Implications For Taphonomy Research Articles

Neotaphonomy of a rodent skeletal accumulation by Strigiformes in an Andean valley. Implications for taphonomy, archaeology and palaeontology

ABSTRACT Holocene accumulations of rodent bones digested by raptors have been found in El Bolsón, a high-altitude valley in Catamarca, Argentina. Yet, so far there were no relevant taphonomic frames of reference to account for them. We thus studied a modern accumulation in Los Viscos rockshelter from a taphonomic perspective. The rockshelter is used for roosting, and the surface is covered by rodent skeletal remains. The analysed sample (NISP = 421) is dominated by remains of Phyllotis vaccarum, and also comprises other cricetid species, cavids, ctenomids and abrocomids. The anatomical, breakage and digestion patterns were compared to data on different predators. The most probable predator related to this accumulation is a Strigiformes (Aves) species. Most variables, including digestion, suggest a low-intensity modifier, probably Tyto alba, an individual of which was spotted around. Although Athene cunicularia may produce similar bone breakage, the prey taxa are not compatible with its diet. Alternatively, intense fragmentation may relate to postdepositional processes such as trampling. We discuss the implications of these findings for understanding the formation of the zooarchaeological and palaeontological record in the area, as well as for helping assess the global variability of Tyto alba taphonomic signature.

The prevalence of invertebrate bioerosion on Mesozoic marine reptile bone from the Jurassic and Cretaceous of the United Kingdom: new data and implications for taphonomy and environment

AbstractInvertebrate bioerosion on fossil bone can contribute to reconstructions of benthic taxonomic assemblages and inform us about oxygenation levels, water depth and exposure time on the seafloor prior to burial. However, these traces are not commonly described in the fossil record. To date, there have been only 13 published studies describing a total of 15 instances of invertebrate bioerosion on marine reptile fossil bones from the Mesozoic globally. We surveyed the collections of several UK museums with substantial occurrences of Mesozoic marine reptiles for evidence of invertebrate bioerosion. Here, we document 153 specimens exhibiting 171 newly recorded instances of invertebrate bioerosion on Jurassic and Cretaceous marine reptile bones. Several major bioeroding taxonomic groups are identified. Within the geological strata of the United Kingdom, there is a higher prevalence of bioerosion in the Cretaceous relative to the Jurassic, despite greater sampling of specimens from the Jurassic. Although biotic turnover and food web restructuring might have played a role, potentially pertaining to heightened productivity during the later stages of the Mesozoic Marine Revolution, we consider it more likely that this temporal change corresponds to differences in depositional environment and taphonomic history between the sampled rock units. In particular, the Cretaceous deposits are characterized by heightened oxygenation levels relative to their Jurassic counterparts, as well as reworking, which would have allowed two phases of bioerosion. A spatiotemporally broader dataset on invertebrate bioerosion on vertebrate bone will be important in further testing this and other hypotheses.

Neoichnology of Chalk cobbles from north Norfolk, England: implications for taphonomy and palaeoecology

The study of marine biota of the North Sea from the perspective of its relevance to palaeontology (Aktuopaläontologie) has enabled modern patterns and processes to be identified that can also be recognised in ancient communities. A collection of Chalk cobbles from the coast of north Norfolk, eastern England, preserves a limited ichnofauna: Gastrochaenolites ornatus Kelly and Bromley; Gastrochaenolites isp.; and Caulostrepsis isp. All cobbles show evidence of physical modification (corrasion) since they were bored; no Gastrochaenolites is complete and no clast has Caulostrepsis on all sides, therefore clasts have been corraded subsequent to boring. Only one producing organism in Gastrochaenolites, probably Barnea sp., is preserved in situ. Gastrochaenolites borings were infested by a range of encrusting organisms after the demise (and removal of shells) of the boring bivalves: thread-like algae; agglutinated worm tubes; cheilostome bryozoan Cryptosula pallasiana (Moll); and serpulids Hydroides norvegica Gunnerus and Pomatoceras triqueter (Linnaeus). Such a suite of encrusting organisms would be impossible to see in a fossil boring filled with lithified sedimentary rock unless it was released by dissolution of the substrate. Such cobbles, corraded since they were infested by borers, leave only portions of traces for identification, commonly only to ichnogenus.

Mechanical properties of the chitin-calcium-phosphate “clam shrimp” carapace (Branchiopoda: Spinicaudata): implications for taphonomy and fossilization

Spinicaudata (colloquially ‘the clam shrimp’) are freshwater branchiopod crustaceans that occur worldwide in lakes and temporary pools. The spinicaudatans are easily recognizable by their bivalved carapace which is unusual among arthropods in that it is subject to only partial molting. During ecdysis (molting), the outer surface of the carapace is not shed, resulting in the retention of the ontogenetic record of an individual through distinct growth-rings representing each molt. When this unusual feature is considered alongside the interesting chemical properties of the carapace, “clam shrimp” present an interesting biological material not seen anywhere else: a multi-laminar calcium-phosphate-chitin composite. In addition, the carapace survives numerous destructive taphonomic processes (including transport, decay, compaction, and desiccation) to become the dominant body component of Spinicaudata preserved in their 380 million year fossil record. Understanding the mechanical properties and chemical composition of this structure may not only aid in a better understanding of the evolutionary history of this group but also facilitate efforts to develop novel materials that retain functional material properties even in harsh aquatic conditions. Therefore, this study aims to provide quantitative information about the composition and mechanics of this unique and interesting biological material and help predict possible biases in the fossilization of different species of Spinicaudata to aid future palaeontological research.

Fish bones, cut marks, and burial: implications for taphonomy and faunal analysis

Willis et al. (2008) demonstrated that butchering fish can result in upwards of 500 cut marks per fish skeleton. However, despite various ethnographic studies that describe fish butchering techniques for consumption and drying, cut marks are rarely observed or described for fish bone from archaeological sites. To test the discrepancy between the experimental results and archaeological observations, we buried 13 butchered fish skeletons for 27 months to observe whether the cut marks are still visible after exposure to post-depositional taphonomic processes. After burial, we observed a general decrease – up to 76%, depending on the species of fish – in the number of cut marks visible on fish bone, accompanied by a shift from cut marks on identifiable elements to cut marks on unidentifiable bones and bone fragments. These results impact the methods for analyzing archaeological fish bone, and contribute to our understanding and interpretation of taphonomy, aquatic faunal assemblages, and prehistoric butchering practices.

The Lateral Continuity of Ediacaran Fossil Surfaces: Implications for Taphonomy and Paleoecology

The Lateral Continuity of Ediacaran Fossil Surfaces: Implications for Taphonomy and Paleoecology

Fish bone chemistry and ultrastructure: implications for taphonomy and stable isotope analysis

This paper reviews the ultrastructure and chemistry of fish bone, with an emphasis on zooarchaeology and stable isotope analysis. On the basis of the chemical composition of the collagen and the relationships between the collagen and mineral phases, fish bone is more susceptible to biotic and abiotic degradation than mammalian bone and is therefore less likely to be recovered in archaeological deposits. The amino acid composition of fish bone differs from that of mammals, most notably with respect to hydroxyproline content. The C:N ratio of fish collagen is, however, very similar and slightly lower than mammalian collagen, and thus the traditional range of acceptable C:N ratios for archaeological bone collagen (2.9–3.6) should not be shifted or extended for fish on the basis of the amino acid composition of collagen. An extensive survey of published archaeological bone collagen C:N ratios demonstrates that fish collagen from archaeological contexts tends to have significantly higher C:N ratios than mammalian collagen. The elevated C:N ratios in fish bone collagen may be the result of abiotic degradation processes that occur within the bone after death, the presence of exogenous humic contaminants, or endogenous lipid contaminants.

Burrow-mediated carbonate dissolution in rudist biostromes (Aurisina, Italy): implications for taphonomy in tropical, shallow subtidal carbonate environments

In Upper Cretaceous rudist biostromes at Aurisina, Italy, marked taphonomic loss of radiolitids by burrow-mediated dissolution and mechanical disintegration illustrates the relation between synecology and early diagenesis in the fossilization of tropical shallow-water bioconstructions. The studied platform succession accumulated in a prevalently open lagoon with bioturbated carbonate sand, rudist thickets, bioclastic dunes, and areas with shelly lime ooze. Rudist biostromes consist of radiolitids and hippuritids, or of radiolitids only, and have an open, parautochthonous rudist fabric with a matrix of bioclastic, bioturbated wackestone. “Swirly” disorientation of bioclasts records early softground bioturbation. Later firmground burrows comprise an irregular network of tunnels and chambers filled with bioclastic packstone to grainstone. The size, geometry and sediment fill of the firmground burrows suggest that they were produced by crustaceans. Radiolitid preservation ranges from complete to relictic. Radiolitid relicts formed by (a) spalling and/or dissolution of the cellular boxwork ostracum of the attached valve, leaving “calcite-tubes” built by a distinct, thin ostracal shell layer, or (b) dissolution of the entire shell, leaving the sedimentary fills of the intertabular spaces of the attached valve as a diagnostic vestige, or (c) shell dissolution within the firm sediment, with subsequent filling of the biomould by bioclastic wackestone to packstone to grainstone. Loss of radiolitids produced a taphonomic bias towards rudists with non-cellular ostracum. Locally, taphonomic loss produced “ghost biostromes” composed nearly entirely of faint radiolitid relicts. Shell dissolution resulted from chemical gradients in the sediment within and near the burrows, and from enhanced microboring and microbial infestation. Dissolution of radiolitids was favoured by the combined effects of chemical instability of hypostracal aragonite and by the structure of the calcitic boxwork ostracum of thin-walled cells. Some biostromes are intercalated with, or are capped or overlain within a short vertical distance, by a hardly recognizable emersion surface, as a consequence of the shallow depth of biostrome accumulation. Taphonomic loss by dissolution is widespread in open, parautochthonous rudist fabrics, and confirms actuogeological results of other authors that bioturbation mediates carbonate dissolution also under shallow tropical waters supersaturated for calcium carbonate. The amount of carbonate dissolved upon burrowing of the biostrome matrix is hardly quantifiable but, by analogy to Recent carbonate environments, may have been large. Within bioconstructions, deep-tiered burrowing occurred at least since the Carboniferous. Taphonomic loss by dissolution thus may have been active in the fossilization of tropical shallow-water mounds and biostromes over much of Phanerozoic times.

Floodplains and paleosols in the Siwalik Miocene sequence: implications for taphonomy and paleoecology of faunas

The Siwalik fluvial deposits of Pakistan are characterized by varying proportions of red to brown silts, fine sands, and minor clays representing overbank deposition. In the Chinji Formation (~15–10.5 Ma), floodplain facies consist of overlapping packages of: 1) well-bedded siltstones and occasional sheet sands or small channel sands, 2) an overlying transitional zone with increased bioturbation and minor pedogenesis, 3) a capping paleosol. These packages are 5–6 m thick and pinch out laterally over 1–2 km; they appear to represent crevasse-splay lobes that aggraded rapidly into low-lying wet areas and then became stable land surfaces. The cycle was repeated as aggradation of the major rivers and/or local subsidence transformed the topographic highs into lows where sedimentation again buried soil surfaces. Floodplains in the Nagri Formation (~10.5–9 Ma) were associated with a larger channel system and were less complex, and those of the Dhok Pathan Formation (~9–6 Ma) were influenced by several contemporaneous river systems and again became more complex.Paleosols are superimposed on all lithofacies and occur every 4–10 m thoughout the 3500 m sequence where overbank deposits are dominant. Paleomagnetic calibration of the Siwalik sequence indicates that paleosols represent 10–50K yrs, on average. Individual paleosols are red-orange or red-brown, 1.6–4.8 m thick, have abundant evidence of bioturbation, ped structure, clay cutans and a zone depleted in matrix carbonate above a lower zone with carbonate precipitates. A long-term record of Siwalik vegetation in Pakistan is contained in the carbon isotope ratios of paleosol carbonate. There is no evidence that paleosols varied in maturity with distance from the major channels; instead vertical and lateral facies relationships were controlled by shifting crevasse-splay lobes and overbank channels.The processes of overbank sedimentation in the Siwalik sequence have important consequences for preservation of vertebrate faunas. Most of the 800+ fossil localities occur in channel fills within overbank facies; relatively few are associated with paleosols or the coarse deposits of major channels. The frequency of overbank channel fills varies through the different formations, resulting in uneven sampling of the vertebrate faunas. Most skeletal remains are attritrional, and bones are disassociated and fragmentary but otherwise well-preserved. This is partly a consequence of bioturbation and minor transport followed by rapid burial within the abandoned channels. The ecological setting of the Siwalik biota was controlled by a mosaic of floodplain environments that changed in complexity through time. In contrast to the Eocene Bighorn Basin floodplains, there was no simple lateral relationship of habitat types with distance from the major channels.

Vertebrate fossil-bearing paleosol units (Willwood Formation, Lower Eocene, Northwest Wyoming, U.S.A.): Implications for taphonomy, biostratigraphy, and assemblage analysis

In the lower 300 m of the fluvial Willwood Formation of northwest Wyoming, most large concentrations of vertebrate fossils consist of disarticulated and broken skeletal remains that occur in widespread, tubular, thin (2 cm-1 m) greenish- and bluish-gray mudstones that are low in percentage of free iron, aluminum, and manganese, relatively high in percentages of organic carbon, and often show evidence of clay eluviation. These units lie atop sesquioxide-rich, sometimes clay-illuviated variegated unit (red, yellow, purple, and mottled variants) and are relicts of the A horizons of podzolic spodosols (aquods). The wide distribution of bone fragments, the numerical proportions of bone elements, weathering of the fragments, and biogenic evidence indicate the vertebrate remains accumulated gradually as litter on the surface of the soils and became incorporated into the A horizon. The bones were disarticulated, broken, and otherwise disturbed by the action of scavengers prior to burial. Occurrence of abundant vertebrate remains in discrete, readily identifiable, and widespread paleosol units makes these units valuable biostratigraphic markers (zonules, faunules). Evidence of geologically short-term lag accumulation of the bones is important to assemblage analysis; the paleosol concentrations result from attritional mortalities that more closely reflect composition of the life assemblage than do remains concentrated by fluvial transport or predators.