These Animals Were Just As Awesome and Fascinating As Dinosaurs

Fossil mammals have been in the shadows for too long.

Pakicetus at the Natural History Museum of Los Angeles.

Courtesy of Brian Switek

If you’re in New York City and need a break from the swarms crowding the sidewalks, I know where you can go. The Milstein Hall of Advanced Mammals in the American Museum of Natural History is almost always quiet. You may bump into the occasional student trying to fill out a science class scavenger hunt or a confused family wondering where the dinosaurs are, but the hall is usually as hushed as a tomb. That’s fitting for a room boasting skeletons of fossil beasts shoved into almost every corner, but it’s also a shame.

I’ve seen the same at other major museums: the Field Museum in Chicago; the Carnegie in Pittsburgh; the Peabody in New Haven, Connecticut; the Los Angeles Museum of Natural History; the Royal Ontario Museum in Toronto; and more. Hordes of children and adult visitors pack the dinosaur halls, but the fossil mammals stand in the shadows—dominated by the reptiles in death just as they were in life. After a mass extinction released mammals from the tyranny of the dinosaurian reign, they became even more strange and spectacular. But even these species have been obscured by the popularity of the scaly and fuzzy reptiles. Some visitors, assuming that any skeleton in a museum must be from the Mesozoic, even go so far as to insult giant sloths, multitoed horses, and enormous elephants by calling them dinosaurs.

It drives me a little bit crazy. When I see parents tugging their kids through a fossil mammal hall, urging, “Let’s go find T. rex!” I want to run over to them and start yelling, “No! Wait! Look there. That’s a prehistoric manatee with legs! And check that one out—it’s a miniature camel that used to live in North America. And this critter, this is a bear-dog, and it was just as ferocious as the name implies.” I’d more than likely have security called on me, but it might just be worth it. The mammals of the past 66 million years—not to mention those that lived alongside the dinosaurs—were some of the most fantastic animals to ever live on this planet. They’re certainly as worthy of our attention and admiration as any dinosaur, and I’m sick of what has basically amounted to willful ignorance about the beasts that have thrived in the aftermath of dinosaurian Armageddon.

The early elephant Moeritherium at the Yale Peabody Museum of Natural History.

Courtesy of Brian Switek

The situation for prehistoric elephants, cats, and wolves wasn’t always so dire. Before there was a word for dinosaurs, or even a concept of what one was, mammals were the greatest stars of prehistory. Thomas Jefferson cited the existence of the American mastodon—which he thought might still be alive in the Western interior—in Notes on the State of Virginia to demonstrate to snooty Europeans that the Americas were capable of producing life just as vibrant and vigorous as that of the Old World. The artist and polymath Charles Willson Peale reconstructed bones of another mastodon excavated in 1801 in what became an extremely popular, and lucrative, museum exhibit in Philadelphia. And during the “Bone Wars” of the late 19th century, the embattled paleontologists Edward Drinker Cope and Othniel Charles Marsh (who hated each other and competed for every new fossil) were as famous for rhino-like brontotheres, early horses, and other mammals they named as they were for all the dinosaurs.

Arsinoitherium at the Natural History Museum, London.

Courtesy of Brian Switek

Dinomania started to take hold in the early 20th century, when the American Museum of Natural History, Field, and Carnegie competed in the “my dinosaur is bigger than yours” contest more formally known as the Second Jurassic Dinosaur Rush. Even then, though, paleontologists still preferred fossil mammals. The bizarre skeletons of Apatosaurus, Stegosaurus, and Tyrannosaurus drove ticket sales, but the experts of the day were more concerned with the creatures that came after the Cretaceous mass extinction. There were far more fossil mammals than dinosaurs, and their history could be traced through the constantly changing arrangements of their teeth, making them ideal for drawing big-picture conclusions of how life evolves through time. Dinosaurs were more of a prehistoric sideshow, so much so that some early 20th century paleontologists proposed that they died off because the reptiles simply got so big and so weird that their bodies couldn’t function anymore. If you wanted to understand what George Gaylord Simpson called the “tempo and mode of evolution,” in his book that squared natural selection with the fossil record, you had to turn to mammals.

The “hell pig” Archaeotherium at the Natural History Museum of Los Angeles.

Courtesy of Brian Switek

I’ve been simultaneously fascinated with and frustrated by why dinosaurs have superseded most fossil mammals as the objects of our prehistoric adoration. It may be the flipside of the question “Why do we love dinosaurs so much?” As far as I can tell, dinosaurs have kept their talons wrapped around our minds for two different reasons. First, as Stephen Jay Gould once argued, they’ve got an excellent marketing team. Dinosaurs are the stars of movies, have inspired enough museum gift shop kitsch to outweigh a Supersaurus, and the discovery of new dinosaur species often makes headlines. We’ve gone beyond dinomania into a kind of dinopsychosis. And, at a more basic level, all this attention seems justified because dinosaurs really were superlative creatures. The ones we love best are often huge and strange, bearing horns, spikes, claws, and teeth that make them unlike anything around us today. In fact, films like Jurassic World and The Good Dinosaur have actively resisted making dinosaurs more birdlike, perhaps because that would connect dinosaurs to the animals around us today, making them just that much less special.

American mastodons.
American mastodons at the La Brea Tar Pits and Museum.

Courtesy of Brian Switek

Yet paleontologists have filled museum cabinets and fossil halls with mammals that, to my mind, are just as strange as any dinosaur. There’s Amebelodon, the “shovel tusker” with a lower jaw modified into a scoop that the herbivore used to saw through vegetation. Whales, such as Pakicetus, started off as hoofed mammals that walked on land. An array of nimravids—like true cats that look like sabercats but belonging to their own distinct lineage—stalked the forests of North America, Europe, and Asia, and even the South American marsupial Thylacosmilus got in on the saber-toothed act. One of my all-time favorites is Uintatherium, a rhino-size herbivore with four blunt horns jutting from its skull and elongated fangs for showing off. Even just this month, paleontologists described Xenomeryx amidalae—a beast with headgear so weird its species name honors a Star Wars character. And that’s not to mention an entire cast of other unusual beasts belonging to unfamiliar lineages like the creodonts (carnivores that ruled before cats and dogs), desmostylians (beasts that looked like hippo-seals), multituberculates (squirrel-like mammals with incredibly complex teeth), chalicotheres (“sloth horses”), and more.

Why should they sound so unfamiliar? Every dinosaur name is a technical term, after all. We’re comfortable with Triceratops, Diplodocus, and Pachycephalosaurus. Why should Astrapotherium, Titanoides, or Syndyoceras stay beyond the pale of our prehistoric imagination? Maybe it’s because we feel we already know fossil mammals. That they’re all just slightly modified versions of elephants, cats, antelope, and the like with a few tweaks. But looking at them this way ignores 66 million years of beastly evolution that created vibrant ecosystems where the strange met the familiar. And this is our history, too: Mammals’ most interesting evolutionary experiments occurred during the time when our own primate lineage proliferated. The age of mammals is still young compared with the preceding 180-million-year-long age of dinosaurs, but evolution has spun off an incredible array of oddities that form the latest chapters in the book of life on Earth.

A giant ground sloth.
A giant ground sloth at the Yale Peabody Museum of Natural History. This one was preserved in bat poop.

Courtesy of Brian Switek

Dinosaurs are strange and deserving of wonder, I’ll admit, but they’re also the cool kids. They’re popular because they’re popular. We’ve turned them into almost unbearable showoffs, underscored by how many newly described species try to claim some association with the famous Tyrannosaurus and Triceratops in pop sci headlines. So maybe it’s just because I’m a nerd and I have an affection for the underdog, but I think it’s time we appreciate our closer relatives. It’s time again for mammalmania.