Archetypally Siluro-Devonian ichnofauna in the Cowie Formation, Scotland: implications for the myriapod fossil record and Highland Boundary Fault Movement

2021

SJG

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Two newly-discovered specimens of the fish locomotion trace Undichna (U. britannica and Undichna isp.), are described from the Middle Devonian Achanarras Limestone Member (Caithness Flagstone Group, NE Scotland). Fish trace fossils have not previously been reported from the Achanarras Limestone Member, despite decades of study of the unit as a key locality for fish body fossils. The traces comprise discontinuous sinusoidal grooves; one showing multiple parallel incisions, created by the fins of an acanthodian fish swimming close to the substrate. The apparent absence of trace fossils attributable to infaunal or epifaunal benthic organisms suggests that the sediment at the bottom of the lake was relatively inhospitable. The low ichnodiversity of the Achanarras Limestone Member is likely due to low oxygen levels in the depositional environment.Thematic collection: This article is part of the Early Career Research collection available at: https://www.lyellcollection.org/cc/SJG-early-career-research

Section: Introductionmentioning

confidence: 70%

First report of fish trace fossils ( Undichna ) from the Middle Devonian Achanarras Limestone, Caithness Flagstone Group

Tindal

Shillito

2021

SJG

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“…The low ichnodiversity and ichnodisparity of the BVG trackways means that they share few similarities with the diverse trackways and infaunal traces known from Silurian-Devonian non-marine strata, and which record the major global onset of arthropod-sediment interactions on land (Minter et al, 2016;Shillito and Davies, 2017). Statistical comparison reveals stronger similarities with other Cambrian-Ordovician subaerial trace fossil sites ( Fig.…”

Section: Tracemaker Behaviormentioning

confidence: 96%

Death near the shoreline, not life on land: Ordovician arthropod trackways in the Borrowdale Volcanic Group, UK

Shillito

2018

Geology

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The Borrowdale Volcanic Group of northern England hosts Late Ordovician arthropod trackways that are frequently cited as the earliest unequivocal evidence for animal life on land, and provides a key geological locality for our understanding of global myriapod evolution and terrestrialization. Original fieldwork at the trace fossil site has identified four additional bedding surfaces that yield 121 new trackways at the site (of a total 158 known individuals), and permit better sedimentological and paleoecological contextualization of the trackways. Contrary to published claims, none of the trackways occur in sandstones but are invariably preserved on bedding planes of dacitic tuffs. Trackway morphology comprises either short straight track segments with discernable footprint impressions (Diplichnites), long looping traces suggesting dragging and footprint amalgamation (Diplopodichnus), or transitional forms. Morphometric comparison of the Diplopodichnus with fossil and recent mortichnia (death traces) suggests they record immediate pre-mortem locomotion of dying myriapods, and modern analogue reveals mechanisms by which abundant volcanic ash within the environment would have elevated arthropod mortality rates. Sedimentary structures including wave ripples, bedding sags and detached large-scale ball-and-pillow structures, show that the tuffs were deposited subaqueously. One newly-discovered instance where trackways intermittently traverse 3-5 cm tracts of subaerially-exposed wave-ripple crestlines attests that the tracemakers were capable of surviving out of water over very short distances. However, the low diversity, semi-subaqueous ichnofauna has greater similarity with other Cambrian and Ordovician sites, recording pioneer tracemakers with limited tolerance of subaerial environments, than it does with the oldest preserved fully-terrestrial trace fossil communities from the Silurian and Devonian. TRACKWAYS OF THE BORROWDALE VOLCANIC GROUP The Borrowdale Volcanic Group (BVG) is a 6 km-thick Upper Ordovician (Sandbian-Katian) succession of volcanic and related rocks that crops out in Cumbria, NW England, and which accumulated in an arc setting associated with subduction of the Iapetus Ocean (Barnes et al., 2006). Trace fossils were first discovered within the group by Mitchell (1956, p. 434), who reported "animal-tracks" on bedding planes at Lum Pot; a 150 m-long outcrop along the River Lickle, which exposes a near-continuous 25 m-thick stratigraphic section from the upper BVG (likely within its constituent Wallowbarrow Tuff Formation (Fig. 1; see Appendix)). The trace fossils were later identified as Diplichnites and Diplopodichnus by Johnson et al. (1994), who described them on the basis of 34 trackways on a 1.9 m2 bedding plane at Lum Pot and 3 trackways on the 0.1 m2 surface of a loose clast from Sour Milk Gill, 19 km north of the original locality. Johnson et al. (1994) documented that the trackways occurred in sandstone, which they interpreted as having been deposited in a freshwater lacustrine environment. S...

“…9A). This particular structure is not unequivocal, and it could also be explained as an instance of an invertebrate burrow (such structures also appearing in alluvial settings for the first time in the early Lochkovian: e.g., Minter et al, 2016;Shillito and Davies, 2017). However, favouring the former over the latter is the slight irregularity to its form, coupled with its context, descending from the base of the same bartop shales that yield parautochthonous cf.…”

Section: Rooting Tracesmentioning

confidence: 99%

The Devonian landscape factory: plant–sediment interactions in the Old Red Sandstone of Svalbard and the rise of vegetation as a biogeomorphic agent

Berry

Marshall

et al. 2021

JGS

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The Devonian Period was a crucial interval in the evolution of plants. During its 60 myr duration, it witnessed the successive evolution of roots, wood, trees and forests, and many of the biogeomorphic phenomena that operate in modern terrestrial environments came online for the first time. The Old Red Sandstone (ORS) of Svalbard consists of a near-continuous Silurian to Late Devonian record of land plant-colonized sedimentary environments and provides a perfect natural laboratory to aid understanding of the facies signatures and evolution of these phenomena. Here we describe and illustrate a catalogue of ORS features that provide evidence for the stepwise appearance of novel plant-sediment interactions, including: preserved plant material and rooting structures, early large woody debris accumulations, cannel coal deposits, and the oldest known vegetation-induced sedimentary structures, in addition to vegetation-influenced motifs of elevated mudrock content and complex alluvial sand bodies. These characteristics are combined to reconstruct changes to non-marine environments in this Devonian ‘landscape factory’. In addition to tectonic and climate influences, plant evolution first served as a control on the construction of the sedimentary record during this period and has persisted as a fundamental influence on Earth surface processes and landforms ever since.