Given that we are nothing but mammals, it is perhaps understandable that humans are rather mammal-centric, something that conservation organisations capitalise on. But where palaeontology is concerned, dinosaurs get all the love. And that does early mammals little justice says Scottish palaeontologist and Palaeocast co-host Elsa Panciroli. Far from mere bit players cowering in the shadows of these “terrible lizards”, mammals have a long and rich evolutionary history that predates the dinosaurs but is poorly known outside of specialist circles. Panciroli’s debut changes all that and does so in a most readable and immersive fashion.
To pick up the tale of mammal evolution, Panciroli takes you all the way back to the Carboniferous (roughly 360-300 million years ago) when higher oxygen levels supported a land of giants. It was here that the first fish made landfall and tetrapods evolved. To get from this distant ancestor to modern mammals, you have to follow the story through groups whose names are likely unfamiliar. To help you visualise these, stylish illustrations from April Neander open each chapter, while the endpapers* provide a helpful family tree drawn by Marc Dando. These do not list all mentioned groups but do present the big picture and I found myself referring to them frequently.
Thus we get to meet the synapsids, one of which you will know: the sail-backed, no-it-is-not-a-dinosaur Dimetrodon. Synapsids included the pelycosaurs (also not dinosaurs), which gave rise to the therapsids: carnivores with more powerful jaws and a stronger bite. Some of these, including the gorgonopsians, pioneered sabre-teeth, proving later groups to be mere copy-cats. Convergent evolution is, quite literally, a recurrent theme that Panciroli mentions whenever she can get away with it. Various therapsids were also the first groups to evolve endothermy or warm-bloodedness, though “like so many of the features associated with mammals [it] emerged scattershot. It wasn’t switched on like a lightbulb, lighting up all therapsids at once” (p. 120).
As the end-Permian mass extinction wiped the slate clean, the age of reptiles had begun. But some of our mammal ancestors survived. Rising like a phoenix from the ashes were, amongst others, the dicynodonts, who would have looked you in the eye from behind tusks and a turtle-like beak. One particularly successful group, possibly because it dug burrows, was Lystrosaurus, a genus that in the early Triassic made up 90% of all vertebrates. A related group, the cynodonts, is largely responsible for the misconception that our ancestors were insignificant during the reign of the dinosaurs, as they evolved to be smaller. But this was a feature, not a bug: “With no space among the giants, they took a different route: they perfected being tiny” (p. 163). They exploited the safety of the night, became nocturnal, and developed sensitive eyes. They also lost some ribs and developed a waist, allowing for more flexibility in their locomotion – early synapsids had ribs all the way down.
“[One] group, the cynodonts, is largely responsible for the misconception that our ancestors were insignificant during the reign of the dinosaurs, as they evolved to be smaller. But this was a feature, not a bug”
The Jurassic saw groups such as tritylodontids, docodontans, and multituberculates flourish. As their names imply, these groups experimented with tooth morphology, which later became important diagnostic fossil characters. None of them left living descendants. Instead, it was the therians who were our direct ancestors, but they did not diversify until after the K-Pg boundary. Interestingly, Panciroli suggests** that it was not the dinosaurs that kept the therians in check, but competition from all the other Jurassic mammal groups. This more recent history of the adaptive radiation into modern marsupials and placental mammals is well known, so she purposefully ends the book where most others start the story of mammal evolution .
This brief exercise in name-dropping provides only a snapshot of what Panciroli discusses, and she does a far better job of it. She weaves in the history of fossil discovery and her own work at dig sites in South Africa and Scotland, or labwork at the European Synchrotron Radiation Facility in France. Next to telling the story of mammal evolution, Panciroli also takes on the task of disarming and deconstructing a large amount of cultural and linguistic baggage, with two issues standing out.
First, as part of a younger generation of scientists, Panciroli is keen to decolonise her discipline. This means acknowledging that the scientific collections on which she herself works are the spoils of empire. Our museums are filled with colonialist plunder. Especially in the first chapter, where she gives a potted history of geology and biology, she repeatedly points to the imperialist framework in which these disciplines were born and how that has shaped conventions and biases to this day. Celebrated figureheads such as Buckland, Darwin, Lyell, Cuvier, Hutton, Lamarck, Owen etc. simultaneously held ideas now considered unsavoury, and they rarely credited Indigenous knowledge or help in the acquisition of fossils. Furthermore, as a woman, she has a few things to say about diversity. Like many academic disciplines, palaeontology remains largely populated by white, Western men, and it has been hard to shake off the image of the “stereotypical male adventurer” and his “macho plundering of the past” (p. 249). Fortunately, the contributions of women are increasingly being acknowledged, and Panciroli here celebrates Polish Mesozoic mammal researcher Zofia Kielan-Jaworowska who was the first woman to lead fossil collection expeditions in Mongolia.
“[…] the long history of evolutionary theory means that outdated modes of thinking continue to permeate our language. […] Panciroli similarly uses every opportunity to remind you that evolution is not goal-directed”
Second, the long history of evolutionary theory means that outdated modes of thinking continue to permeate our language. She shudders at the term “mammal-like reptiles” still used to describe the synapsids: “This first amniote tetrapod was neither mammal nor reptile – neither of those groups had evolved yet” (p. 61). We did not evolve from reptiles, nor are they more primitive compared to us. Panciroli similarly uses every opportunity to remind you that evolution is not goal-directed: “It is random, the route forged by happenstance” (p. 57). It has proven hard to let go of the Scala Naturae, the idea of a linear series of improvements, “like an assembly-line through time” (p. 120) leading ultimately to the perfect organism: us.
This neatly leads to my last observation: Panciroli’s writing is sublime. Her prose is concise without being stunted, her visual metaphors rich without being flowery. Of the late Triassic mammals she writes: “These tiny ancestors were living microchips. They were night-vision goggles. They were fuzzy little ninjas, wielding shuriken teeth to reap their insect prey in silence and stealth” (p. 171). On the break-up of Pangaea: “After their epic 250 million-year snuggle, the continents of Earth were parting ways […] By the end of the Jurassic, the whole world was unzipping itself, with new seas and oceans splashing into the gaps” (p. 203). On the K-Pg event: “The universe drew an iridium line under things. From here on, life would be different” (p. 274). And her description of the tritylodontid herbivore niche is just beautiful: “All of the non-mammalian cynodonts had turned to dust, except for the tritylodontids […]. Natural selection had moulded them into premier leaf-grinding machines. Of course there had been synapsid herbivores before […] but those bulky predecessors were gone. In the world of crocs and dinosaurs, mammals had microscoped themselves into the understorey, and the tritylodontids were left to eat the scenery” (p. 237).
Beyond a few academic textbooks and technical monographs, the deep evolutionary history of mammals has remained largely hidden in the academic literature. Beasts Before Us unleashes their story most spectacularly and engagingly. This beautifully written debut marks Panciroli as a noteworthy new popular science author. May this be the first of many books! You might also want to check out my Q&A with Panciroli published over at the NHBS Conservation Hub.
* Illustrated endpapers are one of my favourite features in a book, and one that, I think, too few publishers and authors use.
** The paper arguing this, still in press when she wrote this book, has just been published in Current Biology.
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: