Concretions in sandstones of the Inner Hebrides, Scotland

Mark Wilkinson (UK) Concretions are a common feature in many sedimentary rocks, yet they seem sometimes to be misunderstood. So, how do concretions form? As well-studied examples, let’s look at the ones found in some of the sandstones of the Scottish Inner Hebrides, notably the islands of Eigg and Skye. The concretions are found in several formations, but perhaps the largest and most spectacular are in the Valtos Sandstone Formation of the Great Estuarine Group. This was originally named the Concretionary Sandstone Series after the prominent metre-scale concretions. It is Bathonian in age (Middle Jurassic) and is interpreted as having been deposited in a coastal environment. The Great Estuarine Group is becoming famous for its abundant dinosaur footprints and much rarer skeletal material. The concretions themselves vary from spherical to elongate volumes of rock and are typically from around 50cm to one metre or more in diameter. They are also often coalesced into groups (Fig. 1). Inside the concretions, the spaces between the sand grains are filled completely with a calcite cement. The concretions are resistant to weathering compared to the host sandstone, which is fairly soft, so stick out from the cliff in a sometimes rather alarming manner as you walk below them. I’ve been visiting the concretions sporadically for around 30 years and some of the ones that I photographed in the cliffs in the 1980s are now lying loose on the beach. None of them have fallen while I’ve been there, touch wood. Fig 1. Concretions on … Read More

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Headbanging, rocking and moonwalking fossils

Mats E Eriksson (Sweden) One can never be too careful when given the opportunity to name a fossil organism that has proved to be new to science. In addition to a meticulous description and accompanying images showing the characteristic traits of the fossil, a unique and formal, Latinized scientific name must be attached to the creature. Many people, who get the chance honour an older colleague or famous palaeontologist, use the name of the discovery site or region to indicate the provenance of the fossil or, of course, christen the fossil after its characteristic looks (for example, Eriksson, 2017a). But you can also glance towards completely different areas, such as the art and music scenes. As a lifelong music fan and hobby musician (who, just like many of my peers, had aspiring yet quite ludicrous ‘rock star dreams’ in my teens) and a palaeontologist by profession, I cannot help myself but feeling blissful and delighted about the possibility of joining my two passions – ‘heavy’ music and palaeontology – in ‘unholy matrimony’. This has, among other things, led me to name some extinct polychaete annelid worms (bristle worms – the marine ‘cousins’ of earth worms and leeches) from the Silurian and Devonian periods after some of my favourite ‘metal’ musicians. These largely soft-bodied animals generally have poor preservation potential, although full body fossils are known from the fossil record. However, some representatives are equipped with resistant jaws (when preserved as microfossils they are known as scolecodonts) that, by contrast to … Read More

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Worm monstrosity: A giant extinct worm

Mats E Eriksson (Sweden) In a new study published in Scientific Reports (Earth’s oldest ‘Bobbit worm’ – gigantism in a Devonian eunicidan polychaete) by Luke A Parry of Bristol University in the UK, David M Rudkin of the Royal Ontario Museum in Canada and me (Mats E Eriksson of Lund University in Sweden), an extraordinary new species of polychaetes (that is, bristle worms – the marine relatives of earthworms and leeches) is described. The new species, Websteroprion armstrongi, is unique among fossil worms and possessed the largest jaws recorded from all of earth history, reaching over one centimetre in length and thus easily visible to the naked eye. Typically, such fossil jaws are only a few millimetres in size and must be studied using microscopes. Despite being only knows from the jaws, comparison of Websteroprion armstrongi with living species suggests that this animal achieved a body length in excess of a metre. This is comparable to that of ‘giant eunicid’ species, colloquially referred to as ‘Bobbit worms’, a name that is bizarrely enough derived from the infamous story of eye-watering amateur surgery involving Lorena and John Wayne Bobbitt. Living ‘Bobbit worms’ are fearsome and opportunistic ambush predators, using their powerful jaws to capture prey, such as fish and cephalopods (squids and octopuses), and drag them into their burrows. Fig. 1. A photograph showing the holotype of Websteroprion armstrongi. (Photo by Luke Parry.) Gigantism in animals is an alluring and ecologically important trait, usually associated with advantages and competitive dominance. It … Read More

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Ghost shrimps: An abundant yet understudied fossil record

Matúš Hyžný (Slovakia) and Adiël A Klompmaker (USA) “Ghost shrimp” usually refers to decapod crustacean species from the family Callianassidae and Ctenochelidae, although sometimes the term is also used for other crustacean groups, such as caprelloid amphipods or, mostly in aquarium trading, for palaemonid shrimps. Here, we use the first definition. In that respect, ghost shrimps are soft-bodied, fossorial (burrowing) decapods with a tail (or pleon) distinctly longer than the main body (or carapace; Fig. 1). They inhabit a variety of marine environments or environments under marine influence, for example, estuaries, marshes and mangroves. Although most species living today have been described from the intertidal environment, there are numerous species dwelling in deeper waters as well. Fig.1. Ghost shrimp body plan. Glypturus acanthochirus: (A) view from above; (B) side-view; and (C) major cheliped. All scale bars 5.0mm wide. (Photos by Matúš Hyžný.) Ghost shrimps exhibit a sophisticated behaviour involving digging complex permanent or semi-permanent burrow systems, and they are important bioturbators. Because they live in high densities (in some cases up to 120/m2 of burrow openings are known), they rework huge amounts of substrate and are considered true ecosystem engineers. Bioturbation enhances organic decomposition, nutrient cycling, redistribution of organic material and oxygenation of sediment (similar to earthworms on land). Numerous organisms benefit from these changes, including bivalves, worms and other crustaceans. Additionally, many animal species live directly within the ghost shrimp burrows as their associates. Not every fossil ghost shrimp is Callianassa Fossil hunters specialising in decapod crustaceans often identify … Read More

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Weird world of fossil worm cocoons

Stephen McLoughlin, Benjamin Bomfleur and Thomas Mörs (Sweden) Fossil hunters occasionally chance upon small glossy red to amber-coloured, roughly circular objects on bedding planes, when they crack open shales that were deposited in ancient swamps and rivers. These curious fossils range from about a millimetre in diameter up to the size of a fingernail (Fig. 1). When well preserved, they are egg shaped, but, in most cases, they have been flattened to a thin flake in the rock by the weight of the overlying strata. Some specimens appear to have a net-like coating on the surface but, otherwise, they offer few clues as to their identity. Indeed palaeontologists have reported these objects for over 150 years and have variously interpreted them as the eggs of insects, parts of lichens, the food-catching devices of ancient invertebrates, the membranous coatings of seeds, or the linings of clubmoss sporangia. Many early palaeobiologists simply labelled them as ‘red eggs’ and avoided assigning them to any particular biological group. Fig. 1. A minute, acid-resistant fossil belonging (Figs. 4 and 5). We have to a category traditionally called ‘red eggs’; from the Early Cretaceous of Western Australia. These strange objects occur mostly in sediments deposited in continental settings, and they have been reported widely in the residues left over after palaeobotanists have dissolved rock samples in the search for fossil spores, pollen and leaf cuticle. Two conclusions can be gleaned from these occurrences: The mysterious fossils likely belong to a land- or freshwater-based organism; andThese objects … Read More

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