Skeletal Disarticulation Research Articles

Funerary Diversity and Cultural Continuity: The British Beaker Phenomenon Beyond the Stereotype

The Beaker phenomenon in Britain is typically represented by a particular form of pottery and its inclusion in graves with flexed or crouched inhumations referred to as Beaker burials. Analysis of the full range of burial evidence, however, reveals a high degree of variability in funerary rites including cremation and skeletal disarticulation. Summed probability distribution analysis of radiocarbon dates provides evidence for continuity of these other, atypical rites from the pre-Beaker Late Neolithic (c.3000–2450 calbc) through the Chalcolithic (c.2450–2200 calbc) and into the Early Bronze Age (afterc.2200 calbc). Regional diversity is apparent in Beaker period funerary treatments and grave good provision between these typical and atypical rites, as is differential selection of rites on the basis of age and biological sex. This evidence for within and between community funerary diversity has implications for understanding the large-scale processes of cultural and genomic transformation across this period of major transition in British prehistory.

Post-mortem movement and skeletal disarticulation after death

ABSTRACT Post-mortem movement relating to the disarticulation or positional change of entire limbs is relevant to a forensic investigator when examining a deceased person. Understanding that the position a body is found is not necessarily the way it was left changes the approach an examiner must take when investigating any death. This study quantified post-mortem movement of a human donor decomposing in an Australian environment over 16 months: 1) progressive measurement of the angles of joints; and 2) distance of separation between the articulating points of bones. ImageJ software was used to calculate angles and the distances between structures from time-lapse images. Movement was detected at all joints of the upper and lower limbs, occurring at all stages of decomposition across the study. Significant movement of the joints occurred as a result of bloat during the early stages of decomposition, and again during the advanced stages of decomposition as the soft tissue desiccated. Disarticulation was observed in the late stages of decomposition in all limbs and was not exclusive to short or long bones. Disarticulation also generated significant movement between skeletal structures in late decomposition. The results demonstrate that it is essential to consider post-mortem movement when investigating unexplained deaths.

Controlled experimental observations on joint disarticulation and bone displacement of a human body in an open pit: Implications for funerary archaeology

The study of death and burial in prehistoric populations is fundamental to understanding the human past. In recent years increasing attention has been given to methods and techniques to understand important aspects of funerary ritual such as body treatment, and concepts of death and decay of the human body. The French-developed methodological approach archaeothanatology aims to understand how the dead body was treated, and which factors influenced the final condition and position of the skeletal remains. A core part of the approach is assessing the anatomical articulation of the joints of the skeleton. Sequences of the relative order in which the joints of the body naturally disarticulate are used to reconstruct body position and condition upon interment. These disarticulation sequences are largely based on observations of archaeological skeletons, in which distinguishing the effects of different variables is highly challenging. Experimental studies (actualistic taphonomy) allow observation of disarticulation and bone movement under controlled conditions.This paper discusses the actualistic experimental study of a willed donated human body to examine the process of decomposition and skeletal disarticulation under controlled conditions. The results support earlier indications that burial environment and variations in body position can greatly affect patterns of disarticulation and bone displacement. Furthermore, the process of disarticulation observed in this study was complex, involving multiple instances of displacement of bones out of anatomical position prior to loss of the connective tissues, as well as cases of disarticulation followed by ‘re-articulation’. This demonstrates that sequences based largely on archaeological data may not capture the entire process. Further actualistic studies are needed to better understand the effects of different variables on disarticulation and final bone position. Such studies provide the opportunity to refine and improve the existing framework used to assess body treatment. Understanding body treatment in the past contributes to the wider conceptualization of human death and burial.

THE UTILITY OF ISOLATED CRINOID OSSICLES AND FRAGMENTARY CRINOID REMAINS IN TAPHONOMIC AND PALEOENVIRONMENTAL ANALYSIS: AN EXAMPLE FROM THE UPPER PENNSYLVANIAN OF OKLAHOMA, UNITED STATES

The crinoid fossil record is dominated by isolated ossicles, pluricolumnals, arm segments, and other fragmentary remains resulting from postmortem skeletal disarticulation; however, few studies to date have focused on dissociated crinoid elements in taphonomic and/or paleoenvironmental analysis. A diverse, abundant, and taphonomically variable crinoid fauna recovered from a thin mudstone interval within the Upper Pennsylvanian Barnsdall Formation in northeastern Oklahoma presents a unique opportunity to test the value of incomplete crinoid remains in reconstructing paleoenvironmental conditions and understanding taphonomic patterns. Isolated radial plates were identified to the most precise level possible, commonly genus or species, and used to calculate the minimum number of completely disarticulated individuals; this value was then compared to the number of articulated specimens representing that same taxon to determine the proportion of individuals with cups that have undergone disarticulation into separate ossicles. Cladid taxa are shown to be particularly prone to total disarticulation, with disparid microcrinoids and, somewhat surprisingly, flexibles demonstrating more resistance to disarticulation. Genus-level taphonomic trends among cladid taxa indicate that genera with large but thin cup plates, short anal sacs, and arms capable of adopting a trauma posture are less prone to total disarticulation. Analysis of fragmentary crinoid material recovered from disaggregation of bulk mudstone slabs reveals that thin horizons containing abundant articulated crinoid crowns are enriched in skeletal material and encrusted ossicles relative to thicker subjacent and superjacent intervals, providing further evidence that such horizons represent periods of sediment starvation on the distal shelf that were episodically punctuated by storm events.

Deciphering taphonomic processes in the Eocene Green River Formation of Wyoming

The Green River Formation, Wyoming, contains such an abundance of well-preserved flora and fauna that this late early Eocene Lagerstatte is one of the best known from North America. Despite having being studied since the mid-nineteenth century, little is known about the taphonomic processes that resulted in a diverse suite of organisms, especially abundant fossil fish, being preserved in exquisite detail. Two distinct patterns of completeness and articulation recur among the fossil fish: complete and fully articulated, or extensive disarticulation of the anterior part of the fish only (‘half and half’ preservation). To decipher the processes involved in the preservation of Fossil Lake fish, specimens of the extant taxon Carassius auratus were decayed experimentally over a 6-month period. Various scenarios approximating conditions in the Eocene lake were replicated in the laboratory and each monitored to record the rate of degradation and how different starting conditions impacted on the taphonomy of the fish. Varying salinity or oxygen level did not induce any discernable differences in the pattern of decay; degradation occurred faster at higher temperatures. Unexpectedly, decay rates varied greatly between replicate samples. Soft tissues decomposed rapidly and extensively, and, even in the absence of any disturbance, the skeletal disarticulation that followed was repeatedly much greater than that exhibited by the vast majority of fossil fish from the Green River Formation. The results indicate clearly that decay in a quiet-water environment is, on its own, insufficient to explain the consistently high fidelity preservation of Green River fish: some additional factor is implicated. We propose that microbial mats at the sediment–water interface were key; fish carcasses became adhered to the sediment surface inhibiting floating, disarticulation and loss of bones, with ‘half and half’ specimens curving laterally and not fully adhering, thus only that part (typically the posterior) in contact with the substrate retained a high degree of skeletal fidelity.

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, explode or sink: postmortem fate of lung-breathing marine vertebrates

What happens after the death of a marine tetrapod in seawater? Palaeontologists and neontologists have claimed that large lung-breathing marine tetrapods such as ichthyosaurs had a lower density than seawater, implying that their carcasses floated at the surface after death and sank subsequently after leakage of putrefaction gases (or ‘‘carcass explosions’’). Such explosions would thus account for the skeletal disarticulation observed frequently in the fossil record. We examined the taphonomy and sedimentary environment of numerous ichthyosaur skeletons and compared them to living marine tetrapods, principally cetaceans, and measured abdominal pressures in human carcasses. Our data and a review of the literature demonstrate that carcasses sink and do not explode (and spread skeletal elements). We argue that the normally slightly negatively buoyant carcasses of ichthyosaurs would have sunk to the sea floor and risen to the surface only when they remained in shallow water above a certain temperature and at a low scavenging rate. Once surfaced, prolonged floating may have occurred and a carcass have decomposed gradually. Our conclusions are of significance to the understanding of the inclusion of carcasses of lung-breathing vertebrates in marine nutrient recycling. The postmortem fate has essential implications for the interpretation of vertebrate fossil preservation (the existence of complete, disarticulated fossil skeletons is not explained by previous hypotheses), palaeobathymetry, the physiology of modern marine lung-breathing tetrapods and their conservation, and the recovery of human bodies from seawater.

TAPHONOMY OF A JUVENILE LAMBEOSAURINE BONEBED FROM THE TWO MEDICINE FORMATION (CAMPANIAN) OF MONTANA, UNITED STATES

The Sun River Bonebed is a monodominant assemblage of late juvenile lambeosaurine elements from the Upper Cretaceous Two Medicine Formation of north-central Montana, United States. Detailed excavation revealed an unusual paleobiologic and depositional signature. Although the bonebed occurs in a succession of beds representing anastomosing stream deposits in a seasonal paleoenvironment, the assemblage consists of a conglomerate of bone and calcareous clasts in a matrix of silty mud and free-floating sand grains. Internally, the bed exhibits normal grading of bone and calcareous clasts, poor sediment sorting, and preferred orientation of elongate elements, all characteristics common to debris flow deposits. The mud-rich matrix, poor sorting, and graded clasts of the bonebed suggest the assemblage was entrained and deposited by a cohesive debris flow, perhaps initiated through entrainment of fine overbank sediment by a seasonal flood. Nearly complete skeletal disarticulation and weathering of some bones indicate a brief period of postmortem exposure prior to debris flow entrainment. Fracture styles suggesting fresh breaks and frequent abrasion may reflect pre-flow trampling or chaotic flow transport. A significant number of elements also exhibit wet rot. The uniformity in taphonomic effects among elements suggests a mass mortality event, a rarity for debris-flow-hosted bonebeds, though the specific cause of death is uncertain. The age class dominance is interpreted to reflect original paleobiology, rather than abiotic postmortem selection, and establishes the Sun River Bonebed as the first bonebed of predominantly late juvenile material, with no adult material, in the Two Medicine Formation.

Preservation of large titanosaur sauropods in overbank fluvial facies: A case study in the Cretaceous of Argentina

Patagonia exhibits a particularly abundant record of Cretaceous dinosaurs with worldwide relevance. Although paleontological studies are relatively numerous, few include taphonomic information about these faunas. This contribution provides the first detailed sedimentological and taphonomical analyses of a dinosaur bone quarry from northern Neuquén Basin. At Arroyo Seco (Mendoza Province, Argentina), a large parautochthonous/autochthonous accumulation of articulated and disarticulated bones that represent several sauropod individuals has been discovered. The fossil remains, assigned to Mendozasaurus neguyelap González Riga, correspond to a large (18–27-m long) sauropod titanosaur collected in the strata of the Río Neuquén Subgroup (late Turoronian–late Coniacian). A taphonomic viewpoint recognizes a two-fold division into biostratinomic and fossil-diagenetic processes. Biostratinomic processes include (1) subaerial biodegradation of sauropod carcasses on well-drained floodplains, (2) partial or total skeletal disarticulation, (3) reorientation of bones by sporadic overbank flows, and (4) subaerial weathering. Fossil-diagenetic processes include (1) plastic deformation of bones, (2) initial permineralization with hematite, (3) fracturing and brittle deformation due to lithostatic pressure; (4) secondary permineralization with calcite in vascular canals and fractures, and (5) postfossilization bone weathering. This type of bone concentration, also present in Rincón de los Sauces (northern Patagonia), suggests that overbank facies tended to accumulate large titanosaur bones. This taphonomic mode, referred to as “overbank bone assemblages”, outlines the potential of crevasse splay facies as important sources of paleontological data in Cretaceous meandering fluvial systems.

Patterns of Appendicular Skeletal Disarticulation: A Taphonomic Investigation of the Hudson-Meng Bonebed

Information from published taphonomic research concerning bison disarticulation frequencies is compared with additional primary data from several recent bison mortality sites to aid in the assessment of patterns of appendicular skeletal disarticulation within a large Paleoindian bison bonebed. Variation in the composition of articulatedbison skeletal segments from the 1991-96 excavations at the Hudson-Meng site (25SXJJ5), Sioux County, Nebraska, is compared with a combined data set of actualistic research from several modern bison mortality sites. Comparison of naturally occurring skeletal disarticulation patterns and archaeologically recorded patterns of disarticulation at Hudson-Meng aids in evaluating the formational history of the bonebed. These data indicate that the patterns of disarticulation from within the main bonebed level at Hudson-Meng closely resemble those from modern mortality sites.

Echinoderm taphonomy, taphofacies, and Lagerstätten

Taphonomic study of echinoderms provides useful information on sedimentary conditions before, during, and after burial. Taphonomic studies of Recent echinoderms indicate that much skeletal disarticulation occurs within a few days after death. However, experiments also indicate that within a short period after death echinoderm carcasses remain rather resistant to disarticulation, and thus may be transported a considerable distance by currents; following periods of a few hours of decay, more delicate portions of echinoderm skeletons are readily disarticulated. Some skeletal modules (e.g., crinoid pluricolumnals) may resist disarticulation for periods of months in quiet- and or cool-water environments. Anoxia promotes intact preservation by excluding scavenging metazoans. Echinoderm ossicles may undergo minor abrasion and/or corrosion if left exposed, and less dense stereom corrodes much more rapidly than dense plates, such as echinoid spines. However, heavily abraded ossicles may indicate prefossilization and reworking.Various groups of echinoderms (e.g., pelmatozoans, asterozoans, echinoids) have differing propensities for degradation and, therefore, produce different arrays of preserved fossil material primarily depending upon the relative rates of burial, bottom-water oxygenation, and turbulence. Echinoderms may be divided into three groups based upon the relative ease of skeletal disarticulation. Type 1 echinoderms include weakly articulated forms (e.g., asteroids and ophiuroids) that rapidly disintegrate into individual ossicles. Type 2 includes those echinoderms whose bodies contain portions in which are more tightly sutured, as well as portions in which the ossicles are somewhat more delicately bound (e.g., crinoids, regular echinoids). Such echinoderms display more varied taphonomic grades from fully intact to mixtures of isolated ossicles and articulated modules. Type 3 comprises those echinoderms (e.g., irregular echinoids) in which major portions of the skeleton are so resistant to disarticulation that they may be broken across sutures rather than coming apart at plate boundaries.Comparative taphonomy of particular types of echinoderm skeletal remains leads to recognition of distinctive taphofacies that characterize particular depositional environments. Taphofacies include two types of characteristic modes of fossil preservation: event taphonomic signatures and background taphonomic signatures. Depending upon normal conditions of environmental energy and rates of sedimentation, the background condition of various types of echinoderms for a given facies may range from articulated, unabraded skeletal modules (in Types 2 and 3) to highly corroded and/or abraded ossicles. Conversely, the occurrence of fully intact fossil echinoderms provides unambiguous evidence of rapid and deep burial of benthic communities. Such well-preserved fossil assemblages can provide a wealth of information regarding the paleobiology of echinoderms, as well as the nature of the depositional events and burial histories.This paper presents a preliminary classification and characterization of background and event aspects of echinoderm taphofacies for carbonate- (9 taphofacies, including reefs and hardgrounds) and siliciclastic-dominated (5 taphofacies) environments. In each case, we recognize a spectrum of echinoderm taphofacies that coincides with a gradient of environments, ranging from nearshore, high energy shoreface through proximal and distal storm-influenced shelf, to deeper ramp and dysoxic basinal settings. Most taphofacies also feature particular styles of obrution (smothered bottom) Lagerstätten. These range from scattered lenses of articulated fossils in some high energy sandstone and grainstone facies to bedding planes of articulated, pyrite coated specimens in dark shales. We classify and discuss the genesis of these types of Lagerstätten and list typical examples. Finally, we present a simple model that integrates the occurrence of various echinoderm taphofacies with concepts of cyclic and sequence stratigraphy.

Taphofacies and bioevents in marine sequences of the Appalachian Basin Middle Devonian

The Middle Devonian (Givetian) Hamilton Group is composed of widespread, time-stratigraphic, discontinuity-bounded depositional cycles which correspond to sequences and sub-sequences. Not only do recurrent lithofacies and biofacies units correlate predictably with given parts of cycles, distinctive taphonomic features also correlate with appropriate parts of transgressive-, early highstand-, and late highstand (regressive) systems tracts within sequences. Transgressive systems tracts (TSTs) are marked by widespread, thin (0.5 to 3 m), winnowed, shelly sandstones or skeletal wacke- to grainstones. Bases are typically heavily burrowed with a distinctive firmground ichnofacies. Internally, the beds display mixtures of variably disarticulated and corraded skeletal fragments, especially pelmatozoan debris. Condensed intervals are typified by sharp diastemic contacts between TSTs and overlying maximum highstand shales. These surfaces of maximum starvation may have thin (centimeters) lags of phosphatic, concretionary, or pyritic diaclasts, bones and conodonts as well as corroded carbonate skeletal debris. Early highstand deposits are characterized by an alternation of discrete storm beds with mudstones which may yield exceptionally well-preserved faunas. Late highstand- and regressive taphofacies display greater evidence of sediment-shell disturbance by bioturbation and repeated storms. The decrease in accomodation space dictates sediment-bypass and mixing with increased evidence of skeletal disarticulation and shell abrasion.A recurring, and somewhat enigmatic phenomenon consists of widespread (to 100s of km) shell and reworked concretion layers, associated with diastems, which occur at the late highstand or early sea level-fall position within offshore, low energy mudstones. These “precursor beds” are sediment-starved lags, which mark abrupt shoaling events followed by a return to deeper-water deposits below the transition to lowstand conditions. These lags either represent the overprint of condensed smaller cycles superimposed on larger ones or they may record a fundamentally new, little-understood, process associated with abrupt sea level drop.Most of the typical Givetian “Hamilton fauna” appears abruptly in the second major sub-sequence (4th order cycle) of the Hamilton Group. The Hamilton fauna was partitioned into distinctive biofacies which were remarkably stable in terms of taxonomic composition, guild structure and relative abundance. These biofacies tracked favored environments and recur through 10 or more basinwide cycles (including sub-sequences) during some 6–7 my. Surprisingly, relative lowstands, represented by sequence-bounding unconformities, appear to have had very little disruptive influence on tracking Hamilton biotas. Very few species became extinct, immigrated, or underwent significant morphological change during the entire Givetian interval. Instead, both the initiation and termination of the Hamilton fauna correspond with major deepening events (Marcellus and Genesee transgressions) of combined eustatic/tectonic origin. In both cases, the major faunal changes (extinctions, immigrations, species evolution) appear to be associated with widespread anoxic black shales in condensed early highstands of sequences. Both of these correspond to global bioevents (Kacak-otomari and Pharciceras events) that have been related to climatic change. This observation suggests that the major transgressions may have been associated with widespread environmental restructuring.

Disarticulation patterns of some modern East African mammals

The sequences of skeletal disarticulation in a broad range of African mammals in a tropical savanna environment suggest that in general the process is very consistent. There is some variation among species, but this cannot yet be convincingly related to higher taxonomic categories or to body size. Disarticulation begins shortly after death, proceeds more or less continuously, and is almost complete after 5 yr. Because of the overall predictability of disarticulation, the stage of disarticulation reached by comparable fossil skeletons provides useful information about their taphonomic history prior to burial.

Concepts in palaeoecology

The large-scale distribution of organisms on land and sea is primarily controlled by temperature. Organisms tend to be geographically associated as ecologically related communities. Under normal conditions of preservation fewer than half the species may be preserved as fossils. Biostratonomic processes such as skeletal disarticulation and shell transport may operate between death and final burial. The final fossil assemblage may be a fossil community consisting of in situ species or a death assemblage consisting of transported remains. The classification of these assemblages is discussed. Physical and chemical aspects of the depositional environment, including salinity, temperature, Eh and pH may be interpreted from the mineralogy, grain size, sedimentary structures and fossils. The resulting picture is nearly always affected by diagenetic and/or evolutionary changes. Biological aspects of the depositional environment may be determined by comparing fossils with their living relatives. By this method the ecology of the living is conferred on the dead. Accuracy, however, decreases with increase in the length of time spanned. Use may also be made of experimental methods. Examples are given of the palaeoecology of individual species, symbiotic relationships, and ecological interpretation of fossil assemblages. The application of palaeoecology to palaeozoogeography is also discussed.

Concepts in palaeoecology

The large-scale distribution of organisms on land and sea is primarily controlled by temperature. Organisms tend to be geographically associated as ecologically related communities. Under normal conditions of preservation fewer than half the species may be preserved as fossils. Biostratonomic processes such as skeletal disarticulation and shell transport may operate between death and final burial. The final fossil assemblage may be a fossil community consisting of in situ species or a death assemblage consisting of transported remains. The classification of these assemblages is discussed. Physical and chemical aspects of the depositional environment, including salinity, temperature, Eh and pH may be interpreted from the mineralogy, grain size, sedimentary structures and fossils. The resulting picture is nearly always affected by diagenetic and/or evolutionary changes. Biological aspects of the depositional environment may be determined by comparing fossils with their living relatives. By this method the ecology of the living is conferred on the dead. Accuracy, however, decreases with increase in the length of time spanned. Use may also be made of experimental methods. Examples are given of the palaeoecology of individual species, symbiotic relationships, and ecological interpretation of fossil assemblages. The application of palaeoecology to palaeozoogeography is also discussed.