Abstract
In the vast majority of fossils, the organic matter is degraded with only an impression or cast of the organism remaining. In rare cases, ideal burial conditions result in a rapid fossilisation with an exceptional preservation of soft tissues and occasionally organic matter. Such deposits are known as Lagerstätten and have been found throughout the geological record. Exceptional preservation is often associated with finely crystalline quartz (e.g., cherts), fine sediments (e.g., muds) or volcanic ashes. Other mechanisms include burial in anoxic/euxinic sediments and in the absence of turbidity or scavenging. Exceptional preservation can also occur when an organism is encapsulated in carbonate cement, forming a concretion. This mechanism involves complex microbial processes, resulting in a supersaturation in carbonate, with microbial sulfate reduction and methane cycling the most commonly suggested processes. In addition, conditions of photic zone euxinia are often found to occur during concretion formation in marine environments. Concretions are ideal for the study of ancient and long-extinct organisms, through both imaging techniques and biomolecular approaches. These studies have provided valuable insights into the evolution of organisms and their environments through the Phanerozoic and have contributed to increasing interest in fields including chemotaxonomy, palaeobiology, palaeoecology and palaeophysiology.
Highlights
Fossils play a significant role in defining the geologic timescale which provides a framework for understanding important events in Earth’s history and the evolution of organisms
We summarise the mechanisms leading to the exceptional preservation of fossils with a special focus on carbonate concretions
In “exceptional” fossil deposits (Konservat-Lagerstätten), well-preserved fossils formed via rapid preservation can provide significant insights into the history of organisms and their evolution
Summary
Fossils play a significant role in defining the geologic timescale which provides a framework for understanding important events in Earth’s history and the evolution of organisms. Red blood cells, along with amino acids from collagen, were reported in 75-Ma-old dinosaur vertebrate bones [5] Such observations reveal biological features that could offer insights into relationships, physiology and behaviour of long-extinct animals. This level of preservation was proven to be possible over much longer geological timescales with the in situ detection of collagen in a 195-Ma-old dinosaur bone [6] and the release of preserved soft tissues from the decalcification of animal bones up to. The detection of cholesterol, red and white blood cells and collagen in a 183-Ma-old fossil vertebra bone encapsulated in a carbonate concretion provided unprecedented insights into the predatory lifestyle and diet of an ichthyosaur-like reptile [8]. For a more extensive discussion of exceptionally preserved fossils in general, the reader is directed to reviews by Cohen and Macdonald [11] and Muscente et al [12]
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