Ichnology is the study of traces created in the substrate by living organisms. This is the first book to systematically cover basic concepts and applications in both paleobiology and sedimentology, bridging the gap between the two main facets of the field. It emphasizes the importance of understanding ecologic controls on benthic fauna distribution and the role of burrowing organisms in changing their environments. A detailed analysis of the ichnology of a range of depositional environments is presented using examples from the Precambrian to the recent, and the use of trace fossils in facies analysis and sequence stratigraphy is discussed. The potential for biogenic structures to provide valuable information and solve problems in a wide range of fields is also highlighted. An invaluable resource for researchers and graduate students in paleontology, sedimentology and sequence stratigraphy, this book will also be of interest to industry professionals working in petroleum geoscience.

Ichnology: Organism-Substrate Interactions in Space and Time

Were molecular data available for extinct taxa, questions regarding the origins of many groups could be settled in short order. As this is not the case, various strategies have been proposed to combine paleontological and neontological data sets. The use of fossil dates as node age calibrations for divergence time estimation from molecular phylogenies is commonplace. In addition, simulations suggest that the addition of morphological data from extinct taxa may improve phylogenetic estimation when combined with molecular data for extant species, and some studies have merged morphological and molecular data to estimate combined evidence phylogenies containing both extinct and extant taxa. However, few, if any, studies have attempted to estimate divergence times using phylogenies containing both fossil and living taxa sampled for both molecular and morphological data. Here, I infer both the phylogeny and the time of origin for Lissamphibia and a number of stem tetrapods using Bayesian methods based on a data set containing morphological data for extinct taxa, molecular data for extant taxa, and molecular and morphological data for a subset of extant taxa. The results suggest that Lissamphibia is monophyletic, nested within Lepospondyli, and originated in the late Carboniferous at the earliest. This research illustrates potential pitfalls for the use of fossils as post hoc age constraints on internal nodes and highlights the importance of explicit phylogenetic analysis of extinct taxa. These results suggest that the application of fossils as minima or maxima on molecular phylogenies should be supplemented or supplanted by combined evidence analyses whenever possible.

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Divergence time estimation using fossils as terminal taxa and the origins of Lissamphibia.

As the chronicle of plate motions through time, paleogeography is fundamental to our understanding of plate tectonics and its role in shaping the geology of the present-day. To properly appreciate the history of tectonics—and its influence on the deep Earth and climate—it is imperative to seek an accurate and global model of paleogeography. However, owing to the incessant loss of oceanic lithosphere through subduction, the paleogeographic reconstruction of ‘full-plates’ (including oceanic lithosphere) becomes increasingly challenging with age. Prior to 150 Ma ∼60% of the lithosphere is missing and reconstructions are developed without explicit regard for oceanic lithosphere or plate tectonic principles; in effect, reflecting the earlier mobilistic paradigm of continental drift. Although these ‘continental’ reconstructions have been immensely useful, the next-generation of mantle models requires global plate kinematic descriptions with full-plate reconstructions. Moreover, in disregarding (or only loosely applying) plate tectonic rules, continental reconstructions fail to take advantage of a wealth of additional information in the form of practical constraints. Following a series of new developments, both in geodynamic theory and analytical tools, it is now feasible to construct full-plate models that lend themselves to testing by the wider Earth-science community. Such a model is presented here for the late Paleozoic (410–250 Ma) together with a review of the underlying data. Although we expect this model to be particularly useful for numerical mantle modeling, we hope that it will also serve as a general framework for understanding late Paleozoic tectonics, one on which future improvements can be built and further tested.

Plate Tectonics in the Late Paleozoic

Fluvial landscapes diversified markedly over the 250 million years between the Cambrian and Pennsylvanian periods. The diversification occurred in tandem with the evolution of vascular plants and expanding vegetation cover. In the absence of widespread vegetation, landscapes during the Cambrian and Ordovican periods were dominated by rivers with wide sand-beds and aeolian tracts. During the late Silurian and Devonian periods, the appearance of vascular plants with root systems was associated with the development of channelled sand-bed rivers, meandering rivers and muddy floodplains. The widespread expansion of trees by the Early Pennsylvanian marks the appearance of narrow fixed channels, some representing anabranching systems, and braided rivers with vegetated islands. We conclude that the development of roots stabilized the banks of rivers and streams. The subsequent appearance of woody debris led to log jams that promoted the rapid formation of new river channels. Our contention is supported by studies of modern fluvial systems and laboratory experiments. In turn, fluvial styles influenced plant evolution as new ecological settings developed along the fluvial systems. We suggest that terrestrial plant and landscape evolution allowed colonization by an increasingly diverse array of organisms.

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Palaeozoic landscapes shaped by plant evolution

The origin of tetrapods from their fish antecedents, approximately 400 million years ago, was coupled with the origin of terrestrial locomotion and the evolution of supporting limbs. Polypterus is a member of the basal-most group of ray-finned fish (actinopterygians) and has many plesiomorphic morphologies that are comparable to elpistostegid fishes, which are stem tetrapods. Polypterus therefore serves as an extant analogue of stem tetrapods, allowing us to examine how developmental plasticity affects the ‘terrestrialization’ of fish. We measured the developmental plasticity of anatomical and biomechanical responses in Polypterus reared on land. Here we show the remarkable correspondence between the environmentally induced phenotypes of terrestrialized Polypterus and the ancient anatomical changes in stem tetrapods, and we provide insight into stem tetrapod behavioural evolution. Our results raise the possibility that environmentally induced developmental plasticity facilitated the origin of the terrestrial traits that led to tetrapods. The most primitive extant bony fish, Polypterus, exhibits adaptive plasticity for life on land when raised on land rather than in water, suggesting that environmentally induced phenotypic plasticity might have facilitated the macroevolutionary transition to life on land. Bichirs (genus Polypterus) are primitive ray-finned fish found in Africa — and sometimes in home aquaria — that have functional lungs derived from the swim bladder and powerful pectoral fins that provide support during occasional forays ashore. This study takes Polypterus senegalus as a model for the immediate ancestors of tetrapods and quantifies the anatomical and behavioural changes that occur when these fish are 'terrestrialized'. When raised on land, bichirs lift their heads higher off the ground, deploy their forelimbs closer to the midline and slip around much less often than those raised underwater and prompted to walk ashore for the first time. These observations, together with changes in bone structure and musculature, suggest that some of the postural changes seen in the earliest tetrapods, or rather their immediate antecedents, might have been made in response to the environment and assimilated by developmental plasticity.

Developmental plasticity and the origin of tetrapods.

The fossil record of the earliest tetrapods (vertebrates with limbs rather than paired fins) consists of body fossils and trackways. The earliest body fossils of tetrapods date to the Late Devonian period (late Frasnian stage) and are preceded by transitional elpistostegids such as Panderichthys and Tiktaalik that still have paired fins. Claims of tetrapod trackways predating these body fossils have remained controversial with regard to both age and the identity of the track makers. Here we present well-preserved and securely dated tetrapod tracks from Polish marine tidal flat sediments of early Middle Devonian (Eifelian stage) age that are approximately 18 million years older than the earliest tetrapod body fossils and 10 million years earlier than the oldest elpistostegids. They force a radical reassessment of the timing, ecology and environmental setting of the fish-tetrapod transition, as well as the completeness of the body fossil record.

Tetrapod trackways from the early Middle Devonian period of Poland

Palaeoenvironments of the Eifelian dolomites with earliest tetrapod trackways (Holy Cross Mountains, Poland)

A glimpse of a fish face — An exceptional fish feeding trace fossil from the Lower Devonian of the Holy Cross Mountains, Poland

The placoderm sandstone (Emsian, Holy Cross Mountains) exposed in the abandoned quarry at Podlazie Hill was revisited and excavated during fieldwork conducted in 2011-2013 Bone-bearing breccias were identified for the first time at this site and subjected to taphonomic analysis Vertebrate remains are dominated by heterostracans, while true placoderms compose less than 20% of the total vertebrate assemblage The high degree of fragmentation of the bones and low degree of abrasion indicate that the remains were reworked and transported before final burial This is consistent with the mixed character of the bone accumulations, which comprise both open-shelf forms (acanthodians, chondrichthyans) as well as those related to marginal-marine environments (placoderms and sarcopterygians) The bone-bearing succession has been subdivided into five depositional facies attributed to a coastal lagoon influenced by stormy, possibly tidal conditions The occurrence of the invertebrate trace fossil Ilmenichnus sp accompanied by Lockeia and Monomorphichnus supports this interpretation

https://gq.pgi.gov.pl/article/download/9323/pdf_1183

Storm origin of bone-bearing beds in the Lower Devonian placoderm sandstone from Podlazie Hill (Holy Cross Mountains, central Poland)

Opinions differ on whether the evolution of tetrapods (limbed vertebrates) from lobe-finned fishes was directly linked to terrestrialization. The earliest known tetrapod fossils, from the Middle Devonian (approximately 390 million years old) of Zachelmie Quarry in Poland, are trackways made by limbs with digits; they document a direct environmental association and thus have the potential to help answer this question. However, the tetrapod identity of the tracks has recently been challenged, despite their well-preserved morphology, on account of their great age and supposedly shallow marine (intertidal or lagoonal) depositional environment. Here we present a new palaeoenvironmental interpretation of the track-bearing interval from Zachelmie, showing that it represents a succession of ephemeral lakes with a restricted and non-marine biota, rather than a marginal marine environment as originally thought. This context suggests that the trackmaker was capable of terrestrial locomotion, consistent with the appendage morphology recorded by the footprints, and thus provides additional support for a tetrapod identification.

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Piotr Szrek

Papers

Tetrapod trackways from the early Middle Devonian period of Poland

Palaeoenvironments of the Eifelian dolomites with earliest tetrapod trackways (Holy Cross Mountains, Poland)

A glimpse of a fish face — An exceptional fish feeding trace fossil from the Lower Devonian of the Holy Cross Mountains, Poland

Storm origin of bone-bearing beds in the Lower Devonian placoderm sandstone from Podlazie Hill (Holy Cross Mountains, central Poland)

Non-marine palaeoenvironment associated to the earliest tetrapod tracks