In the final analysis, it is the morphology of the trace as an expression of animal behaviour that is the basis of the name.
As ichnologists we must admit that the introduction and discussion of different ichnotaxonomic philosophies reminds us of the inherent subjectivity in any scientific endeavor. Ostensibly the ICZN should constrain such subjective interpretation and bring order to the field. In practice this is difficult, and a certain degree of chaos and ambiguity still reigns. Nonetheless the science progresses, and names, however reliable or controversial, are used for descriptions and dialog between ichnologists.
Although it is not uncommon to find expressions of doubt about the need to use a formal taxonomy to classify trace fossils, ichnotaxonomic classification is an unavoidable companion to preservational and ethological schemes. If a formal name is available, simple descriptors (e.g. vertical burrows and meniscate traces) should be avoided. The ichnotaxonomic classification, albeit imperfect, provides the best common ground on which to base more theoretical elaborations and practical applications (Buatois et al., 2002a). In any case, in modern ichnology contrasting philosophical perspectives have been adopted to classify trace fossils. However, exchange of ideas during and after the 1998, 2002, 2006, and 2010. Workshops on Ichnotaxonomy have resulted in a growing consensus among practicing ichnologists (Bertling et al., 2006). In this chapter, we turn our attention into the theoretical and practical aspects involved in classifying trace fossils from a taxonomic standpoint. We first address some philosophical problems involved in this approach. Then, we focus on a detailed review of the different ichnotaxobases currently in use and the problems associated with compound and composite trace fossils. Subsequent to that, we move on to some recent ideas and proposals with respect to the uses of hierarchies in trace-fossil taxonomy and the peculiarities of vertebrate ichnotaxonomy. Finally, we review some practical aspects involved in the recognition of trace fossils in both outcrops and cores.
The prevalent notion that trace fossils are comparatively rare in nonmarine facies is more a reflection of insufficient reconnaissance than of a true dearth of specimens.
Vemos las cosas según como las interpretamos. Lo llamamos previsión: saber de antemano, estar prevenidos. Usted en el campo sigue el rastro de un ternero, ve huellas en la tierra seca, sabe que el animal está cansado porque las marcas son livianas y se orienta porque los pájaros bajan a picotear en el rastro. No puede buscar huellas al voleo, el rastreador debe primero saber lo que persigue: hombre, perro, puma. Y después ver. Lo mismo yo. Hay que tener una base y luego hay que inferir y deducir. Entonces – concluyó – uno ve lo que sabe y no puede ver si no sabe…Descubrir es ver de otro modo lo que nadie ha percibido. Ése es el asunto.. – Es raro, pensó Renzi, pero tiene razón –.
Historically invertebrate ichnology has focused on marine ichnofaunas. However, studies have gradually moved into freshwater and, more recently, terrestrial environments. As a result, continental ichnology has experienced a remarkable development during the last 15 years, and our perspective on this topic has changed dramatically. Earlier case studies started to show that continental invertebrate ichnofaunas were more varied and abundant than originally envisaged (e.g. Bromley and Asgaard, 1979; Bown, 1982; Pollard et al., 1982; Frey et al., 1984b; Walker, 1985; Ekdale and Picard, 1985; D’Alessandro et al., 1987; Gierlowski-Kordesch, 1991; Pickerill, 1992). It rapidly became clear that continental environments were as numerous and diverse as marine settings, and that such variability was indeed reflected in the ichnological record (Frey and Pemberton, 1987). Subsequent work focused on the expansion of the continental dataset, but more significantly in the proposal of archetypal ichnofacies in addition to the Scoyenia ichnofacies (Smith et al., 1993; Buatois and Mángano, 1995b, 2004a, 2007; Bromley, 1996; Genise et al., 2000, 2004b, 2010a). Also, the potential and limitations of the ichnofabric approach to the study of freshwater and terrestrial ichnofaunas have been addressed in a number of studies (e.g. Buatois and Mángano, 1998, 2007; Genise et al., 2004a; Buatois et al., 2007a). More recently, proposals have been made to define continental ichnofacies based on vertebrate trace fossils (Lockley et al., 1994; Hunt and Lucas, 2006a, 2007). There has also been a recent revival of continental neoichnology (e.g. Scott et al., 2007b; Smith and Hasiotis, 2008; Hembree, 2009; Genise et al., 2009). The fields of invertebrate and vertebrate ichnology have evolved independently, and research involves two separate scientific communities to a great extent (Lockley, 2007). This is certainly not a significant problem in marine ichnology, but it has had a negative impact on continental ichnology. The need to integrate vertebrate and invertebrate datasets has long been recognized (e.g. Buatois and Mángano, 1995b, 1996), but little progress has been attained. However, a series of recent papers seem to show that a better articulation between invertebrate and vertebrate ichnology is possible (e.g. Melchor et al., 2006; Lockley, 2007; Hunt and Lucas, 2007; Minter et al., 2007b; Scott et al., 2007b; Krapovickas et al., 2009). Integration of both datasets will be essential to produce more robust depositional models of continental environments.
Invertebrate trace fossils can be used for the stratigraphic correlation of otherwise nonfossiliferous clastic sequences, provided that they share particular “fingerprints” and thus reflect behavioral diversification within taxonomically coherent groups of (commonly unknown) tracemakers.
In contrast to body fossils, trace fossils are often characterized by long temporal ranges and narrow facies ranges (see Section 1.2.8). As a consequence, trace fossils are highly useful in paleoenvironmental analysis and less so in biostratigraphic studies. Although most ichnogenera display long temporal ranges, it is also true that some biogenic structures can preserve specific fingerprints of their producers. If the producers record significant evolution, then the trace fossils may also yield biostratigraphic implications (Seilacher, 2007b). There are some ichnofossils that reflect particular kinds of animals in which body morphology and behavior underwent closely related evolutionary transformations through time (Seilacher, 2000). The more complex (in terms of fine morphological detail) a structure is, the more direct its biological relationship, distinctive its behavioral program, and hence, larger its biostratigraphic significance. Historically invertebrate trace fossils have been applied in biostratigraphy in two main areas: the positioning of the Proterozoic–Cambrian boundary (e.g. Seilacher, 1956; Banks, 1970; Alpert, 1977; Crimes et al., 1977; Narbonne et al., 1987; Crimes, 1992, 1994; Jensen, 2003) and the establishment of relative ages in lower Paleozoic clastic successions based on Cruziana and related trilobite trace fossils (e.g. Seilacher, 1970, 1992a, 1994; Crimes, 1975). In recent years, attempts have been made to incorporate other ichnotaxa, such as Arthrophycus and related trace fossils (e.g. Seilacher, 2000; Mángano et al., 2005b). In the field of vertebrate ichnology, tetrapod trackways have a long tradition in biostratigraphy, particularly in upper Paleozoic–Mesozoic strata (e.g. Haubold and Katsung, 1978; Lucas, 2007). In this chapter we will address the utility of both invertebrate and vertebrate trace fossils in biostratigraphy.
This success stems mainly from the intimate connection of ichnology with sedimentology and the importance of both fields for paleoenvironmental and basin analysis, which becomes more and more important in petroleum exploration. This useful connection, however, also had its price. In the hand of biogeologists, trace fossils easily lose their significance as unique biological documents.
One of the triumphs of the palaeobiological approach to palaeontology is the insight functional morphology has given us about the life activities of long dead organisms.
Although the significance of trace fossils in paleoenvironmental reconstructions is responsible for the rapid development of ichnology, we should not forget that ichnofossils are produced by living organisms and, as such, the biological nature of trace fossils is at the core of any study on animal–substrate interactions. In this chapter, we analyze the paleobiological facet of trace fossils. In order to do so, we revise concepts from benthic ecology and paleoecology. First, we explore the concept of modes of life, addressing feeding strategy, position in relation to the substrate–water interface, and level of motility. Second, we elaborate on the different modes that organisms have to interact with and, in particular, penetrate into the substrate. Third, we look at basic locomotion and burrowing mechanisms from a historical perspective, revisiting the pioneering work of Schäfer and the synthesis by Trueman. We exemplify all these mechanisms with examples form the trace-fossil record. Finally, we close this chapter by introducing the new paradigm of movement ecology and its potential implications in ichnological studies.
Decían que había como mil pichis escondidos en la tierra, ¡enterrados! Que tenían de todo: comida, todo. Muchos decían tener ganas de hacerse pichis cada vez que se venían los Harrier soltando cohetes.
Organisms burrow in response to many biotic and environmental factors. Ichnological studies provide detailed information on environmental parameters involved during sediment deposition and, therefore, serve as a basis for sedimentary environment and facies analysis. To that end, ichnological analysis should focus on the paleoecological aspects of trace-fossil associations (e.g. ethology, feeding strategies, ichnodiversity) and should avoid the simple use of a checklist approach because this may lead to paleoenvironmental misinterpretations. The paleoecological approach needs to be integrated with facies analysis, and should never aim to replace it. Many factors define the niche and survival range of animal species. However, the key to the analysis is the identification of major control factors, which are called limiting factors (Brenchley and Harper, 1998). In this chapter, we revise the response of benthic organisms to different environmental parameters, evaluate the role of taphonomy, and address a set of concepts that should be employed in paleoecological analysis of trace fossils, such as ichnodiversity and ichnodisparity, population strategies, and the notion of resident and colonization ichnofaunas. Then, based on the concept of ecosystem engineering, we discuss how organisms affect the environment. Finally, we address what biogenic structures can tell us about organism–organism interactions and spatial heterogeneity.
And what had he felt, I asked Mario, when he’d seen it there, the huella?
“One thing is to see artifacts presumably made by somebody and another is to see the pisada someone made, what their foot left in the earth. That’s what gives you the sense of humanity, right?”
Desert Memories (2004)
While the previous chapter deals with processes occurring at the scale of deep time, we now move into a more recent past, a time witnessing human activities. For the implications of trace fossils in paleoanthropology, information is based on the study of human fossil footprints (Kim et al., 2008a). Human footprints also play a major role in archaeology, although sources of information are found in many other ichnological datasets, such as bioerosion and bioturbation structures, and other vertebrate tracks as well (Baucon et al., 2008). The aim of this chapter is to review recent research in the area of ichnological applications in paleoanthropology and archaeology. The first half of the chapter will be devoted to review the fossil record of human footprints, from the Pliocene to the Holocene. The second half will explore the uses of ichnology in archaeology.
For my part, following out Lyell’s metaphor, I look at the natural geological record, as a history of a world imperfectly kept, and written in a changing dialect; of this history we possess the last volume alone, relating only to two or three countries. Of this volume, only here and there a short chapter has been preserved; and of each page, only here and there a few lines.
Trace fossils are proving to be one of the most important groups of fossils in delineating stratigraphically important boundaries related to sequence stratigraphy.
The appearance of sequence stratigraphy in the late eighties resulted in a revolution in the study of sedimentary rocks. The shift from seismic stratigraphy (Vail et al., 1977) to sequence stratigraphy brought the incorporation of outcrops and cores as sources of data in stratigraphic analysis (Posamentier et al., 1988; Posamentier and Vail, 1988; Van Wagoner et al., 1990). Coincident with this shift, ichnological studies began to emphasize the importance of trace fossils in sequence stratigraphy (e.g. Savrda, 1991b; MacEachern et al., 1992; Pemberton et al., 1992b). In little more than a decade, the field experienced a rapid increase in the number of studies devoted to exploring the applicability of ichnology in refining sequence-stratigraphic analysis (e.g. MacEachern et al., 1992, 1999a, 2007c; Savrda et al., 1993; Taylor and Gawthorpe, 1993; Pemberton and MacEachern, 1995; Ghibaudo et al., 1996; Martin and Pollard, 1996; Buatois et al., 1998d, 2002b; Pemberton et al., 2001, 2004; Carmona et al., 2006). At present, ichnological aspects are currently covered in sequence-stratigraphic textbooks (e.g. Catuneanu, 2006). The aim of this chapter is to provide a detailed review of the applications of ichnology in sequence stratigraphy. Although a large part of this chapter deals with the recognition of discontinuity surfaces in marine siliciclastic successions, we will also cover other topics which are commonly overlooked in the literature. These include characterization of parasequences, parasequence sets, and systems tracts, but also the potential of trace fossils to address sequence-stratigraphic issues in carbonates and continental deposits.
I confess frankly, it was the warning voice of David Hume that first, years ago, roused me from dogmatic slumbers, and gave a new direction to my investigations in the field of speculative philosophy.
We now come to the more immediate subject of this volume, namely the amount of earth which is brought up by worms from beneath the surface.
The Formation of Vegetable Mould Through the Action of Worms with Observations on their Habits (1881)
The ichnofabric approach represents a relatively new trend in ichnology that started in the second half of the eighties, becoming much more popular since the nineties. As is the case of the ichnofacies model, the ichnofabric approach has been frequently misunderstood. Earlier studies involving ichnofabrics put too much emphasis on assessing bioturbation and other more significant aspects, such as tiering or evaluation of successive bioturbation events, were commonly overlooked. Even worse, the idea that measuring the intensity of bioturbation could replace trace-fossil identification as ground data for paleoenvironmental interpretations persisted for some years. At present, the idea that ichnofabric analysis is simply measuring the degree of bioturbation has been mercifully abandoned by all serious workers. If the ichnofabric approach is understood as a comprehensive way of analyzing bioturbated deposits, then the wealth of information that may be obtained is huge and not only restricted to paleoenvironmental reconstructions but also of significant potential in understanding reservoir properties, benthic paleoecology, and evolutionary paleoecology. German philosopher Immanuel Kant expressed that his reading of his British peer David Hume roused him from his dogmatic slumber and led him to become a “critical philosopher”. In the same vein, the focus of this chapter, the ichnofabric approach, with its emphasis on taphonomic aspects, helps us to avoid taking the trace-fossil record at face value, permeating the whole interpretative process with some healthy criticism. We will start by providing the basics of the tiering concept before moving into a review of the ichnofabric concept, including aspects of quantifying the degree of bioturbation, visual strategies to present ichnofabric data, the paramount role of taphonomy, and the different types of ichnofabrics. Then, we will present the concept of ichnoguild, which, in our view, is central to the ichnofabric approach. Later, we will briefly review recent developments in the field of paleosol ichnofabrics. We will then address the general role of bioturbation, bioerosion, and biodeposition, before moving to the issue of bioturbation-enhanced permeability and reservoir characterization, a recently developed topic, which is having a strong impact in the petroleum industry. Finally, we will compare the ichnofacies and ichnofabric approaches.
Anyone can make the simple complicated. Creativity is making the complicated simple.
Ichnofacies stand today as one of the most elegant but widely misunderstood concepts in ichnology.
The ichnofacies model was introduced in a series of papers originally published in German by Seilacher (1954, 1955b, 1958, 1963b), and later expanded into English (Seilacher, 1964a, 1967b). In doing so, he created from a series of apparently disparate worldwide observations an elegant and coherent conceptual model. This body of work resulted in the first paradigm in ichnology, and transformed this field of research from a parochial discipline practiced by a few into a mainstream paleontological and geological science with a rich conceptual framework and multiple fruitful applications. Subsequently, the model was refined and expanded in a series of papers (e.g. Frey and Seilacher, 1980; Bromley et al., 1984; Frey and Pemberton, 1984, 1985, 1987; Bromley, 1990, 1996; Pemberton et al., 1992b; Bromley and Asgaard, 1993a; Lockley et al., 1994; Buatois and Mángano, 1995b, 2009; Gibert et al., 1998, 2007; Genise et al., 2000, 2010a; Ekdale et al., 2007; Hunt and Lucas, 2007; Minter and Braddy, 2009), remaining at the core of ichnology, both as a theoretical framework and as a tool. The aim of this chapter is to provide an updated review of the ichnofacies model, addressing not only marine softground and substrate-controlled ichnofacies, but also invertebrate and vertebrate continental ichnofacies. Vertebrate ichnofacies are still in flux and what is presented herein should be understood as a preliminary “state-of-the-art” rather than a consensus view on the matter.
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