PaleoBios, Volume 14, Supplement to Number 4 1993 CALIFORNIA PALEONTOLOGY CONFERENCE ABSTRACTS DINOSAUR SKIN IMPRESSIONS FROM THE UPPER CRETACEOUS NESLEN FORMATION, EAST-CENTRAL UTAH Brian G. Anderson, Department of Earth Sciences, University of California, Riverside, CA 92521; and Reese E. Barrick, Department of Geological Sciences, University of Southern California, Los Angeles, CA 90089 Impressions of dinosaur integument were recently found associated with partially articulated post- cranial skeletal elements in the Campanian Neslen Formation of east-central Utah. The fossils occur in a very fine-grained calcific sandstone, which was deposited in a low to moderate energy marginal marine environment. Overlying the dinosaur remains is abundant, scattered coniferous plant material, including external molds of relict logs containing well- preserved Teredolites. Other trace fossils comparable to Palaeophycus are concentrated within sediments surrounding the skeleton, and appear to be associated with the body cavity and /or plant material. Additionally, enigmatic cylindrical and botryoidal molds (possibly of internal tissue) occur subjacent to skin impression in several specimens. The skin impressions consist predominantly of small tubercles ranging from 1.5 to 5.0 mm in relief. Reverse impressions reveal six-sided polygonal scales 3.5 to 7.0 mm wide. Larger discrete and clustered tubercles up to 11.0 mm in diameter and 2.5 mm in relief occur in some of the samples. These forms exhibit radiating grooves extending from the top to the base of the tubercle. General morphological features of the integument suggest that the remains are from a hadrosaur, based on comparison with Los Angeles County Museum of Natural History Lambeosaurus specimen LACM-17712. With further study, it may be possible to correlate different impression morphologies to specific body regions. CARBON ISOTOPE TRENDS WITH DEPTH IN MICROBIAL MATS FROM BAHIA SAN QUINTIN, BAJA CALIFORNIA NORTE, MEXICO Julie K. Bartley, Department of Earth and Space Sciences, University of California, Los Angeles, CA 90024-1567 Three kinds of direct evidence contribute to current understanding of Archean life: stromatolites, microfossils, and chemical fossils. These data indicate that stromatolitic prokaryotic ecosystems (microbial mats) had become established by 3500 Ma, and perhaps earlier, but the scarcity of ancient fossils makes detailed interpretation of Archean ecology difficult. Models based on modern ecosystems are needed to aid in the interpretation of their early analogues. This project is concerned with inferring the ecology of ancient microbial mats by examining potential chemical fossils in modern microbial mats and comparing the results of these studies with data from the fossil record. Cores of Li/ngbya-dominated microbial mats were collected from a locality near Bahia San Quintin, Baja California Norte, Mexico, and the organic matter was analyzed for carbon isotopes. Whole-core samples have 13C values between -U.9%o and -19.6%o (relative to the PDB standard), consistent with previously published results. All cores have lighter (12C-enriched) 13C values with depth. This observation is rather unexpected, because it is generally assumed that only the photosynthetic upper mat layer displays significant carbon isotope fractionation. Because heterotroph cell material generally has carbon isotopic values similar to those of its food source, the lower (heterotrophic) mat layers are expected to have 13C values similar to those of the upper layers. Several explanations for the observed trend are possible. First, there could be a deep source of light organic carbon, producing an isotopic Page 2 1993 Cal Paleo Abstracts PaleoBios 14(4) Supplement overprint on the heavier microbial mat material. Second, methanogenesis may be occurring at depth, generating isotopically light methane that is fixed into biomass elsewhere in the mat. Third, past environmental conditions may have produced microbial mats with light organic carbon, and this signature is preserved. Further fieldwork is necessary to distinguish among these possibilities. Deeper cores and denser sampling will allow a clearer picture of the microbial carbon cycle at this site. More mats will be grown in the laboratory in order to control growth conditions and hence better analyze isotope-depth trends. SEASONAL PALEOTEMPERATURES AND THE C02 OF SEA WATER IN THE WESTERN AND EASTERN EQUATORIAL ATLANTIC: RESULTS FROM INDIVIDUAL PLANKTONIC FORAMINIFERA K. Billups; and H. J. Spero, Department of Geology, University of California, Davis, CA 95616 Attempts to reconstruct absolute sea surface temperatures and the carbon isotopic composition of sea water using fossil planktonic foraminiferal isotope data have been limited. This is due to 1) the use of multiple shell samples in isotopic studies which average environmental information, 2) difficulties in interpreting the intraspecific variability contained in fossil foraminiferal assemblages when individual shells are analyzed and 3) imprecise estimates of the isotopic composition of sea water (18Ow) at a given interval in a core. Because foraminifera have life cycles that are two to four weeks long, each shell in a fossil assemblage records environmental information with a high temporal resolution. If a sufficient number of shells of a species are individually analyzed, then it should be possible to obtain the absolute seasonal temperature extremes and the 13C of sea water COz of the water column inhabited by that species. We present results from the carbon and oxygen isotope analyses of individual Orbulina universa, a mixed layer species and Neo-globoquadrina duterei, a thermocline dweller, for the late Holocene, Last Glacial Maximum, Penultimate Interglacial, and Penultimate Glacial from the western and eastern equatorial Atlantic. To help interpret the isotope data, we employ models derived from laboratory and plankton tow studies. Our core top results show that both species closely track the modern hydrographic conditions of their environments, and hence offer the means to confidently reconstruct paleo-environmental changes. EVOLUTION AND THE FOSSIL RECORD: A NON-LINEAR DYNAMICAL PERSPECTIVE John Bragin, UCLA Center for the Study of Evolution and the Origin of Life, Los Angeles, CA 90024-1567 Individuals, species and ecological communities are all open dissipative systems for which models based on equilibrium concepts are inadequate and misleading. The behavior over time of these entities, including the evolution of species and communities at both micro and macro levels is best treated by non-linear differential equations with transitions between stability and instability. Dynamical analysis using periodic (oscillatory) and aperiodic (chaotic) functions may help illuminate several problems raised by the fossil record that have been difficult to address in the past. These include the relationship of gradual to punctuated evolutionary change; the advent of major innovations such as multicellularity and hard parts; and the apparent "locking-in" of some body plans in the Cambrian while other body plans were apparently eliminated entirely from any future evolutionary developments. At present I am focusing on three aspects of such an analysis: feedback loops (with time delays and gain changes); patterns generated by the recursive logistic equation; and perturbations in evolutionary development caused by catastrophic events. RECOGNITION OF POTENTIAL STRATIGRAPHIC BREAKS IN POORLY- FOSSILIFEROUS SECTIONS USING CARBON- ISOTOPE STRATIGRAPHY: NEOPROTEROZOIC-CAMBRIAN UNITS, EASTERN CALIFORNIA-WESTERN NEVADA. Frank. A. Corsetti, Preston Cloud Research Laboratory, University of California, Santa Barbara, CA 93106 Correlating pre-Phanerozoic stratigraphic sections can be extremely difficult; in the absence of index fossils (or radiometric ages), other techniques, such as sequence stratigraphy. PaleoBios 14(4) Supplement 1993 Cal Paleo Abstracts Page 3 magnetostratigraphy and chemostratigraphy, can be used to solve correlation problems. These methods, however, commonly give equivocal answers, and are most useful when integrated with one another. Carbon isotope chemostratigraphy and trace fossil biostratigraphy were combined in an attempt to resolve correlations between Neoproterozoic rocks in the White/Inyo-Death Valley area of eastern California-western Nevada. In the White/Inyo region, a positive- isotopic excursion of 4%o(PDB) is present in the lowermost Deep Spring Formation, and is associated with "zone I" trace fossils (latest Vendian) and "small shelly fossils" of disputed age (latest Proterozoic or Tommotian). A negative isotopic excursion is observed through the remaining Deep Spring, and is associated with "zone III" trace fossils. In Death Valley, a similar positive excursion is found in the D- member of the Stirling Quartzite, and is associated with "zone I" trace fossils, an "ediacaran-style" soft-bodied fossil (Ernietta), and possible cloudinid shelly fossils. A negative excursion is seen in the overlying Lower Wood Canyon Formation, and is associated with "zone III" trace fossils. The positive carbon isotopic excursion is tentatively correlated with the pronounced isotopic maximum in the latest Vendian of the Siberian Platform. The negative excursion is correlated with a similar trend in the latest Tommotian-Atdabanian on the Siberian Platform. Thus, a hiatus, potentially encompassing the latest Vendian and most of the Tommotian, is postulated to be present within the Lower Deep Spring Formation in the White/Inyo region, and between the Stirling Quartzite/lowermost Wood Canyon and the rest of the Lower Wood Canyon Formation in Death Valley. The field evidence for this hiatus is cryptic (as are other major unconformities, such as the Taconic Unconformity and those found in the Grand Canyon sequence). The recognition of this potential hiatus may impact the global significance of the presumed "Tommotian small shelly fossils" of the White/Inyo region, and well as the placement of the Neoproterozoic- Cambrian boundary in this sequence. SEARCHING FOR HUMAN ORIGINS IN BIOLOGICALLY BASED FEATURES OF BIPEDALISM- SPECIFICALLY, THE NON- STABILIZED ELBOW Davey Davison, Department of Anthropology, University of California, Los Angeles, CA 90024 Tracking the evolution of man from his ancestors within the Miocene Hominoidea is largely a search for locomotor features that could have evolved into the autapomorphies associated with hominid bipedality. The non-stabilized elbow may be such a marker of bipedal adaptation. Quadrupedal primates have stabilized elbows. Key features of this stabilization are located on the distal humerus. A steep, sharp lateral margin of the olecranon fossa with a medially extended flange protects the ulna from dislocating laterally when compressive weight or tensile weight is applied to the joint. Bipeds have a shallow olecranon fossa and no flange — a non-stabilized elbow. My research will observe these features in a quadrupedal primate growth series. This has several goals: (1) to contribute additional data for recognizing bipedality in fragmentary specimens, especially the upper limb; (2) to provide data for identifying locomotion patterns in primates; and (3) to determine if the flange observed in the Miocene Hominoidea is ontogenetic and, therefore, occurs during development or whether it is an inherited phylogenetic trait. The results could have important implications for understanding the biological basis of bipedality. PHYLOGENY OF THE GASTROPOD FAMILY COLUMBELLIDAE (NEOGASTROPODA: BUCCINACEA) Marta J. de Maintenon, Museum of Paleontology, University of California, Berkeley, CA 94720 Following middle Eocene origination, the prosobranch family Columbellidae diversified rapidly into most shallow marine habitats and is well represented in many late Tertiary faunas. Understanding this rapid radiation will require a robust phylogenetic hypothesis that uses all available sources of data. A preliminary phylogenetic analysis of several west Atlantic and east Pacific columbellid species suggests that Page 4 1993 Cal Paleo Abstracts PaleoBios 14(4) Supplement traditional classification, based only on characters from the shell and radula, does not accurately reflect the evolutionary history of the family. Anatomical data are available for several species and show major differences, particularly in reproductive anatomy, among species currently considered to be congeners. A phylogenetic analysis using a more inclusive data set will certainly produce a more robust picture of columbellid evolutionary history, which may be used in conjunction with biogeographic and biostratigraphic data from the fossil record, to provide a clearer understanding of the origin and evolution of the Columbellidae. ASSEMBLAGES OF FOSSIL TERRESTRIAL VERTEBRATES ON PLEISTOCENE PALOS VERDES ISLAND, SOUTHERN CALIFORNIA Denny V. Diveley, and Lawrence G. Barnes, Section of Vertebrate Paleontology, Natural History Museum of Los Angeles County, 900 Exposition Blvd., Los Angeles, CA 90007 Palos Verdes Peninsula, a prominent topographic high on the coast of Los Angeles County, in southern California, was an island at several times resulting from high stand fluctuations of the sea coincident with extreme Pleistocene interglacial periods. A sequence of marine terraces on the slopes of the peninsula records these high sea level stands; some of the terraces nearly encircle the peninsula. The molluscan fossils recovered from these terrace deposits have been studied and dated using a variety of techniques. Several of these terraces have also produced terrestrial vertebrates, including birds, fresh water pond turtles, and both small and large mammals. These inhabitants of the Pleistocene Palos Verdes Island may have populated the island either by migrating across the intervening Los Angeles Basin during low stands of the sea (as exists today), by waif dispersal or swimming across the ocean during high sea levels. Proboscideans, both mammoth and mastodon, have been found in the Pleistocene deposits of the peninsula, and they may have reached this island by swimming. For example, this dispersal phenomenon has been used to explain the presence of mammoths on the northern Channel Islands. Other mammals such as Glossotherium (ground sloth), Capromeryx (pronghorn), Bison, Camelops (camel), Equus (horse), and Canis dirus (dire wolf) are more problematical. Undoubtedly, these animals could not swim across the ocean, and therefore, probably reached the island during low stands of the sea and were then subsequently isolated. The existence of Clemmys (pond turtles) suggests that there must have been a supply of fresh water on the relatively small island. We hope to analyze the proboscidean specimens in search of possible indications of island dwarfism. The ages of the marine terrace deposits do not necessarily correspond to their relative topographic sequence. The provenance of vertebrate fossils relative to dated terrace deposits would provide a possible chronology of various dispersal events to the island. MIOCENE RODENTS OF PAMPA CASTILLO, AISEN PROVENCE, CHILE. Holly E. Dodson, Department of Geological Sciences, University of California, Santa Barbara, CA 93106 A newly discovered fossil mammal fauna at Pampa Castillo, Aisen Province, Chile (47S, 72W) contains a rich rodent assemblage which has the potential to stabilize and refine South American Land Mammal chronology. The rodent taxa found throughout the 300 meter section at Pampa Castillo include Neoreomys, Spaniomys, Prolagostomus, Eocardia, Stichomys, Perimys, Acarichemys, Simplimus, and Scleromys, indicating a Santacrucian age (18 to 15 Ma). This previously undescribed rodent assemblage may help determine whether certain high elevation sites, referred to the Santacrucian Land Mammal Age, are actually younger than better known sites from coastal Argentina. The Pampa Castillo rodent assemblage may contain species indicative of a younger age (more highly evolved) than similarly aged coastal sites. Comparisons of the Pampa Castillo rodents to Santacrucian age rodents from coastal Argentina, Friasian (15 to 12 Ma) age rodents from Alto Rio Cisnes, Rio Frias, Chile, and other Friasian rodents in Argentina as well as Colombia, have raised some questions as to the validity of the Friasian Land Mammal Age and made clear the necessity of radioisotopic dating to better constrain the middle to late Miocene South American Land Mammal Ages. PaleoBios 14(4) Supplement 1993 Cal Paleo Abstracts Page 5 MIOCENE UPWELLING AND THE EVOLUTION OF CARIBBEAN REEF INVERTEBRATES. Evan N. Edinger, Department of Geology, University of California, Davis, CA 95616 The Caribbean region was highly productive during the Miocene, much more so than during either the Paleogene or the Quaternary. This pattern is suggested by widespread Miocene phosphorites and increased bioerosion, and by diversity patterns in corals, molluscs, and large foraminifera. Zooxanthellate and non- zooxanthellate invertebrates show different evolutionary and biogeographic responses to this oceanographic change. Extensive Miocene phosporites in Florida, the Greater Antilles, Jamaica, and Venezuela indicate upwelling along continental margins and high islands. Intensity of coral bioerosion on Puerto Rican reefs also appears to have been greater in the Miocene than the Oligocene. Intensity of bioerosion is generally correlated with nutrient levels. Caribbean coral diversity was reduced by about half between the Oligocene and Middle Miocene; many of the coral genera eliminated from the Caribbean survived in the Indo-West Pacific. In Puerto Rico, extinction was concentrated in shelf-edge reef habitats. All Miocene reefs reported in the Caribbean are shallow-water patch reefs, similar to modern Eastern Pacific reefs growing in upwelling zones. Higher relief shelf edge barrier reefs occur in the Oligocene and Quaternary. Caribbean molluscs reached their greatest diversity during the Miocene, and suffered significant extinction/biogeographic restriction at the Plio-Pleistocene boundary. Miocene type gastropods still flourish in upwelling zones off Northern Venezuela, and in the Eastern Pacific. Diversity of large symbiont-bearing foraminifera declined roughly in parallel with that of reef corals. The Caribbean invertebrates illustrate the differential evolutionary response of zooxanthellate (corals and large forams) vs. azooxanthellate marine invertebrates to upwelling and nutrient levels. THE MYSTERY OF THE "SPLIT" TOOTHED TYRANNOSAURS Gregory M. Erickson, Department of Integrative Biology, University of California, Berkeley, CA 94720 During the summer field season of 1990, a Museum of Paleontology (UC Berkeley) crew unearthed an unusual tyrannosaur (presumably an albertosaurid) tooth in Late Cretaceous sediments (Prince Creek Formation) from the North Slope of Alaska. This tooth exhibited two striking anomalies. The first being a "split" anterior carina row, the second an "extra" carina segment on the posterior face of the tooth. I began an investigation of these particular phenomena by examining hundreds of isolated Late Cretaceous tyrannosaur teeth and several intact dentitions in hopes of documenting further instances of such anomalies. To provide a comparative base, all available large theropod teeth of non-tyrannosaur taxa were examined as well as the teeth of a Komodo monitor. The purpose of this investigation was to determine the frequency and character of such phenomena, to ascertain geographic and stratigraphic variability in these anomalies, and to document similar defects in other serrate toothed taxa. Finally, I hoped to establish a likely hypothesis for the cause of the tooth defects. The results of this study reveal that approximately 10% of all tyrannosaur teeth have some degree of carina "splitting" and 0.4% have "extra serration rows". These dental anomalies were found in Tyrannosaurus rex, Daspletosaurus sp., Albertosaurus sp., Alectrosaurus olseni, and possibly 3 other tyrannosaurs. Similar phenomena were not observed in other non-tyrannosaurid taxa. An application of "Wolpert's law of positional theory" is theorized as the mechanism by which these peculiar anomalies form. Trauma, aberrant tooth replacement, and genetic factors may have influenced the development of the dental defects. Documentation and characterization of dental variation is important (even in reptilian research) as it may help to alleviate the assignments of dubious taxa based on "apparently" new morphs of teeth. DEEP- OR COLD-WATER CORAL BIOHERMS IN THE FOSSIL RECORD H. F. Filkorn, Department of Earth Sciences, Geology, University of California, Riverside, CA 92521-0423 Deep- or cold-water scleractinian coral bioherms are fairly common in modern oceans, but they are relatively rare in the fossil record. Only four Mesozoic and five Tertiary age deep- or cold- water coral bioherms have been described. Three of those four reported Mesozoic age occurrences are in Upper Triassic strata. The only other described Mesozoic age occurrence is a build-up of Archohelia dartoni Wells, 1933, in the Cretaceous Western Interior Basin of North America. The apparent rarity of these structures Page 6 1993 Cal Paleo Abstracts PaleoBios 14(4) Supplement in the fossil record is potentially directly related to a recognition problem created by the circular reasoning that coral build-ups must have formed in warm, clear, shallow marine environments. Living deep- or cold-water scleractinian corals are also known as azooxanthellate corals because they lack the photosynthesizing algal symbionts (zooxanthellae) which typify living shallow-water reef-building corals. Therefore, azooxanthellate corals are not restricted to the marine photic zone and the colonial growth forms are often primary contributors to bioherms in modern deep- or cold-water marine environments. The living members of Archohelia are known to be azooxanthellate and are very closely related to other commonly occurring, widely distributed coral genera which are presently forming bioherms in deep- and cold-water environments. The Archohelia build-up in the Cretaceous Western Interior Basin is the earliest known record of a modern azooxanthellate colonial coral. Fossil scleractinian corals are generally considered to be rare in the Cretaceous Western Interior Basin. Of the few coral genera reported from that region, the only well-defined colonial form is Archohelia. Archohelia is also one of the few genera reported from the Cretaceous Western Interior Basin that is not extinct. The first reported Cretaceous occurrence of Archohelia was described as the new species A. dartoni Wells, 1933 (Turonian; Lamy, MM); this same occurrence is the only one listed for that genus in all subsequent studies of Cretaceous corals in North America. SOUTHERN COMPONENT WATER EVOLUTION DURING THE MIDDLE MIOCENE OCEAN/CLIMATE TRANSITION: OXYGEN AND CARBON ISOTOPIC EVIDENCE FROM THE SOUTHWEST PACIFIC B. P. Flower, and J. P. Kennett, Department of Geological Sciences and Marine Science Institute, University of California, Santa Barbara, CA 93106 Major changes in oceanographic circulation and climate occurred in the middle Miocene from 16 to 12.5 Ma in association with high latitude cooling and major growth of the East Antarctic ice sheet. A suite of DSDP sites were drilled on the Lord Howe Rise and the Challenger Plateau on DSDP Leg 90 in part to trace the Neogene evolution of intermediate- and deep- waters in the southwest Pacific. Benthic oxygen and carbon isotopic records are presented from six DSDP sites in the southwest Pacific. Sites 588A, 590B, 593, and 594 from a meridional transect at intermediate water depths from 31 to 51S paleolatitude, while sites 591B and 206 complete a depth transect with site 590B at 36S from 1200 to 3100 m. High-resolution benthic foraminiferal isotopic records from site 588A define the character of the middle Miocene oxygen and carbon isotopic signals, including four 180 and four 13C events useful for global correlation. Two intervals of distinctly low 180 at 15.3 and 14.9 Ma were followed by a two-step increase in 180 from 14.5-14.1 and from 13.3-12.8 Ma. Covariance between benthic and planktonic 180 from 14.5-14.1 Ma suggests an increase in 180 seawater of 0.7 %o due to East Antarctic ice growth. The 180 of Globoquadrina dehiscens, an inferred thermocline-dwelling planktonic foraminifera, underwent one increase of 0.7 %o from 14.5-14.1 Ma at all sites, coincident with the increase in benthic foraminiferal 180, supporting an increase in mean ocean 180 of 0.7 %o from 14.5-14.1 Ma. Comparison of southwest Pacific oxygen isotopic records suggests deep water cooling was at intermediate depths and at higher latitudes, and was initiated at about 14.9 Ma. In particular, preferential cooling of deep intermediate waters at site 591B (2000 m, 36S) diminished a bathyal thermocline present near 2800 m prior to 14.9 Ma. The 14.5-14.1 Ma 180 increase was accompanied at intermediate sites by the establishment of benthic foraminiferal communities dominated by Epistominella exigua, reflecting colder deep and intermediate waters characteristic of the later Neogene. Oxygen isotopic results suggest cold Pacific Deep Water in the southwest Pacific expanded from 14.9-14.1 Ma and from 13.3-12.8 Ma, reflecting increased production of Southern Component Water in the Antarctic. Increased SCW production therefore probably initiated about 14.9 Ma, preceding major middle Miocene East Antarctic ice growth from 14.5-14.1 Ma, and reached late Neogene production rates from 13.3- 12.8 Ma. THE EARLIEST KNOWN PORIFERANS: BATH TUB SPONGES FROM THE EDIACARA FAUNA OF SOUTH AUSTRALIA James G. Gehling, Department of Earth and Space Sciences, University of California, Los Angeles, CA 90024-1567 Sponges, commonly regarded as the earliest branch of the metazoans, have been notably PaleoBios 14(4) Supplement 1993 Cal Paleo Abstracts Page 7 absent from inventories of Neoproterozoic macrofossil assemblages. Exceptions are possible spicular remains that most often have proven to be glass shards. In South Australia, new discoveries from the Ediacara Member of the Rawnsley Quartzite appear to represent the first record of intact sponges from the Precambrian. Judging from commonly preserved spicular elements, sponges appear to have been well represented in Early Cambrian strata. Recently discovered, complete hexactinellid sponges from the Atdabanian of South Australia are of the same complexity as Burgess Shale sponges, showing clearly preserved monact and hexact spicules and regular ostia arranged in a diagonal pattern. If the existence of coelenterate grade metazoans is accepted in the Ediacara Fauna, then a Late Proterozoic fossil record of sponges is to be expected. A collection of disc-shaped Ediacaran fossils from Bath Tub Gorge and the Chace Range, in South Australia, is characterized by external molds of a dome-shaped organism with a reticulate meshwork, peripheral fringe and a central crater. They are interpreted as sponges that had a convex profile and central osculum. Surface ornamentation in the form of a quadrate net strongly suggest an hexactinellid spicular skeleton. While the absence of preserved skeletal material is characteristic of the taphonomy of Ediacaran organisms, these sponges are known from specimens in negative hyporelief, suggesting a greater structural resilience than discoidal cnidarian fossils from the same facies. Subtle differences in preservation between collection sites have aided the reconstruction of the external form and internal framework of this sponge. The preservational style is comparable to that of dictyosponges of the Upper Mississippian of Alabama, as described by Rigby and Keyes (1990). OUTCROP-SCALE VARIABILITY IN EOCENE PATTERNS OF MOLLUSCAN PREDATORY BEHAVIOR James W. Hagadorn, Department of Geological Sciences, University of Southern California, Los Angeles, CA 90089-0740 Outcrop-scale variability in paleoenvironmental and taphonomic regimes may be a source of significant bias in inter- and intra-formational paleontologic and sedimentologic analyses. Many paleobiology, ethologic and paleoecologic trends described from Cenozoic Gulf Coastal strata are based on single or multiple (time averaged) samples from an outcrop within a formation or a time period. It is often assumed that a few samples from a single horizon are representative of the entire horizon or formation being studied. This study seeks to determine the minimum error involved in making these assumptions by studying small scale variations in levels and character of molluscan predation, through examination of predatory boreholes in fossil molluscs. Faunal and sedimentologic variability are examined at outcrop-scale in the Gosport Sand and the Moodys Branch Formations from Alabama and Mississippi. These Gulf Coastal sediments provide ideal information to study this problem, as they contain abundant, well- preserved molluscan assemblages (from a variety of sedimentary regimes) which can be used to estimate paleoenvironmental and taphonomic bias. Outcrops are sampled at five or more (vertically equivalent) laterally different locations and at multiple (laterally equivalent) vertical locations. Predator borehole morphology, size, and location are measured in each fossil mollusc population. Analysis of these samples facilitates initial evaluation of outcrop-scale variations in predatory behavior and activity. These small- scale variations in predatory activities can be used to test the significance of large-scale, long- term trends in predation described in earlier studies. If the background noise, expressed by outcrop-scale variability, is greater than the variation in signal exhibited in longer term trends in predation, then these long-term trends may be insignificant. BARSTOVIAN MAMMALS FROM HUMBOLDT COUNTY, NEVADA Ralph Hitz, Department of Geological Sciences, University of California, Santa Barbara, CA 93106 Two seasons of collecting in northwestern Nevada have yielded mammal fossils consisting of isolated teeth, partial jaws, numerous ankle bones, and fragmentary postcranial material. The locality is situated near Badger Mountain on the Charles Sheldon Antelope Refuge, Humboldt County, Nevada. Although the fossils were collected almost exclusively from the surface their source appears to be fluvially reworked volcaniclastic deposits. These deposits are part Page 8 1993 Cal Paleo Abstracts PaleoBios 14(4) Supplement of the undifferentiated High Rock Sequence, a moderately thick, regionally (northwestern Nevada) wide spread unit. Preliminary study of the collection identifies artiodactyls, perissodactyls, a probable proboscidean, carnivores, and rodents. Based on correlations using Equid species this new fauna appears to be middle Barstovian (middle Miocene) in age. Neogene mammalian faunas are relatively rare in the northern Great Basin. The Virgin Valley and High Rock Canon faunas are also Barstovian in age; the Thousand Creek is slightly younger, and the Massacre Lake fauna is Hemingfordian in age. All occur within the High Rock Sequence. This new fauna stands to augment the somewhat sparse Virgin Valley and High Rock Canon faunas, helping to clarify the composition and character of Barstovian faunas from this area. The use of fossiliferous beds may also, with additional work, help break down the High Rock Sequence into smaller, more workable units. LIFE ORIENTATION OF STROPHOMENID BRACHIOPODS: OVERTURNING THE CONCAVO-CONVEX PARADIGM Halard Lescinsky, Department of Geology, University of California, Davis, CA 95616 Concavo-convex Paleozoic brachiopods are usually assumed to have lived with their convex valves against the sediment. In this traditional view, the shell commissure would have been elevated above the muddy substrate to prevent fouling of the mantle cavity and lophophore. Abundant evidence from shell encrusting organisms however, suggests that the brachiopods actually lived in the reverse orientation with the convex valve on top. Concavo-convex strophomenid and orthid brachiopods in 7 published studies and in 14 new collections, have far more epibionts on their convex valves than their concave valves. Several epibiont growth patterns observed in the collections suggest encrustation on a live host. Epibiont growth occasionally ends linearly at the hinge, or is upturned at the commissure to allow the shell to open. Shell borings are sometimes associated with successive growth lines in the shell. Disarticulated specimens are rarely encrusted on their internal surfaces and articulated shells may have little or no sediment infilling. Each of these patterns indicates that the brachiopods were living with the convex valve up, and not that epibionts settled primarily on dead overturned shells. If concavo-convex brachiopods lived with their convex valves up as suggested here, the adaptive significance of the concavo-convex shell shape requires reevaluation. No longer can the shape be assumed to serve an anti-fouling role in soft substrates. The shape may alternatively have been selected for stability in currents, as suggested by flume studies, or some other function that remains unknown. A lack of certainty about the function of the concavo-convex shape underscores the difficulty in using design criteria in functional reconstruction. A COMPARATIVE STUDY OF LATE CAMBRIAN SHELL CONCENTRATIONS FROM THE HOUSE RANGE, UTAH AND WEST CENTRAL WISCONSIN Xing Li, Mary L. Droser, Department of Earth Sciences, University of California, Riverside, CA 92521 As fossil concentrations are a primary source for paleontological analyses, it is critical to understand the taphonomy of fossiliferous deposits from different settings. The Eau Claire Formation (west-central Wisconsin) and the Big Horse Limestone Member of the Orr Formation (House Range, Utah), both within the Upper Cambrian Cedaria and Crepicephalus trilobite zones, were compared to determine the taphonomic comparability of the shell concentrations from different tectonic settings. Both units are interpreted as shallow marine intertidal to subtidal deposits, but represent terrigenous clastic and carbonate environments respectively. The Eau Claire Formation is dominated by trilobites and inarticulate brachiopods. The Big Horse is dominated by trilobites exhibiting a high species diversity. Field observation and laboratory analyses demonstrate that shell beds from the Eau Claire and Big Horse Limestones differ quantitatively and qualitatively in terms of abundance, physical dimension, and internal complexity. Shell concentrations in the Eau Claire are primarily pavements and thin lenticular beds (usually less than 15 cm thick) with simple internal fabric; whereas many shell beds in the Big Horse Limestone are well developed three dimensional deposits (thickness ranging from one cm to tens of cm) with a complex internal fabric - usually showing features of amalgamation PaleoBios 14(4) Supplement 1993 Cal Paleo Abstracts Page 9 and/or accretion. However, shell concentrations in both units show relatively low fragmentation, are usually poorly to moderately sorted and have only rare articulated shells. Sedimentary features within the shell beds are also similar in both formations, in that shells usually occur at the base of graded beds and most shell beds are loosely-densely packed. ENVIRONMENT AND ECOLOGY OF PALEOGENE CORALLINE ALGAE FROM LIMESTONES OF THE WESTERN SANTA MONICA MOUNTAINS John D. Mack, and Ivan P. Colburn, Department of Geology, California State University, Los Angeles, CA 90032 Coralline algae are the main constituents of discontinuous biohermal limestone beds in the western Santa Monica Mountains. These beds have previously been reported on by Antisell (1857), Waring (1917), Hoots (1930), Yerkes and Campbell (1979), Strathearn et al. (1988), and Mack and Colburn (1990). Colburn and Novak (1989) recognized the formation containing these bioherms as the Santa Susana Formation (sensu lato). They also reported algal rich biostromal sandstone beds in the same formation at Solstice Canyon. Mack and Colburn (1990) identified twelve species of coralline algae from the bioherms, biostromal sandstones, and interbedded mudstones in the Santa Ynez Canyon and Solstice Canyon districts. The species are within the genera "Archaeolithothamnium", "Litho- thamnium", Mesophyllum, and Lythophyllum. Thin -section analysis of systematically collected specimens of limestone pods from the bioherms revealed that laminar algal thalli, mostly "L." grahami and "L." guatemalense, dominate the lower part of the limestone pods; in the middle part of the pods mammiform and stubby branching corallines, mostly "L." cf. faurai and "A." keenanii, are dominant; and strongly branching corallines such as "L." diagramaticum and Mesophyllum cf. atascaderum become dominant in the upper third of the pods. The upward change in morphology is similar to autogenic ecologic succession of Walker and Alberstadt (1975). The dominance of thin encrusting algae in the lower part of the limestone pods is similar to the stabilization stage of Walker and Alberstadt (1975), during which the substrate was hardened and made suitable for larger encrusting types to be established. In the pods, as in Walker and Alberstadt (1975) succession, the stabilization was followed by the colonization stage represented by the appearance of the mammelon and stubby branching corallines through to the first appearance of strongly branching algae. The upward diversification is represented in the Paleogene limestone pods by the dominance of open, strongly branching corallines. The maximum stage (highest stratigraphically) of thin encrusting algae of Walker and Alberstadt's (1975) succession is not recognized in the limestone pods. In the Santa Ynez Canyon district five stratigraphically separated mudstone specimens obtained from a 16 m thick interval containing a limestone bioherm and analyzed for forams. Benthic and planktic forams were in each mudstone specimen and foram assemblages thus obtained indicate the Paleocene/Eocene boundary occurs within the bioherm. Heitman reported that the stratigraphically lowest sample assemblage has a middle to outer marine shelf environmental aspect. The stratigraphically higher assemblages indicate a gradual deepening to an outer shelf to upper slope environment. Based on lithologic and paleontologic evidence, the algal limestone bioherms and biostromes of the Santa Susana Formation in the Santa Monica Mountains developed in an unrestricted middle shelf below storm wave base in subtropical to tropical waters. The shelf environment was dominated by siliciclastic terrigenous sediment during the latter part of a late Paleocene and early Eocene marine transgression. For a geologically brief period local deposition was interrupted and a luxuriant growth of strongly branching and thin encrusting coralline algae was able to flourish. CONFIDENCE INTERVALS ON STRATIGRAPHIC RANGES WITH TIME- VARYING FOSSILIZATION POTENTIAL Patricia Marshik, Department of Earth and Space Sciences, UCLA, Los Angeles, CA 90024 Because the fossil record is incomplete, observed stratigraphic ranges nearly always underestimate true temporal ranges. Strauss and Sadler (1989) provide equations for applying confidence intervals to the endpoints of stratigraphic ranges. Confidence intervals are potentially useful for a variety of applications including distinguishing sudden from gradual Page 10 1993 Cal Paleo Abstracts PaleoBios 14(4) Supplement extinctions, determining ancestor-descendent relationships, and correlating fossiliferous rock units. However, Strauss and Sadler's equations were derived under the assumption that fossil horizons are randomly and uniformly distributed over observed stratigraphic ranges, or, in other words, that the probability of recovering fossils is independent of stratigraphic position. In many cases, fossil horizons are not distributed in this manner. Sequence stratigraphy data indicate that depositional environments shift with time, often in a systematic fashion. Since many species are facies-controlled, such changes have profound implications for fossil distribution, and, consequently, for the calculation of confidence intervals. In addition, taphonomic biases have significant effects on the distribution of fossil horizons within a section. An analytic method has been developed for calculating confidence intervals for sections with biased preservation by re-deriving Strauss and Sadler's (1989) equations without the assumption that the probability of collecting a fossil is equal at all positions in a section. In addition to being on a sound theoretical basis, the method has been tested through the use of repeated computer simulations. This technique for calculating confidence intervals requires the determination of a piece-wise continuous Fossil Recovery Potential (FRP) function, i.e., a function that specifies the probability of collecting a fossil at each position within a stratigraphic section. The presence of hiatuses internal to the observed range of the organism is unimportant. External hiatuses can be dealt with mathematically, but the loss of information will be reflected in the range extensions calculated. The determination of an FRP function is simplified by the fact that only the relative probability of collection at any point in a section is required. Variables that do not change with stratigraphic position, such as the structure and composition of the skeleton, can be disregarded. Techniques for generating such a function have been explored using data from the Ocean Drilling Project, with emphasis on making the method as generally applicable as possible. A consistent method for removing preservational bias from the fossil record has important implications for future paleobiological and stratigraphic research. TAPHONOMY OF THE LATEST EOCENE CEDARVILLE FLORA, NORTHEASTERN CALIFORNIA: IMPLICATIONS FOR THE INTERPRETATION OF FOSSIL FLORAS PRESERVED IN REGIONS OF EXPLOSIVE VOLCANISM Jeffrey A. Myers, Department of Geological Sciences, University of California, Santa Barbara, CA 93106 A fossil flora of Eocene/Oligocene age (33 mya) collected from the Lower Cedarville Formation, Warner Mountains, NE California, demonstrates that explosive volcanism exerts a profound effect on the growth, transport, deposition and preservation of plant assemblages. Plants represented in the Lower Cedarville flora grew upon unstable surface of a thick volcaniclastic debris avalanche deposit reworked by rain- generated lahars. Multiple fossil plant localities occur within a laterally continuous but only locally exposed bed of reworked volcaniclastic debris, deposited in fluvial, overbank splay, floodplain, and lacustrine facies approximately 10-30 km distal to the vent(s). Two localities have been collected. The MacGinitie Ridge locality, 5 km north of Cedarville, CA records rapid deposition within or on the margin of a small ephemeral lake. The flora-bearing sequence preserves a detailed microstratigraphy, including a basal layer composed entirely of articulated fern fronds, overlain by a horizon composed of unreworked megaphyll-sized leaves. The megaphyll layer is, in turn, overlain by a layer composed of in situ or rafted leaves and fructifications of angiosperms and conifers. As many as five stacked megaphyll/mixed-taxa couplets have been identified at some sites. These horizons may represent seasonal leaf-fall, flood events, or abcission in response to plinian ashfall. A preliminary study of the composition of the flora allies it to modern mixed mesophytic forest communities of southeast Asia. The Steamboat Canyon locality, approximately 15 km south of MacGinitie Ridge, is dominated by fluvial sandstone interbedded with lignitic mudstone, inferred to represent interbedded channel and floodplain facies. The massive, poorly-sorted and non-erosively based fluvial sandstone intervals may record inundation of floodplain PaleoBios 14(4) Supplement 1993 Cal Paleo Abstracts Page 11 environments by rain-generated lahar runout flows. All of the plant debris at this locality has been fragmented or rolled during transport, and may represent vegetation growing at a moderate distance from the site of deposition. Compositionally the flora may represent a microhabitat ecologically distinct from the MacGinitie Ridge assemblage. Paleoecologic and paleoclimatic interpretations derived from plant assemblages preserved in volcaniclastic settings, like the Lower Cedarville flora, must take into account the unusual life and taphonomic processes characteristic of these environments. High resolution Ar40/39 dating of plant-bearing volcaniclastic sequences has the potential to record evidence of short-term climatic change; but the physiognomic and vegetational signal obtained from this type of study are dominated by processes linked to local disturbance, rather than to global climate change. CARPOIDS OR CALCICHORDATES? INFERENCES FROM A DEUTEROSTOME CLADOGRAM KJ. Peterson, Department of Earth and Space Sciences, University of California, Los Angeles, CA 90024-1567 The primary difficulty in assessing scenarios of the ancestry of craniates, chordates and deuterostomes is the lack of understanding of deuterostome relationships. Five deuterostome cladograms have been proposed and the only congruence among the five trees is the monophyly of Chordata, Echinodermata and Enteropneusta; there is no consistency in any of the proposed sister groupings, nor is there agreement in the monophyly of Deuterostomia, Hemichordata and Pterobranchia. Hence, a new attempt at defining the Deuterostomia and elucidating deuterostome relationships is made and the resulting cladogram used to evaluate the many conflicting scenarios of craniate, chordate and deuterostome origins. Five higher taxa are considered in this analysis: the Phoronida (a lophophorate phylum and the outgroup), and the deuterostomes Echinodermata, Pterobranchia, Enteropneusta and Chordata. Echinoderms and chordates are both considered monophyletic, but Hemichordata may not be monophyletic, thus, the enteropneusts and pterobranchs are treated separately. Nineteen taxic (not transformational) characters are used to produce the tree (Phoronida (Echinodermata (Pterobranchia (Enteropneusta, Chordata)))). Five conclusions stem from this cladogram: 1) the monophyly of Deuterostomia is supported by five synapomorphies; 2) a broader analysis indicates that there are also five characters which support a close relationship between lophophorates, specifically phoronids, and deuterostomes; 3) echinoderms are the most primitive deuterostome clade; 4) Hemichordata is paraphyletic and, thus, Hemichordata should be abandoned as a formal taxonomic unit with Pterobranchia and Enteropneusta both elevated to the taxonomic rank of phyla; and 5) enteropneusts are the sister group to the chordates. This deuterostome cladogram allows one to evaluate previous scenarios and here I use the results to evaluate the calcichordate theory of Jefferies. This scenario is firmly rejected if for no other reason that echinoderms and chordates are not sister groups. Thus, identifying chordate autapomorphies (e.g. a notochord) in carpoid echinoderms is erroneous and carpoids are best interpreted as primitive echinoderms, not as chordates. A new cornute from the Upper Ordovician of Morocco is reconstructed and supports this contention. Important conclusions concerning the new cornute include: 1) a single thecal orifice exists at the anterior end and because no other thecal orifices are found, this opening is best interpreted as the orifice for both the mouth and anus (i.e. carpoids possessed a U- shaped gut, a deuterostome plesiomorphy); 2) the posterior locomotory appendage, whose locomotory function is analogous to that of "hemichordates" and chordates, has a morphology so similar to that of mitrates that Jefferies' contention of homoplasy between the mid and hind regions of the cornute and mitrate aulacophores is rejected; and 3) because the aulacophores of cornutes and mitrates are most likely homologous, Jefferies' dorsal/ventral orientation of mitrates is rejected. This analysis demonstrates why the relationships of the Recent phyla must be understood before enigmatic fossil taxa like carpoid echinoderms can be properly interpreted and placed phylogenetically. The utilization of a fossil group as a transformational form between two Recent phyla is allowable if and only if the Recent phyla are shown to be sister taxa. Because scenarios are concerned with the evolutionary events that occurred between taxa, the Page 12 1993 Cal Paleo Abstracts PaleoBios 14(4) Supplement morphology of any aberrant group of fossils with no modern analogs may be interpreted in a fashion consistent with almost any given scenario, as the analysis of the calcichordate theory demonstrates. Thus, aberrant fossils are not useful in establishing the relationships between phyla; it is the relationships of phyla that dictate the position of the fossils. NEW TERRESTRIAL MICROMETAZOAN FOSSILS IN AMBER G. O. Poinar, Department of Entomology; and Benjamin M. Waggoner, Museum of Paleontology and Department of Integrative Biology, University of California, Berkeley, CA 94720 Terrestrial micrometazoa include members of the phyla Rotifera, Nematoda, Gastrotricha, Annelida, Tardigrada, and Arthropoda; they may be succinctly defined as terrestrial or semi- aquatic animals under 1 mm in length. Free- living micrometazoa such as nematodes are often ecologically important in Recent terrestrial and aquatic communities; also, many micrometazoa are parasitic on larger organisms. Micrometazoa almost never fossilize due to their small size and usual lack of mineralized hard parts. Amber is the only source for fossils of this kind, sometimes the only source of fossils for whole phyla; it can be an important source for tracing ecological interactions, including parasitism, from Cretaceous to Recent time. The only known fossil tardigrades are from Canadian amber of the Upper Cretaceous. Almost all fossil nematodes have been found in amber; most are from the Tertiary amber of the Baltic region, Chiapas, and the Dominican Republic, but a parasitic mermithid has been found in the Lower Cretaceous amber of Lebanon. This is the oldest known fossil nematode, attesting to the great age of the mermithid parasitic lifestyle. Pre-Holocene rotifer fossils have been found only twice, both times in Upper Eocene amber from the Dominican Republic. In both cases, the rotifers are bdelloids, which today are all obligate parthenogens; this suggests that parthenogenesis in this group is not a recent development but has been in place for up to 35 million years. Among the annelids, enchytraeids are known from Baltic amber and small lumbricids from Dominican amber, although few have been described. Many small arthropods are known from amber (for example, oribatid mites are common in Baltic amber), but among recent significant finds has been the discovery of parasitic mites attached to various insects, in Late Cretaceous to Oligocene amber. MORPHOLOGICAL EVOLUTION AND CLIMATE CHANGE IN MIDDLE PLEISTOCENE CYNOMYS AT PORCUPINE CAVE, COLORADO Tina I. Rouse, Department of Integrative Biology and Museum of Paleontology, University of California, Berkeley, CA 94720 Porcupine Cave, a high elevation Middle Pleistocene site in the Colorado Rocky Mountains, contains many chambers filled with well- stratified deposits of skeletal material that have been collected primarily by woodrats (Neotoma). This material spans a period of 400,000 years where little else is known. Ongoing studies of biostratigraphy and paleomagnetism suggest that the top of the stratigraphic sequence in The Pit locality dates to somewhat younger than ?400 Ka and the bottom to ?800 Ka or more. Biostratigraphic analysis of mammal fossils from other parts of the cave supports these dates. During the deposition of the fossils, the region experienced a series of transitions between cool, moist glacial conditions and the warmer, drier interglacial periods. Major sedimentary changes provide independent evidence that both glacial and interglacial stages are represented by the fossiliferous levels. The stratigraphic sequence alternates between loess beds and packages of brown nodular clay interlayered with flowstone. The most likely interpretation based on preliminary data is that the loess represents effectively dry warm interglacial periods, whereas the clay-pellet beds and flowstone represent relatively humid glacial ones. The 2900 m elevation means that the biota at the site should have been particularly responsive to climatic changes since what might be perceived as a mild climate change in effective temperature or precipitation at low elevation should be accentuated with altitudinal gradients. Dental remains of small mammals are extensive, allowing analysis of effects of climate change on populational morphology. Prairie dogs, genus Cynomys, are being studied. Both subgenera of prairie dogs are present, appearing in upper strata which include a glacial- interglacial transition. Currently the subgenera are generally allopatric. Assignment of the PaleoBios 14(4) Supplement 1993 Cal Paleo Abstracts Page 13 specimens to species is being addressed with the aid of computer morphometric program MORPHOSYS, which also will be utilized to analyze population-level morphological changes, if any, that take place across climate transitions. Morphological and ecological comparisons to modern Cynomys species, as well as other Pleistocene specimens, are in progress. EVOLUTION IN CAMBRIAN TRILOBITES: SEQUENCE STRATIGRAPHIC CONSIDERATIONS Matthew R. Saltzman, Department of Earth and Space Sciences, University of California, Los Angeles, 90024. Biomere boundaries are non-evolutionary extinction events that appear to have unique chronostratigraphic significance. The lithostratigraphic equivalents, sequence boundaries, are systematically out of phase with the extinctions which occur at or within drowning events (transgressive systems tracts) and thus, within sequences. Evidence for deepening comes from measured sections of the Pterocephaliid biomere in the House Range, west-central Utah and Fox Creek, northwest Wyoming. The sequence stratigraphic context supports a mechanism for the extinctions that involves gradual displacement of shallow-water faunas by deeper cold-water faunas; however, demonstrable diachroneity of biomere boundaries is not apparent within the limits of current biostratigraphic resolution. The quasi-isochronous nature of biomere boundaries requires a large scale environmental perturbation coincident with increasing relative sea-level rise that was lethal to the shelf fauna. Preliminary geochemical evidence (stable isotopes) supports rapid environmental change. The sedimentologic record across biomere boundaries varies with shelf topography such that inundation of a mature shelf-margin sand body (e.g, Du Noir and Big Horse Limestones) is effectively instantaneous, in contrast to a ramp like setting where changes are more gradual. Following the transgressive surface the rate of relative sea level fall increased and accommodation space on the shelf steadily decreased. This allowed for the re- establishment of distinct open-shelf and restricted shelf biofacies. The iterative evolutionary pattern documented within biomeres can thus be explained in terms of sea level history and ideas concerning adaptive radiations following the extinctions must take this into account. Sequence boundaries themselves are marked by local extinctions of the restricted biofacies and gradual evolution in deeper waters. Replacement of shallow water taxa by these deeper-water faunas across biomere boundaries confuses the issue of onshore-offshore patterns in evolution. THREE-DIMENSIONAL RECONSTRUCTION OF BLASTOID HYDROSPIRES Ronald Schmidtling, Department of Earth and Space Sciences, UCLA, Los Angeles, CA, 90024-1567 The exterior morphology of blastoids is well described in the paleontological literature. However, the interior is less well-known. A detailed analysis of the interior would provide a basis for developing a deeper understanding of the fluid flow through blastoid hydrospires. The three-dimensional structure of the hydrospire of the Pennsylvanian blastoid Pentremites rusticus will be determined using brain-sectioning equipment at the Neurology labs at UCLA. A digital camera with a resolution of approximately 4 micrometers will be used to take images directly from cut surfaces. This is a more straight-forward approach than secondary techniques such as the use of acetate peels and slides. Once captured, the digital layers will be processed into a 3-D computer image. This will allow more precise measurements to be made of the volume enclosed by the hydrospires, and of the exact configuration of incurrent hydrospire pores and excurrent spiracles. In addition, the 3- D computer image may be broken down into separate parts that may be studied in isolation, which should enable a greater understanding of fluid flow through the animal. Digital photography and the 3-D reconstruction of complex structures using computer imaging should be valuable in the analysis of a wide range of fossil groups. INVESTIGATION OF EVOLUTIONARY PROCESSES IN PLANKTONIC FORAM- INIFERA USING STABLE ISOTOPIC ANALYSIS Cynthia E. Schneider and James P. Kennett, University of California, Santa Barbara, CA 93106 How does evolution proceed in large pandemic populations of planktic organisms, in which gene Page 14 1993 Cal Paleo Abstracts PaleoBios 14(4) Supplement flow is readily maintained over great distances? Geographical models of speciation have been proposed for planktic foraminifera. Both land barriers (e.g. the Isthmus of Panama) and environmental barriers (e.g. the Polar Front) are thought to have effectively segregated populations of planktic foraminifera resulting in allopatric speciation events. However, neither of these types of barriers can easily explain the apparent gradual evolution or anagenesis of some planktic foraminifers occurring within a single water mass. The evolution of the Late Neogene planktic foraminifera, Globorotalia (Globoconella), in the southern temperate latitudes, its central biogeographic range, provides one of the best documented cases of anagenesis (Malmgren and Kennett, 1981). Are descendent morphotypes evolving in biotic sympatry with their ancestors or are they segregated in the water column? To determine if segregation exists, coeval ancestor and descendent morphotypes of Globorotalia (Globoconella) were isotopically analyzed from South Pacific D.S.D.P. sites 593, 592 and 590. Evidence for segregation comes from small (.20%o to 30%o) but consistent 180 differences observed between morphotypes. Preliminary isotopic evidence suggests that the evolution of Globorotalia (Globoconella) may have been facilitated by vertical and/or seasonal segregation of ancestor and descendent morphotypes. RECOVERY FROM THE END-PERMIAN MASS EXTINCTION EVENT: PALEOECOLOGY OF LOWER TRIASSIC MARINE INVERTEBRATE ASSEMBLAGES IN THE GREAT BASIN Jennifer K. Schubert, and David J. Bottjer, Department of Geological Sciences, University of Southern California, Los Angeles, CA 90089-0740 Little is known about the rebound and diversification of marine life following the end- Permian mass extinction event, the most devastating biotic crisis of the Phanerozoic. Limestone units representing three transgressions of an Early Triassic epeiric seaway in the Great Basin (Montana, Idaho, Nevada and Utah) provide a previously untapped opportunity to learn about the nature and timing of biotic recovery over a geographically extensive seaway. Diversity of invertebrate assemblages (based on bulk sample analysis) at both higher and lower taxonomic levels remains quite low long (3-5 million years) after the extinction event. Assemblages are quite similar over the geographically extensive area of the Great Basin, based on recurrence of a few abundant bivalve genera. Throughout the Early Triassic, faunas are dominated by a few rather abundant molluscs, primarily bivalves, and are characterized by morphologically "simple" cosmopolitan taxa, commonly described as ecologic generalists. Only a few life habits are represented; most organisms are suspension- feeders living at or near the sediment surface. These Early Triassic assemblages are composed mainly of Paleozoic or Paleozoic-like taxa, along with some key "stem groups" destined to give rise to important Mesozoic and Cenozoic clades. Each of the three limestone intervals is distinct and represents a different stage in the partial recovery. The fauna from the youngest Early Triassic seaway, for instance, can be contrasted with older faunas in both taxonomic makeup and community structure. Abundant occurrence of the first Mesozoic crinoid (progenitor to all post-Paleozoic crinoids), and the earliest post-Paleozoic echinoids, signal an increase in higher-taxonomic and guild diversity. The fauna in the oldest Lower Triassic limestones consists of just a few very abundant genera, primarily the inarticulate brachiopod Lingula and the pectinacean bivalve Claraia, which exhibit a worldwide abundance spike in the earliest Triassic and may have acted as "disaster forms." Disaster forms are long-ranging, conservative generalists that are commonly found in refugia or marginal settings, but proliferate in normal marine environments during times of biotic crisis, when ecologic constraints may be relaxed. These results may be compared with data on the aftermaths of other mass extinctions, to see if any generalizations about biotic recovery can be made. AMINO ACID DISTRIBUTION IN ANCIENT AND DERIVED PROTEINS Erik Schultes, Department of Earth and Space Sciences, University of California, Los Angeles, CA 90024-1567 The distribution of amino acid residues in existing protein sequences has been analyzed as a possible test of the origin of life hypotheses that postulate a prebiotic syntheses of amino acids. Only a subset (e.g. G, A, V, E, D) of the 20 biological amino acids predominate in experimental prebiotic syntheses. Therefore, PaleoBios 14(4) Supplement 1993 Cal Paleo Abstracts Page 15 protoenzymes may have been built from, and might thus have reflected, this amino acid distribution. If these protoenzymes originated before amino acid biosynthetic pathways (i.e. if they mediated such pathways), and if these ancient sequences were incorporated into the enzymes of the last common ancestor of all living organisms, then owing to the highly conserved nature of functional sequences, existing proteins might be expected to contain small sequences or repeated sequences reflecting the prebiotic amino acid distribution. However, this approach is not without problems. Biases in amino acid distributions with respect to functional and mutational constraints occur in existing protein sequences. The ancient sequences of protoenzymes would have been subjected to greater than 3.5 billion years of evolutionary history. Any primordial signal will be obscured by substitutions and augmentations of non-prebiotic amino acids. Moreover, protoenzyme amino acid distributions are dependent on the particular origin of life scenario postulated. With these caveats in mind, I have compared the amino acid distributions of various proteins. The potential influence of physiological biases in the amino acid distributions of contemporary sequences has been addressed by comparing sequences from what are presumed to be ancient, early-evolving proteins (ferredoxin, cytochrome c, nucleotide binding structure in dehydrogenase, kinase, and flavodoxin enzymes, nitrogenase, RuBisCO, and amino acid biosynthetic enzymes) with sequences from more recently derived proteins (e.g. enzymes mediating the oxygen- dependent steps of sterol and fatty acid biosynthesis). OVERVIEW OF RECENT SUBTIDAL STROMATOLITES OF THE BAHAMAS Russell S. Shapiro, Preston Cloud Research Laboratory, University of California, Santa Barbara, CA 93106; Kenneth R. Aalto, Department of Geology, Humboldt State University, Areata, CA 95521; and Robert F. Dill, Caribbean Marine Research Center, Lee Stocking Island, Bahamas Stromatolites are growing today in high energy, subtidal environments of the Exuma Cays, Bahamas. Situated on the eastern margin of the Great Bahama Bank, bordering the deep Exuma Sound, the stromatolite sites are flooded with normal marine waters twice daily. These currents can be quite strong, sculpting the oolitic shoals where the stromatolites are found into flood tidal deltas with superimposed sand waves and dunes. The stromatolites range in size from approximately 20 to 200 cm high and display the following forms: club, linear, coalesced, arabesque, molar, and shingled. Active meiofauna have been observed in stromatolites in all of the locales, including annelid worms, nematodes, and copepods. Initial growth conditions are poorly understood; however, preliminary coring and hand sample collection reveals the substrate to be either eroded Pleistocene paleosol, or Holocene beachrock, coral heads, or a mudstone of variable age, deposited on the paleosol. Stromatolites are also known to grow on stabilized conch shells and oncolites. All of the locales share the following traits: dynamic environment, subtidal waters, oolitic sands, and mats composed primarily of filamentous green algae, diatoms, and cyanobacteria. Although the sites are fairly similar in overall physico-chemical attributes, some key differences must be addressed. At Bock Cay, the field is shallow (1-2 m below MSL) and is more influenced by wave action than tides. Also, the stromatolites here are aligned into long linear rows (1 m x ~30 m), with relatively few club forms. Here laminations within the stromatolites are better developed than at other locations. At Iguana Cay, the tidal channel is open at both ends to the incoming current so the sands have been piled up into a large "sand pyramid" rather than a sinuous delta. Large bioherms composed of crustose coralline algae are found at the northern edge of the channel. The stromatolites at Lee Stocking Island show the most variety in form, possibly due to the larger size of the field, more variable currents, and pronounced dune migrations. At both Lee Stocking Island and Iguana Cay, the stromatolites exhibit poor lamination, and original fabrics are usually disrupted by boring organisms. Previous workers have either argued vehemently for or against the use of the Bahamian stromatolites as a modern analog for ancient stromatolites. It is the opinion of the authors that studies of the Recent examples are not conclusive, and it would be premature at this stage to render a verdict either way. Page 16 1993 Cal Paleo Abstracts PaleoBios 14(4) Supplement LATERAL VARIABILITY OF ICHNOFABRIC IN THE EOCENE TORREY SANDSTONE, SOLANA BEACH, CALIFORNIA Carol M. Tang, Department of Geological Sciences, University of Southern California, Los Angeles, CA 90089-0740 The preservation of biogenic sedimentary structures is dependent upon many physical and biological factors. Thus, in nearshore, high- energy environments where these factors are highly variable, one would expect ichnofabric (sedimentary rock fabric resulting from biological activity) to vary as well. Previous ichnofabric studies investigated the extent of bioturbation in different nearshore depositional systems. In this study, lateral variability of ichnofabric in a nearshore environment is documented and analyzed statistically. A laterally extensive outcropping of the Eocene Torrey Sandstone can be found at Solana Beach, California. The Torrey Sandstone contains many well-preserved individual Ophiomorpha and Thalassinoides burrows as well as less distinct structures due to bioturbation. Together, both of these types of structures make up the ichnofabric. To measure the extent of bioturbation, ichnofabric index values were recorded for field- of-views 50 cm wide by 35 cm long. The ichnofabric index methodology allows for the semi-quantitative evaluation of the extent of bioturbation and for statistical analysis with tests designed for ranked variables. Grids with 8 columns and 4 rows were measured out along the Torrey Sandstone at 25 meter intervals starting from a randomly-selected origin. Ichnofabric index values were recorded twice for each field- of-view (35 x 50 cm) in the grid, averaged, and then analyzed statistically with the Friedman two-way analysis of variance. Our results indicate that the extent of bioturbation, as measured by ichnofabric indices, in this high-energy, nearshore environment is indeed highly variable. Ichnofabric can vary significantly within one 4 meter long grid and between grids spaced at 25 meters apart. By comparing the variability of bioturbation in different depositional environments, one may be able to characterize environments based on variations in ichnofabric as well as on discrete burrows. In addition, by studying the variability of ichnofabrics, one may be able to better understand the controls on bioturbation and the variability of physical and biological parameters in different environments. PHYLOGENY OF NORTH AMERICAN ARTIODACTYLS AND THE EVOLUTION OF THE POSTCRANIAL SKELETON Jessica M. Theodor, Department of Integrative Biology and Museum of Paleontology, University of California, Berkeley, CA 94720 The fossil record of artiodactyls shows an early radiation in the Eocene, followed by further diversification in the Miocene. The earliest fossil artiodactyl, Diacodexis, shows relatively specialized limb proportions and morphology of the manus and pes, in addition to many primitive features: retention of the third trochanter of femur, presence of a clavicle. This mixture of postcranial features has been used to argue that a) Diacodexis is more closely related to the selenodont clade than to the suiform clade, or b) that the suiform clade must have undergone secondary loss of these specializations in the postcranial skeleton. Analysis of correlated features of the postcranial skeleton may clarify the phylogeny of the earliest forms. Study of the functional implications of characters of the tarsus using computer models should show whether such patterns are under functional constraint or are of purely phylogenetic interest. The phylogeny of the Artiodactyla is complex. Most of the character data used in phylogenetic analysis of this clade are cranial or dental. Trees based primarily upon cranial and dental data show an extremely complicated pattern of convergence and reversal in postcranial characters. These levels of postcranial homoplasy in current phylogenies suggest that the evolutionary history of the locomotor system in early Artiodactyla is considerably more complicated than previously thought. Further phylogenetic analysis, using more postcranial data, is necessary to better understand the pattern of locomotor evolution in this diverse clade.