Come Meet Your Folks: Warm Blood Is Required

By Edward Rothstein

New York Times, May 14, 2009

You don’t usually associate the American Museum of Natural History with a carnival barker sales pitch — Step right up, folks! Never before seen by human eyes! — but the playful tone of its fine new exhibition, “Extreme Mammals,” comes close. It boasts “the biggest, smallest and most amazing animals of all time.”

This exhibition, which opens on Saturday, has as many exclamation marks as a Ripley’s “Believe It or Not” show. And where they are missing, you feel like inserting them, even when some of its creatures are represented only by fossils and skulls, drawings and skeletal reproductions:

A bee-sized bat!

A beaver with horns!

Whales with teeth “as big as a slice of pizza!”

An Indonesian pig with teeth that grow through the top of its skull bones!

Ten-thousand-year-old coarse black hair — fresh-frozen from the pelt of an extinct mammoth!

And — live! — nocturnal “sugar gliders,” the show’s only living creatures! In the dim display they look like flying squirrels whose bulbous eyes put the doe-eyed caricatures of Japanese anime to shame.

This pace is kept up throughout. At the entrance you are dwarfed by a life-size model of the “largest land mammal ever,” an 18-foot-tall, 20-ton, extinct vegetarian Indricotherium, which looks like a cross between an elephant and a rhinoceros, if both had been designed by Dr. Seuss. Turn again, and you see the “smallest mammal ever,” a 50-million-year-old 1.5-inch Batodonoides, reconstructed from a recently discovered “tiny fossil jaw”: it looks like a jumbo mosquito with teeth, meriting an urgent, quick swat.

Extreme mammals indeed. Anything extreme, of course, has always been sought by collectors: it is guaranteed to inspire amazement. Though the word now often means little more than hype, John J. Flynn, the museum’s paleontologist and the show’s curator, makes it appropriate. He has done so not by highlighting nature’s freaks and exceptions — the mutations and bizarre accidents that amaze and horrify — but by exploring the edges of our awareness about the animal kingdom’s most familiar group.

To a certain extent all animal categories are arbitrary; we choose which kinds of associations are important, creating order out of miscellany, taming the chaos of variation. Paleontologists don’t use categories like “animals that swim,” “animals with cute faces” or “animals that taste good,” because these categories — which might turn out to be very useful in certain circumstances — don’t tell us much about their kinship and history. Or about our own.

At first glance at these astonishingly diverse creatures, which include koala bears, armadillos, platypuses, beavers, whales and humans, it might seem that mammalia as a category is also arbitrary: is there any significant connection between the lumbering Indricotherium and the gnatty Batodonoides?

Look around here and you are struck not by uniformity and shared traits but by intricate variation. There is a display of mammalian “headgear”: antlers, tusks, horns and protrusions. There are teeth that grind, others that chop and the comb-like baleen of whales — fine, toothlike filaments that filter smaller animals for eating. There are descriptions of mammalian “marriages” with one female and many males (naked mole rats), one male and many females (lions), multiple partners (bonobos) and monogamous alliances (Blandford’s foxes).

Part of the show’s excitement is the dizzying variation of life forms contained in this single category. Why, then, even come up with a concept of “mammal”?

It may well have been because humans were finding similarities with our own species. Mammals, we learned in school, are a class of vertebrates. Like us they have bones in their backs. Like us their infants feed on milk produced by the female’s mammary glands. Mammals have hair or fur. They are warm-blooded, and they are not hatched from eggs.

By definition, it seems, a typical mammal — one that is not extreme — is us. Or as the exhibition advertising puts it, “Come and meet your relatives!”

But as the show soon teaches us, even these resemblances don’t always hold. While the “vast majority” of mammals give birth to live young, marsupials will host them in a pouch (the kangaroo, we learn, can simultaneously provide different kinds of milk for its differently aged offspring) and mammalian monotremes like the “short-beaked echidna,” which resembles a spiny platypus, even lay eggs. Humans are also less typical than it might seem: we are the only mammalian bipeds that don’t hop (at least as the dominant means of locomotion). A more reliable defining characteristic, it seems, is something found only in the study of physical remains: all mammals and only mammals have three bones inside the middle ear.

This earbone criterion may seem esoteric — until we learn that the evolution of that bone structure is related to the development of a single lower jaw, which in turn, is associated with the fact that mammals, unlike, say, lizards, have differentiated teeth that allow for different kinds of chewing. Many seemingly arbitrary physical characteristics are actually associated with a particular kind of survival. Mammals developed nocturnally effective eyesight, as well as larger brains for strategizing, which is where humans may be the most extreme of all.

In this exercise of classification that brain is being put to strenuous use, because the particular characteristics are so variable that scientists today define mammals not using physical criteria but evolutionary origins: “All mammals alive today descended from a single, shared ancestor.”

The ascendance of those descendants had much to do with a loose assemblage of features: warm blood, nocturnal eyesight, large brains. Were mammals the dinosaurs’ nemesis? Some credit here is given to the recently discovered Repenomamus, a cat-size creature, perhaps the largest mammal in the age of the dinosaurs: 130-million-year-old Repenomamus fossils have been found with dinosaur bones inside their bellies.

So these extreme mammals really are, in a strange way, our relatives, a multibranched, variegated web of life forms, many extinct (as are 99 percent of all species that ever lived) but some of which are still being discovered: the last display shows a reconstruction of a striped rabbit, a new species discovered in 1999 in Laos.

The lesson may be that nothing about mammals is that extreme, because nothing about them is really commonplace. This show might even be considered a self-centered declaration of evolutionary triumph. It is something that only a mammal could have conceived.

“Extreme Mammals” opens Saturday and runs through Jan. 3 at the American Museum of Natural History, Central Park West and 79th Street; amnh.org; (212) 769-5100 or (212) 769-5200. Timed entry tickets required for nonmembers.