Fieldwork in the badlands of the San Juan Basin of New Mexico, USA.
Tom Williamson.
Me collecting fossils of the mammals that took over from the dinosaurs.
Photo courtesy of the author
Fossil teeth of a mammal living within a few hundred thousand years of the end-Cretaceous asteroid impact, from New Mexico.
Photo courtesy of the author
Tom is blessed with a skill I lack, one that is very useful for a paleontologist. He has a photographic memory. He claims that he doesn’t, but that’s either false modesty or delusion. Tom can recognize each little hillock and crag in the desert, which all look the same to me. He can recall with precise detail almost every fossil he’s ever collected at these sites, which is stunning, because he has collected thousands, perhaps tens of thousands by now.
Fossils are littered all over this landscape, constantly eroding out from the Paleogene rocks. Aside from a few bird bones here and there, these are not dinosaur fossils. They are the jaws and teeth and skeletons of the things that took over from the dinosaurs, the species that went on to start the next great dynasty of Earth history, the dynasty that includes many of the most familiar animals of the modern world, including us.
Mammals.
As you recall, mammals got their start alongside the dinosaurs, born into the violent unpredictability of Pangea over 200 million years ago in the Triassic. But mammals and dinosaurs then went their separate ways. While dinosaurs bested their early crocodile competitors, sailed through the end-Triassic extinction, and then grew to colossal sizes and spread throughout the land, mammals remained in the shadows. They became adept at surviving in anonymity, learning how to eat different foods, hide in burrows, and move around undetected, some even figuring out how to glide through the canopy and others how to swim. All the while, they remained small. No mammal living with dinosaurs got bigger than a badger. They were bit players in the Mesozoic drama.
In New Mexico, however, it is a different story. Those thousands of fossils that Tom can meticulously catalog in his mind belong to a staggering diversity of species. Some are tiny shrew-size insectivores, not too different from the vermin that scurried under the feet of dinosaurs. Others are badger-size burrowers, saber-toothed flesh-eaters, and even cow-size plant-guzzlers. They all lived during the early part of the Paleogene, within half a million years of the asteroid impact.
Already, a mere five hundred thousand years after the most destructive day in the history of Earth, ecosystems had recovered. The temperature was neither nuclear-winter cold nor greenhouse hot. Forests of conifers, gingkos, and an ever-increasing diversity of flowering plants once again towered into the sky. Primitive cousins of ducks and loons loitered near the lakeside, while turtles paddled offshore, oblivious to the crocodiles lurking underneath. But the tyrannosaurs and sauropods and duckbills were no more, replaced by the sudden bounty of mammals that exploded in diversity when presented with an opportunity they had been craving for hundreds of millions of years: a wide open playing field, free of dinosaurs.
Among the mammals that Tom and his crews have discovered is a skeleton of a puppy-size creature called Torrejonia. It had gangly limbs and long fingers and toes and probably would have looked, dare I say it, pretty cute and cuddly. It lived about 3 million years after the asteroid hit, but its graceful skeleton doesn’t seem that out of place in the world we know today. You can almost envision it leaping through the trees, its skinny toes gripping the branches.
Torrejonia is one of the oldest primates, a fairly close cousin of ours. It is a stark reminder that we—you, me, all of us humans—had ancestors that were there on that terrible day, that saw the rock fall from the sky, that endured the heat and earthquakes and nuclear winter, that eked out passage across the Cretaceous-Paleogene boundary, and then once on the other side, evolved into tree-leapers like Torrejonia. Another 60 million years or so of evolution would eventually turn these humble proto-primates into bipedal-walking, philosophizing, book-writing (or reading), fossil-collecting apes. If the asteroid had never hit, if it had never ignited that chain reaction of extinction and evolution, the dinosaurs would probably still be here, and we would not.
There is an even starker reminder, a greater lesson in the dinosaur extinction. What happened at the end of the Cretaceous tells us that even the most dominant animals can go extinct—and quite suddenly. Dinosaurs had been around for over 150 million years when their time of reckoning came. They had endured hardships, evolved superpowers like fast metabolisms and enormous size, and vanquished their rivals so that they ruled an entire planet. Some invented wings so they could fly beyond the bounds of the land; others literally shook the Earth as they walked. There were probably many billions of dinosaurs spread all over the world, from the valleys of Hell Creek to the islands of Europe, that woke up on that day 66 million years ago confident of their undisputed place at the pinnacle of nature.
Then, literally in a split second, it ended.
We humans now wear the crown that once belonged to the dinosaurs. We are confident of our place in nature, even as our actions are rapidly changing the planet around us. It leaves me uneasy, and one thought lingers in my mind as I walk through the harsh New Mexican desert, seeing the bones of dinosaurs give way so suddenly to fossils of Torrejonia and other mammals.
If it could happen to the dinosaurs, could it also happen to us?
Acknowledgments
MY CONTRIBUTION TO THE FIELD of dinosaur research has been relatively recent and relatively small. Like all scientists, I stand on the shoulders of those who came before me, and I’m helped up by those who work alongside me. I hope this book conveys how exciting things are right now in the field of paleontology and how everything we’ve learned about dinosaurs over the last few decades stems from a communal effort, the work of a diverse group of wonderful people all over the world, men and women, from field volunteers and amateurs to students and professors. There is no way I can thank everyone by name, and I would no doubt forget a bunch of important people if I tried. To all whose names and stories appear in these pages and to everyone I’ve worked with, thank you for accepting me into the global community of paleontologists and for making the last fifteen years of my life such an incredible ride.
That said, some people deserve special mention here. I’ve been incredibly privileged to have had three excellent advisors—my undergraduate mentor Paul Sereno at the University of Chicago, Mike Benton when I did my master’s at the University of Bristol, and Mark Norell for my PhD at the American Museum of Natural History and Columbia University. I realize now how lucky I was and also how annoying I must have been as a student. These three guys gave me incredible fossils to work on, took me along on fieldwork and research trips around the world, and most important, told me when I was being too ridiculous. I can’t help but think that no other young dinosaur researcher has been so fortunate in the mentor department.
I’ve worked with a lot of people, and most have been very good colleagues—dinosaur paleontologists, at least the modern generation, generally are an agreeable bunch and get along with one another. But some have crossed that line from collaborator to friend, and I would like to particularly thank Thomas Carr and Tom Williamson first and foremost, as well as Roger Benson, Richard Butler, Roberto Candeiro, Tom Challands, Zoltán Csiki-Sava, Graeme Lloyd, Junchang Lü, Octávio Mateus, Sterling Nesbitt, Grzegorz Niedźwiedzki, Dugie Ross, Mátyás Vremir, Steve Wang, and Scott Williams.
I’ve had a lot of lucky breaks in my young career, none bigger than somehow convincing the University of Edinburgh to hire me while I was finishing up my PhD. Rachel Wood has been the best mentor that a junior faculty member could ever hope for, and she still never lets me pay for coffee, food, beer, or whiskey. Sandy Tudhope, Simon Kelley, Kathy Whaler, Andrew Curtis, Bryne Ngwenya, Lesley Yellowlees, Dave Robertson, Tim O’Shea, and Peter Mathieson have been the best types of bosses—always supportive but never overbearing. Geoff Bromiley, Dan Goldberg, Shasta Mar
rero, Kate Saunders, Alex Thomas, and the other young guns have made working in Edinburgh fun. Nick Fraser and Stig Walsh have welcomed me into their group at the National Museum of Scotland, and Neil Clark and Jeff Liston have welcomed me into the bigger community of Scottish paleontologists. One of the perks of being on a faculty is that I can advise my own students, and a wonderfully diverse and gifted group has already passed through my lab: Sarah Shelley, Davide Foffa, Elsa Panciroli, Michela Johnson, Amy Muir, Joe Cameron, Paige dePolo, Moji Ogunkanmi. You probably don’t realize how much I have learned from each of you.
Science is hard enough; writing is harder. My two editors, Peter Hubbard at William Morrow in the United States and Robin Harvie in the United Kingdom, have helped mold my anecdotes and rambling into a narrative. A few years ago, Jane von Mehren heard me on the radio and thought that I might have a story to tell; she convinced me to put together a book proposal and has been an amazing agent since then. Also, a big thanks to Esmond Harmsworth and Chelsey Heller at Aevitas, for all of your help negotiating contracts and payments and foreign rights and other fun things. Huge kudos to my buddy, the incomparable artist Todd Marshall, for the original illustrations that enliven my prose, and to my dear friend Mick Ellison, the world’s best dino photographer, for letting me use some of his stunning photos. And thanks to my two family lawyers, my dad, Jim, and brother Mike, for making sure each contract was perfect beyond a reasonable doubt.
I’ve always loved to write, and I’ve had a lot of people help me along the way. Lonny Cain, Mike Murphy, and Dave Wischnowsky gave me the opportunity to work in the newsroom of my hometown newspaper—the Times in Ottawa, Illinois—for four years. The panic of the deadline and the thrill of chasing sources made me learn fast. Many folks published my (often awful) teenage writings on dinosaurs in their magazines and on their websites, especially Fred Bervoets, Lynne Clos, Allen Debus, and Mike Fredericks. More recently, Kate Wong at Scientific American, Richard Green at Quercus, Florian Maderspacher at Current Biology, and Stephen Khan, Steven Vass, and Akshat Rathi at The Conversation have given me both a platform and tough editorial love. When I got started writing this book, Neil Shubin (one of my undergrad profs) and Ed Yong both gave very helpful advice.
I’d like to thank many funding agencies—too numerous to name here—for regularly turning down my grant applications, giving me ample time and freedom to write this book. On the other hand, my sincere gratitude goes to the National Science Foundation and the Bureau of Land Management (and the US taxpayers who fund them), the National Geographic Society, the Royal Society and the Leverhulme Trust in the UK, and the EU-funded European Research Council and Marie Skłodowska-Curie Actions (and the European governments and taxpayers who fund them) for supporting me. I’ve also received many small grants from various sources and ample support from the American Museum of Natural History and the University of Edinburgh.
I have the best family of anyone I know. My parents, Jim and Roxanne, let me drag them to museums on family vacations and made sure that I could study paleontology in college. My brothers, Mike and Chris, went along with it. Nowadays, my wife, Anne, goes along with it too. She tolerates my absences on fieldwork, the times I need to sneak upstairs to write, and the various dinosaur-obsessed houseguests and pub mates that I inevitably attract. She even read through drafts of this book, even though she has no interest in dinosaurs whatsoever. Much luv! Anne’s parents, Peter and Mary, have let me spend a lot of time in their house in Bristol, England, a quiet place to write. I have some other cool in-laws too: my wife’s sister Sarah and Mike’s wife, Stephenie.
Finally, my thanks to all of the unsung heroes, the folks who usually remain anonymous but without whom our field would grind to extinction. The fossil preparators, the field technicians, the undergraduate assistants, the university secretaries and administrators, the patrons who visit museums and donate to universities, the science journalists and feature writers, the artists and photographers, the journal editors and peer reviewers, the amateur collectors who do good and donate their fossils to museums, the folks who administer public lands and process our permits (particularly my friends in the Bureau of Land Management, the Scottish Natural Heritage, and the Scottish government), the politicians and federal agencies who support science (and stand up to those who do not), the taxpayers and voters who support research, all the science teachers at all levels, and so many more.
Notes on Sources
My main source of information for this book was personal experience—the fossils that I’ve studied, the fieldwork I’ve done, the museum collections I’ve visited, and many discussions with scientific colleagues and friends. In writing this book, I picked over many of the scientific papers I’ve written for various journals, my textbook Dinosaur Paleobiology (Hoboken, NJ: Wiley-Blackwell, 2012), and pop-science pieces I’ve written for Scientific American and the Conversation. The following notes mention some supplementary material and sources that I used, which I direct you to for more information.
PROLOGUE: THE GOLDEN AGE OF DISCOVERY
I tell the story of my journey to Jinzhou to study Zhenyuanlong in one of my pieces for Scientific American, “Taking Wing,” vol. 316, no. 1 (Jan. 2017): 48–55. Junchang Lü and I described Zhenyuanlong in a 2015 paper in Scientific Reports 5, article no. 11775.
CHAPTER 1: THE DAWN OF THE DINOSAURS
There are two well-written pop-science books on the end-Permian extinction, one by my former master’s advisor Mike Benton (When Life Nearly Died: The Greatest Mass Extinction of All Time, Thames & Hudson, 2003) and the other by the great Smithsonian paleontologist Douglas Erwin (Extinction: How Life on Earth Nearly Ended 250 Million Years Ago, Princeton University Press, 2006). Zhong-Qiang Chen and Mike Benton wrote a short semitechnical review of the extinction and subsequent recovery for Nature Geoscience (2012, 5: 375–83). Updated information on the timing and nature of the volcanic eruptions that caused the extinction was published by Seth Burgess and colleagues: Proceedings of the National Academy of Sciences USA 111, no. 9 (Sept. 2014): 3316–21; and Science Advances 1, no. 7 (Aug. 2015): e1500470. Some excellent technical papers on the extinction have been written by Jonathan Payne, Peter Ward, Daniel Lehrmann, Paul Wignall, and my Edinburgh colleague Rachel Wood and her PhD student Matt Clarkson, whom I once roped into filling in on a faculty committee only a few days after he finished his thesis.
Grzegorz Niedźwiedzki has published numerous papers on the Permian-Triassic tracks of the Holy Cross Mountains of Poland. In many of these, he is joined by his friends Tadeusz Ptaszyński, Gerard Gierliński, and Grzegorz Pieńkowski of the Polish Geological Institute. Pieńkowski is a charming chap who was active in the Solidarity movement in the 1980s and was rewarded for his political activism with a consul general post in Australia when democrats assumed power after the fall of Communism. He kindly opened his guesthouse to us and plied us with kielbasa when we were traveling through the northeastern Polish lake district on our way to try to find fossils in Lithuania. Our joint work on Prorotodacylus and early dinosauromorph tracks was first published in 2010 as Stephen L. Brusatte, Grzegorz Niedźwiedzki, and Richard J. Butler, “Footprints Pull Origin and Diversification of Dinosaur Stem Lineage Deep into Early Triassic,” Proceedings of the Royal Society of London Series B, 278 (2011): 1107–13, and later as a longer monograph with Grzegorz as the lead author in Anatomy, Phylogeny, and Palaeobiology of Early Archosaurs and Their Kin, ed. Sterling J. Nesbitt, Julia B. Desojo, and Randall B. Irmis (Geological Society of London Special Publications no. 379, 2013), pp. 319–51. Important work on Triassic tracks from other parts of the world has been published by Paul Olsen, Hartmut Haubold, Claudia Marsicano, Hendrik Klein, Georges Gand, and Georges Demathieu.
The family tree of dinosaurs and close relatives that I developed during my master’s degree work was published as “The Higher-Level Phylogeny of Archosauria,” Journal of Systematic Palaeontology 8, no. 1 (Mar. 2010): 3–47.
The chapter focuses on the tracks of early dinosauromorp
hs that I’ve studied and only briefly mentions the skeletal fossils of these animals. There is a growing record of skeletons belonging to species like Silesaurus (the “intriguing new reptile fossils” found in Silesia alluded to in the text, studied by Jerzy Dzik, the “very senior Polish professor”), Lagerpeton, Marasuchus, Dromomeron, and Asilisaurus. A semitechnical review of these animals was published by Max Langer and colleagues in Anatomy, Phylogeny, and Palaeobiology of Early Archosaurs and Their Kin, pp. 157–86. Nyasasaurus, the puzzling creature that may be the oldest dinosaur or merely a close cousin, was described by Sterling Nesbitt and colleagues in Biology Letters 9 (2012), no. 20120949.
Cherry Lewis’s biography of Arthur Holmes (The Dating Game: One Man’s Search for the Age of the Earth, Cambridge University Press, 2000) is a good introduction to the concept of radiometric dating, the history of its discovery, and how it is used to date rocks. The sticky subject of dating Triassic rocks is discussed in an important paper by Claudia Marsicano, Randy Irmis, and colleagues (Proceedings of the National Academy of Sciences USA, 2015, doi: 10.1073/pnas.1512541112).
Paul Sereno, Alfred Romer, José Bonaparte, Osvaldo Reig, Oscar Alcober, and their students and colleagues have written many papers on the Ischigualasto dinosaurs and the animals living alongside them. The single best source of information is the 2012 Memoir of the Society of Vertebrate Paleontology, Basal Sauropodomorphs and the Vertebrate Fossil Record of the Ischigualasto Formation (Late Triassic: Carnian–Norian) of Argentina, which includes a historical review of the Ischigualasto expeditions and a detailed anatomical description of Eoraptor, both written by Sereno.
Two interesting developments were published right as this book was going to press. First, the Ischigualasto plant-eating Pisanosaurus, which I discuss as an early member of the ornithischian dinosaur lineage, was redescribed and reclassified as a non-dinosaur dinosauromorph closely related to Silesaurus (F. L. Agnolin and S. Rozadilla, Journal of Systematic Palaeontology, 2017, http://dx.doi.org/10.1080/14772019.2017.1352623). So it is possible that there are currently no good ornithischian fossils from the entire Triassic Period. Secondly, Cambridge PhD student Matthew Baron and colleagues published a new family tree of dinosaurs, placing theropods and ornithischians in their own group (Ornithoscelida) exclusive of sauropods (Nature, 2017, 543: 501–6). This is an exciting but controversial idea. I was part of a team, led by Max Langer, that reassessed Baron et al.’s data set and argued for the more traditional ornithischian-saurischian subdivision of dinosaurs (Nature, 2017, 551: E1–E3, doi:10.1038/nature24011). This will surely be a huge subject of debate for many years.
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