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

To access this post, you must purchase Annual subscription, 12 Month Subscription or Monthly subscription.

Jade: Imperial green gem of the East (Part 1) – mining the gem

Sonja McLachlan (UK) In this, the first of a five-part series exploring the mineral Jade, I will explore  the various locations around the world in which Jade is found and mined. The world geography of jade mining Imperial jade, in all the colours and forms in which it is found, has appealed to many Eastern cultures since early times. It has been extensively mined and collected across the ages by many different people. However, in 1863, it was finally realised that the name “Jade” was being applied to two different minerals: jadeite and nephrite. Both jadeite and nephrite deposits are found in various places around the world. However, the jadeite mineral is much more rare than nephrite and, therefore, has a greater value to both the miner and collector. Nephrite deposits Nephrite jade deposits have been found in Khotan and Yarkand in Turkestan in China. Khotan is a city oasis and located on the famous “Jade” or “Silk Road”. New Zealand jade or “Pounamu” is found only in river boulders on the South Island. Deposits are also found in the Swiss Alps at Salux, Val de Faller, Poschiaro and the Gottard Range. Nephrite jade has been found in British Columbia, Canada where it is surface-mined. Large-scale mining began in Canada in 1995 and    currently  approximately 100  tonnes  a  year  are  mined and  sent  to  China. The finest jade found here is called “Polar Jade” and is especially translucent and green, which is rare in nephrite specimens. Jadeite deposits The most … Read More

To access this post, you must purchase Annual subscription, 12 Month Subscription or Monthly subscription.

Fossil folklore: Molluscs

Paul D Taylor (UK) The final article of this series on fossil folklore focuses on molluscs, excluding the ammonites, which were covered earlier (see Fossil folklore: ammonites in Deposits, Issue 46, pp. 20–23). Molluscs are second only to arthropods in the number of species living today and the resistant calcareous skeletons possessed by the majority of species accounts for their extremely rich fossil record. Most fossil molluscs belong to one of three major groups – bivalves (oysters, clams and so on), gastropods (snails and slugs) and cephalopods (ammonites, belemnites and so on). Added to these are a few minor groups, such as the monoplacophorans and scaphopods (tusk shells). Fossil molluscs are usually recognisable instantly as belonging to this phylum because of their close similarities with the shells of familiar species of modern molluscs. Some, however, are not quite so straightforward. These are more likely to have been the sources of fanciful stories about their origins and significance. Among the more obscure ancient molluscs are those dubbed ‘difficult fossils’ by Martin Rudwick in the context of the early history of palaeontology and doubts over the origin of fossils. They include the solid internal casts (steinkerns) formed by lithification of sediment enclosed by the shell and subsequent loss of the defining shell itself. In addition, there are some mollusc fossils – notably belemnite guards – that bear little resemblance to any living species, adding to their enigmatic nature. Belemnites: thunderbolts and Devil’s Fingers The first fossils I ever came across were belemnites … Read More

To access this post, you must purchase Annual subscription, 12 Month Subscription or Monthly subscription.

What’s so special about South Devon?

Professor John CW Cope (National Museum of Wales, Cardiff UK) Take a trip to the South Devon coast around Easter time and you are bound to come across student parties from universities engaged in fieldwork. What is it about this area that makes it so popular as a centre for this? The simple answer lies in a single word — variety. There is probably no other area in the UK where such a wide variety of rock types and ages is well-exposed in such a small geographical compass. Let’s have a look at some of the factors. The geological succession The oldest rocks exposed in South Devon are of Devonian age and, unlike many other areas of the UK, the Devonian rocks are in marine facies virtually throughout. Looking back over the history of geology, the age of these rocks had initially proved difficult to identify and it was only after Murchison had seen the marine successions in The Rhineland and Russia that he realised that these marine rocks were the equivalent of the Old Red Sandstone farther to the north. The Devonian rocks present a variety of marine facies, with the Middle Devonian limestones being of particular note. The limestones are a local development whose presence, in an otherwise deeper water succession, is due entirely to local shallowing of the water caused by thicknesses of volcanic rocks extruded along extensional fault lines as the local basins developed. This shallowing allowed reef-building organisms to flourish and the principal ones of … Read More

To access this post, you must purchase Annual subscription, 12 Month Subscription or Monthly subscription.

First description of dinosaur fossils by Al-Andalusī in the twelfth century

Dr Ahmed K Al-Rawi (The Netherlands) Western sources refer to a few scholars who were the pioneers in describing huge fossilised animals that are now known to be the remains of the long extinct dinosaurs. Around 1677, the British scholar, Robert Plot, was widely believed to have written the first description of a dinosaur fossil, after finding a fossilised object, which looked like the bones of a giant creature (Haven, 2007, p. 67; Parsons, 2004, p.15; Fastovsky & Weishampel, 2009, p. 309; Martin, 2009, p. 57). However, Plot was not able to identify the fossil, assuming first that it belonged to an elephant; and he later suggested that it belonged to giant human beings: “There happily came to Oxford while I was writing of this, a living Elephant to be shown publickly at the ACT, An. 1676, with whose Bones … I compared ours; and found those of the Elephant not only of a different Shape, but also incomparably different to ours, though the Beast were very young and not half grown. If then they are neither the Bones of Horses, Oxen, nor Elephants, as I am strongly persuaded they are not… It remains, that (notwithstanding their extravagant Magnitude) they must have been the bones of Men or Women: Nor doth any thing hinder but they may have been so, provided it be clearly made out, that there have been Men and Women of proportionable Stature in all Ages of the World, down even to our own Days” (Plot, 1677, … Read More

To access this post, you must purchase Annual subscription, 12 Month Subscription or Monthly subscription.