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Fossil Focus

Fossil Focus: Ammonoids

Fossil Focus
by Kenneth De Baets1, René Hoffmann2, Jocelyn A. Sessa3 and Christian Klug4. Introduction: Ammonoids (Ammonoidea) are an extinct group of marine invertebrates with an external shell. They were cephalopods, and hence closely related to modern cuttlefish, squid, octopuses and the pearly nautilus. In a non-scientific context, they are commonly called ammonites, but that term really includes only Jurassic and Cretaceous forms in its stricter scientific sense. The Ammonoidea as a whole lived from the Early Devonian to the earliest Palaeogene period, covering a timespan of about 350 million years. Normally, only their shells, also called conchs, or their internal moulds are found in the fossil record. Conchs from adult ammonoids range from about 5 millimetres to 2 metres in diameter. Due to

Fossil focus: Stuck in time — life trapped in amber

Fossil Focus
by Leyla J. Seyfullah*1 and Alexander R. Schmidt1 Introduction: Some of the most extraordinary fossils ever discovered, from insects to plants and feathers, are preserved in amber. Amber is the term for various solidified forms of plant resin that occur in the rock record. It can be found in many different colours, shapes and sizes (Fig. 1). Until the past decade, it was thought to be very rare, but new discoveries have shown that it is more abundant in terms of both geographical coverage and presence through time than was previously thought. Although many amber deposits do not contain fossils, some do. Fossils (also known as inclusions) in amber often have exquisite, three-dimensional preservation, retaining fine surface and structural details, and are frequently preserved at lea...

Fossil focus: Acanthodians

Fossil Focus
by Richard Dearden*1 Introduction: The acanthodians are a mysterious extinct group of fishes, which lived in the waters of the Palaeozoic era (541 million to 252 million years ago). They are characterized by a superficially shark-like coating of tiny scales, and spines in front of their fins (Fig. 1). The acanthodians’ heyday was during the Devonian period, about 419 million to 359 million years ago, but their fossil record stretches back to the Silurian period (around 440 million years ago). One specialized filter-feeding group, the Acanthodiformes, persisted until the end of the Permian period (about 252 million years ago), disappearing in the end-Permian mass extinction. Acanthodian fossils were first described by the eminent Swiss palaeontologist Louis Agassiz during the nineteenth c

Fossil Focus: Seals, sea lions and walruses

Fossil Focus
By Morgan Churchill*1 Introduction Pinnipeds (seals, sea lions and walruses) make up the second most numerous group of marine mammals (behind whales), with 35 species found throughout the world’s oceans and in several freshwater lakes. They are represented by 3 living families: the Phocidae (earless seals; 19 species), found around the globe; the Otariidae (sea lions and fur seals; 15 species), restricted to the North Pacific and Southern Hemisphere; and the Odobenidae (walrus; 1 species), confined to the Arctic. Two additional extinct families are recognized: the Desmatophocidae and the Enaliarctidae of the North Pacific. Pinnipeds show a variety of adaptations for aquatic living, including flippers for moving through water, changes in teeth related to capturing and feeding on slippery

Fossil Focus: Ichthyosaurs

Fossil Focus
By Ryan Marek*1 Introduction A literal translation of ichthyosaur is 'fish lizard', yet ichthyosaurs were neither fish nor members of the lizard family; they were a group of highly successful marine reptiles who lived from the early Triassic period to the late Cretaceous period, around 248 million to 90 million years ago. Ichthyosaurs were among the first diapsids  (a group of animals which have evolved two holes on each side of their skulls, includes birds and all reptiles except turtles) to evolve a thunniform (fish-like) body plan as an adaptation to life in the sea (Fig. 1). They were also the first air-breathing vertebrates to evolve this body plan; the only other group to do so was the whales and dolphins, millions of years later. Most ichthyosaurs after the Triassic had the fish-l

Fossil Focus: The place of small shelly fossils in the Cambrian explosion, and the origin of Animals

Fossil Focus
by Aodhan Butler *1 Introduction: Darwin, the Cambrian explosion and the origin of animals. The small shelly fossils (or SSFs) of the early Cambrian period (approximately 541 million to 509 million years ago) could in many ways be described as the world’s worst jigsaw puzzle. This article will attempt to give a brief tour of the significance, history and biology of this humble yet potentially hugely important group of fossil organisms and how they may help in answering fundamental questions about how and when the major groups of animals evolved on Earth. A palaeontological mystery… “To the question why we do not find rich fossiliferous deposits belonging to these assumed earliest periods prior to the Cambrian system, I can give no satisfactory answer.” Charles Darwin, On the Origin of
Fossil Focus: Oreodonts

Fossil Focus: Oreodonts

Fossil Focus
by Joshua Ludtke*1 Introduction: Oreodonts make up an extinct group of small, medium and large hoofed mammals. They are among the most commonly represented mammals in more than 40 million years of the North American fossil record; among completely extinct groups, the oreodonts may be the most abundantly preserved group of fossil mammals. This abundance has allowed them, after their extinction, to spread across the globe. Since at least the 1840s, fossil collectors from around the world have visited the North American west to excavate oreodonts, and their fossils have ended up in both public museums and private collections worldwide (see Fig. 1). What is an oreodont? Oreodont is the informal term for any member of the taxon Merycoidodontoidea. Oreodonts are placental mammals; some f...

Fossil Focus: Cambrian arthropods

Fossil Focus
by David A. Legg*1 Introduction: The arthropods make up a major and highly successful group of animals that includes insects and their kin (hexapods); arachnids and their kin (chelicerates); millipedes and centipedes (myriapods); crabs, lobsters, shrimp and their relatives (crustaceans); and the extinct trilobites. In fact, arthropods are the most diverse, abundant and ubiquitous animal phylum. Members of the group outnumber those of all other phyla on Earth, both in terms of species, with more than 1,200,000 currently described (and a potential 10,000,000 remaining to be described), and in terms of abundance. For example, if you gathered all the world’s Arctic krill in one place, it has been estimated that they would weigh 500 million tonnes! Arthropods are found in all oceans and on al

Fossil Focus: Elasmosaurs

Fossil Focus
by Sven Sachs1 and Benjamin P. Kear2 Introduction: Elasmosaurs were a group of marine reptiles that lived during the Cretaceous period (about 145 million to 66 million years ago). They were fully adapted to an aquatic lifestyle, and had a distinctive body plan comprising a compact, streamlined body, long, paddle-like limbs and an extremely elongated neck with a large number of vertebrae (Fig. 1). The first named elasmosaur was Elasmosaurus platyurus from the Late Cretaceous (Campanian stage, about 83.6 million to 72.1 million years ago). It was found in Kansas and described by the famous US scientist Edward Drinker Cope  (1840–97, Fig. 2), who, when he first wrote about it in 1868, believed that the almost complete series of 72 neck vertebrae came from a massively long tail. Today, many

Fossil Focus: Dinosaurs down under

Fossil Focus
by Stephen F. Poropat*1,2 Introduction: Ask the average person in the street to name an Australian dinosaur, and you will be lucky if you get a correct answer. If they say crocodile, they are in the right postcode but have the wrong address. If they say emu, then they are correct, strictly speaking, but they are either lucky or being smart. If they say kangaroo, back away slowly and avoid eye contact. If they say koala bear, run home and take a few Panadol. I could forgive most people for not being able to identify any Australian dinosaurs. First and foremost, there are not many to know: only 18 Australian dinosaurs (including one bird, Nanantius) from the Mesozoic era (251 million to 66 million years ago) have been officially named. And yet, the first discovery of Mesozoic dinosaur r...