Taphonomic Model Research Articles

Taphonomic analysis of Saurichthys from two stratigraphic horizons in the Middle Triassic of Monte San Giorgio, Switzerland

Excavations of Middle Triassic strata at Monte San Giorgio (Switzerland–Italy) have famously recovered a range of reptiles whose affinities, morphology and preservation have been extensively described. The locality has also yielded a contemporaneous and equally diverse fish fauna that has yet to be described to the same degree. To address this imbalance, a taphonomic study was undertaken using the actinopterygian Saurichthys, a relatively abundant taxon found in the Besano Formation (latest Anisian–earliest Ladinian) and Cassina Beds of the Meride Formation (early Ladinian). Specimens from each horizon were scored for articulation and completeness across ten anatomical units, the resulting datasets being used to determine a taphonomic model and investigate preservational variation through time. Saurichthys showing moderate to high articulation and high completeness occur in both horizons but states of low articulation and moderate completeness are only present in the Besano Formation. The same feature is apparent in corresponding unit plots, suggesting different environmental conditions were present during deposition of each horizon, specifically those that reduced articulation and completeness during a prolonged residence on the sediment surface.

The Role of Bubo virginianus magellanicus as Rodent Bone Accumulator in Archaeological Sites: A Case Study for the Atuel River (Mendoza, Argentina)

AbstractMicromammalian bone assemblages from modern pellets of the strigiform Bubo virginianus magellanicus, from the upper Atuel River (southern Mendoza, Argentina), were taphonomically analysed. The results allow us to place B. v. magellanicus in the category of intermediate modification (Category 2). This sample has also been compared with results from other members of this genus, in order to classify B. v. magellanicus as a taphonomic agent. The participation of the Bubo species in archaeological accumulations has been documented, but in Argentina, the role of B. v. magellanicus has been reported up to the present. It is partly because of the sequence of one archaeological site in the south of Mendoza Province called Laguna El Sosneado‐3 (LS‐3). However, considering the absence of a current taphonomic model of this owl, this participation was mentioned as a hypothesis. In the current investigation, archaeological and modern samples have been compared. The results indicate that the skeletal element assemblages recovered from LS‐3 were accumulated by strigiform birds. Taphonomical evidence of light modifications on units I and IV indicates that Tyto alba (Category 1) was probably the main species involved in these units, whereas the taphonomical evidence on skeletal element assemblages recovered from units II and III suggests the action of a strigiform with a major category of modification such as B. v. magellanicus. Copyright © 2015 John Wiley & Sons, Ltd.

The assessment of the internal architecture of an MIS 3 cave bear bone assemblage. Case study: Urşilor Cave, Western Carpathians, Romania

Urşilor Cave is one of the most complex MIS 3 cave bear settlements of Europe: it incorporates a large number of cave bears' palaeoichnofabrics (bioglyphs: nests, footprints, scratch marks, fur imprints, etc.) and several bone assemblages of different age and genesis. This study has the aim of analyzing the spatial orientation and the internal architecture of the bone assemblage from the excavation chamber of the scientific reserve (lower level of the cave) in order to assess the environmental conditions of the bone deposition. As such, almost 580 long bones were analyzed for spatial orientation, and almost 100 plates of bone levels were documented at every 10cm of depth (mapped, photographed and topographed). The obtained results point to an in situ thanatocoenosis (typical for cave traps) and reveal the taphonomic conditions at the time of the bone layers' deposition. Moreover, the taphonomic approach helped us to better understand the obtained radiocarbon data (on cave bear fossils)—which previously indicated a non-concordance with the stratigraphy—and to perform a taphonomic model for the bone’ deposition from the excavation chamber. Moreover, we report here the discovery of two fossil carnivore skeletons (a cave bear and a cave lion), one of the best preserved and anatomically connected, documented in such environments.

New occurrences of Sphenothallus in the lower Cambrian of South China: Implications for its affinities and taphonomic demineralization of shelly fossils

Sphenothallus , a tubular fossil that occurs in Paleozoic strata around the world, may be related to cnidarians or ‘worms,’ but its affinities remain controversial due to preservational variations among localities. Here, to test hypotheses regarding Sphenothallus taphonomy and affinities, we investigate the preservation of new fossils from the lower Cambrian Shuijingtuo Formation at Heziao and Jijiapo (Hubei Province) and the equivalent Niutitang Formation at Siduping (Hunan Province) in South China. Morphology and allometry suggest that the fossils represent a single species, and their biostratinomy and authigenic mineralization indicate that they underwent similar pre-burial and early diagenetic processes, particularly transport and focused degradation via microbial sulfate reduction. However, the compositions and microstructures of the tests vary among localities. The Heziao tests consist of lamellar phosphatic material covered interiorly and exteriorly by layers of carbonaceous material. In contrast, the Siduping tests consist of non-lamellar phosphatic material associated with carbonaceous material, and the Jijiapo tests consist entirely of carbonaceous material. Based on these observations and experimental taphonomic data—which show that hydrochloric acid treatment of Heziao samples produces fossils that compositionally and microstructurally resemble the Jijiapo specimens—we propose that the new tests constitute a taphonomic continuum between shelly and carbonaceous preservation. This taphonomic model suggests that the preservation of shells as carbonaceous fossils results from kerogenization of the organic matrixes and subsequent or concomitant demineralization of the biomineralized microstructures of the shells. Hence, variations in Sphenothallus test composition and microstructure among localities may reflect varying extents of test demineralization, and the carbonaceous layers in Heziao specimens may have formed via demineralization of the tests' exterior and interior phosphatic lamellae. Our reconstruction based on this model indicates that pristine Sphenothallus tests consist of exteriorly sculptured and interiorly unsculptured organophosphatic lamellae. Thus, Sphenothallus microstructurally resembles and may be related to conulariids, and potentially, cnidarians. • Sphenothallus fossils in Shuijingtuo and Niutitang formations of Hubei and Hunan. • We provide data on their taphonomy, allometry, compositions, and microstructures. • Data illuminate Sphenothallus affinities and taphonomic diversity of Cambrian shells. • Sphenothallus microstructurally resembles conulariids and may be a cnidarian. • Data support taphonomic model for preservation of shells as carbonaceous fossils.

Experimental study of bone modification by captive caracal (Caracal caracal); a model for fossil assemblage analysis

Medium-size animals such as rabbits and hares are common occurrences in fossil assemblages, and make up a large part of the diet of many carnivores. However their mode of accumulation, especially in African localities is poorly understood. This investigation undertook experimental feeding of domestic rabbit carcasses to captive caracal (Caracal caracal), in order to create a taphonomic model of bone modifications that can be applied to fossil assemblages. We investigated the modification patterns of both the feeding refuse (non-ingested) and the scatological remains. The anatomical composition, breakage patterns, digestive modifications and tooth marks are described. The caracals preferentially fed on high yield parts of the rabbit carcass and discarded low yield parts like the cranium and feet, a pattern that has been observed in wild and captive coyotes when food resources are abundant. Rabbit remains from the caracal displayed poor survival, relative to other small carnivores. Fragmentation in the scat assemblage was high. Bones were extensively but lightly digested and carnivore tooth marks were frequent. This investigation provides a model of bone modification in a carnivore that while common in fossil localities has received little taphonomic attention. The study also exhibits how detailed actualistic investigations can provide information that may aid palaeoecological interpretations.

A new ecological model for the ∼565 Ma Ediacaran biota of Mistaken Point, Newfoundland

Ediacaran macrofossils immediately precede the first animal ecosystems of the Cambrian Period and have excited much attention for potentially containing ancestors of the modern animal phyla. Ediacaran fossil surfaces have been variously interpreted as vertically tiered census populations comparable to animal ecosystems, or as osmotrophic ecosystems exploiting turbulent flow regimes. These hypotheses are highly dependent upon the taphonomic interpretation of Mistaken Point, Newfoundland as a consensus population representing the associations of the organisms in life. Reanalyses of these surfaces, however, indicate that this taphonomic model is inconsistent with the range of preservation states seen in each taxon. We present a new taphonomic model, for Mistaken Point surfaces in Newfoundland Canada, and describe it using an index of decay. This reveals a complex history of life, death, and decay at these sites. Data gathered from large scale casting projects in Newfoundland show that only 15–40% of individuals were killed by ash flows, rather than the whole population as previously interpreted. This shows that Ediacaran organisms at Mistaken Point, Newfoundland, had a diverse range of ecological relationships with the microbial mat system. Frondose organisms are engaged in chemical exchange with the sediment and the water column with the stem penetrating through the microbial mat. Reclining forms, such as Fractofusus, lived exclusively above the microbial mat and drew nutrients from the dead organisms on which they typically grew. The ecology is based on organism interaction with the sediment–water interface quite unlike that of modern vertically tiered metazoan communities that have developed since the start of the Cambrian Period.

Comparative Taphonomy, Taphofacies, and Bonebeds of the Mio-Pliocene Purisima Formation, Central California: Strong Physical Control on Marine Vertebrate Preservation in Shallow Marine Settings

BackgroundTaphonomic study of marine vertebrate remains has traditionally focused on single skeletons, lagerstätten, or bonebed genesis with few attempts to document environmental gradients in preservation. As such, establishment of a concrete taphonomic model for shallow marine vertebrate assemblages is lacking. The Neogene Purisima Formation of Northern California, a richly fossiliferous unit recording nearshore to offshore depositional settings, offers a unique opportunity to examine preservational trends across these settings.Methodology/Principal FindingsLithofacies analysis was conducted to place vertebrate fossils within a hydrodynamic and depositional environmental context. Taphonomic data including abrasion, fragmentation, phosphatization, articulation, polish, and biogenic bone modification were recorded for over 1000 vertebrate fossils of sharks, bony fish, birds, pinnipeds, odontocetes, mysticetes, sirenians, and land mammals. These data were used to compare both preservation of multiple taxa within a single lithofacies and preservation of individual taxa across lithofacies to document environmental gradients in preservation. Differential preservation between taxa indicates strong preservational bias within the Purisima Formation. Varying levels of abrasion, fragmentation, phosphatization, and articulation are strongly correlative with physical processes of sediment transport and sedimentation rate. Preservational characteristics were used to delineate four taphofacies corresponding to inner, middle, and outer shelf settings, and bonebeds. Application of sequence stratigraphic methods shows that bonebeds mark major stratigraphic discontinuities, while packages of rock between discontinuities consistently exhibit onshore-offshore changes in taphofacies.Conclusions/SignificanceChanges in vertebrate preservation and bonebed character between lithofacies closely correspond to onshore-offshore changes in depositional setting, indicating that the dominant control of preservation is exerted by physical processes. The strong physical control on marine vertebrate preservation and preservational bias within the Purisima Formation has implications for paleoecologic and paleobiologic studies of marine vertebrates. Evidence of preservational bias among marine vertebrates suggests that careful consideration of taphonomic overprint must be undertaken before meaningful paleoecologic interpretations of shallow marine vertebrates is attempted.

Migrant deaths and the Kater Radez I wreck: from recovery of the relict to marine taphonomic findings and identification of the victims

On March 1997, during a naval blockade imposed by Italy to prevent illegal immigration, the motorboat Kater Radez I full of Albanian refugees clashed with an Italian warship with 120 people approximately on board. The boat sank quickly after the collision just in the middle of the Otranto Canal (Mediterranean Sea). Only 34 individuals survived the accident; 58 died, mostly women and children, and dozens were missing. After 7months spent at depth of 800m approximately underwater to constant temperature of 4°C, the motorboat was rescued, and totally, 52 bodies were recovered from the holds. The management of the mass disaster is summarized focusing on the procedures applied in the recovery of the boat and victims, and the identification process. The purpose of the article is to present the unique taphonomic model of decomposition dealing with marine sequestered environments. The postmortem changes have been revised according with a skeletonization scoring system. Surprisingly, most of the victims were in good condition with soft tissues still present except at the head/neck region and the hands resulting in the body parts mostly pre-skeletonized. Closed compartments as well as heavy clothing in multiple layers protected the bodies from animal activity of marine scavengers. Presumptive positive identification was obtained in 49 out of 52 bodies based on the correspondence between ante- and postmortem data. An additional purpose of the article is also to focus on the practice of coercive actions disproportionate to the risk of unauthorized entry criticized by several international organizations for migration and recently condemned by the European Court in Strasbourg.

An enormous Jurassic turtle bone bed from the Turpan Basin of Xinjiang, China

A spectacular new terrestrial Konzentratlagerstätte is introduced from the Turpan Basin of Xinjiang, China that probably belongs to the late Middle Jurassic Qigu Formation. It contains a mass accumulation of "xinjiangchelyid" turtles preliminarily identified as Annemys sp. In the zone with the highest turtle concentration, complete and articulated turtle skeletons are tightly packed at a density of up to 36 turtles per square meter. The fossiliferous layer is thickened here and shows an erosional base. This high concentration zone outcrops approximately 10m in length and shows no decrease in turtle density after exposing 2m of the layer into the hillside. Adjacent is a more expansive zone of at least 10m by 30m. In this region, the fossiliferous layer is evenly thick, and approximately five, fully disarticulated turtles are present per square meter. A conservatively estimated 1,800 turtles may, therefore, have been deposited at this site. It is likely that these aquatic turtles gathered in a retreating water hole in a riverine environment during a drought, much as some aquatic turtles will do today, but perished when the habitat dried up completely. A following catastrophic rainfall event caused a debris flow, possibly channelized in a dry river bed, which transported complete turtles, disarticulated turtles, and mudstone clasts and deposited them after a short distance. This taphonomic model is consistent with previous environmental reconstructions of the Turpan Basin during the late Middle Jurassic in predicting the episodic breakdown of regional monsoonal circulation resulting in a seasonally dry climate with severe episodic droughts.

Taphonomic analysis of fish in rift lacustrine systems: Environmental indicators and implications for fish speciation

Two rift-basin lacustrine successions (Cacheuta and Los Rastros Formations) in the Middle Triassic of Argentina were studied to test two different hypotheses: 1) fish taphonomy is useful as an indicator of environmental conditions for these two paleolakes; and 2) fish taphonomy is useful for understanding environmental effects on speciation. The fish fossils are found, in two lacustrine deposits, as isolated and disarticulated scales and cranial bones, clumps and stringers of scales, articulated body segments, and complete specimens. Four taphofacies are defined for Cacheuta specimens (Ca-A to Ca-D), and three taphofacies are defined for Los Rastros fish assemblages (LR-A to LR-C). A Principal Components Analysis was performed, with the taphonomic features supporting the seven taphofacies defined.A taphonomic model is proposed that characterizes a lacustrine-deltaic environment developed in the rift basin and identifies three sub-environments, each one with its particular fossil assemblages. The fish assemblages in the Los Rastros Formation suggest that the fishes preserved in delta-front and turbidity-current deposits (LR-B and LR-C taphofacies) were allochthonous to the lake and probably inhabited the delta plains and affluent fluvial system. In contrast, the isolated fish remains, preserved in open-lake deposits (LR-A taphofacies), likely represent both autochthonous and/or allochthonous specimens. In the Cacheuta Formation, articulated and isolated fish remains preserved in open lake deposits (Ca-A and Ca-D tafofacies), might represent autochthonous lacustrine specimens, based on the good preservation of the material. The fish remains preserved in underflow and turbidity current deposits (Ca-B and Ca-C taphofacies) were allochthonous to the lake and probably inhabited the delta plain and affluent fluvial system.The fish taphonomic study of two different rift-basin lacustrine successions allows test of the two proposed hypotheses. Fish taphonomy was useful as an indicator of environmental conditions beacuse the differences in fish preservation allowed differentiation of the sub-environments and reconstruction of the environmental conditions and dynamics of the rift lake basins. Also, fish taphonomy was useful for understanding environmental effects on speciation by characterizing the environments and dynamics that promote the development of new fish species, recognizing fish-inhabited environments, and identifying the generalist and specialist species.

A taphonomic model for the Mesosauride assemblage of the Irati Formation (Paraná Basin, Brazil)

The Irati Formation (Permian, Parana Basin, Brazil) is made up of a succession of black bituminous and nonbituminous shales and mudstones with interbedded carbonate layers, which record deposition in marine environments. Mesosaur remains are abundant at several sites in this formation, where they occur preserved in centimetre- thick beds and displaying various degrees of skeletal disarticulation. This paper seeks to establish a model to explain the processes that generated the mesosaurian taphocoenosis in the Irati Formation. Three types o successions containing mesosaur remains were analysed: 1) Carbonate turbidite facies in the State of Sao Paulo; 2) Carbonate tempestite facies in Rio Grande do Sul; 3) Black shale facies in the State of Parana. Three taphonomic classes are established: Class I) articulated skeletons; Class II) partially articulated skeletons; Class III) isolated bones (including Class IIIA with complete isolated bones and Class IIIB with fragmented isolated bones). Based upon the sedimentological and taphonomic evidence, a taphofacies model is proposed. The hypothesis here advanced is that all accumulations of mesosaur remains resulted from catastrophic mortality caused by storm events. The basic assumption is that these reptiles died and were buried through the action of successive storms that occurred in the Irati Sea. The taphonomic model points to repeated episodic events of burial, erosion, reworking and redeposition of skeletons and suggests significant time averaging.

Float or sink: modelling the taphonomic pathway of marine crocodiles (Mesoeucrocodylia, Thalattosuchia) during the death–burial interval

A taphonomic model is erected for a dataset of 19 Steneosaurus (Mesoeucrocodylia; Thalattosuchia) from the Toarcian Posidonienschiefer Formation (Lower Jurassic) of Germany. These were deposited in a quiet-water, marine, basin. Their taphonomy is compared with that of an additional seven thalattosuchians from other Jurassic localities (Peterborough and Yorkshire, UK; Nusplingen, Germany). The skeletal taphonomy of the specimens is assessed in terms of the articulation and completeness of nine skeletal units. Steneosaurus from the Posidonienschiefer Formation exhibit variable levels of articulation in the nine units. Completeness also varies but the head, neck and dorsal units are complete in all specimens. Carcasses reached the sediment–water interface shortly after death. Loss of fidelity occurred primarily as individuals lay on the sediment, and disarticulated elements tended to remain in the vicinity of the carcass. Those elements absent from specimens are the smaller, more distal, bones of the limbs and tail; these were removed preferentially by weak bottom currents. Smaller specimens are consistently less complete. Specimens from other localities broadly follow the same taphonomic pathway, suggesting a consistent pattern for the skeletal taphonomy of the carcasses of marine crocodiles. Loss of completeness in some specimens is more exacerbated, the result of stronger current activity at the sediment–water interface.

Asymmetry in an Ordovician conulariid cnidarian

Sendino, C., Zagorsek, K. & Taylor, P.D. 2012: Asymmetry in an Ordovician conulariid cnidarian. Lethaia, Vol. 45, pp. 423–431. Conulariids are fossils of the presumed polyps of an extinct scyphozoan cnidarian group. Their cone-shaped skeletons normally show perfect tetraradial symmetry. However, in the Ordovician species Metaconularia anomala (Barrande 1867) from Drabov (Czech Republic), tetraradial symmetry is compromised in three ways: (1) the skeleton often shows torsion; (2) the four sides may vary in width at the same level within one individual; and (3) one side may be deleted to give a triradial skeleton. Almost 2000 specimens were studied in museum collections. About 56% of analysed specimens are twisted in an anticlockwise direction (sinistral) when viewed from the apex towards the aperture, 28% show no torsion, 1% exhibit clockwise torsion (dextral) and the remaining 15% cannot be classified. Maximum measured torsion rate was 1.5°/mm. A significant negative correlation between torsion rate and length suggests that more highly torted individuals may have survived less well. Almost 5% of individuals show loss of one side for at least part of their lengths. Although many individuals have four sides of equal width, in a significant proportion the sides are of unequal width, up to a maximum/minimum side width ratio of 2 (i.e. widest face twice the width of the narrowest). In the absence of a satisfactory taphonomic model to explain the asymmetries, they are regarded as mirroring asymmetries in the living conulariids, with the strong preference for sinistral torsion interpreted as an example of a fixed asymmetry that was genetically controlled and heritable. It is speculated that the signalling protein Nodal as well as Hox-like genes were involved in controlling the asymmetries described in M. anomala.

Taphonomy of dense concentrations of juvenile ammonoids in the Upper Cretaceous Mancos Shale, east-central Utah, USA

Dense concentrations of juvenile ammonoids were recently discovered in the Upper Cretaceous Mancos Shale of east-central Utah. In this paper, we describe this remarkable fossil occurrence and propose a taphonomic model to explain it. Large accumulations of cephalopods are not uncommon in the stratigraphic record, though concentrations of juveniles are relatively rare. Lithologic, geochemical, and stratigraphic evidence suggest that the unusual fossil occurrence we document here resulted from a combination of factors. We think the cause of these dense concentrations of juvenile ammonoids involves the hypothesized semelparous reproductive strategy of ammonoids, environmentally driven mass mortality, and a peculiar taphonomic phenomenon. In our model, an important role is played by the adverse oceanographic conditions common during the extreme greenhouse global climate regime of the Cretaceous, manifested by the well-known Ocean Anoxic Events around the time when these deposits were formed. The proposed mechanisms responsible for the mass accumulations we report here have operated at other times in Earth history, and may help explain similar occurrences elsewhere in the fossil record.

Testing the impact of environmental zone on experimental taphonomic faunal models

Traditional paradigms governing the generation of actualistic taphonomic faunal models suggest that outcomes will vary depending on the particular environmental zone in which data is generated. Scavenging experiments were carried out in two distinct environmental zones (temperate and semi-arid) in New South Wales, Australia, to test the validity of this prevailing paradigm. The results of this study suggest that a particular environmental zone may not be as important a variable as other taphonomic factors, such as natural versus cultural agents of accumulation. These observations are part of larger study whose goal is to provide a working taphonomic model for faunal accumulations in open archaeological sites derived from Australian contexts.

Young bivalves on insect wings: A new taphonomic model of the Konservat-Lagerstätte Hagen-Vorhalle (early Late Carboniferous; Germany)

Taphonomic conditions of insects from the Late Carboniferous (Pennsylvanian) Konservat-Lagerstätte Hagen-Vorhalle (western Germany) are remarkably unique but have not been the focus of detailed work thus far. Their particular preservation is conspicuous and furthermore shows significant differences between “Palaeoptera” and Neoptera. The first are almost always completely preserved while the latter invariably lack an abdomen. Furthermore all Neoptera bear tiny bivalve prodissoconchs (~ 0.8–1.2 mm) or few dissoconchs (~ 1.3–1.4 mm) exclusively on the dorsal wing membrane. Taking into account geological, sedimentological, paleontological and paleo-oceanological data a novel taphonomic model is presented here. After a short period of drifting along the water/air contact layer “Palaeoptera” sank directly to the bottom whereas the soft-tissued abdomens of Neoptera began to decay under these oxic conditions. After loosing their abdomen the corpses sank to a pycnocline in a strongly stratified water body where a second period of drifting took place. At this stage the wings were settled by attaching bivalve larvae derived from a river. When the weight of the shells increased the insect/bivalve association broke through the pycnocline and sank to the bottom where they were finally embedded and fossilized.

Infrared mapping resolves soft tissue preservation in 50 million year-old reptile skin

Non-destructive Fourier Transform InfraRed (FTIR) mapping of Eocene aged fossil reptile skin shows that biological control on the distribution of endogenous organic components within fossilized soft tissue can be resolved. Mapped organic functional units within this approximately 50 Myr old specimen from the Green River Formation (USA) include amide and sulphur compounds. These compounds are most probably derived from the original beta keratin present in the skin because fossil leaf- and other non-skin-derived organic matter from the same geological formation do not show intense amide or thiol absorption bands. Maps and spectra from the fossil are directly comparable to extant reptile skin. Furthermore, infrared results are corroborated by several additional quantitative methods including Synchrotron Rapid Scanning X-Ray Fluorescence (SRS-XRF) and Pyrolysis-Gas Chromatography/Mass Spectrometry (Py-GC/MS). All results combine to clearly show that the organic compound inventory of the fossil skin is different from the embedding sedimentary matrix and fossil plant material. A new taphonomic model involving ternary complexation between keratin-derived organic molecules, divalent trace metals and silicate surfaces is presented to explain the survival of the observed compounds. X-ray diffraction shows that suitable minerals for complex formation are present. Previously, this study would only have been possible with major destructive sampling. Non-destructive FTIR imaging methods are thus shown to be a valuable tool for understanding the taphonomy of high-fidelity preservation, and furthermore, may provide insight into the biochemistry of extinct organisms.

Three-dimensionally preserved arthropods from Cambrian Lagerstätten of Quebec and Wisconsin

Three new types of arthropod are described from Cambrian intertidal lithofacies of the Elk Mound Group and St. Lawrence Formation of Wisconsin and the Potsdam Group of Quebec. These arthropods are preserved ventrally in sandstone in life position and in three dimensions, allowing detailed characterization of limb morphologies, labrums, and other organs such as eyes. A taphonomic model is presented, illustrating this unusual, uncompressed, three-dimensional style of preservation.Arenosicaris inflatan. sp., from the Terreneuvian-Furongian Elk Mound Group and the Furongian St. Lawrence Formation, is the earliest unambiguous occurrence of a malacostracan phyllocarid. This 3 cm long arthropod had ovate valves, five pairs of biramous pleopods, and at least 3 pairs of thoracopods.Mosinieia macnaughtonin. sp., a large (>10 cm long) euthycarcinoid of uncertain affinity with flattened or paddle-like appendages also occurs in Elk Mound strata.Mictomerus melochevillensisn. sp. represents a new euthycarcinoid family and is the first known non-trilobite arthropod from the middle Cambrian-Furongian Potsdam Group of Quebec.M. melochevillensisn. sp. is large (8–10+ cm long), with as many as eleven pairs of well-preserved homopodous, uniramous, non-paddle-like limbs. BothM. macnaughtoniandM. melochevillensisdiffer substantially from previously known euthycarcinoids in limb morphology and represent the oldest known representatives of the group. Additionally, bothM. melochevillensisn. sp. andM. macnaughtonin. sp. possess morphologies that are consistent with abundant subaerial and subaqueousDiplichnitesandProtichnitestrackways known from these units, suggesting that these may be the earliest land-going animals.

Three-dimensionally preserved arthropods from Cambrian Lagerstätten of Quebec and Wisconsin

Three new types of arthropod are described from Cambrian intertidal lithofacies of the Elk Mound Group and St. Lawrence Formation of Wisconsin and the Potsdam Group of Quebec. These arthropods are preserved ventrally in sandstone in life position and in three dimensions, allowing detailed characterization of limb morphologies, labrums, and other organs such as eyes. A taphonomic model is presented, illustrating this unusual, uncompressed, three-dimensional style of preservation. Arenosicaris inflata n. sp., from the Terreneuvian-Furongian Elk Mound Group and the Furongian St. Lawrence Formation, is the earliest unambiguous occurrence of a malacostracan phyllocarid. This 3 cm long arthropod had ovate valves, five pairs of biramous pleopods, and at least 3 pairs of thoracopods. Mosinieia macnaughtoni n. sp., a large (>10 cm long) euthycarcinoid of uncertain affinity with flattened or paddle-like appendages also occurs in Elk Mound strata. Mictomerus melochevillensis n. sp. represents a new euthycarcinoid family and is the first known non-trilobite arthropod from the middle Cambrian-Furongian Potsdam Group of Quebec. M. melochevillensis n. sp. is large (8–10+ cm long), with as many as eleven pairs of well-preserved homopodous, uniramous, non-paddle-like limbs. Both M. macnaughtoni and M. melochevillensis differ substantially from previously known euthycarcinoids in limb morphology and represent the oldest known representatives of the group. Additionally, both M. melochevillensis n. sp. and M. macnaughtoni n. sp. possess morphologies that are consistent with abundant subaerial and subaqueous Diplichnites and Protichnites trackways known from these units, suggesting that these may be the earliest land-going animals.

Quantitatively evaluating the sources of taphonomic biasing of skeletal element abundances in fossil assemblages

The predominantly unknown nature and magnitude of the total taphonomic biasing that affects fossil assemblages commonly limits the testing of paleoecological hypotheses by the quantitative comparison of fossil assemblages. Multiple regression analyses of a suite of taphonomic characteristics against a measure of the total taphonomic biasing of a fossil assemblage can be used to generate a taphonomic model that identifies and quantifies many of those taphonomic processes that are important in biasing fossil assemblages. By examining the parameters of regression-based quantitative taphonomic models, key elements of the taphonomic history of a fossil assemblage can be reconstructed and such histories compared between fossil assemblages. We discuss the methodology pertinent to the building of quantitative taphonomic models and illustrate the effectiveness of such an approach using a case study considering two samples (857 specimens) of an Oligocene mammalian fossil assemblage from the Scenic Member of the Brule Formation, South Dakota. It is possible to quantify all of the taphonomic biasing affecting bone abundances in each of the two sampled assemblages using a small number of taphonomic characteristics. The most important of these characteristics is bulk density. The control of biasing by density is attributed to a combination of the increased resistance to physical damage of dense bones as well as the decreased probability of transport. Element shape and surface area to volume ratio are shown to have a significant but lesser control on assemblage biasing. Comparison of the taphonomic models for each sampled assemblage using currently viable methods demonstrates that the two assemblages are not statistically isotaphonomic. This interpretation may change with the gathering of additional data.