Fossils are our prime source of information about life in the past. As I delve deeper into palaeontology and earth sciences, the process of fossilisation increasingly fascinates me. How does dead biological tissue fossilise? What information is lost, what is added, and what is distorted in the process? And, ultimately, how true or filtered a picture of past life does the fossil record provide? The edited book Fossilization brings together scientists from a range of disciplines working on cutting-edge topics. The result is a well-written if somewhat eclectic collection of chapters that addressed some of my queries and also answered questions I did not even know I had.
Fossilization: Understanding the Material Nature of Ancient Plants and Animals, edited by Carole T. Gee, Victoria E. McCoy, and P. Martin Sander, published by Johns Hopkins University Press in May 2021 (hardback, 290 pages)
This book needs some context. Despite the single-word title, Fossilization is not a textbook that will introduce you to taphonomy, the process of fossilisation. (I might be overlooking something, but my impression is that there is no good recent textbook and I would need to refer readers to older books such as Life History of a Fossil or Taphonomy.) Nor does this edited collection strive to be an as-broad and as-inclusive overview as possible. No, essentially Fossilization is a showcase of the research being done at DFG Research Unit FOR 2685 at the University of Bonn in Germany. Funded by the Deutsche Forschungsgemeinschaft (the German Research Foundation), this is a consortium of nine research projects under a program titled “The Limits of the Fossil Record: Analytical and Experimental Approaches to Fossilization”.
What these projects are, however, is interdisciplinary. As two of the editors clarify in their introduction, the focus of this research unit is the small: evidence at the histological, cytological, and molecular level. This is where palaeontology starts touching on neighbouring disciplines and progress requires the know-how and input from e.g. microbiologists, organic chemists, mineralogists, geochemists, pharmacists, and petrologists. Furthermore, “fossilisation” is much more than just bones turning to stone. It is an umbrella term for several geochemical processes that vary with both tissue chemistry and the environment, encompassing processes such as silicification (of wood), pyritization (of arthropods), permineralization (of bones), and others.
“[…] there are two preservation pathways [in amber] with radically different outcomes: either decay with loss of all soft tissue so that only an arthropod-shaped void remains or, spectacularly, complete preservation.”
Next to an introductory and a concluding chapter, Fossilization contains eight chapters that break down into four chapters on palaeobotany, two on fossil animals, one on amber preservation, and one on Raman spectroscopy, all of which clock in at between 20–40 pages. Throughout, attention is paid to the many modern variations of microscopy, spectroscopy, and spectrometry that can be brought to bear on fossil material. What stood out is how readable these chapters are. I am not much of an expert in any of the above disciplines, yet found that I could follow along with most chapters just fine. And some of this material is outright fascinating.
Thus, there is a chapter on soft-tissue preservation at the microscopic level, think cells or blood vessels, in dinosaur and other tetrapod bones. Is this original material or biofilm produced by bone-degrading bacteria? I remember this discussion making news headlines a few years ago. A review of studies so far concludes that the evidence points towards the former. Another chapter looks at the fossilisation of reproduction-related tissues and structures in avian dinosaurs and birds, and what analytical methods you could use to detect them. So far we have found evidence of e.g. ovarian follicles, shell membranes, eggshell pigmentation, and medullary bone (this is incidentally the same study that Lomax referenced in Locked in Time).
Two chapters stood out in particular. Chapter 5 looks at soft-tissue preservation of arthropods trapped in amber. The authors argue that there are two preservation pathways with radically different outcomes: either decay with loss of all soft tissue so that only an arthropod-shaped void remains or, spectacularly, complete preservation. They then discuss what factors might be responsible for this dual pathway. Chapter 8 draws heavily on the work of one of the authors, Conrad C. Labandeira, and reviews fossil evidence for insect-plant interactions, looking both at traces of insect damage, but also at structural and chemical defences in plants. We know that insects and plants coevolved but these authors propose a model of four phases during the last 400 million years of arthropod herbivory expanding and, in response, plant defences developing. This is a fascinating idea that is crying out for a popular treatment, and if I had to point a university press towards an idea for a new book, this chapter is it.
“Given the book’s somewhat eclectic selection of topics and relatively high price tag, who is this for? [individuals] might wish to only consult a few chapters. I would thus argue that this book is particularly suitable for academic and institutional libraries.”
More technical chapters give an introduction to Raman spectroscopy and how it can be used in palaeontology, and the structure and chemistry of silica in mineralized wood. Fossil wood also features in a chapter on experimental silicification of wood in the laboratory with comparisons to the fossil record. This chapter mentions the interesting phenomenon of in vivo mineralization where living trees in certain environments, for example Yellowstone National Park, are already fossilising during their lifetime. Finally, there is a chapter on colour in the palaeobotanical record which gives a thorough introduction to colour in living plants and then asks whether the colours we see in fossil plants result from original material, their degradation products, or from later diagenetic processes. A colour plate section, relevant especially to the last chapter, is included.
Given the book’s somewhat eclectic selection of topics and relatively high price tag, who is this for? Depending on your interests and background, your mileage may vary and you might wish to only consult a few chapters. I would thus argue that this book is particularly suitable for academic and institutional libraries. For them, it is a worthwhile investment as edited collections of this kind are often picked up by the likes of Springer or Elsevier who publish print-on-demand books with production values not nearly half as nice as Fossilization at double the price.
Disclosure: The publisher provided a review copy of this book. The opinion expressed here is my own, however.
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Fossils can tell us what animals living in the distant past looked like. Over the centuries, palaeontologists have made incredible strides in reconstructing extinct life forms, helped along by cumulative experience, technological advances, and a steadily increasing body of rare but truly exceptionally preserved fossils. But reconstructing their behaviour—surely that is all just speculative? In Locked in Time, palaeontologist and science communicator Dean R. Lomax, with the able help of palaeoartist Bob Nicholls, presents fifty of the most exceptional fossils that preserve evidence of past behaviour: from pregnant plesiosaurs to a pterosaur pierced by a predatory fish. I was eagerly awaiting this book from the moment it was announced, but I was still caught off-guard by some of the astonishing fossil discoveries featured here.
Locked in Time: Animal Behavior Unearthed in 50 Extraordinary Fossils, written by Dean R. Lomax and illustrated by Robert Nicholls, published by Columbia University Press in May 2021 (hardback, 312 pages)
Locked in Time effectively consists of fifty vignettes organised around five themes. Perhaps surprisingly, this is not the first popular science book on behaviour revealed by the fossil record. Anthony J. Martin wrote Dinosaurs Without Bones in 2014, focusing on ichnology, the study of trace fossils such as fossil footprints, scratch marks, or nests. Lomax, however, casts his net far wider than just dinosaurs and has scoured the scientific literature for both trace and body fossils that reveal how these animals likely behaved in life. Some examples require careful inference, while others, cases that the pioneer Arthur Boucot called “frozen behaviour”, are blindingly obvious.
There are some truly astonishing fossils featured here. An ichthyosaur that died while giving birth proves beyond a doubt they were live-bearing. A pair of turtles was unfortunate enough to end up caught in the act of mating for eternity. There are well-known fossils such as the pregnant mother fish Materpiscis, the battle between a Protoceratops and a Velociraptor featured on the book’s cover, or the tall spiral structures once nicknamed Devil’s corkscrews by flummoxed fossil hunters that turned out to be burrows, some even containing fossilised beavers. There is violence: the skulls of two fighting male mammoths that died with tusks still interlocked; but also tranquillity: the fossil troodontid Mei long that was found in a posture reminiscent of modern-day birds resting or sleeping. There is the fossil that got Lomax started on this project: a metres-long trackway of a horseshoe crab scurrying over a lake bottom with the individual fossilised at the end of it! There is palaeopathology, parasites, and even fossil farts.
But make no mistake, Locked in Time is much more than a book of trivia and factoids. Palaeoethology, the study of behaviour of organisms in the fossil record, is a proper subdiscipline of palaeontology and has bearings on the study of palaeoecology. And for all the spectacular fossils and occasional puns, Lomax also subtly educates his reader on more serious topics. Three things struck me in particular.
“There is palaeopathology, parasites, and even fossil farts. But make no mistake, Locked in Time is much more than a book of trivia and factoids.”
First, as Lomax acknowledges, not all interpretations of behaviour are uncontested. Are the fossils of the primitive bird Confuciusornis sanctus that display exquisitely preserved ornamental feathers really males? Further research showed the fossils without these feathers to contain medullary bone, a temporary tissue associated exclusively with reproductively active females. The ornamented individuals showed no such evidence, strengthening the case for sexual dimorphism in this species. Or what of the 200-year-old claim that ichthyosaurs were cannibals? It took until the 1990s when further detailed studies of presumed stomach contents concluded that there were no signs of bite marks or etchings by stomach acids, strengthening the case that these were instead embryos. An important theme that Lomax highlights repeatedly is the utility of studying the behaviour of animals alive today. Although care is in order, comparisons with the behaviour of extant animals and the traces they leave can help demystify the behaviour of extinct animals.
Second, Lomax reveals the inner workings of palaeontology. It is not uncommon for fossils to linger for years or even decades after excavation pending the availability of funding and a skilled preparator. One specimen of the plesiosaur Polycotylus latipinnus was dug up in 1987 but not prepared until 2011, finally revealing its pregnancy. Sometimes technological advances breathe new life into old fossils, such as the burrow containing the therapsid Thrinaxodon liorhinus that was discovered in 1975. Not until 2013, when it was examined with powerful x-rays at a synchrotron facility, did the partially prepared fossil reveal a thus-far hidden injured amphibian that had crawled into the burrow and nestled itself against the likely dormant Thrinaxodon. In other cases, palaeontologists have to beware of frauds, as traders occasionally doctor fossils to make them fetch a higher price on the marketplace—some stories could just be too good to be true.
Third, Lomax proves himself to be a gentle educator. He will immediately explain jargon (e.g. Lagerstätten, ecdysis, or anamorphosis) and only introduce it where appropriate. And though this is popular science, Lomax is keen to bust myths. No, the large shark Megalodon is no longer alive, and there is zero evidence for either Dilophosaurus or other dinosaurs being capable of spitting acid, no matter what Jurassic Park tried to tell you. He beautifully channels deep time when writing “Before dinosaurs even appeared, trilobites were already fossils under their feet” (p. 110), and explains why trace fossils are much more common than body fossils: “Over its lifetime, an animal might leave behind countless footprints […] but only one skeleton” (p. 105).
“An important theme that Lomax highlights repeatedly is the utility of studying the behaviour of animals alive today. Although care is in order, comparisons […] can help demystify the behaviour of extinct animals.”
Finally, seeing is believing, and Locked in Time is richly illustrated. Most vignettes include photos and schematic drawings of the fossils, and my jaw dropped on numerous occasions. Given that disarticulated and fragmentary fossils are the norm, the selection that Lomax has curated here is truly breathtaking. Furthermore, all vignettes include a single or double-page spread with palaeoart from Bob Nicholls, tastefully reproduced in grayscale.
He was featured in Dinosaur Art and wrote the introduction to Dinosaur Art II where he discussed his Psitaccosaurus reconstruction mentioned here on p. 75. Nicholl’s artwork is heavily informed by science and adds much flavour to this book.
In an interview I did with Lomax, published at the NHBS Conservation Hub, he mentioned having made an initial selection of 100 fossils, so many fascinating examples did not make the cut. Other interesting studies were unfortunately published too recently to be considered for inclusion, such as the 2021 Caneer et al. paper discussing possible tracks made by a Tyrannosaurid rising from a prone position, or the 2021 Lockley et al. paper on the sand-swimming trace fossils left by a Pleistocene golden mole.
Locked in Time is an outstanding and highly original piece of popular science that overflows with Lomax’s enthusiasm and passion for his topic. Even if your shelves are already heaving with palaeontology books, make space for one more. Believe me, you have not seen a book like this before.
Disclosure: The publisher provided a review copy of this book. The opinion expressed here is my own, however.
Other recommended books mentioned in this review:
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“The Tales Teeth Tell: Development, Evolution, Behavior”, written by Tanya M. Smith, published by MIT Press in November 2018 (hardback, 277 pages)
Following its subtitle, the book is divided into three parts of three chapters each. With the same kind of clarity she must be applying to her lectures, Smith gives the reader a thorough introduction to how teeth actually form during embryonic development and continue developing after birth. Interestingly, much like trees, developing teeth lay down “growth rings”, or really growth lines, on a daily basis. As Smith explains, there are other patterns repeating on longer time scales that are still poorly understood.
These growth lines react to environmental stressors, including (!) birth. The study of baby teeth has revealed so-called neonatal lines, indicating the moment a child is born. Although teeth stop growing at some point, this record of growth lines can be used to estimate the age of archaeological remains of children, outperforming other methods. Furthermore, diseases and other stressors affect the deposition of growth lines, some so clearly visible that no microscope is needed. As other authors have pointed out (see e.g. Built on Bones: 15,000 Years of Urban Life and Death and The Story of the Human Body: Evolution, Health, and Disease), the development of agriculture and urban civilization led to new kinds of diseases. The change to softer, more easily digestible food meant less tooth wear. But a bigger and more insidious problem is that our bodies showed an evolutionary response by reducing the growth of our jaws (see also Jaws: The Story of a Hidden Epidemic). This, in turn, has led to new problems in the form of crowding and misalignment of teeth.
“[…] the study of baby teeth has revealed so-called neonatal lines, indicating the moment a child is born.”
Smith’s coverage of evolution is similarly insightful. Starting with the earliest jawless fishes some 500 million years ago, she walks the reader through the evolution of teeth (see also Vertebrate Palaeontology and Your Inner Fish: The Amazing Discovery of Our 375-Million-Year-Old Ancestor). Did tooth-like structures on armour plating migrate into the mouth over time to form the first teeth, or did external skin teeth and internal oral teeth evolve separately? The jury is still out on this, writes Smith. But once they arrived on the scene, a spectacularly diverse array of dentitions evolved in fish, amphibians, reptiles, and mammals (for more technical coverage, see The Teeth of Non-Mammalian Vertebrates and Mammal Teeth: Origin, Evolution, and Diversity). And though modern birds are toothless, she describes some of the fascinating experiments that have shown they retain the potential to grow teeth.
Due to their high mineral content, teeth are basically ready-made fossils, and, under the right conditions, can even conserve DNA. I have enthused about ancient DNA before (see my review of Who We Are and How We Got Here: Ancient DNA and the New Science of the Human Past), something with which Smith has first-hand experience. That book and others such as Our Human Story: Where We Come from and How we Evolved reveal how the picture of human evolution has become rather complicated. The study of teeth can obviously add to that story (see also What Teeth Reveal About Human Evolution), though – spoiler alert – they do not necessarily make it any less complex. Take for example the reduction in tooth size during our evolutionary history. Though attractive as possible explanations, the timing of tool use and cooking (see Catching Fire: How Cooking Made Us Human) do not match up with the changes in tooth size detected in the fossil record.
“though modern birds are toothless […] they retain the potential to grow teeth.”
It is only during the third part of her book, where she looks at what teeth reveal about behaviour, that Smith overlaps substantially with some of the topics that Ungar covered. She is similarly critical of the Palaeolithic diet and reviews what dental microwear (microscopic patterns of wear and tear), fossilised dental plaque, and isotope analysis instead reveal about our past diets (see also Evolution’s Bite and Evolution of the Human Diet: The Known, the Unknown, and the Unknowable). And if you are not squeamish, she ends with a fascinating look at the use of teeth as tools (all those things your mum told you never to do!), stone age dentistry, and tooth decoration. That last one was practised in the past, and is still done so by some tribes, and refers to the filing, grinding, and drilling of teeth… while they are still in the mouth.
Smith writes enthusiastically about new technologies such as synchrotron imaging, which uses a type of particle accelerator to non-destructively scan the inside and outside of valuable archaeological samples. More importantly, she also shows them. MIT Press went to town on The Tales Teeth Tell, producing a full-colour book printed on slightly glossy paper. Smith has made good use of this and included many excellent colour photos and illustrations that bring her tales alive.
Although this is pure speculation on my part, it is tempting to think that Smith read Ungar’s book, took careful notes, and made sure to minimise overlap when writing hers (edit: the author has since confirmed this was not the case). Regardless, this book is just as good. (Should you pick one? No, get both!) Even if it gets technical in a few places, Smith’s writing is informative, absorbing, and manages to elegantly cover a wide range of topics.
Disclosure: The publisher provided a review copy of this book. The opinion expressed here is my own, however.
Other recommended books mentioned in this review:
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