes their presence in North America to dispersal through a marine corridor between the Tethys and Paleopacific oceans. Trend-surface analysis of modern and Permian biogeographic data is a new approach to understanding the origin of these exotic faunas and constraining the paleolongitude of the circum-Pacific terranes which contain them. The eastward decline in generic diversity of Recent Indo-Pacific corals and larger foraminifera across the Pacific Ocean may be used as a model for the distribution of their respective ecological and biogeographical analogs, namely, Permian Tethyan rugose corals and fusulinids in the Paleopacific Ocean.

In order to test the method, data on the generic diversity of modern corals were compiled from 137 areas in the Indian and Pacific Oceans. A second-order polynomial surface was constructed from the biogeographical data. It is nearly symmetrical about the Equator, and the average pole to its plane of symmetry is located ≤1° away from the pole of the Earth's axis of rotation. It is closer to the actual pole than are mean virtual magnetic poles obtained from Quaternary lavas at three well-sampled islands: Hawaii, Tahiti and Easter Island. Trend-surface analysis of the biogeographic data on larger foraminifera yields similar results. Thus the estimate of the position of the Earth's pole of rotation using biogeography rivals that obtained from the best available palaeomagnetic data.

The same kinds of data may also be used to place longitudinal constraints on paleogeographic reconstructions. The gradual decline in diversity of corals eastward across the Pacific Ocean may be used to find the location of an island if its paleomagnetically-derived latitude and the value of coral diversity are both known. In order to test this approach, the values for coral diversity at Hawaii, Tahiti, and Easter Island were removed from the data, and a second-order polynomial surface was obtained from the reduced data set. The islands were then returned to the map using their paleomagnetically-derived latitudes and the longitudes obtained from the contour lines of the diversity surface. Easter Island, Hawaii and Tahiti were placed approximately 600 km northeast, 3,700 km southeast and 600 km southeast of their actual sites, respectively. These distances are small compared with the total width of the Pacific and Indian oceans (26,000 km). Evidence that latitudinal and longitudinal gradients in faunal diversity existed during the Permian provides the rationale for the application of the proposed method to fossil data of that age.

Six representative samples of the Lower Oxford Clay (LOC) and the Middle Oxford Clay (MOC) sediments have been assessed for total organic carbon (TOC from 1.2 to 14.2%), hydrogen indices (HI from 813 to 130), and carbon isotopic values (δ13C from −23.1 to −27.7±) (Kenig et al., this symposium), and have been extensively studied using petrographic techniques. The use of the scanning electron microscope and particularly the backscattered electron mode was emphasized as it is the most suitable tool to study the relationships between organic matter and minerals at a micrometric scale.

The bulk mineralogy appears similar in all samples studied. The argillaceous matrix is predominantly composed of illite and kaolinite with detrital mineral grains of quartz, feldspar, mica (biotite and muscovite) and calcitic bioclasts (e.g. coccoliths). Diagenetic features consist mainly of dissolution of quartz grains, rim epigenization of quartz grains to kaolinite, and the presence of pyrite. The concentration of pyrite increases with the concentration of organic matter. Both framboidal and euhedral forms of pyrite are present Euhedral pyrite crystals are more abundant in organic-rich samples, indicative of the more reducing conditions occurring in the organic-rich sediments. In organic-rich samples, coccoliths are concentrated in well preserved fecal pellets, suggesting a relatively high sedimentation rate. Preservation of coccospheres indicates a low energy environment of deposition and mild diagenesis. Unusually well-preserved biotite crystals may be indicative of the proximity of sediment sources and of the weakness of diagenetic processes.

In organic-rich samples, organic matter is encountered as elongated “patches” 20 to 50 μm in length and composed of several particles of marine phytoplanktonic origin; and as thin isolated particles closely associated with clays. These thin particles are both of marine phytoplanktonic and of terrestrial origin (woody debris, vegetal tissues and rare palynomorphs). In organic-poor samples, the frequency and the size (5 to 20 μm) of the patchy composite particles of phytoplanktonic organic matter decrease. Palynological studies indicated that 80% to 95% of the organic matter is amorphous and probably of marine origin. However, the proportion of structured organic matter, woody debris and vegetal tissues, increases from 5% to 20% as the TOC decreases.

None of the samples studied exhibited laminations at a sub-millimetric scale. However, the organic “patches” in the organic-rich samples lie parallel to the plane of stratification even if there is no obvious stratification of the mineral matrix. Clay minerals show a random and disorganized distribution that may be indicative of microbioturbation, even in the most organic-rich samples.

Organic and mineral microtextures are controlled by the environment of deposition and the diagenetic history of the sediments and are related to geochemical parameters as HI, δ13C and TOC. Microbioturbation would indicate that the water column was never anoxic. In contrast, euhedral pyrites crystals suggest anoxia in the organic-rich sediments. The decrease in size of organic “patches” with decrease in TOC, as well as the variable distribution of coccoliths, may be indicative of changes in primary productivity and sedimentation rate.

Many macroevolutionary patterns have been explained in the past on the basis of expectations and prejudice rather than quantitative testing. Large-scale ecological replacements have been a prime example, where expectations of progress and competitive advantage have coloured interpretations. Equally, no doubt, others have looked for, and found, evidence for entirely noncompetitive processes to explain major replacements (reviewed, Benton 1987).

A partially quantitative approach is presented, based on a study of tetrapod families, marine and nonmarine, through the interval from Devonian to the present day. New data bases of the history of tetrapod diversification have the advantage over older attempts of (1) a fully cladistic phylogeny, and hence monophyletic families; (2) a detailed overview of stratigraphy and improved range data; (3) palaeobiogeographic control; and, (4) definition of ecological categories in terms of mean body size categories, diet, main habitat types (fully marine; partially marine/ coastal; freshwater; aquatic/terrestrial; lowland; upland; arboreal, aerial).

The bulk of the diversification of tetrapods is correlated with increases in the ranges both of habitats occupied and of diets (Benton 1990). However, tetrapod families came and went, and a large proportion of the diversification could have been driven by competition and progressive replacement of archaic families by competitively superior ones in ecological relays. In order to test this, the ranges of all tetrapod families were plotted against time and sorted into a variety of habitat, dietary, and palaeogeographic categories.

The results do not support a generalised view of competitive ecological relays. The majority of families appear to have arisen within new cells of the matrix, and did not apparently overlap in time with, or follow closely after, any potential competitors. This would be the minimum requirement for a postulate of competition. Only some 5% of cases could be open to a competitive explanation, and these include certain well known examples, such as multituberculates/ rodents, plesiadapiforms/ rodents, ichthyosaurs/ mosasaurs. The present study has narrowed the odds againt large-scale competition as a significant motor of large-scale biotic replacements. Most new taxa of tetrapods appear to have arisen in response to the availability of empty adaptive space.

Environmental shifts may also be detected during the course of tetrapod evolution, with expansions offshore to ever more fully aquatic lifestyles among marine tetrapods (because they all arose from terrestrial ancestors!), and with expansions from lowland tropical zones to temperate belts, uplands, and marginal lifestyles (burrowing, climbing, flying) among nonmarine tetrapods.

Long-term cycles are evident in the stratigraphic distribution(appearances/extinctions) and dominance changes of Mesozoic calcareous nannofossils. These assemblage turnovers correspond to major episodes of biological extinction recognized in inverterbrate genera and families. The identified Mesozoic nannofossil assemblage turnovers are gradual, in contrast to the well-documented and geologically instantaneous terminal Cretaceous event. Such continuity indicates a non-catatrophic cause and suggests that these turnovers are unrelated to the terminal Cretaceous “accident”. Their timing instead corresponds to interpreted sea level trends and paleoceanographic changes in the sections studied.

Current evidence is based on a limited number of sections spanning the Pliensbachian to Cenomanian, although published literature and a thorough analysis of the Cenomanian show that these turnovers can be recognized over a wide geographic area. These preliminary conclusions are based on detailed sample analyses of marine sections selected for their nannofossil content. This has eliminated any taxonomic or preservational bias and problems related to compiled literature ranges.

Major dominance changes are recorded in the Pliensbachian, Bajocian, Tithonian, and Aptian. The Pliensbachian turnover is evident at the family and ordinal level, whereas the younger dominance changes occur at the generic level. A major diversification during the Pliensbachian resulted in the replacement of the Jurassic Family Crepidolithaceae by the important Jurassic placolith families. The Bajocian and Tithonian turnovers were initiated by dominance changes within the common imbricate placolith family, Ellipsagelosphaeraceae. The Tithonian turnover was most dramatic including: (1) a major diversification near the Jurassic/Cretaceous boundary; (2) the extinction of several genera; and (3) the establishment of a dominant low latitude assemblage (Nannoconus, Conusphaera, Micrantholithus). Species appearances and extinctions characterize the Cretaceous turnovers. There was an increase in species extinctions during the Hauterivian, Aptian, and Cenomanian. The Aptian also includes the extinction of the aforementioned low latitude assemblage and the subsequent diversification and radiation of more cosmopolitan floras, which continued until the end of the Albian. The highest number of nannofossil species extinctions within any Mesozoic stage (except for the terminal Cretaceous) are recorded in the Cenomanian. Although several of these species extinctions are associated with the Cenomanian/Turonian boundary anoxic event, most preceeded this event.

The passage of time cannot be measured in vacuo. Recognition of the time-continuum can only be made by reference to physical and/or biotic events in the geohistorical (rock) record. Inasmuch as these events in the rock record must be measurable in some fashion, they must be related to an objective and retrievable reference standard. Thus the “holy trinity” of litho-bio-and chronostratigraphy can serve as the material (concrete) evidence for the totally conceptual geochronologic units which have no objective existence apart from the natural world.

Geochronology is defined here as the conceptual division of continuous time as measured (geochronometry) by the progression in an ordinal series of events. This is best achieved by an approach which integrates four independent data sets: magnetostratigraphy, sea-floor spreading magnetic anomalies, biostratigraphy and isotopic dating. This integrated approach has resulted, until recently, in an ordinal framework capable of measuring the passage of time with greater resolution (precision), though perhaps with less accuracy, than a radiometric approach alone. Recent improvements in the field of isotopic dating-the single crystal laser fusion (SCLF) 40Ar/39Ar technique - now render possible dates with analytical precision of <1% in the early to mid-Cenozoic. The implication for high resolution correlation is clear: until recently biostratigraphy and biochronology have been routinely able to achieve a degree of chronologic resolution considerably higher than that of isotopic dating with its inherently large analytical errors. Laser fusion dating is now capable of providing numerical values for parts of the stratigraphic record with comparable or greater precision than classical biostratigraphy and biochronology. It is clear, now more than ever, that an accurate and precise biostratigraphy is important as we continue to improve upon the geochronologic framework which underlies attempts at high resolution correlation between marginal, platform and deep-sea stratigraphies.

A review of the philosophic and methodologic approach of various Cenozoic geochronologic schemes and their strengths and weaknesses will be presented together with a brief discussion of a new, and as yet unpublished, revision to Cenozoic geochronology. Recent assessment of sea floor anomaly patterns indicate a need to stretch the spacing of the interval between anomalies 3A to 5 resulting in an age increase of about 0.5my for Anomaly 5 from 8.92–10.42Ma (BKVC85) to 9.6–11.0Ma; the revised age estimates are consistent with those of McDougall (1984) based on radioisotopic dating of Icelandic basalts. No other major (age) revisions to Neogene chronology are contemplated. However, discrete adjustments are required in the late Neogene as magnetostratigraphic boundaries and biostratigraphic datum events are (re)correlated to the recently proposed astronomically calibrated orbital time scale of Hilgen and Langereis. In the Paleogene the major change is centered on readjustment of the Eocene which, while retaining its relative duration of ~21my, has younger (~34Ma) and older (~54.5Ma) limits, respectively, not unlike some estimates made over 20 years ago. Emphasis on implications for Paleogene geochronology will be stressed with particular reference to events around the Paleocene/Eocene boundary and the integration of correlative NW European and Gulf and Atlantic Coastal Plain stratigraphies in a sequence stratigraphic framework. The continuing efforts being devoted to revising Cenozoic geochronology have as their overiding goal the simple yet scientifically elusive objective of “getting it right”.

A prolific assemblage of foraminifera dominated by vaginulinids and nodosariids recovered from Callovian-Oxfordian sequence exposed in central Kutch, Western India, is correlated with Jurassic foraminiferal assemblages from other localities of Kutch, a few other Indian regions and also from certain regions of the world. The Kutch assemblage has a distinct Tethyan affinity. A comparative study indicates that during Dogger and Malm epochs, Kutch was having sea connections with Central Arabia, Iran, Afghanistan, Rajasthan, Somalia and Madagascar.

Two morphotypes of Globigerinella siphonifera (Types I and II) can be clearly distinguished in their natural environment based on differences in symbiont distribution, which is dependent on the structure of the pseudopodial network. Laboratory experiments have demonstrated that the life cycle and ecological requirements of Types I and II differ considerably as well. However, qualitative observation of the empty shells reveals no significant differences between these two morphotypes. Therefore, a “fixed-axis” coiling model has been developed to simulate foraminiferal shell morphology with a computer. The model is based on the assumption that isometry is the primary rule implemented in planktonic foraminiferal development. Four parameters (rate of radius increase, number of chambers per whorl, translation rate, and relative distance from the center of any chamber to the coiling axis) and two scaling factors (initial chamber size and number of chambers) suffice to generate geometric models of the shells of these planispirally coiled organisms.

Values for the four parameters extracted from digitized SEM microphotographs of dissected specimens of G. siphonifera demonstrate significant differences between the Types I and II. These are primarily due to a different rate of radius increase and a different number of chambers per whorl. Type I has a higher rate, which in combination with its lower number of chambers per whorl results in a more lobate test and a 22% smaller adult shell size than Type II. We suggest that the smaller surface area-to-volume ratio in the Type I population can be explained by increased respiration due to higher oxygen production during symbiotic photosynthesis; TEM has demonstrated that Type II contains twice as many symbionts than Type I and each symbiont contains a higher concentration of chloroplasts.

The fixed axis model was also used to describe the ontogeny of G. siphonifera. The model shows that early chambers in log-spirally coiled structures must deviate from a strict isometric arrangement. To maintain exponential growth, the juvenile stage of Types I and II is more planispiral, more umbilicated, and contains more chambers per whorl than the adult stage. Future investigations will focus on the transformation of the shape parameters during later ontogenetic development and during cladogenesis.

Isotopic biogeochemistry (13C, 15N) of fossil collagen is nowadays currently used to infer extinct animals and prehistoric man diet, and a wide developement of this technic is expected in the near future. In prehistoric specimens, only parts of bones and teeth are usually available and we have to be sure that isotopic values from any part of a single skeleton do not differ significantly before comparing isotopic values from different specimens.

Isotopic investigations on recent lower jaws from several mammal species show that δ13C values do not differ significantly between bone and teeth collagen but that δ15N values present an enrichment (up to 2–3 ±) in teeth collagen compared to bone in species with teeth that stop growing (reindeer Rangifer tarandus, sheep Ovis aries, bear Ursus americanus, wolf Canis lupus). On the contrary, species with continuously growing teeth (horse Equus caballus) present almost identical δ13C and δ15N values in bone and teeth collagen. Such δ15N values variations are very probably linked to teeth replacement chronology and time of weaning in the different species and for each tooth. Species with continuously growing teeth show similar evolution of isotopic variations in teeth and bone collagen during their lifetime.

Quaternary mammals almost 45 000 years old from France present a similar variation pattern for isotopic values in bone and teeth collagen. Cave bears (Ursus spelaeus) from Aldene and Mialet caves present slightly more negative δ13C values (-0.3 to -1.1 ±) and significantly more positive δ15N values (1.5 to 2.2 ±) in teeth than bone collagen from same fossil individuals. On the site as a whole, collagen δ13C values for definitive teeth are on average 0.7 and 1.1 ± more negative than for bone and δ15N values for definitive teeth are on average 3.1 and 1.9 ± heavier than for bone in Aldene and Mialet caves respectively. In Aldene cave, collagen δ13C values for deciduous teeth are on average 1.5 ± more negative than for bone and collagen δ15N values for deciduous teeth are on average 4.4 ± heavier than for bone. In Marillac, reindeers (Rangifer tarandus) present collagen δ13C values for definitive teeth almost identical than for bone and collagen δ15N values for definitive teeth are on average 1.8 ± heavier than for bone. On the contrary, there is no significant difference between δ13C and δ15N values from horses (Equus caballus) bone and teeth collagen, for a single individual as well as on average of several specimens.

δ13C and δ15N values seem to be equivalent between teeth and bone collagen only for species where teeth grow continously during the whole lifetime. In species where teeth stop growing in adult life, teeth collagen δ15N values seem to be significatly enriched in comparison with bone collagen δ15N values (1 to 3 ±), probably because of an 15N-enriched diet (milk) during the first stages of growing and no subsequent renewal of teeth collagen. The enrichment seems to be even more important for deciduous teeth.

Further investigations on recent mammals teeth and bones are thus urged to obtain a more accurate estimate of intra-individual isotopic variations according to individual age in the most studied species, including man.

The Willwood Fm. of the southern Bighorn Basin of Wyoming, U.S.A., comprises 700 m of lower Eocene alluvial molasse, nearly all of which contains relict pedogenic features. These rocks are grouped into pedofacies–alluvial sediment prisms, thick with immature paleosols proximal to streams and thinner with mature paleosols distally. Pedofacies are bounded by either trunk-stream channel or crevasse-splay deposits, which represent time-stratigraphic markers. The floodplain widths of the Willwood rivers varied from 15 to 20+ km. Paleosols occur throughout the Willwood Formation and the most mature paleosols required about 60 Ka to form whereas the least mature, required 0.5 to 1.0 Ka. Paleosol thicknesses vary from about 0.3–8.0 m and are directly related to net sediment accumulation rate (NSAR) and profile maturity. Pedofacies also reflect NSAR controls; pedofacies are continuously superposed, 15–35-m-thick, and represent time intervals of 30–60 Ka.

In the earliest Eocene, paleosol maturity rose sharply, and NSAR plummeted (Fort Union Fm./Willwood Fm. contact), after which maturity gradually declined (and NSAR rose) throughout the early Eocene. This decline was punctuated by two episodes of severe decline, each corresponding with major increases in NSAR, increased tectonism, and episodes of faunal turnover (“Biohorizons” A and B). Above the biohorizons, species earlier tied to particular paleosol maturities were replaced by closely related though more generalized species with no marked paleosol preferences. Time-stratigraphic reconstruction of the Willwood Fm. shows that “Biohorizons” B and C record the same faunal event; B the extinctions, and C the immigrations.

The 1,300 Willwood fossil vertebrate localities, which are distributed throughout the entire formation, occur in the surface horizons of cumulative alluvial paleosols. All fossil accumulations in paleosols are attritional and formed during pedogenesis. The most complete remains occur in immature paleosols, whereas the most abundant remains are found in mature paleosols. Within the large-scale Willwood ecologic setting, studies of discrete (m's to tens of m's thick) stratigraphic intervals suggest that the paleontology and sedimentology of these intervals can be significantly influenced by lateral differences in paleosol hydromorphy (soil wetness) and maturity (lateral position of a fossil-bearing paleosol with respect to an ancient river channel). These smaller-scale controls on fossil occurrences are important for distinguishing between real and apparent changes in faunal compositions over time and emphasize the value of three-dimensional stratigraphic analysis for interpreting paleontologic events.

Supported by National Geographic Society grant 3985-89.

The evolution of ammonoid sutures has long been cited as an example of the evolution of increased biological complexity. The complexity of sutures has increased, on average, but the exact nature of this increase, and any benefit associated with this increase has yet to be documented. We measure the fractal dimension of >600 ammonoid species and document the change in complexity of sutures between and among seven orders: Ammonitida, Anarcestida, Ceratitida, Clymeniida, Goniatitida, Phylloceratitida, and Prolecanitida. The average complexity of sutures and range of complexity of sutures increased from the Devonian to the Triassic. With the rise of the Ammonitida, average complexity of sutures remained constant or dropped slightly through the Mesozoic. However, the simplest sutures continue to originate over that same interval. The evolution of increased complexity is the result of increased number of complex forms, not selective loss of simple ones. (See figure 1)

We then compare the stratigraphic ranges (longevity) of a genus with the fractal dimension of a member of the genus. Increased sutural complexity does not significantly increase or decrease the susceptibility of a genus to extinction. In other words, there is no differential survival among simple and complex forms. We also show that in ancestor-descendant pairs, descendants do not demonstrate a propensity to become either more complex or more simple than their ancestors. These observations suggest that it may be difficult to demonstrate that the evolution of biological complexity is the result of natural selection. Increased complexity may be the result of experimentation with other anatomical features or the result of an evolutionary random walk.

The Coconino Sandstone is a Permian deposit of cross-bedded sandstone which is distributed over much of northern Arizona. Vertebrate fossil trackways are abundant in the Coconino Sandstone, and invertebrate trackways are present but less abundant. No other fossils have been found in this formation.

A number of papers dealing with the systematics and paleoecology of these tracks have been published, but underprints have not previously been reported from the Coconino Sandstone. A slab from north of Seligman, Arizona bears intersecting trackways of an invertebrate and two tetrapods. A portion of the slab contains the surface on which the animals were walking. On the remainder of the slab a thin layer bearing that upper surface has broken away to reveal another surface with well preserved underprints of both invertebrates and tetrapods (systematic and behavioral aspects of these trackways will be described in a separate paper).

The underprints are very distinct, deep depressions with uniformly rounded edges, while the original tracks are shallower and much less distinct because some sand slumped into them. It appears that as the animal lifted its foot out of a track the sand partly filled in the depression, but in underlying laminae the contour of the underprint was protected by the sand pushed down from above by the animal's foot.

Comparison of this slab with other fossil trackways from the Coconino Sandstone suggests that a number of these trackways may be underprints. Evidence favoring that interpretation are the clarity and depth of the footprints and their uniformly rounded edges. This interpretation also suggests an explanation for some footprints that are so deep that the sand on the front edge of the track overhangs the footprint impression. The Coconino Sandstone is composed of fine sand and does not show evidence of clays or other material that could provide the cohesion to retain such steep, even overhanging, surfaces. If these footprints are underprints, the deep, undercut impressions may have been preserved by the continuity of the overlying laminae while the surface depressions were partly filled by slumping sand.

It might be expected that underprints would be less distinct and detailed than the actual print. That may be true for tracks made in a substrate with an ideal consistency for preserving the tracks, but in pure, fine sand slumping of sand at the surface can apparently obliterate footprint details that are preserved in the underprints.

Appreciating the biological component of taphonomic patterns is necessary for accurately interpreting the mode of formation of fossiliferous assemblages. This study documents taphonomic patterns in three Late Ordovician trilobite genera (Flexicalymene, Isotelus, Ceraurus) and identifies four biological factors that affect incorporation of trilobite exoskeletal elements into the fossil record:

1) Exoskeletal architecture. Recurring patterns of displaced tergites and points of disartiuclation indicate differential susceptibility of the exoskeleton during ecdysis, and presumably also during decay of a carcass. Disolcations are most common at articulation points, e.g., between cephalon and thorax, among thoracic segments, and between the thorax and pygidium. There is no evidence that facial sutures were lines of weakness except during ecdysis.

2) Exoskeletal thickness. Thickness is a better predictor of preservation potential than the position, shape, function, or size of a tergite. For example, Ceraurus and Flexicalymene have hypostomata of similar shape and size, but the thicker Ceraurus hypostoma is more frequently preserved (or at least identified) than the thin ventral plate of Flexicalymene.

3) Ecdysis. Molting potentially releases the greatest number of trilobite tergites to the fossil record. Molt ensembles are recognized by recurring assemblages of tergites (e.g., thoracopygidia, cephalothorax, multiple thoracic segments) although individual elements (e.g., hypostomata and librigenae) are shed as well. Distinguishing individual molt elements from tergites disarticulated via scavenging or post-mortem transport of carcass or exuvia is problematic. Ecdysis often releases intact exoskeletal elements: most breakage probably occurs later. during post-ecdysial transport or scavenging of the exuvia.

4) Predation/scavenging. These effects are characterized by broken (vs. disarticulated) exoskeletal elements. The impact of these processes on the trilobite fossil record is difficult to assess: sublethal wounds are easiest to recognize, the product of successful predation/scavenging is most often unidentifiable comminuted trilobite debris. The products of successful predation/scavenging are identified as such indirectly by their association with the remains of possible predators or by their presence in coprolites.

The Middle Devonian (Givetian) Hamilton Group is composed of widespread, time-stratigraphic, discontinuity-bounded depositional cycles which correspond to sequences and sub-sequences. Not only do recurrent lithofacies and biofacies units correlate predictably with given parts of cycles, distinctive taphonomic features also correlate with appropriate parts of transgressive-, early highstand-, and late highstand (regressive) systems tracts within sequences. Transgressive systems tracts (TSTs) are marked by widespread, thin (0.5 to 3 m), winnowed, shelly sandstones or skeletal wacke- to grainstones. Bases are typically heavily burrowed with a distinctive firmground ichnofacies. Internally, the beds display mixtures of variably disarticulated and corraded skeletal fragments, especially pelmatozoan debris. Condensed intervals are typified by sharp diastemic contacts between TSTs and overlying maximum highstand shales. These surfaces of maximum starvation may have thin (centimeters) lags of phosphatic, concretionary, or pyritic diaclasts, bones and conodonts as well as corroded carbonate skeletal debris. Early highstand deposits are characterized by an alternation of discrete storm beds with mudstones which may yield exceptionally well-preserved faunas. Late highstand- and regressive taphofacies display greater evidence of sediment-shell disturbance by bioturbation and repeated storms. The decrease in accomodation space dictates sediment-bypass and mixing with increased evidence of skeletal disarticulation and shell abrasion.

A recurring, and somewhat enigmatic phenomenon consists of widespread (to 100s of km) shell and reworked concretion layers, associated with diastems, which occur at the late highstand or early sea level-fall position within offshore, low energy mudstones. These “precursor beds” are sediment-starved lags, which mark abrupt shoaling events followed by a return to deeper-water deposits below the transition to lowstand conditions. These lags either represent the overprint of condensed smaller cycles superimposed on larger ones or they may record a fundamentally new, little-understood, process associated with abrupt sea level drop.

Most of the typical Givetian “Hamilton fauna” appears abruptly in the second major sub-sequence (4th order cycle) of the Hamilton Group. The Hamilton fauna was partitioned into distinctive biofacies which were remarkably stable in terms of taxonomic composition, guild structure and relative abundance. These biofacies tracked favored environments and recur through 10 or more basinwide cycles (including sub-sequences) during some 6–7 my. Surprisingly, relative lowstands, represented by sequence-bounding unconformities, appear to have had very little disruptive influence on tracking Hamilton biotas. Very few species became extinct, immigrated, or underwent significant morphological change during the entire Givetian interval. Instead, both the initiation and termination of the Hamilton fauna correspond with major deepening events (Marcellus and Genesee transgressions) of combined eustatic/tectonic origin. In both cases, the major faunal changes (extinctions, immigrations, species evolution) appear to be associated with widespread anoxic black shales in condensed early highstands of sequences. Both of these correspond to global bioevents (Kacak-otomari and Pharciceras events) that have been related to climatic change. This observation suggests that the major transgressions may have been associated with widespread environmental restructuring.

The distribution of molecular markers in sediments provides a reservoir of unique information concerning biogeochemical processes in the geological past, and how these processes respond to environmental change. However, sedimentary systems themselves are biologically dynamic and these markers, and their precursors, have been subjected to bacterial degradation and modification. Recent research indicates that key changes in sedimented organic matter take place during the earliest stages of sediment burial and diagenesis where bacterial activity is also intense. Hence, effective interpretation of the distribution of biomarkers from deep sediment layers and sedimentary rocks requires knowledge of the rates and processes of bacterial decomposition under a range of environmental conditions.

Algae are important primary producers in the marine environment. The prymnesiophyte alga Emiliania huxleyi was selected as a subject for study as it is a source of long chain ketones which are geochemically important biomarkers. The ratio of the ketones C37:2 to C37:3 is temperature sensitive and has been used as a palaeotemperature indicator (UK37).

Preliminary sediment slurry incubations were carried out to optimize experimental design (concentration of decay organism, concentration of sediment in slurry, ability to obtain defined microbial environments over long term incubations, aerobic and anaerobic), and quantitative analytical scheme (extraction and separation technique, type and concentration of internal standards). Subsequent experiments on aerobic bacterial degradation of E. huxleyi demonstrated rapid increase in bacterial activity and biomass. This was accompanied by major changes in lipid classes. The dominant aliphatic hydrocarbons, three isomers of nC31:2, were rapidly degraded and completely removed by 78 days. In contrast, in preliminary anaerobic incubations, the same compounds remained unchanged. By 78 days a significant reduction in the total algal sterols was accompanied by a small increase in total stanols; hence the cholestanol/cholesterol ratio increased markedly. The abundance of the long chain unsaturated ketone C37:3 decreased relative to C37:2 resulting in an increase in the UK37 ratio. The reasons for these changes are unclear. However, they indicate that bacterial degradation may have to be taken into account in the interpretation of UK37 ratios in terms of paleotemperatures.

Further experiments are in progress to clarify the interpretation of these results and provide information on the more recalcitrant biomarkers.

New material of Mixosaurus nordenskioeldii from the Middle Triassic Sulphur Mountain Formation of Wapiti Lake, British Columbia, includes cranial elements with complete upper and lower dentitions, and associated post-cranial material. It demonstrates that skulls with a Phalarodon-like dentition are associated with a Mixosaurus type of post-cranium. The upper and lower dentitions differ in the degree of anteroposterior elongation of the molariform teeth and in the rate of tooth differentiation. These new specimens demonstrate that the separation of the Svalbard material into Phalarodon and Mixosaurus (Merriam, 1911; Wiman, 1916) represents a separation of upper and lower dentitions and confirms that Phalarodon fraasi is the junior synonym of Mixosaurus nordenskioeldii.

Mixosaurus nordenskioeldii is more derived than M. cornalianus in the following characters: 1) Anterior end of both jaws edentulous, 2) Posterior crushing teeth laterally compressed domes, elongate anterolaterally, 3) Skull with large parietal crest, extending well forward between the orbits, 4) Sixth digit present in manus (developed from a neomorph in M. cornalianus).

A well preserved stapes is present in the new material of Mixosaurus from British Columbia. This is one of the oldest preserved ichthyosaur stapes and demonstrates that this element was primitively long and slender in the Ichthyopterygia.

The cheek region in Mixosaurus is formed by two large bones traditionally identified as the quadratojugal and the squamosal. The homologies of these elements are reinterpreted as the squamosal and the supratemporal.

Small skeletal sediment particles, by virtue of their size, experience physical sedimentological conditions different from those affecting large (i.e., > 4 mm) particles. In shallow, high-energy marine carbonate environments with an overall fine-grained (< 4 mm) sediment composition, grain-to-grain impacts are probably of insufficient magnitude to overcome the cushioning effect of water and cause abrasive wear. Very large skeletal grains within such a setting will promote physical degradation, but biological activity (microboring, bioerosion) is more effective in modifying particle surfaces and diminishing grain size. Only in eolian environments are collisions between small grains effective in causing abrasion. Quartz sand, a particularly important abrasive agent in the destruction of large skeletal parts under even moderate energy regimes, also appears to be appreciably important for the degradation of small skeletons only under eolian conditions.

Conodonts are small (0.2–2.0 mm), phosphatic teeth, which may have belonged to an extinct (Cambrian-Triassic) group of jawless fish. They occur principally in marine and marginal marine sedimentary rocks; most specimens probably were deposited as discrete particles or as components of fecal masses. Because the extent and nature of degradation of a skeleton reflects its taphonomic history, evaluation of the susceptibility of conodonts to physical abrasion is important. Bioerosion, probably the principal cause of degradation of calcareous skeletons, was probably insignificant in alteration of conodonts. Their mineralogical composition made conodonts unlikely substrates for endoliths, and they were insufficiently abundant to serve as a recyclable source of phosphate for larger metazoans. Chemical breakdown of skeletal apatite would not have occurred, although atmospheric exposure may have promoted degradation of organic laminae, causing exfoliation.

Experimental studies of abrasion (elements of Palmatolepis sp., Polygnathus sp. - U. Devonian, Iowa) plus petrographic examination of conodont bearing marine, marginal marine, and eolian facies of the Morgan Formation (M. Pennsylvanian, Utah and Colorado) suggests that abrasion of conodonts is insignificant in aqueous environments, and likely to occur to a major degree only under eolian conditions. High-energy (25.6 cm/sec) conditions were simulated in a tumbler containing quartz sand (4Φ − 2Φ), artificial sea water and moderate conodont abundances (50 specimens/kg). Abrasion produced under these artificially extreme conditions (e.g., continuous motion for up to 20 km travel distance) was at a scale detectable only with SEM. “Dry” tumbling experiments were ineffective, as noted by other authors simulating conditions for abrasion of mineral grains. Eolian conditions were simulated in a glass “wind tube” (see Kuenen, 1960, Journal of Geology) using a similar range of quartz sand sizes. Air velocity of approximately 100 cm/sec produced subtle visually detectable abrasion following 5 hours of exposure/transport in 2Φ quartz sand (1667 specimens/kg), but exhibited no visual evidence of abrasion under similar conditions with 3Φ sand.

The Morgan Formation is a mixed carbonate/siliciclastic sequence that reflects repeated episodes of submergence and exposure of a carbonate shelf and laterally adjacent siliciclastic eolian “sand sea.” It represents a virtually ideal ancient example for the interpretation of the effects of natural sedimentary processes because of its well-documented environmental heterogeneity and contains both abraded and unabraded conodonts. Conodonts sampled from high-energy subtidal carbonate facies of the Morgan are unabraded, irrespective of the presence of quartz sand; platform and delicate ramiform elements are all represented. Conodonts sampled from mixed siliciclastic/carbonate eolian facies are extremely abraded; only the most durable Pa elements of Adetognathus sp. and Idiognathodus sp. are preserved, although fine surface details and denticles are worn and anterior blades are missing. Laboratory simulations confirm the interpretation that marine processes are generally insufficient to physically abrade small phosphatic skeletal grains and that highly abraded Morgan conodonts experienced extremely long residence times in the eolian environment where they were transported, repeatedly buried, and exposed to bombardment and abrasion by quartz sand.

Supported by NSF EAR9004300

A post-larval development sequence of complete specimens of Eoparisocrinus crossmani provides a unique opportunity to examine growth and functional morphology. Food particles are caught by the tube-feet in the arms which must provide enough material to nourish a volume of tissue. Tissue volume is assumed to be proportional to crown volume. Ignoring the stem is justified inasmuch as most soft parts are housed in the crown. Crinoid arms grow by terminal addition of new plates at their distal tips in conjunction with calcite deposition on old plates. New branches appear where axillary plates are initiated. Consequently, the growth rates for number of brachials and length of food-gathering system compared to crown volume are much faster than if the data were isometric. The number of food particles collected is related to the number of food-catching tube-feet which can be estimated if the length of the arms and height of the covering plates are known. The size of the largest food item is constrained by the food groove width. Thus, food-gathering capacity is defined as the number of food-catching tube-feet multiplied by food groove width. Food-gathering capacity is the product of two linear dimensions so the expected exponent for food-gathering capacity and crown volume comprises 0.67. The computed exponent is significantly larger than the isometric value so the food-gathering capacity increases much more rapidly than if E. crossmani retained the same shape at all ages, and the ratio of food-gathering capacity:crown volume only declines slightly over the known growth range. Student's t tests indicate that all Ordovician inadunate crinoids examined follow nearly identical ontogenetic trajectories. Conversely, Ordovician camerates are characterized by larger food gathering capacities at equivalent crown volumes. This suggests that the feeding habits of Ordovician inadunates and camerates were quite different.

The ecological niche of a stalked crinoid is at least partially categorized by three parameters. Stem length limits the highest elevation above the seafloor. The column of E. crossmani becomes longer during ontogeny due to the formation of new columnals and height growth of old ones. Consequently, individuals gradually “move up” through various levels until the adult elevation of about 50 mm is reached. The growth rates of stem length relative to crown size are slow in the youngest and mature animals but quite rapid in juveniles. The food groove width defines the size of the largest food particle that can be trapped and transported down the arms to the mouth. The exponents for the average food groove width versus cup height or crown volume are slightly less than the corresponding isometric values. The food groove width is augmented less rapidly than if the shape were constant, because distal plates and branches are more narrow and have more slender food grooves than proximal plates. Growth curves for food groove width versus stem length and elevation were generated for E. crossmani and its common associates. Together, elevation and food particle size define the main dimensions of the niche. The various taxa are more or less separated by different food groove widths at most comparable elevations with two exceptions. One deals with adults of Eoparisocrinus crossmani and juveniles of Cupulocrinus crossmani which sometimes occur together. This overlap would have been of short duration if the juveniles were growing rapidly. The youngest crinoids of all species probably intergraded. This pattern minimizes ecological overlap and probably competition between the different species. Tube-foot spacing is correlated with feeding habits and environment. The tube-foot spacing of E. crossmani is constant regardless of size which suggests that it employed the same type of feeding mechanism throughout post-larval ontogeny.

Long term environmental changes, induced both by natural and anthropogenic causes, cannot be assessed by looking solely at historical records of temperature, rainfall, water quality, etc. Frequently, such records are nonexistent. Where they do exist, they are often too short to be of much use. However, sediments contain a stratigraphic record of environmental change that allows comparison of the historic period influenced largely by humans, with prehistoric time when climate was the major determinant of environmental conditions.

The stratigraphic record contains various fossilized organic materials which reflect environmental conditions at the time of the their deposition. Most abundant are pollen and spores of aquatic and terrestrial plants. Correspondence between pollen assemblages and vegetation has been found in all parts of the world. Therefore stratigraphic changes in pollen taxa reveal much information regarding the vegetational history of a region. Knowledge of the ecological requirements of various taxa can then be used to infer past climatic conditions. For example, dominance of Juglans (walnut) pollen indicates wet conditions while abundance of Pteridium (bracken fern) spores is an indicator of fire, suggesting drier conditions. Pollen can also be used to trace human disturbance to the environment. Sharp increases in the pollen of Ambrosia (ragweed) in sediment cores indicate large scale land clearance by man.

Seeds preserved in sediments provide another measure of temporal vegetational change. Generally, seeds are not dispersed far from the parent plant; hence they provide a more local record of vegetation than pollen. A decrease in seeds of aquatic plants and increase in seeds of higher ground taxa when accompanied by increased sedimentation rates is an indicator of infilling of an aquatic environment. If unaccompanied by increased sedimentation, the change more likely represents lowering of sea level. Disappearance of seeds of taxa sensitive to turbidity and eutrophication provide another long term record of human disturbance.

Distributions of diatoms are affected by temperature, salinity, oxygen, light availability and nutrient levels in the water. Therefore changes in diatom species preserved in the sediments can be used as indicators of climate, turbidity, anoxia and eutrophication in aquatic ecosystems.

Many inorganic substances preserved in sediments also provide a long term record of changes in the environment. Nitrogen and phosphorus can be measured in cores and used as a surrogate record of water quality in lakes and estuaries. Sharp increases in sedimentary accumulation of metals record wastewater discharge and fuel emissions, related to human activity.