Say “dinosaurs”, and most people imagine fossilised bones and spectacular museum displays. But body fossils are not the only remains we have with which to reconstruct dinosaur lives. Nor, and this might sound controversial, are they the most important. Or so argues palaeontologist, geologist, and ichnologist Anthony J. Martin. Ichnology is the study of animal traces, whether modern or fossilised. Most traces are ephemeral and disappear within hours or days, but occasionally some are buried and end up in the fossil record. With tongue firmly planted in cheek, and with more puns than you can shake a T. rex thigh bone at, Martin forays into the rich dinosaur trace fossil record: from footprints, burrows, and nests, to teeth marks and fossil faeces. For all the jokes, and despite having been published in 2014, he raises some really interesting points.
Dinosaurs Without Bones: Dinosaur Lives Revealed by Their Trace Fossils, written by Anthony J. Martin, published by Pegasus Books in April 2015 (paperback, 484 pages)
You might indeed ask, why review this book now? Way back in 2018 I reviewed Martin’s 2017 book The Evolution Underground on the evolutionary history of burrowing behaviour and was suitably impressed. I vowed to search out his previous book, though I did not intend to wait this long. Having just reviewed Lomax’s book Locked in Time, now was the right time to make up for that.
Animals of all sorts leave behind traces wherever they go and dinosaurs were no exception. Footprints are probably the first thing to come to mind and a logical place to start. From the US, to Europe, to South America, they have been found on every continent except Antarctica*. Martin discusses how the number of toes and their orientation can reveal what group of dinosaur left the footprint and how their size can be used to estimate its maker’s size. Where multiple footprints form a trackway, their distance can reveal gait and velocity, or whether dinosaurs moved alone or in (family) groups. And with technological advances, we can extract more information from footprints than ever before.
One interesting thing Martin reveals here that I was not aware of, is that most fossil tracks are probably undertracks. That is, the subsurface deformation of the substrate caused by the pressure of the foot. Most tracks likely soon weathered beyond recognition, so unless you find clear skin impressions, the prudent assumption is that you are dealing with undertracks. As he points out: “The decided preservational advantage of this phenomenon is that such tracks were already buried, protecting them from destruction” (p. 33).
“One interesting thing Martin reveals here […] is that most fossil tracks are probably undertracks. That is, the subsurface deformation of the substrate caused by the pressure of the foot […]”
But feet can do much more than just walking and Martin examines trace fossil evidence of dinosaur nests and fossil burrows. Beyond traces made by feet, bones can record tooth marks, though care is needed to distinguish attacks on living animals from post-mortem scavenging. In turn, food leaves tell-tale traces of microwear on a tooth’s surface. More exotic—and controversial—are gastroliths or stomach stones that can act as digestive aids, though likely not all were swallowed on purpose. And then there is that which comes out at the other end. You might have heard of coprolites (fossil dung), and Lomax introduced me to urolites (fossil traces of urination). But what of enterolites (fossil stomach contents) and cololites (fossil intestinal contents)? Or, my favourite, regurgitalites—which is what you think it is.
For some behaviours we do not have clear evidence, while others are highly unlikely to leave traces in the fossil record. But this does segue nicely into one of the most important themes of this book: search image. At several points, Martin encourages readers and researchers alike to ask themselves: what would the traces left by certain behaviours look like? Take sauropod footprints. Given their size you might think they are hard to miss and yet: “In the early days of dinosaur tracking probably more than one paleontologist or geologist walked by their footprints without a second glance, thinking they were some sort of large erosion-caused features. Once these footprints were correlated with the sizes and shapes of sauropod feet […] sauropod tracks magically appeared in the search images of paleontologists worldwide” (p. 22). An important point of reference, and one that Martin profiled for his home turf of Georgia in his previous book, are the traces left by animals alive today, specifically birds. Because, as he reminds you towards the end of the book by shortly recapping the evolution of birds, technically speaking birds are living, flying, feathered dinosaurs.
“[…] one of the most important themes of this book [is] search image. At several points, Martin encourages readers and researchers alike to ask themselves: what would the traces left by certain behaviours look like?”
The other thing to note is Martin’s writing style. All of the above is served up with a healthy dollop of frequently irreverent humour. Some of it borders on dad-jokes though, so let me give you some tasters. He frequently lampoons his own profession: “[…] even dinosaur-track experts have doubts about the identity of some three-toed dinosaur tracks, especially if a rival dinosaur-track expert identified them” (p. 22), and regarding peer review “[…] the scientists who review journal articles are doing it as unpaid volunteers, finding time to perform this important duty in between all of their other tasks such as teaching, grading, research, walking the dog, or (most heinous of all) sleeping” (p. 76). The rear part of a dinosaur “[…] is properly called an ischial callosity, and not the more appealing term “dinosaur butt”” (p. 39). On front teeth: “If a theropod’s potential food item, such as a small ornithopod, was still alive and having issues with a proposal that it should devote its life to feeding a theropod, then the front teeth were the most persuasive tools used by that theropod” (p. 181). And on urolites: “Paleontologists who do such research could be assured of making a big splash with it, while also going against the flow of others’ prejudices. Afterwards, they will be flushed with success, and their colleagues pissed off” (p. 247). If the above made you laugh, you will have a blast with this book. I certainly did.
Dinosaurs Without Bones is great popular science: fascinating, thought-provoking, and told with verve and wit. This is an excellent companion book to Lomax’s Locked in Time and a very nice introduction to trace fossils and ichnology. My only regret is that I waited so long before finally reading it.
* That was true when this book was published in 2014. When I followed up on this, I found one news item claiming the 2016 find of a dinosaur footprint on Antarctica. However, when reading the actual 2019 paper in the open-access journal Polar Research, the authors are a bit more circumspect, attributing this footprint to “a primitive amniote, procolophonid or therapsid“.
Other recommended books mentioned in this review:
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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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