Fossil Focus: Xiphosura

Fossil Focus
by Jason A. Dunlop*1 Introduction: The Xiphosura are commonly known as horseshoe crabs because the front part of their bodies is horseshoe-shaped. They have sometimes been called king crabs, although this name is also used for a group of large true crabs. Despite their various common names, xiphosurans are not crustaceans. Older studies assumed that they were some sort of crab, mostly because they have gills and live in the sea, but careful anatomical studies towards the end of the nineteenth century showed that they are actually more closely related to arachnids. The name Xiphosura means ‘sword tail’ and refers to another obvious feature of these animals: a long, pointed tail spine. Horseshoe crabs — especially earlier fossil ones — also look quite a lot like trilobites. This has led to

Life as a Palaeontologist: How I learnt to stop worrying and love the fossils

Life as a Palaeontologist
by Sarah King*1 Introduction: If you’re visiting this website, the chances are that you’re interested in palaeontology, perhaps even as a career. However, to someone who is not yet in academia, it may be difficult to imagine how to embark on such a career path, and the world of science can seem strange and inaccessible. Even though this perception is beginning to change, as science becomes more entrenched in the public consciousness — by means of popular television and radio programmes, among other things — and the public rightly demands to know where its money is being spent, the process of becoming a professional scientist and the day-to-day routine of a palaeontologist are still generally unknown to the majority of people. This article aims, in some small way, to rectify this. It w

Patterns in Palaeontology: Parsimony and Palaeobiology

Patterns in Palaeontology
by Javier Ortega-Hernández *1 Introduction: The principle of parsimony, also known as Occam’s razor, has been widely attributed to the English Franciscan friar William of Occam (c. 1288–1348). It states Pluralitas non est ponenda sine necessitate, which translates to ‘Plurality is not to be assumed without necessity’. In other words, when one is faced with a problem or question that can have several different answers, the solution that requires the fewest assumptions is most likely to be correct, unless there is evidence that proves that it is false. Parsimony has an enduring influence in most scientific activities, as it allows researchers to make comparisons and choose between different hypotheses that aim to explain a phenomenon using the same body of evidence. The incomplete nature

Fossil Focus: The preservation of colour

Fossil Focus
by Holly E. Barden*1 Introduction: Colour is important in modern ecosystems, but the colours of extinct organisms are very rarely preserved in the fossil record. Colouration is most commonly seen in fossilized brachiopod shells and arthropod carapaces; however, establishing that these colours are original and not artefacts of fossilization processes is difficult. Until recently, few studies have attempted to do so, but within the past few years the subject has become an active area of research, with significant developments. There have been several studies investigating the morphological and geochemical evidence of pigments in birds and dinosaurs, as well as work on the colouration of insects. Such analyses have paved the way for major leaps forward in our understanding of the behaviour ...

Fossil Focus: Animal embryos

Fossil Focus
by John Cunningham*1 Introduction: Animal embryos are small (typically less than 1 millimetre across), soft and squidgy, so it was traditionally considered impossible for them to be preserved in the fossil record. However, over the past 15 years or so a series of remarkable discoveries have shown that embryos can indeed be fossilized under exceptional circumstances. The microscopic fossils that have been identified as embryos are almost exclusively from the Ediacaran and Cambrian periods, around 635 million to 488 million years ago. This spans the period of time when the major groups of animals are thought to have first appeared, so these fossils allow palaeontologists to study the embryology of some of the earliest animals, shedding light on the evolution of development. The first fo

Fossil Focus: Vertebrate tracks and trackways

Fossil Focus
by Peter Falkingham*1 Introduction: The fossilized footprints and trackways of vertebrates are often overlooked in favour of the skeletal remains of the animals that made them. At museums, for instance, many more people will crowd around the dinosaur skeletons than around the dinosaur tracks nearby, and yet fossilized tracks can provide us with information about extinct animals that is simply not available from the bones alone. A track is the result of an interaction between an animal and a surface, or substrate. The final track shape (morphology) is directly determined by three factors: Producer: the shape of the track-maker's foot Behaviour: the motion and loading (kinematics and kinetics) of that foot Substrate: the conditions of the surface when the track is made (sandy, mudd...

Fossil Focus: Arachnida

Fossil Focus
by Jason A. Dunlop*1 Introduction: Arachnida is one of the major arthropod groups. It includes spiders (Araneae), scorpions (Scorpiones), mites (Acari) and harvestmen (Opiliones), as well as a number of rarer and less familiar groups (Fig 1). The name Arachnida was introduced by the French zoologist Jean-Baptise Lamarck and is derived from Greek mythology: in one story, the maiden Arachne challenged the goddess Athene to a weaving contest, and was subsequently transformed into a spider — condemned to weave for evermore. There are about 100,000 living species of arachnids, with mites and spiders representing the most diverse and species-rich groups. Fossil arachnids are considerably rarer, with more than 1,700 described species (well over half of which are spiders) and a record that exten

Fossil Focus: Chasmataspidida

Fossil Focus
by Jason A. Dunlop*1 Introduction: Chasmataspidida (Fig 1) are rare, extinct arthropods known only from the early to mid Palaeozoic Era. They are probably closely related to either xiphosurans (horseshoe crabs; Fig 2) or eurypterids (sea scorpions; Fig 1); some chasmataspid fossils were originally misinterpreted as members of one of these two groups. They were first discovered in the 1950s, and were only recently recognized as a group distinct from horseshoe crabs. Chasmataspids are currently the oldest known examples of the Euchelicerata lineage —all Chelicerata except Pycnogonida (sea spiders) — and palaeontologists date the origins of these euchelicerates back to at least the late Cambrian Period. Morphology: Most chasmataspids are a few centimetres long. The body is divided int

Patterns in Palaeontology: The Paleocene–Eocene Thermal Maximum

Patterns in Palaeontology
by Phil Jardine*1 Introduction: The Paleocene–Eocene Thermal Maximum (PETM) is one of the most intense and abrupt intervals of global warming in the geological record. It occurred around 56 million years ago, at the boundary between the Paleocene and Eocene epochs. This warming has been linked to a similarly rapid increase in the concentration of greenhouse gases in Earth’s atmosphere, which acted to trap heat and drive up global temperatures by more than 5 °C in just a few thousand years. The fossil record gives us the means of understanding how life was affected by the PETM, and so provides an excellent opportunity to study the relationships between evolution, extinction, migration and climate change. The early Palaeogene world: At the time of the PETM, the world was already much w

Fossil Focus: Coal swamps

Fossil Focus
by Ben Slater*1 Introduction: Coal swamps are the classical terrestrial (land-based) ecosystems of the Carboniferous and Permian periods. They are forests that grew during the Palaeozoic Era (encompassing the Carboniferous and Permian) in which the volume of plant biomass dying and being deposited in the ground was greater than the volume of clastic (grains of pre-existing rock) material, resulting in a build-up of peat. This was subsequently buried, and eventually turned into coal over geological time. These swamps gave rise to most of the major, industrial-grade coal reserves that are mined today. The palaeontology of these coal-forming ecosystems is well known from the Carboniferous rocks of Euramerica (modern day Europe and North America), owing to the history of coal exploitation ...