Actualistic Studies Research Articles

The taphonomy of birds

The taphonomy of birds can be investigated with actualistic studies complemented by reviewing Konversat Lagerstätten such as Messel, Green River and Solnhofen.Two field sites were chosen in southern Florida: 1, a freshwater (16–23 ppt salinity) environment in which biogenic carbonate muds were being deposited and 2, a marine (30–34 ppt salinity) environment in which pyritous carbonate muds were being deposited. Ninety-six specimens (36 genera, 40 species) were used in this study (these were obtained from a wildlife centre where they died of natural causes). Experiments were set up in both marine and freshwater sites in the following categories: large protected, unprotected; small protected, unprotected. Protected specimens were placed in metal cages coated with small mesh (1.5mm2) nylon netting.The specimens were allowed to degrade under natural conditions. The following variables were recorded daily over a seventy day period: air and water temperature, humidity, rainfall, wind and current speed and direction, salinity, dissolved oxygen content, pH, and water depth. Specimens from each of the eight categories were sampled at day 1, 4, 7, 11, 28, 56, and 70.Scavengers play a major role in the early taphonomic processes. Unprotected specimens were rapidly removed from the study area by large predators such as alligators (Alligator mississippiensis) and American crocodiles (Crocodylus actus), and Turkey vultures (Cathartes aura). Even protected specimens were prone to attack by more “intelligent” large scavengers such as racoons. Smaller predators include crayfish in the freshwater site and the carnivorous gastropods (Crown conch) in the marine environment. The Crown conch was observed to be a voracious feeder and large numbers rapidly strip all flesh from any carcass within reach of the bottom.Decay proceeds rapidly in the warm waters of the field sites. Within the carcasses temperatures approach optimum bacterial temperatures and large bacterial colonies form within muscle blocks after only one day. The initial decay of the muscle fibres is also rapid (one day) as the muscle myofibrils start to break into short lengths and the myoseptum starts to disintegrate, and has totally disappeared after seven to fourteen days (depending on the initial mass of the bird).From graphs showing plots of percentage weight loss (weight loss as a percentage of original weight) versus time decay can be seen to follow an exponential curve ie. most rapid decay occurs early (as soft tissues decay) then weight loss slows down (after 10 days for small specimens and 28 days for large specimens) as by this time nearly all but the most resistant soft tissues have decayed and the weight loss is due to the removal of skeletal matter to the sedimentary record. Feathers are resistant to the initial stages of decay and the primary and secondary feathers remain attached to the wing bones for up to twenty-eight days even when the soft tissues have been totally removed.The results of the decay experiments have provided directly comparable specimens to those that can be found within the fossil record. This comparison of fossil and modern analogues allows a series of taphonomic thresholds to be defined in the fossilisation of birds.

Food procurement and transport by human and non-human predators

This study investigates food procurement and transport habits of a variety of large social predators in order to develop reliable criteria for identifying hunting and scavenging strategies of hominids from Pleistocene archaeofaunas. The study is concerned with ungulates in the intermediate body size range and focuses upon anatomical composition of bone accumulations in natural shelters. The comparisons document strong links between predator strategies, assemblage size and anatomical content, and some spatial characteristics of food supply. By using non-human predator behaviours as an independent source of measurement, the study demonstrates significant niche separation between Middle and Upper Paleolithic hominids in Mediterranean Europe. Implications for actualistic studies of food transport by modern humans are discussed in light of these findings.

Taphonomic pathways and comparative biofacies and taphofacies in a Recent intertidal/shallow shelf environment

The development of taphonomic approaches to facies analysis requires a foundation in facies-based actualistic studies. Modern intertidal and shallow shelf environments at Provincetown Harbor. northern Cape Cod, Massachusetts (USA) provide an opportunity to compare pattcrns and controlling factors in molluscan biofacies and taphofacies distributions. Variation in faunal composition, ecologic variables, and taphonomic attributes of molluscan death assemblages produce distinct patterns of environmental zonation: (1) Faunal composition (biofacies) primarily tracks variation in substrate type among environments (sand, rock, peat, and Zostera marina beds). (2) Ecologic variables (equitability, infauna: epifauna ratio, gastropod:bivalve ratio, and predation on M. mercenaria) appear to reflect tidal exposure time. (3) Taphononic attributes (fragmentation, abrasionm, corrosion, bioerosion, and encrustation) of the common bivalve M. mercenaria track environmental energy, in particular its effects on the stability and reworking of hardparts at the sediment surface. Shells in different environments proceed along different taphonomic pathways - the order of acquisition of taphonomic features by hardparts. An encrustation/bioerosion-dominated pathway characterizes low energy environments; the upper intertidal and deeper subtidal. An abrasion-dominated pathway characterizes the high energy lower intertidal and shallow subtidal. Contrasting pathways produce distinct proportions of taphonomic attributes in time-averaged samples; proportions that delineate taphofacies. Integrated taxonomic, ecologic and taphonomic data provide a more complete picture of environmental processes than any approach alone. Taphonomic data not only furnish information not readily provided by other approaches, but free paleoecology from the constraints of taxonomic uniformitarianism. □Taphonomy, comparative taphonomy, taphofacies, biofacies, cluster analysis, multidimensional scaling, taphonomic pathways, Recent, actualism, intertidal, molluses.

Archaeological Significance of Rabbit-Raptor Interactions in Southern California

Taphonomy of small fauna is not as well known as actualistic studies performed with large faunal remains. Yet small fauna like rabbit may dominate an archaeological assemblage. Small fauna was a primary meat source for many prehistoric groups in North America. Raptors also damage and disperse rabbit bones. Taphonomic research with rabbit-raptor interactions was undertaken in a lacustrine environment in southern California to determine the role played by raptors in damaging and dispersing rabbit bones which may subsequently be introduced into archaeological sites. Raptors often damage, disperse, and accumulate rabbit bones in a number of areas, including open-air localities and within abandoned human structures. Potential diagnostic characteristics of rabbit bones damaged by raptors are offered as baseline end-effects of raptors exploiting rabbit carcasses. Archaeologists can compare rabbit bones excavated from archaeological sites to these bones known to be damaged by raptors. This information is crucial to archaeologists for accurately interpreting rabbit bones modified by human action, and thus past subsistence strategies over time.

Taphonomy of Middle Pennsylvanian Mazon Creek Area Fossil Localities, Northeast Illinois: Significance of Exceptional Fossil Preservation in Syngenetic Concretions

Mazon Creek area fossil localities (Pennsylvanian: Westphalian D) in northeast Illinois provide an extraordinary preservational window for the study of Late Paleozoic terrestrial, fresh-water, and estuarine marine organisms. Marine animals were killed by episodic pulses of turbidfresh water associated with floodingfrom distributaries, and terrestrial organisms were introduced into coastal waters from upstream sources. Rapid burial entombed remains, commonly before significant decomposition had occurred, and very early diagenesis ensured fossil preservation as molds and composite impressions within sideritic concretions. The taphonomy of these deltaic, fossil-bearing beds is complex. Episodic engulfment of organisms is indicated by animal escape activity and by the presence of upended plant fragments. Numerous, distinctive, cyclic repetitions of siltstone-claystone laminae, each recording a single tidal (flood-ebb) event, are observed in areas yielding marine organisms; these indicate that rapid but extremely regular deposition was also important. Concretion formation was probably influenced, but not necessarily triggered, by decay processes. Siderite precipitation reflects three key conditions: the availability of iron, rapid burial of organic material, and a low to nonexistent supply of sea-water sulfate to centers of interstitial microbial activity. A regional (seaward) decrease in the quality offossil preservation is observed away from the coastal depocenter, and an interval of sparsely fossiliferous facies (a taphonomic discontinuity) occurs between the delta complex and shell-rich, normal marine deposits. The preservational significance of early diagenetic siderite is discussed; we argue that paleoenvironmental interpretations of analogous or similar nearshore deposits lacking fossiliferous concretions must be made cautiously. The potential value of Mazon Creek-type facies in the study of other Pennsylvanian nearshore deposits, including many superficially barren shales, is stressed. The association of the fossilbearing concretions with inferred estuarine-deltaic facies points to the need for future actualistic studies of comparable modern coastal environments.

Plant foods in savanna environments: A preliminary report of tubers eaten by the Hadza of northern Tanzania

Abstract Recently interest has been re‐directed towards the importance of plant foods in the evolution of human diet, and especially of deeply buried roots and tubers. The hypothesised qualities of these foods which have been stressed are their relative abundance in savanna areas, their nutritive value, their availability year round, and the minimal competition from other animals. It has been suggested that their inclusion in the diet would have conferred some selective advantage to hominids using simple tools such as digging sticks. This paper presents one of the first attempts of an actualistic study designed to measure quantitatively aspects of this food source that would be of importance to human consumers. The setting is a savanna area in northern Tanzania which is inhabited by a group who still extensively exploit tubers for food, the Hadza.

Taphonomy's contributions to paleobiology

Taphonomy established itself in paleontology primarily as a subdiscipline of paleoecology, but it has evolved into a much broader study of the ways in which preservation affects the fossil record. The past decade has seen a change in emphasis from descriptive taphonomic studies of fossil assemblages to more experimental, process-oriented investigations of necrolysis, stratification, and diagenesis of organic remains in modern environments. These actualistic studies are increasing the sophistication of taphonomic analysis in the fossil record by sharpening the diagnosis of bias in paleontological data and by providing a baseline for quantitative modeling of preservational patterns. The analysis of bias is also expanding into the evaluation of temporal resolution in the fossil record (sample acuity, stratigraphic completeness), and taphonomic research is thus contributing to broad-scale problems in evolution, biogeography, and biostratigraphy. In addition, taphonomic studies are providing new insights into paleoenvironmental reconstruction and into the direct paleobiological significance of post mortem processes such as the behavior of scavengers and the role of dead hardparts in structuring benthic communities. One of taphonomy's most promising new frontiers is comparative analysis applied to different taxonomic groups within assemblages and across environments, tectonic settings, and climatic regimes. All of this currently active research is contributing to a better understanding of the fossil record as the result of a dynamic, evolving, integrated system of biological and sedimentological processes that have both limited and enhanced knowledge of Earth history.

Toward the definition of criteria for the recognition of artificial bone alterations

Cutting, fracturing, flaking, and polishing of bones and other osseous materials may in some instances be interpreted as evidence of former human activity. Such interpretations must avoid confusion with the wide variety of natural processes that alter bones. Reliable criteria are prerequisite to sound inferences based on bone, regardless of whether they have been redeposited or recovered from primary assemblages. Criteria must be defined by means of actualistic studies (neotaphonomy) and experiments that demonstrate causal relationships between patterns of alteration and the processes that produce them. The criteria can be empoyed in the interpretation of fossil bones (paleotaphonomy) on the basis of uniformitarian principles. At the present time, such relationships are relatively well understood in the case of cut marks on bones, and modest progress has been made in investigating fractured and flaked bones. Polished bones are little understood and difficult to interpret.