Caught between two mass extinctions: The rise and fall of Dicroidium

Chris Mays and Stephen McLoughlin (Sweden) In the aftermath of Earth’s greatest biotic crisis 251.9 million years ago – the end-Permian mass extinction – a group of plants arose that would come to dominate the flora of the Southern Hemisphere. Recovery of the vegetation from the end-Permian crisis was slow; but steadily, one group of seed plants, typified by the leaf fossil Dicroidium, began to diversify and fill the dominant canopy-plant niches left vacant by the demise of the Permian glossopterid forests (Fielding et al., 2019). Eventually, Dicroidium re-established a rich peat-forming vegetation across Gondwana through the Late Triassic, dominating the flora between 30°S and the South Pole (Kustatscher et al., 2018). Indeed, few fossil plant assemblages of this age can be found in Gondwana that do not contain this plant. The importance of Dicroidium is not just its role in showing biogeographic and tectonic linkages between southern lands or its value in determining the age of continental strata. Dicroidium and its associated plant groups were so successful that they were major contributors to the development of thick coal seams in the Late Triassic that are now mined to produce electricity. Although Dicroidium is generally envisaged as a plant of cool temperate climates, the very first fossils that might belong to this group are from the Permian-Triassic transition of Jordan, located near the palaeoequator (Blomenkemper et al., 2018). Nevertheless, the distribution of Dicroidium soon shifted to high southern latitudes in the Early Triassic and they overwhelmingly dominated the southern vegetation … Read More

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Triassic beasts and where to find them

Sue Beardmore (UK) Located amid the scenic Southern Alps, on the Swiss-Italian border, is Monte San Giorgio, a mountain that rose up like many across Central Europe as a result of continental collision between Africa and Europe during the Alpine Orogeny. It is not particularly big or distinct by alpine standards but it is special, a status emphasised by the designation of its slopes as a UNESCO World Heritage site initially in 2003 for the Swiss part with the neighbouring Italian area added in 2010. To begin, the rocks outcropping on the mountain form an almost complete stratigraphic sequence from the Permian through to the Jurassic (Fig. 1), not only an extended interval of time but an important one around the massive Permo-Triassic extinction. The same rocks provide a context for the equally important Middle Triassic vertebrate, invertebrate and plant fossils, now numbering more than 20,000, that have been found at the locality over the last 170 years. Fig. 1. A stratigraphic section of the rocks at Monte San Giorgio. © Commissione Scientifica Transnazionale Monte San Giorgio, 2014. In particular, it is the diversity, relative abundance and excellent preservation of the vertebrate fossils that has thrown the locality into the spotlight. These occur in six main fossiliferous horizons deposited in a shallow marine basin, the Monte San Giorgio Basin, one of many depressions on a carbonate platform between the Eurasian continent to the north and west, and the open waters of the vast Tethys Ocean to the south and east. … Read More

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Daily lives of fossil reptiles

Robert Coram (UK) The Mesozoic and Cenozoic deposits of Southern England have long been a rich source of fossil reptiles. Past finds of great historical importance include some of the earliest known examples of dinosaurs, ichthyosaurs and pterosaurs. Fossil material, including new species, continues to be revealed, mainly at rapidly eroding coastal sites. All these reptiles would have been active participants in their local ecosystems, whether on land or in the sea. Much information about the roles they played and their interactions with other organisms can be gleaned from their skeletal anatomy and from comparison with living relatives such as crocodiles. What this article is concerned with, however, is evidence of specific incidents in the lives, and deaths, of individual reptiles; tiny snapshots of opportunities, mishaps and the daily drudge of staying alive. These add more detail and colour to our knowledge of the lifestyles of these long-vanished animals. This evidence will be provided by four selected terrestrial and marine deposits from southern England, spanning the last quarter of a billion years of Earth history (Fig. 1). Fig. 1. Geological map showing locations of deposits discussed in the text. (1) Triassic Otter Sandstone of South Devon; (2) Jurassic Lower Lias of the Somerset (a) and Dorset (b) coasts; (3) Cretaceous Wealden beds of the Isle of Wight (IOW on map); and (4) Paleogene Hamstead beds of the Isle of Wight. Trace fossils in a desert world – the Triassic Otter Sandstone Rocks dating from the Triassic period, laid down between … Read More

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Jurassic Coast (or is it?) with the Geologists’ Association

Mervyn Jones (UK) Since 2012, the Geologists’ Association (GA) has put on annual field trips to the Dorset coast led by Prof John CW Cope (of the National Museum Wales), who is author of the definitive Field Guide No 22. The second edition was published in April 2016 (Geology of the Dorset Coast (2nd ed)). In fact, the trips were started to celebrate the publication of the first edition of the guide. The Dorset Coast is often equated with the ‘Jurassic Coast’ when, in fact, the geology stretches from the topmost Triassic, near the Devon border, through Jurassic and Cretaceous successions, to Eocene deposits at Studland. For this and other reasons, it attracts amateur geologists in large numbers. John’s guide provides essential information including descriptions of the succession and practical guidance about access. What’s missing are the entertaining stories that John Cope can provide and the context provided by exploring inland a bit. Day 1 – Saturday (1 October) For our fifth field meeting, we met up in Lyme Regis (in the car park next to the newly-restored house originally owned by John Fowles – see below) – a town to stir the heart of any geologist. Our mission for the weekend was to look at the unconformity below the Cretaceous, as it oversteps the older Jurassic and Triassic strata progressively in a westerly direction. En route, we observed the instability of the cliffs and suffered the same ourselves, as we scrambled over the boulders and shingle. On this occasion, … Read More

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Invertebrate fossils from the Lower Muschelkalk (Triassic, Anisian) of Winterswijk, The Netherlands

Henk Oosterink (The Netherlands) During the Muschelkalk part of the Ansian (240mya), the Central European area (Germany, Poland, Denmark, The Netherlands and north-eastern France) was covered by a shallow sea, referred to as the Muschelkalk Sea. While there were frequent regressions and transgressions (leading to both marine and terrestrial fossil being present in these regions), it is from this sea that the limestones from this quarry were deposited and in which most of the fossilised animals discussed in this article lived. The quarry in the Muschelkalk at Winterswijk, in the east of the Netherlands (Fig. 1), is especially well known for the skeletons, bones, footprints and tracks of Middle Triassic reptiles. I wrote about these in Issues 15 and 20 of Deposits. However, fossils of invertebrates, such as molluscs, brachiopods and arthropods can also be found. Included in the molluscs are bivalves, cephalopods and gastropods, and from the brachiopods, the Inarticulata are present. From the arthropods, there are Malacostraca, Merostomata and insects. Fig. 1. Lower Muschelkalk quarry near Winterswijk (Eastern Netherlands). Mollusca Bivalves Some strata contain a large number of moulds of bivalves. These are situated quite high in the profile and, if you find this level, it is important to split the rock along an irregular dark-grey line (Fig. 2). If you do this, you will find the moulds of the convex upper side of the separated shells on one slab, with the negative impression visible on the other. This makes clear that these are valves swept together by … Read More

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Giant trilobites and biotite nodules in Portugal

Peter Perkins (UK) The generally accepted reason for the fame of Arouca is Princess Mafalda, born 1195, who was responsible for the convent becoming Cistercian. Here is an interesting story – she was beatified in 1793. However, I won’t go into that now, but it is well worth investigating. For this article, there are other reasons for its fame, at least among geologists. Arouca is 38km to the south east of Oporto, in northern Portugal, and gives its name to one of two geoparks in Portugal. In Arouca Geopark (Fig. 1), which has an area of 330km2 (just a little smaller than the Isle of Wight), there are two quite remarkable geological features, one palaeontological and the other concerning igneous petrology. Fig. 1. Map of Arouca Geopark. A geopark is an area of significant size that has a particular geological heritage, with a certain number of sites of special importance – scientific quality, rarity, aesthetic appeal and educational value. It must also have a sustainable strategy for development to be accepted as a member of the worldwide network of geoparks. There are 42 in Europe, in 16 countries. The other Portuguese Geopark is Naturtejo, through which the River Tagus flows. There are nine geoparks in the British Isles, for example, NW Highlands (Scotland), Copper Coast (Ireland), Fforest Fawr (Wales) and the English Riviera. The website, http://www.europeangeoparks.org, gives website addresses for all. The geology of Portugal is very complex. There are no strata younger than Triassic, except for Holocene deposits in … Read More

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Dinosaurs footprints on the Isle of Skye, Scotland

Mark Wilkinson (UK) If you think of dinosaur hunting, you probably imagine trekking through a parched landscape, reaching the crest of a low hill and catching the first glimpse of a complete skeleton lying half exposed in the next depression. While this might just be true in some parts of the world, the reality of hunting for dinosaurs in Scotland could not be much more different. Hence, a cold and damp day in April 2015 found a small group of geologists from the University of Edinburgh on a slippery foreshore on the northwest extremity of the Isle of Skye. We were hoping not for complete skeletons but, if we were lucky, an occasional bone or tooth – well, perhaps we were hoping, but plenty of geologists have been here before, so the chances of a large find seemed pretty slim. Having said that, the total number of dinosaur bones that have been found in Scotland is still small, so that any bone is likely to be of interest – and could well be a new species, or evidence that a larger taxonomic group known from elsewhere was present on the island in the Jurassic. To add extra scientific interest, the exposures on Skye include a thick Middle Jurassic sequence, representing a time of a rapid dinosaur evolution, but with a poor fossil record worldwide. So any find might be of great importance. We visited several locations on the excursion. There are well-known dinosaur footprints at Staffin Bay on the east … Read More

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Triassic salt in the High Atlas of Morocco

Chellai El Hassane (Morocco), Ghanmi Mohamed (Tunisia) and Doblaas Miguel (Spain) The Triassic terrestrial deposits at the northern edge of the High Atlas near Marrakech are mainly represented by thick sequences of massively layered, red sandstone. These are topped by a formation of silt and pink-brown clay containing large deposits of evaporites consisting mainly of rock salt and gypsum. The silt and clay formations form domed structures characterised by intruded gypsum and irregular (disharmonic) folds capped by fine sandstone beds, as well as by small, isolated anticlines only a few metres in scale. The direction of folding shows no relationship to that of the major tectonic folding that gave rise to the Atlas Mountains. In contrast, the folding is closely linked to the deposition of rock salt and gypsum in the High Atlas near Marrakech during the Late Triassic. The same phenomenon is observed in the passive margins of the Atlantic of western Morocco. Lithostratigraphy These Triassic formations are the most prominent features of the landscape, with thicknesses that can reach up to 400m. They consist essentially of two formations: F5 (the Oukaïmeden sandstone) and F6 (the Superiors Silts), which correspond to the uppermost part of the Triassic, as defined in the Ourika valley by Biron (1982). The first formation consists of thick (400m) beds of detrital sandstones with fine to medium-sized, diamond-shaped sedimentary bodies, interbedded with layers (a few centimetres to several metres thick) composed of red clay as well as red and brown silts. These are overlain by … Read More

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Triassic reptiles from the Lower Muschelkalk of Winterswijk

Henk Oosterink (Netherlands) The Lower Muschelkalk (from the Anisian age of the Middle Triassic) of the quarry at Winterswijk in The Netherlands is well known for its beautiful and sometimes abundant finds of reptile footprints and bones. A few, almost complete, skeletons have even been found. Most of the bones come from marine reptiles within the Sauropterygia (that is, ‘winged lizards’, referring to their paddle-like flippers) group. The quarry is one of the most important sites for Triassic reptiles in the world. Every year, between 2,000 and 3,000 people visit this quarry on excursions and during open days, most being fossil collectors. Many new forms of life The Triassic Period is characterised by an explosive development of many reptile groups. For instance, at the end of this period, the dinosaurs appeared. Many new forms of life developed in terrestrial and marine environments. In the Tethys Ocean and its epicontinental seas, some reptiles adopted a semi-aquatic lifestyle allowing them to be functional in the sea as well as on land. Many of these reptiles belonged to the Sauropterygia. Sauropterygians are diapsids – reptiles are divided into two groups, anapsids that include turtles and diapsids that have two holes in the skull behind the orbit. Their skulls have upper temporal openings and, on the back of the skull, the quadrate is immovable and is connected to the squamosal. The sauropterygians lived mainly in the sea, but they did come ashore, for instance, to lay their eggs. This reptile group appears for the … Read More

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Natural wonders of the Maghreb in Morocco

Sebastian Lüning (UK) Morocco is a popular tourist destination. Most people travel to the white beaches of Agadir to sunbathe and relax, to watch the magicians on Djemaa el-Fna square in Marrakech, or to go shopping in the UNESCO-protected Osouk of Fes. However, Morocco has much more to offer. Some of the most attractive specimens found at international fossil fairs originate from this country. Morocco is home to exceptionally well-preserved trilobites and attractive Orthoceras assemblages from the Palaeozoic. The beds containing these fossils are systematically mined in the Anti-Atlas. Other fossils, such as goniatites and ammonites, complement the diverse palaeontological national treasure. Fig. 1. Location map of geological sites mentioned in this article. 1) granites near Tafraoute, 2) algal mats near Ouarzazate, 3) Ordovician glaciation, 4) Silurian graptolithic shales, 5) Orthoceras limestones, 6) Devonian mud mounds and Merzouga sand dunes, 7) Triassic Argana river sands, 8) Cascades d’Ouzoud, 9) Friouato karst shaft, 10) Dades Gorge, 11) blowholes near Agadir and Cretaceous oysters, 13) Amesfrane cliff. These fossils are part of an exciting geological past. This article aims to guide you through the highlights of Morocco’s geological history, exploring the stories behind the country’s natural wonders and its multi-million-year-old inhabitants. Concealed in its spectacular mountain chains are some fascinating snapshots from the past. Our trip will commence at the very beginning of this history and will take us gradually forward through time. We will visit various sites on a route starting in the Precambrian of the Anti-Atlas, in the southern part … Read More

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Triassic fossils of West Texas

Rick Day (USA) I found my first Triassic fossil when I was about 15 years old on a backpacking trip in Tule Canyon, Briscoe County in Texas. After setting up camp, I walked over to a small, red-coloured hill. On its slope, I found a small, unusual bone fragment approximately 5cm by 5cm by 1cm and I remember being really excited. It was the first petrified bone I had ever found and it seemed strange to me. The bone fragment was flat on one side and had dimples and pits on the other side. It just didn’t look like anything I had ever seen before. Fig. 1. My first phytosaur skull. All the teeth and part of the rostrum is restored. Leptosuchus? I carried this unusual bone fragment in the glove compartment of my car for years, hoping to find someone who could identify it. However, I was never able to find anyone who knew anything about the fossil. Eventually, I became interested in geology and learned for myself the geology and paleontology of the region where I live. This eventually led to my becoming a science teacher. In time, I was able to identify my strange little fossil bone as being a scute fragment from the back armour of a Thecodont Reptile called an Ateosaur. (A “scute” is thickened, horny or bony plate that can be seen today on the shells of turtles or on the backs of crocodiles.) For those unfamiliar with Ateosaurs, these were the heavily armored … Read More

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