Extreme Mammals is divided into nine sections and offers extensive detail on the evolutionary history and great family tree of mammals.
- Introduction: Upon entering the gallery, visitors are asked “What is extreme for mammals?” and discover models of the largest and smallest land mammals ever found: an overwhelming 15-foot-tall model of Indricotherium, an ancient rhinoceros-relative that was the largest mammal to walk the Earth; and a life-sized model of the extinct shrew-like Batodonoides, the smallest extinct mammal ever, which weighed less than a twentieth of an ounce, or the equivalent of a dollar bill. The most extreme sizes for creatures living today include the 200-ton blue whale, the largest animal—mammal or otherwise—ever known; and the bumblebee bat, the smallest living mammal, literally no bigger than a bee and as light as a dime.
- What is a Mammal? Visitors are introduced to the basics of mammal evolution and biology. There are more than 5,400 mammal species alive today, classified into 20 different groups, called orders. About 300 million years ago, the evolutionary branch of the tree of life that includes mammals split off from the branch containing reptiles. For over 130 million years, mammals lived side by side with dinosaurs, and some early mammal relatives are even mistaken for dinosaurs, such as the sail-back synapsid Dimetrodon. The fossil skull of the more mammal-like Cynognathus shows the specialized or differentiated teeth of early mammal ancestors. Additional characteristics unique to mammals include nursing their young with milk; three middle-ear bones; a diaphragm for breathing; a secondary palate that allows simultaneous eating and breathing; and a warm, stable body temperature.
- What is Extreme? Typical characteristics of mammals—having hair, possessing three middle ear bones, and being warm-blooded—are extreme compared to other groups of animals. The skeletons of Uintatherium—the first giant mammal that evolved after large dinosaurs became extinct—an opossum, and a cast of a human skeleton, illustrate a range of combinations of “normal” and “extreme” mammal qualities. Standing five-feet-tall at the shoulders, the Uintatherium’s huge body, bony horns, dagger-like teeth, and tiny brain for its body size are all unique features compared to other mammals. And humans are out of the ordinary with their large brain for their body size and ability to walk upright on two legs.
- Head to Tail: Horns, tusks, noses, brains, body armor, and tails have come a long way in the evolutionary history of mammals. The purposes of these traits may include self-defense, recognizing kin, or attracting mates. For example, the Indonesian babirusa pig (Babyrousa babyrussa), a skull of which is on display, uses teeth that grow through the bones and skin of the top of its snout for display and fighting. The complete fossil carapace of a glyptodont shows how this car-sized armadillo-relative was covered with a thick, bony shell, or carapace, to protect itself from large predators. The life-sized model of Macrauchenia features a camel-like body, giraffe-like neck, and elephant trunk-like nose.
- Reproduction: Giving birth to live, well-developed offspring is “normal” for most mammals, but more than 300 species of living extreme mammals do things differently. Monotremes, mammals that lay eggs, and marsupials, mammals that give birth to very immature offspring and often have pouches, are each extraordinary when it comes to reproduction and far removed from the more common placental mammals, which have babies that develop for a long period within the womb. Just a handful of mammals lay eggs, including the platypus and echidnas featured in this section. However, egg-laying is the norm in other vertebrate groups like birds, reptiles, and amphibians. Among the eight taxidermy specimens on display in this section is a specimen of the spectacled bear, which shows how some placental mammals also give birth to unusually immature young. Adult spectacled bears tip the scales at around 200 to 300 pounds, but they weigh less than one pound at birth.
- Mammals in Motion: Whether they move around on land, in water, or by air, mammals have developed amazing features to get from one place to another. The life-size cast skeleton model skeleton of the Glossotherium chapadmalensis, an extinct ground sloth that was a slow-moving knuckle walker, shows how gigantic these mammals could grow to be. About 50 million years ago, some groups of mammals began to shift from land to ocean life. A life-size relief model of Ambulocetus natans, the extinct “walking whale,” vividly depicts a transitional form between modern-day whales and their extinct land-living ancestors. The cast of the skull and partial skeleton of Puijila darwini, or “walking seal relative,” has otter-like limbs and a seal-like head. Discovered in the High Arctic in 2007, scientists have described Puijila darwini as another example of a transitional fossil—a missing link in the evolution of pinnipeds, the group that includes today’s seals, sea lions, and walruses. A few mammals glide through the air, such as lemurs and squirrels, but only bats can truly fly. Onychonycteris finneyi, a spectacular 52-million-year-old bat fossil on display, represents the most primitive bat species known to date and demonstrates that these animals evolved the ability to fly before they could echolocate, or detect objects by emitting sounds and gauging their reflections. Of the more than 5,400 species of mammals that exist today, over 1,100 are bats.
- Extreme Climates: A large-scale, intricately detailed diorama of Ellesmere Island, located 600 miles from the North Pole, provides an insightful glimpse of this area 50 million years ago. At that time, the Earth was significantly warmer and Ellesmere Island was covered mostly with forests. This reconstruction shows a once warm, humid, and swamp-like forest, unlike the bitter-cold Arctic of today, that was home to mammals that lived in marshes or could climb trees. Among the models of extinct mammals in the diorama, are Vulpavus, a carnivore that had a long thin body and tail, well suited for quick movements both in trees and on the ground; Coryphodon, a short-tusked hippo-like wader; and Thuliadanta, an extinct tapir that had a flexible, trunk-like snout.
- Extreme Isolation: Madagascar, Australia, and South America existed as isolated islands and continents for tens of millions of years, leading to the evolution of an incredible diversity of mammals found nowhere else on Earth. Impressive fossils of the extinct hoofed plant-eaters Scarrittia and Astrapotherium illustrate the concept of convergent evolution, the appearance of similar features in distantly related organisms living in similar environments. While Scarrittia looked like a rhino or horse, it was not closely related to either. Astrapotherium developed large tusks and a long trunk, but was not closely related to elephants found on other continents. On display are several of their recent groundbreaking discoveries from South America, including a cast of the earliest known complete monkey skull ever found on that continent, perfectly preserved in volcanic ash.
- Extreme Extinction: Mass extinctions, or the rapid loss of a great number of species, have happened at least five times over the past 500 million years, with the possibility of a sixth occurring today. Climate change, hunting by humans, an impact or atmospheric explosion of a comet, and the introduction of new diseases are some of the drivers that may have been behind the permanent disappearance of many large mammalian species about 12,000 years ago. Today, human-caused environmental changes and habitat loss threaten more species. Concluding the exhibition are the remarkable fossil skulls and skeletons of Smilodon fatalis, a massive saber-toothed cat, and Canis dirus, the dire wolf, both of which roamed North America and died out at the end of the last Ice Age. On view is a model specimen of one of the last-known Tasmanian wolves (also known as Tasmanian tigers). After intense hunting, the species went completely extinct as recently as the mid-1930s. Remarkably, even with 25 percent of living species of mammals on the brink of extinction, there are many more mammals yet to be discovered. Scientists have found hundreds of previously unknown species of mammals in the last few decades, including several featured here, such as the tube-lipped nectar bat, from the Andes Mountains of Ecuador and a striped rabbit from the Annamite Mountains of Laos and Vietnam—a life-size model of which is included in the exhibition.