Abstract The field of Ichnology bridges the gap between the areas of paleontology and sedimentology, but has connections to many subdisciplines within these areas. Biogenic structures record the behavior of their tracemakers and provide valuable information in paleoecologic and paleoenvironmental analysis. As in situ ethologic structures, trace fossils or ichnofossils yield valuable insights into the paleoecology of ancient benthic communities and the environmental dynamics of depositional systems. Ichnology is truly a multifaceted field, and a broad selection of its facets is represented in the 28 papers of this volume. The papers are the product of Ichnia 2004, the First International Congress on Ichnology, convened by Jorge F. Genise and held from 19 to 23 April 2004 at the Museo Paleontológico Egidio Feruglio in Trelew, Patagonia, Argentina. Seven papers connected with the congress, containing ichnotaxonomy, were published separately, in Ichnos, volume 13, issue 4, edited by J.F. Genise, R.N. Melchor, R.G. Netto, and A.K. Rindsberg. Several symposium volumes, books, and short-course notes have been published in recent years ( Pemberton et al., 2001 ; Buatois et al., 2002 ; Kowalewski and Kelley, 2002 ; Hasiotis, 2002 ; Kelley et al., 2003 ; Buatois and Mángano, 2003 ; McIlroy, 2004 ; Webby et al., 2004 ; Miller, 2007 ; Seilacher, 2007 ), and ichnology can be considered a particularly active research area in steady growth. The 28 papers herein are arranged in five groups that reveal the broad scope of ichnology. One of the

Abstract: Two basic approaches are used to assess the paleobiology of continental associations between insect herbivores and their host plants. First is a biological approach that emphasizes phylogeny of extant representatives of lineages with fossil records. Second is a paleobiological approach that provides intrinsic evaluation of fossil associational evidence, of which there are several types of studies. One type of study is intensive examination of single insect-herbivore associations that involve a continuum from generalists to specialists requiring detailed autecological deductions about life habits. Another tack is assessment of herbivore damage patterns from selected plant hosts through slices of time for understanding the ecological evolution of a component community. Alternatively, comprehensive analyses can be made of the feeding patterns within a single or a series of regional floras. The record of plant-insect associations has five advantages. Associational data (1) are typically present in deposits that lack insect body fossils; (2) often surpass in abundance and usefulness insect body fossils in the same deposit; (3) frequently antedate their respective insect body fossils; (4) provide invaluable behavioral data that are unavailable from body fossils; and (5) supply crucial data for testing hypotheses in paleobiology and evolutionary biology that otherwise are unachievable. Disadvantages involve difficulties in circumscribing insect culprits, absence of extant ecological data to which fossil data can be compared, and lack of attention by paleobotanists and botanists in collecting damaged specimens. An associational view of fossil land plants and insects provides a dynamic, process-oriented view of ecosystem evolution that is needed in paleobiology.

Abstract: Organisms are homeostatic organic wholes. Their organization is understandable, and fractally repeated, from the level of the cell to whole individual organisms, through higher taxonomie groups up to the level of the biosphere. This is not fully appreciated by most biologists and paleontologists owing to emphasis on investigation of the parts (individual organs) that constitute static anatomy, rather than the dynamic morphological interrelationships. The morphodynamic approach, which is largely synonymous with a holistic heterochronic approach, also allows us to view organisms as complex systems: i.e., as manifestations of iterative or recursive fractal organization. Using the Schadian paradigm, already successfully applied to an understanding of modern mammals, and the relationships between morphology (form), physiology, and behavior, it is possible to gain insight into reiterating, recursive, or fractal patterns of organization in dinosaurs, pterosaurs, and other extinct archosaurs. Once these whole-body morphodynamic relationships are understood, as inherent, intrinsic, or “formal” aspects of vertebrate development, all natural groups of organisms can be seen in a new light: i.e., recurrent patterns of morphological organization (convergence) are seen as necessary correlates of physiological organization and behavior. In turn, all these organic attributes help us understand dynamic evolutionary development of any natural taxonomic group (clade). Thus, ontogeny reiterates and creates phylogeny (and vice versa) in a series of fractal, recursive manifestations of form, physiology, and behavior. Appreciation of the intricacy of this complex fractal organization is an exercise in pattern recognition, with surprising implications, especially for paleontology. First, it confirms the interrelatedness of all organisms, one of the central tenets of modern evolutionary theory. Second, it supports the view that higher natural taxonomic groups, already recognized by biology and paleontology, are in reality superorganisms, with inherently similar organizational structure, modified only by spatial and temporal scaling (heterochrony). Thus, all have their own inherent spatio-temporal developmental trajectories (form, life span, and relative emphasis of proximal and distal—or inner and outer/peripheral organs). Third, convergence and iterative evolution can be understood as an inherent quality of a reiterating or recursive fractal system and not merely as an adaptation to external pressures of the environment. This inference is strongly supported by evo-devo studies. Fourth, the modification of the natural organic system, in part or wholly, will lead to a compensation or ripple effect throughout the whole system. Moreover, the phylogeny of a particular group may not be controlled by external environmental pressures to the degree often supposed. Rather, such phylogenies may be natural heterochronic cycles of repeated growth at levels of organization corresponding to higher taxonomic groups (= superorganisms). Such intricate, inherent (or formal) organic organization reveals lawful patterns of morphological relationships that extend beyond isolated and/or shared character recognition. Thus, it may be possible to predict the general form and physiology of the whole animal from an analysis or understanding of the parts (a process akin to modeling). This is particularly useful in paleontology. The morphodynamic approach does more than revive Cuvier’s principle of the correlation of “some” parts. It impels us to recast our previously static understanding of morphology in the light of the inherently dynamic nature of complex systems, showing us how “all” parts are ultimately related.

Abstract: Invertebrate trace fossils are usually considered as stratigraphically less useful than vertebrate footprints. This is because they commonly lack diagnostic “fingerprints”, which are more closely related to the anatomy of the producer than to the biological purpose, or function, of the trace. Exceptions are trilobite burrows (Cruziana) , arthrophycid burrows, ichnospecies of Oldhamia, and Treptichnus pedum. Even if their makers are unknown, they represent taxonomically coherent groups of animals, whose evolving behavior marks geologic time. Cruziana ichnospecies can also be used in paleogeography.

Abstract: The hitherto rarely recorded ichnogenus Lapispira Lange is a concentrically arranged double helicoidal U-burrow, subperpendicular to bedding, without branching. It is redescribed on the basis of abundant material occurring in Sinemurian to Pliensbachian deposits at the Atuel valley area of the Neuquén basin (Mendoza, Argentina). The regular coiling remains remarkably constant, with greatest diameters in arenites and smallest in silty sandstones. The burrows are generally filled with massive, fine to very fine sandstone, mainly finer and better size-sorted than the host sediments. The unlined burrow walls may show scratch traces and are usually mined by small Chondrites isp., though less densely than in the surrounding beds. Architectural, taphonomical, constructional, and functional aspects of Lapispira are discussed. Though its trace maker is unknown, some structural details hint at decapod crustaceans as the likely producers. This deliberate complex trace can be regarded as a mixed-purpose one, reflecting somewhat different activities, thus defying straightforward ethologic allocation. Lapispira bispiralis Lange is a presumably elite, facies-dependent burrow: in the studied area it occurs in storm- and fair-weather sandstones deposited in the shoreface and offshore-shoreface transition zone (where it attains the largest sizes); only exceptionally does it appear also in very fine silty sandstones (offshore tempestites). The overall distribution of the ichnogenus shows a wider stratigraphic and geographic range than previously acknowledged, though the facies fidelity is maintained.

Abstract: The trace fossil Zoophycos has long been considered an archetypical example of a deposit-feeding trace. The important discovery that at least some types of Zoophycos actively introduce surface material into the burrow sparked a new interest in alternative ethological explanations. Recently proposed ethological explanations for the trace fossil Zoophycos include gardening of microorganisms. In the gardening model, organic-rich material is collected on the sediment surface and introduced into the burrow as substrate for the cultivation of microorganisms. Because microorganisms are known to fractionate strongly against 13 C, especially under low oxic to anoxic conditions, it is argued that any gardening activity in the trace would result in a noticeable shift in δ 13 C between spreiten and adjacent host sediment. In order to test this hypothesis, δ 13 C org of spreiten material and directly adjacent host material was measured in 12 host-spreite couples from three cores from the eastern North Atlantic. The results show δ 13 C org values ranging from -23.6‰ to -21.6‰ for host sediment and between -23.4‰ and -21.8‰ for Zoophycos material. The difference in the couples is usually only a few tenths of a permil. The minimal difference between Zoophycos and host material suggests that gardening plays an insignificant role. However, the trace material generally displays a significant enrichment in organic carbon compared to surrounding host sediment. Therefore, the gardening hypothesis is rejected in favor of a cache model, where food is squirreled away for poorer times.

Abstract: Most families of the endobenthic spatangoid echinoids possess a subanal fasciole surrounding drain-constructing podia and correspondingly construct a single drain tube or a pair of them. The drains conduct used respiration water away from the echinoid. In vitro studies of spatangoid echinoids in the laboratory in aquaria have led to the description of some spurious behavior patterns. These probably derive from the use of inadequately spacious aquaria and of insufficient duration of experiments, and have led to abnormal behavior of the echinoids. Some of these “mythical” behavior patterns have been repeated in the literature, especially in textbooks. Trace fossils of burrowing echinoids are abundantly and well preserved as Scolicia (twin drains) and Bichordites (single drain), and these trace fossils provide evidence that the spurious modes of behavior observed in laboratory conditions are artefacts and do not exist in nature. Some members of the family Schizasteridae burrow deeply down to ca. 20 cm in fine-grained sediment. However, the schizasterids possess no subanal fasciole, and little evidence of drain construction has been reported for the family. Nevertheless, large podia are present, which suggests the ability for construction and maintenance of two drains. In the Pleistocene Lindos Bay Clay of the Rhodos Formation of Rhodes, Greece, abundant individuals of Schizaster canaliferus are preserved in silty clay. The sediment is totally bioturbated, containing abundant Scolicia isp. The echinoids occur in intimate association within these trace fossils and are undoubtedly genetically connected with them. The Scolicia have two basal drain strings, clearly indicating that S. canaliferus constructs a pair of drains. Preservation of the hair-thin drains in Scolicia is considered to involve precipitation of early cement, as in Bichordites. In this way, the slender empty tubes escape obliteration by compaction.

Abstract: This paper reports the facies analysis and ichnology of a logged section in the lower part of the Mulichinco Formation (Early Valanginian), at Vega de Escalone in the Neuquén Basin, western Argentina. Four facies associations (A-D) have been defined, and they record deposition below the storm wave base (A), mainly as gravity-flow deposits (coquinas) devoid of any evidence of bioturbation. Hummocky cross stratification, wave and current ripples, and mud intervals record the offshore transition (B). Wave and current ripples and heterolithic stratification record the shoreface and a shallowing-upward trend (C). The uppermost part of the succession exhibits tidal influence (D). Trace fossils documented in the shoreface (C) include abundant Asteriacites lumbricalis, Lockeia isp., Gyrochorte comosa, Planolites isp., and fugichnial trace fossils that indicate a stressed environment affected by changes in sedimentation rate and probably salinity. In heterolithic ripple troughs, abundant Asteriacites lumbricalis are well preserved, protected by mud drapes, and they include evidence of horizontal displacement and vertical superposition. Lockeia and Planolites intersect Asteriacites, and Gyrochorte comosa is a facies-crossing trace fossil. Trace fossils in the tidally influenced interval (D) are restricted in diversity and distribution. Some bedding planes contain monospecific assemblages of Asteriacites lumbricalis; others contain J-shape burrows and Gyrochorte comosa. Trace fossils can be assigned to the Cruziana ichnofacies while vertical burrows in hummocky cross stratification are interpreted as records of the Skolithos ichnofacies. This apparent inversion in the trace-fossil distribution according to the marine ichnofacies can be a response to the change from an opportunistic to a background fauna.

Abstract: The Triassic red beds of the Caturrita Formation (Paraná Basin, southern Brazil) contain abundant Skolithos, common Taenidium, and rare Arenicolites in low-angle, trough cross-bedded fine-grained sandstones interpreted as crevasse-splay deposits, forming a Skolithos- dominated composite piperock and providing easily mappable horizons. Skolithos cf. serratus is the dominant trace fossil, being closely spaced (~ 160 burrows/m 2 ), slightly inclined, and having sharp, irregular boundaries with delicate scratch ornament. The average burrow length is approximately 0.2 m, but some may extend as deep as 0.4 m into the substrate. They crosscut a previous monospecific Taenidium barretti ichnocoenosis, formed by vertical meniscate burrows, which is superimposed on a previous Skolithos linearis ichnocoenosis, formed by abundant S. linearis, subordinate horizontal T. barretti, and rare Arenicolites isp. Colonization was firstly generated in softgrounds, maybe under subaqueous conditions, and reveals gradual substrate desiccation, the S. cf. serratus being produced in firmgrounds. The analyzed specimens of Skolithos resemble modern tiger beetle and midge larva burrows, while Taenidium is similar to modern oligochaete burrows. The dense concentration of vertical burrows reveals opportunistic colonization and suggests important environmental (climatic?) changes opening the colonization window to insects in floodplains. This highlights the stratigraphic significance of the colonized surfaces, which represent nondepositional hiatuses.

Abstract: Continental ichnofaunas display a progressive increase in bioturbation depth and intensity through the Phanerozoic. Ichnologic data from Cenozoic fluvial deposits of the Chaco Basin, Subandean zone of Bolivia, indicate widespread colonization of deep infaunal ecospace by the Miocene. Trace fossils are described from the Tariquia Formation, which records deposition in anastomosed fluvial systems. Although the Tariquia ichnofauna is of low diversity and does not display significant compositional variations throughout the succession, ichnofabric analysis reveals some degree of variability linked to different taphonomic pathways that helps to understand depositional dynamics and environmental conditions during accumulation of this fluvial unit. Intense and deep bioturbation occurs in medium- to very fine-grained crevasse sandstone and overbank mudstone. Less pervasive bioturbation is recorded in deposits of abandoned main channels. The Tariquia ichnofauna is dominated by Taenidium barretti, representing an example of the Scoyenia ichnofacies. Overbank deposits are totally bioturbated (BI = 6), showing complete destruction of the primary sedimentary fabric. Main-channel and crevasse-splay sandstones display an upward increase in degree of bioturbation. The top of the channel and crevasse-splay sandstone represents colonization surfaces that allow direct measurements of maximum burrowing depth. Taenidium barretti extends up to 2.2 m into the crevasse sand sheets. Depth and intensity of bioturbation of the main-channel and crevasse sands seem to be a function of time between depositional events. Main-channel and crevasse sandstones underlying thick packages of bioturbated overbank mudstones are intensely bioturbated, recording prolonged periods of low-energy sediment fallout between crevassing events. Conversely, the lowest degree of bioturbation is found in amalgamated channel sandstone units underlying thin intervals of overbank mudstones, reflecting high-frequency depositional episodes.

Abstract: This paper reports the first ichnologic investigation in the San Rafael Basin, carried out in the glacial to postglacial transition, recorded in the El Imperial Formation at the Rio Atuel canyon. Following previous published stratigraphic schemes, three units were recognized in the field, but the upper one is ichnologically sterile and not studied in this paper. The lower unit shows evidence of glacial influence but lacks marine indicators and was deposited in a shallow paleovalley. Almost exclusively, the ichnofossils include locomotion traces produced by arthropods (Diplichnites and Diplopodichnus) or molluscs (Archaeonassa). Palynomorphs are terrestrial and show evidence of intense transport and deterioration. The middle unit contains a more varied range of ethologic categories: pascichnia (e.g., Mermia, Gordia, Cochlichnus), repichnia (e.g., Paganzichnus, Diplopodichnus, Didymaulichnus, Diplichnites, Undichna), and fodinichnia (e.g., Treptichnus) documented in transgressive deposits that record the glacial retreat and early postglacial interval. Many previous detailed studies carried out in contemporary successions of the basins of western Argentina have been the object of intense debate about the marine or nonmarine nature of these successions. In the middle unit, ichnofossils occur together with palynomorphs that show degradation and pyritization and contain scarce acritarchs suggesting brackish-water rather than fresh-water conditions in a fjord depositional system.

Abstract: The concept of “brackish water” encompasses a wide range of salinities that occupy a continuum between fresh water (< 2‰ salinity) and fully marine waters (35‰ salinity). Ichnological assemblages in brackish-water settings are inherently variable, as a consequence of temporal and geographic variations in such factors as average salinity, magnitude of salinity fluctuations, nature of the colonized substrate, presence and/or duration of subaerial exposure, and fluctuations in hydrodynamic energy. Trace-fossil suites attributable to brackish-water conditions are recognizable as departures from archetypal, fully marine expressions of recurring ichnofacies. These departures are characterized principally by impoverishment of assemblage diversities. Facies-crossing forms, such as Planolites, Teichichnus, “Terebellina”, Cylindrichnus, Skolithos, Palaeophycus, and Ophiomorpha, are persistent, particularly with decreasing salinities and/or increasing environmental stresses. Ichnogenera that are largely “confined” to the open-marine realm versus those “diagnostic” of brackish-water environments are variable, and depend in part upon the nature of the adjoining open system and the age of the study interval. Nevertheless, with increasingly stenohaline conditions, ichnogenera such as Helminthopsis, Helminthorhaphe, Cosmorhaphe, Phycosiphon, Zoophycos, Chondrites, Asterosoma, Rosselia, Rhizocorallium, Bergaueria, Schaubcylindrichnus, Scolicia, and Conichnus tend to be more recurrent. Additional aspects of brackish-water suites include size reduction of ichnogenera, introduction of monogeneric and monospecific suites, and repeated juxtaposition of facies-crossing elements of both the Skolithos Ichnofacies and the Cruziana Ichnofacies. This paper summarizes the ichnological characteristics of a large number of well-studied Cretaceous intervals that reflect brackish-water deposition. These units define four broad settings: (1) restricted or barrier-barred bays (e.g., Ostracode Zone, Paddy Member, and the Grand Rapids Fm); (2) open, non-barred bays (e.g., McMurray Fm, Basal Colorado Sandstone, Viking Fm, and Ben Nevis Fm); (3) riverine estuaries (e.g., McMurray Fm, Grand Rapids Fm, Waseca Fm, Glauconite Fm, and Ostracode Zone); and (4) barred, wave-dominated estuaries (e.g., Viking Fm, Bluesky Fm, and Bow Island Fm). Subenvironments within these broad groupings can be further delineated, using a combination of ichnological characteristics and primary sedimentological features. Although general ichnological trends from fully marine conditions into brackish-water settings can be determined, the aforementioned complexities serve to inhibit the development of a universally applicable, recurring brackish-water “ichnofacies”. As such, brackish-water deposits are best characterized by comparison with their genetically related open-marine counterparts.

Abstract: The Middle Jurassic Lajas Formation of the Neuquén Basin, Argentina, is interpreted as a 400-600 meter thick aggradational, macrotidal tide-dominated deltaic system. Tide-dominated systems are most commonly found in estuarine settings, and thus the biota found in such settings are generally influenced by lowered salinities. This paper documents the ichnology of the tide-dominated Lajas Formation, which includes a diverse ichnofauna, much of which is subject to tidal conditions, though not necessarily to reduced salinity. The ichnogenera recorded include: Asteriacites, Arenicolites, Asterosoma, Dactyloidites, Didymaulichnus, Diplocraterion, Chondrites, Cruziana, Helminthorhaphe, Macaronichnus, Ophiomorpha, Parahaentzschelinia, Palaeophycus, Planolites, Polykladichnus, Protovirgularia, Rhizocorallium, Rosselia, Schaubcylindrichnus, Scolicia, Siphonichnus, Taenidium, Teichichnus, and Thalassinoides. The range of tidal environments from which the trace fossils were collected encompasses tidal flats, tidal channels, and tide-dominated delta fronts, passing offshore into shelf mudstones of the Los Molles Formation and landward into the fluvial deposits of the Challaco Formation. The paleoenvironmental controls on the distribution of ichnotaxa are discussed in relation to Lajas Formation ichnology and sedimentology.

Abstract: A section approximately 30 m thick in the uppermost part of the deltaic lower Pleistocene Tursi Sandstone at Rabatana has been analyzed. It contains Bichordites monastiriensis, rare Macaronichnus segregatis, and very rare Rosselia socialis (Bichordites ichnoassemblage) in the lower part, and abundant B. monastiriensis and R. socialis, and rare M. segregatis ( Bichordites-Rosselia ichnoassemblage), in the upper part. Ichnofabric and sedimentologic features indicate upper- to middle-shoreface conditions in the lower part of the section, decreasing in energy up section to lower-shoreface conditions. The Bichordites ichnoassemblage is related to unstable conditions on the sea floor, which favored infaunal colonization by vagile irregular echinoids. The Bichordites-Rosselia ichnoassemblage is related to more stable conditions in a probably deeper and / or protected environment, and to clearer waters in a declining deltaic system. Under such conditions, colonization by sedentary ?terebelloid tracemakers of R. socialis, which fed on the sea floor, was possible. The low trace-fossil diversity is related to intense bioturbation by echinoids, which prevented colonization by other tracemakers, except for the Rosselia tracemakers.

Abstract: The fossil record (including trace fossils) is remarkably reduced after the end-Permian mass extinction. Faunal recovery increased continuously during the Mesozoic, and a marked restructuring of shallow marine benthic communities during Jurassic and Cretaceous time is known as the Mesozoic Marine Revolution. While middle and late Mesozoic trace-fossil associations are diverse and well studied around the world, those of the Triassic are minimally documented. Especially the bioerosional aspects are poorly understood compared to other periods. An abundant and diverse ichnofauna in the Middle Triassic of the Germanic Muschelkalk Basin provides insights into the ichnologic record at the beginning of the Mesozoic. For more than two centuries, this basin has been the subject of numerous studies, and several ichnogenera were established from the German Triassic (e.g., Rhizocorallium, Trypanites, Balanoglossites, Pholeus). A first overview allows the estimation of about forty invertebrate ichnotaxa, which can be grouped into three categories in terms of their appearance: (1) Burrow trace fossils—besides well-known ichnotaxa such as Bergaueria, Cochlichnus, Conichnus, Curvolithus, Lockeia, Phycodes, Protovirgularia, Rhizocorallium, and Thalassinoides, this group also contains ichnotaxa that are poorly known elsewhere, e.g., Archaeonassa, Arachnostega, and Pholeus. Occurrences of the oldest Mesozoic nearshore Zoophycos from the Muschelkalk are important for the interpretation of the general evolutionary trends of the tracemakers and their behavioral convergence. Of special interest is the interpretation herein of complex trace fossils, such as Mixoteichichnus coniungus and Balanoglossites triadicus. (2) Bioerosion trace fossils— many horizons of the Muschelkalk succession are characterized by omission surfaces and allow the study of bioeroded firmgrounds and hardgrounds with well-established ichnotaxa (e.g., Trypanites weisei). Most bioerosion trace fossils are recognized in the German Triassic for the first time, including ichnospecies of Gastrochaeonolites, Caulostrepsis, Maeandropolydora, and Palaeosabella. (3) Meiobenthic trace fossils—micritic bedding planes exhibit a diverse trace-fossil association with burrows and trails, where in many instances the producer itself is preserved at the end of the trace. The tracemakers, preserved by recrystallization, are mainly in the size range of meiofaunal species and commonly appear as worm-like (nematoid) or arthropod-like organisms. Cochlichnus, Helminthopsis, and Helminthoidichnites are the most common ichnotaxa of this group.

Abstract: A three-dimensionally preserved skull and parts of the postcranial skeleton of an ichthyosaur ( Leptonectes ) was found vertically oriented within on-average slowly deposited (0.5 m/My) Lower Jurassic shallow-water marls. The ichthyosaur sank headfirst into the seafloor because of its center of gravity, as anatomically similar comparably preserved specimens suggest. The skull penetrated into the soupy to soft substrate until the fins touched the seafloor. There is no evidence either for active penetration of the ichthyosaur during death agony or an acceleration by explosive release of sewer gas that would have pushed the skull into the substrate. Ichnofabrics and crosscutting relationships among trace fossils preserved therein allow analysis of stratigraphic completeness. In spite of on-average slow accumulation, the ichthyosaur-hosting sediments formed rapidly during three distinct but similar deposition-bioturbation phases. First, 10 to 15 cm of mud accumulated rapidly. Biodeformational structures subsequently produced therein imply a soupy consistency. As sedimentation slowed down, muds slightly dewatered and consolidated, as reflected by trace fossils with distinct outlines (Palaeophycus and Planolites, thereafter Thalassinoides and Chondrites). The contact with the overlying depositional interval is obliterated by biodeformational structures. Hence, the previously rapidly deposited mud must still have been soft. A short time after the third deposition-bioturbation phase, the ichthyosaur parts penetrated into the still-soft mud and started to be degraded microbially. Below the bioturbated zone, but before compaction, a concretion started to form around the ichthyosaur parts and led to their excellent preservation. During further burial, the skull-hosting concretion experienced differential compaction and moved downward relative to the underlying beds. The skull-hosting concretion penetrated through condensed deposits representing three ammonite zones. Restoring differential compaction, the initial porosity of the sediment can be estimated to have been > 70%. Compared to modern analogues, such muds are soft, as ichnofabrics imply.