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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When I recently reviewed The Real Planet of the Apes, I casually wrote how that book dealt with the evolution of Old Work monkeys and apes, ignoring New World monkeys which went off on their own evolutionary experiment in South America. But that did leave me wondering. Those New World monkeys, what did they get up to then? Here, primatologist Alfred L. Rosenberger provides a comprehensive and incredibly accessible book that showed these monkeys to be far more fascinating than I imagined.
New World Monkeys: The Evolutionary Odyssey, written by Alfred L. Rosenberger, published by Princeton University Press in September 2020 (hardback, 350 pages)
Most people are probably not very familiar with these monkeys. Technically known as platyrrhines, they are predominantly arboreal (i.e. living in trees), small to medium-sized primates. You might know the insanely loud howler monkeys from nature documentaries. Perhaps you have heard of capuchin monkeys or spider monkeys. But you could be forgiven for not having heard of marmosets and tamarins, or the even more obscurely named titis, sakis, and uacaris. A total of 16 genera are recognized, but outside of the scientific literature and abovementioned technical books, these monkeys are not all that well known. And that is a shame as, from an evolutionary perspective, this is a unique group.
Now, before Rosenberger gets to this, it helps to better know these monkeys. Accompanied by many excellent illustrations and photos, the first half of New World Monkeys is dedicated to their ecology, behaviour, and morphology. Topics covered include their diet and dentition; locomotion and the anatomy of hands, feet, and prehensile tails; but also brain size and shape; and their social organization and ways of communicating via sight, sound, and smell.
The platyrrhines are a diverse bunch with some remarkable specialisations. In the family Cebidae we find the smallest members, some of whom, the Marmosets and Pygmy Marmosets, have teeth specialized for gouging the bark of gum trees and feeding on the gum that is released in response. In the family Pitheciidae we find the only nocturnal member, the Owl Monkeys, which have concomitant morphological adaptations such as enlarged eyes. In both this and the closely related Titi Monkeys, individuals have the adorable habit of twining their tails when e.g. socializing or sleeping. The family Atelidae is home to species with exceptionally prehensile tails whose underside ends in a pad with a fingertip-like surface. The Muriquis and the aptly-named Spider Monkeys use them as a fifth limb in locomotion, as demonstrated by a striking photo of a Black-faced Spider Monkey on plate 13. Here we also find the well-known Howler Monkeys, whose skull is heavily modified to support the exceptionally loud vocal organs in their throat and neck.
“[…] the whole radiation has been remarkably stable for at least 20 million years. Today’s New World monkeys are virtually unchanged from their ancestors […] This stands in sharp contrast to the evolutionary history of Old World monkeys […]”
Despite these differences, platyrrhines are closely related and form what is called an adaptive radiation. Just like the textbook example of Darwin’s finches, many members have evolved unique adaptations and ways of living to minimise competition and maximise resource partitioning. Two ideas feature prominently in this book to explain how platyrrhines have evolved and what makes this adaptive radiation both so diverse and so interesting.
One idea is what Rosenberger calls the Ecophylogenetics Hypothesis. If I have understood him correctly, this combines information on a species’s ecology and phylogeny, its evolutionary relationships. It can offer hypotheses on how ecological interactions have evolved, but it also recognizes that ecological adaptations are shaped and constrained by evolutionary relatedness. For the platyrrhines, taxonomically related members are also ecologically similar. To quote Rosenberger: “[…] phylogenetic relatedness literally breeds resemblance in form, ecology, and behavior” (p. 96) and “Each of the major taxonomic groups that we define phylogenetically is also an ecological unit […]” (p. 97).
The other idea that makes the platyrrhines so interesting is dubbed the Long-Lineage Hypothesis. An extensive chapter on the fossil record documents how the whole radiation has been remarkably stable for at least 20 million years. Today’s New World monkeys are virtually unchanged from their ancestors, living the same lifestyles and occupying the same ecological niches. Some fossils have even been classified in the same genus as their living counterparts. This stands in sharp contrast to the evolutionary history of Old World monkeys where there has been a constant churn, whole groups of primates evolving and going extinct with time.
“Without ever losing academic rigour or intellectual depth, Rosenberger quietly proves himself to be a natural-born teacher and storyteller […]”
What stands out, especially when Rosenberger starts talking taxonomy and evolution, is how well-written and accessible the material here is. He takes his time to enlighten you on the history, utility, and inner workings of zoological nomenclature, making the observation that “names can reflect evolutionary hypotheses“. Here, finally, I read clear explanations of terms such as incertae sedis (of uncertain taxonomic placement), monotypic genera (a genus consisting of only a single species), or neotypes (a replacement type specimen). Similarly, there are carefully wrapped lessons on how science is done—on the distinction between scenarios and hypotheses, or how parsimony and explanatory efficiency are important when formulating hypotheses. 
Without ever losing academic rigour or intellectual depth, Rosenberger quietly proves himself to be a natural-born teacher and storyteller, seamlessly blending in the occasional amusing anecdote.
A final two short chapters conclude the book. One draws on the very interesting question of biogeography, i.e. on how platyrrhine ancestors ended up in South America, which was long an island continent. Rosenberger convincingly argues against the popular notion of monkeys crossing the Atlantic on rafts of vegetation* and in favour of more gradual overland dispersal. The other chapter highlights their conservation plight as much of their tropical forest habitat has been destroyed by humans.
With New World Monkeys, Rosenberger draws on his 50+ years of professional experience to authoritatively synthesize a large body of literature. As such, this book is invaluable to primatologists and evolutionary biologists and should be the first port of call for anyone wanting to find out more about the origins, evolution, and behaviour of these South and Central American primates.
* One mechanism that Rosenberger does not mention is that tsunamis could be behind transoceanic rafting, as argued in a recent Science paper. This looked at marine species in particular and I doubt it would make much of a difference for terrestrial species. Most of the objections Rosenberger gives would still apply.
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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When it comes to modern palaeoartists, Mark Witton has become a leading light in my opinion. Next to bringing a background as a professional palaeontologist to his artwork, he also wrote The Palaeoartist’s Handbook, which is a unique resource for this field as far as I can tell. Who could be better suited to produce a homage and sequel to one of the most iconic palaeoart books of all times: Knight’s Life through the Ages?
Life through the Ages II: Twenty-First Century Visions of Prehistory, written by Mark P. Witton, published by Indiana University Press in April 2020 (hardback, 157 pages)
In the pantheon of palaeoart few names loom as large as that of American artist Charles R. Knight (1874-1953). Of the several books he wrote, his 1946 Life Through the Ages is the one that stood the test of time, having been reprinted on multiple occasions. In Life through the Ages II, Witton provides a gorgeously illustrated tour of life on Earth, reflecting how the state of science has advanced in the intervening seven decades.
In his introduction, which is both a celebration and overview of Knight’s career and artwork, Witton encourages readers to seek out Knight’s book and have them side by side to see first-hand how palaeoart has changed. I am unfortunately not so lucky to have that book at hand, but Witton provides some helpful pointers. Where Knight’s book contained thirty-three images, mostly charcoal sketches and a few colour illustrations, Witton presents sixty-two pieces, all in glorious full-colour. The format is the same, however, with short descriptive texts and images on facing pages.
Before you embark on this chronological tour through the history of life there is a very brief introduction to the geologic timescale, the biological classification of lifeforms, and the reconstruction of extinct animals in art, which recaps some of the main points of The Palaeoartist’s Handbook. An appendix contains brief notes with sources and justifications or caveats for each illustration. The only thing I felt was missing was an introduction to Witton’s method of making art. An interview with him in Dinosaur Art II revealed that he primarily works digitally, although to my eyes his works might just as well have been painted on canvas.
“The notes in the appendix reveal a careful artist who holds himself to exacting standards of authenticity […] no posture, no limb placement, no choice of bodily proportions has gone without serious research and thought.”
In that same portfolio, Witton encouraged novice palaeoartists to explore animal groups that others have shunned. This ethos underlies Life through the Ages II, as Witton presents a very representative and balanced whistle-stop tour of some major highlights in life’s evolution. Whether it is the birth of Earth, hydrothermal vents as the cradle of life, or the first cyanobacteria building dome-like structures called stromatolites, Witton shows you can make dramatic artwork out of static subjects. Before we get to the tetrapods, there is similarly attention for early invertebrates in the Ediacaran and Cambrian periods, the invasion of land by plants, and the rise of fishes.
Once life developed four limbs, Witton continues to aim for a taxonomic balance in his depictions. Thus there are temnospondyls (a precursor to amphibians), the bizarre whorl-toothed shark Helicoprion, synapsids other than Dimetrodon such as dicynodonts and the mammal-like cynodonts, and early reptiles in the form of erythrosuchids. We also get Witton’s speciality, pterosaurs, a beautiful depiction of the last land whales, and an aquatic sloth. Even when painting a staple subject such as Brontosaurus, his choice of setting, two males engaged in neck-to-neck combat in the pouring rain, is memorable.
Witton’s style is characterised by a subdued use of colours and tones that feel earthy and organic to me, making for atmospheric pictures. Some are downright eerie, such as a giant, floating crinoid barge or his near-Lovecraftian depiction of a giant ammonite. There is as much attention to the backdrop of skies, vegetation, or mountains, as there is for the subjects in the foreground. The notes in the appendix reveal a careful artist who holds himself to exacting standards of authenticity while acknowledging the sometimes limited state of our knowledge. So, he asks readers to be sceptical of his depiction of the Ediacaran biota and warns them that more complete, future remains of Plathyhystrix could render his depiction obsolete. No posture, no limb placement, no choice of bodily proportions has gone without serious research and thought.
“Witton exhorts students of palaeoart to study animal behaviour. Nature is not constantly red in tooth and claw. Although there are some spectacular pieces here […] there are plenty of tranquil tableaux.”
There are two other areas of Witton’s work where this realism shines through. He is not afraid of soft-tissue reconstruction, basing his depictions on careful study of skeletal modifications that hint at attachment points for muscles. Brontosaurus is depicted with a fleshy, muscular neck, the embrithopod Arsinoitherium with large horns covered in horn sheath, and the rhinocerotoid Paraceratherium with a tapir-like proboscis. Similarly, Witton exhorts students of palaeoart to study animal behaviour. Nature is not constantly red in tooth and claw. Although there are some spectacular pieces here (the giant shark Cretoryxhina breaching to catch a pterosaur, two hyena-like carnivores disembowelling a Miocene horse), there are plenty of tranquil tableaux. Arsinoitherium standing watch, the land whale Georgiacetus lounging on a rocky outcrop, the entelodont Daeodon resting after a meal, two rambunctious indricotheres mucking about, or a giant pangolin eyeing up an anthill. Even the ankylosaurid Zuul, destroyer of shins, is caught in a moment of quiet.
The text contains concise overviews of the periods and subjects depicted, highlighting where our thinking has advanced. Such as the more nuanced view that the Cambrian explosion was perhaps not an explosion after all, the idea that coelacanth should not really be called a living fossil anymore, or the increasingly blurred boundary of dinosaur–bird transition. What I particularly liked is that the homage to Knight is subtle. Sure, as Witton also tweeted, his depiction of Dimetrodon that graces the cover is a straight update of Knight’s piece, his giant Mesozoic sea lizards swimming at the surface is a tribute to a way of depiction that has fallen out of favour, and the group of sauropods in the background of the Mesozoic mammal painting are a straight throwback – and Knight’s name comes up several times in the appendix. But he is not constantly the subject of attention. Witton’s body of work stands firmly on its own two legs.
Life through the Ages II is a beautiful palaeoart portfolio that pushes the envelope where realistic compositions and reconstructions are concerned. These are images that would not look out of place framed on your wall. If you can buy just one palaeoart book this year, make it this one. It has me seriously considering purchasing a print or supporting Witton’s work through his Patreon page.
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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