Mammals in the extreme: the biggest, smallest, and most amazing mammals of all time finally have emerged--and are on view for all to see.
THE EXHIBITION "Extreme Mammals: The Biggest, Smallest, and Most Amazing Mammals of All Time" explores the surprising and often extraordinary world of extinct and living mammals. Featuring spectacular fossils and other specimens, vivid reconstructions, and live animals, it examines the ancestry and evolution of numerous species, ranging from huge to tiny, from speedy to sloth-like, and displays animals with oversized claws, fangs, snouts, and horns.
"Ranging from the familiar to the wildly exotic, mammals represent some of the most fascinating and extraordinary creatures ever to have lived, including, of course, humans," notes Ellen V. Futter, president of the American Museum of Natural History. "By looking closely at this one amazing class of animals ... 'Extreme Mammals' offers visitors a fun and intriguing opportunity to learn about how life evolved, why ,animals may, despite sharing some key characteristics, look and behave so differently from one another, and how there can be such extraordinary diversity within a single group."
The exhibit examines how some lineages died out while others diversified to form the groups of well-known mammals living today. Highlights include taxidermy specimens--from the egg-laying platypus to the recently extinct Tasmanian wolf (also known as Tasmanian tiger)--and fleshed-out models of extinct forms, such as Ambulocetus, a "walking whale." There is an entire skeleton of the giant hoofed plant-eater Uintatberium, with its dagger-like teeth and multiple horns; the skeleton model of Puijila darwini, a newly discovered extinct "walking seal," from the High Arctic, with webbed feet instead of flippers; a life-size model of Indricotherium, the largest land mammal that ever lived; one of the oldest fossilized bats ever found; and an impressive diorama featuring the once warm and humid swamps and forests of Ellesmere Island, located in the High Arctic, about 50,000,000 years ago.
Through the use of dynamic media displays, animated computer interactives, hands-on activities, touchable fossils, casts, taxidermy specimens, and a colony of live sugar gliders--extreme marsupials from Australia--the exhibition highlights distinctive mammalian qualities and illuminates the shared ancestry that unites these diverse creatures.
"Mammals are old--as old as the dinosaurs, but all dinosaurs, except for the lineage that gave rise to living birds, went extinct 65,000,-000 years ago," explains Michael J. Novacek, curator of the Division of Paleontology. "Mammals survived this great extinction event and even further diversified, evolving into the wondrous and sometimes strange creatures that are still with us today. This exhibition not only brings us close to this great flourish of mammals present and past, it shows how mammals are powerful examples of evolution in action."
Adds "Extreme Mammals" curator John J. Flynn: "This exhibition highlights the striking array of living and fossil mammals, so our visitors can explore the remarkable diversity of species, anatomies, and ecological specializations that occur in mammals. Extinct mammals often are viewed with curiosity, awe, or admiration because they are so different from familiar living organisms. In 'Extreme Mammals,' such unusual taxa are compared to their ancestors, closest relatives, or contemporaries to document and explain what is 'normal' and what is 'extreme.' The exhibition focuses on the extraordinary qualities of extinct and living mammals, revealing them to be much more than just furry, warm-blooded animals that nourish their young with milk."
The exhibition is divided into nine sections: Introduction; What is a Mammal?; What is Extreme?; Head to Tail; Reproduction; Mammals in Motion; Extreme Climates; Extreme Isolation; and Extreme Extinction.
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 lndricotherium, an ancient rhinoceros relative that was the largest mammal to walk the Earth, as well as a life-sized model of the extinct shrew-like Batodonoides, the smallest extinct mammal ever, which weighed less than one-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? Before exploring more extremes, 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 300,000,000 years ago, the evolutionary branch of the tree of life that includes mammals sprit off from the branch containing reptiles. For over 130,000,000 years, mammals rived side by side with the now extinct large dinosaurs, and some early mammal relatives even are mistaken for dinosaurs, such as the sail-back synapsid Dimetrodon, a fossil featured in this section. The fossil skull of the more mammal-like Cynognathus shows the specialized or differentiated teeth of early mammal ancestors, but not all the characteristics of the riving groups of mammals. 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. While many features of an opossum are normal for mammals, like its body size, the Virginia opossum's prehensile tail, which it uses like an extra limb to grasp or hang from branches, is an exceptional feature. Standing five feet tall at the shoulders, the Uintatherium's huge body, bony horns, dagger-like teeth, and tiny brain (for its body size) all are 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. There are very few other bipedal mammals--and they mostly are hoppers like kangaroos. Humans also have some normal features compared to other mammals, such as three middle ear bones and five digits on each hand and foot.
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 instance, 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 skeleton 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. Younger visitors are given the opportunity to crawl into a model of a Glyptodont's shell to experience what it feels like to be sheltered by this protective body armor. The rife-sized model of Macrauchenia features a camel-like body, giraffe-like neck, and elephant trunk-like nose. While a specimen with a preserved nose never has been found--Macrauchenia became extinct 10,000 years ago--the reconstruction of its unusual proboscis or trunk is based on skull features found in mammals with such specialized noses and a comparison of early and later members of the same group.
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 off spring and often have pouches, each are 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. Are monotremes really that unusual for laying eggs? 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. Sugar gliders--live and on display in a specially designed habitat--may look like American "flying" squirrels, but they actually am marsupials and more closely related to kangaroos and koalas. Like all marsupials, sugar gliders give birth to very immature young that typically grow to independence in a pouch while drinking their mother's milk. Among the eight taxi-dermy specimens on display in this section is a 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 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 skeleton of the Glossotherium myloides, an extinct ground sloth from South America that was a slow-moving knuckle walker, shows how gigantic these mammals could grow to be. About 50,000,000 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 truly can fly. Onychonycteris finneyi, a spectacular 52,000,000-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. First discovered in Wyoming in 2003, this bat species was described last year in a study led by Nancy Simmons, chair of the Division of Vertebrate Zoology and a curator at AMNH. 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 50,000,000 years ago. At that time, the Earth was significantly warmer and Ellesmere Island mostly was covered 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 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. In contrast to the lush vegetation and diverse mammals 50,000,000 years ago, today the plants on Ellesmere Island only are a few inches tall at most, and fewer than a dozen species of land mammals live there, including musk ox, caribou, polar bear, and Arctic hare.
Extreme Isolation. How do new species evolve? One way is when a population of animals is cut off completely from others of the same group and they no longer can interbreed. 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. As trapotherium developed large tusks and a long trunk, but was not closely related to elephants found on other continents. A scientist-at-work video explores the unique mammalian forms that existed while South America was an isolated continent during most of the past 90,000,003 years. On display are several of their recent groundbreaking discoveries from South America, on loan from the National Museum of Natural History of Chile, including 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, has occurred at least five times over the past 500,000,000 years, with the possibility of a sixth underway 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. At present, 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 taxidermy 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% 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.
"Extreme Mammals: The Biggest, Smallest, and Most Amazing Mammals of All Time" is on view through Jan. 3, 2010 at the American Museum of Natural History, New York. It begins touring in the spring. Scheduled stops include the California Academy of Sciences, San Francisco (April 3-Oct. 11, 2010); The Cleveland Museum of Natural History (Oct. 29, 2010-April 15, 2011); and the Canadian Museum of Nature, Ottawa (June 4, 2011-Nov. 6, 2011).
DID YOU KNOW ...?
Facts About Mammals
* The tiny creature Batodonoides, with an estimated body weight of 1.3 grams, was so small it could have climbed up a pencil. It lived approximately 50,000,000 years ago and is related to modern shrews and moles.
* The smallest mammal alive today is Craseonycteris thonglongyai, which is slightly larger than Batodonoides. This bumblebee bat, as its name implies, is no bigger than a bee and weighs only about as much as a dime. It beats its tiny wings so quickly that it can hover in place like a hummingbird. Bumblebee bats live in Thailand and Myanmar. They are so rare that they were unknown to science until 1974.
* The tiny bat Anoura fistulata, discovered in 2005, lives in the Andes Mountains of Ecuador. Its tongue is longer than the rest of its body. In fact, it has the longest tongue relative to body length of any mammal. This adaptation helps the bat lap nectar from long-tubed flowers---especially the night-blooming plant Centropogon nigricans. Researchers think this newly discovered bat is the only species that can pollinate this flower.
* Indricotherium is the largest land mammal ever discovered. A fully grown adult weighed up to 20 tons--the size of three or four adult African elephants, which are the largest land mammals alive today. Indricotherium lived in the forests of Central Asia between about 34,000,000 and 23,000,000 years ago. It was a plant-eater that could stretch its long neck to nibble leaves high in the treetops. Indricotherium needed to eat massive amounts of vegetation to survive and, as the Central Asian forests gave way to open grassland habitats, this huge mammal became extinct. Its closest living relative is the rhinoceros.
* The blue whale is the largest known animal ever--mammal or otherwise. Blue whales can grow to nearly 200 tons--10 to 20 times bigger than Indricotherium and are up to 108 feet in length. Its tongue alone can weigh more than four tons, and its heart is the size of a small car. No land animal could carry this much weight, but it is possible for animals to evolve to larger sizes in the ocean because the buoyancy of water helps support them.
* Whales once walked on four legs but, as they adapted to live full-time in aquatic environments, their front legs evolved into flippers. Tiny, invisible-from-the-outside remnants of hind legs remain in their skeletons, but they perform no known current function.
* All mammals--and only mammals--have three bones inside their middle ear. It is one of the ways scientists recognize a mammal, even when they have nothing but a fossil skull to examine. Over millions of years of evolution, some jaw bones moved inside the ear, leaving mammals with a single jaw bone.
* Mammal extinctions are occurring rapidly: during the past 500 years, at least 75 mammal species are known to have died out, with many more barely hanging on. Nearly 25% of today's living mammal species are threatened with extinction.
* Unlike other mammals, monotremes, like the platypus, never evolved to give live birth, but instead lay eggs like their amniote ancestors. Monotremes produce milk for their young but lack nipples, so their milk just oozes out of mammary gland ducts and collects in grooves on patches of skin, where the nursing babies lap it up or suck it from tufts of fur.
* A mother kangaroo can have three babies at the same time, all in different stages of development. Even with two nursing joeys, a red kangaroo might have an extra fertilized egg in her belly, in suspension. This egg does not begin to grow until one of the older offspring stops nursing.
* The oddest thing about naked mole rats is not their appearance--or that they neither are moles nor rats. Their social structure is perhaps the most extreme found in mammals: an entire colony of 20 to 300 actually is a single family led by a "queen," who is the only female that breeds. Only one to three males in the colony will mate with the queen. Other members serve as soldiers that protect the group, while others are workers that dig tunnels and gather food. This highly specialized colonial social structure is common in insects like ants and bees, but very unusual for mammals.
* Ossicones are bony cores that develop first as knobs of cartilage covered by skin. A baby giraffe's ossicones lie flat against the head at birth and pop upright about a week later. The knob later "ossifies," or becomes bone. Ossicones usually are covered with skin and fur.
* Antlers--a pair of branched bones that are shed annually-grow each year from a permanent bony, skin-covered base. They grow up to an inch a day.
* The male babirusa, a pig from Indonesia, has teeth that protrude from the top of its snout, used for fighting. These upper canines do not grow downward as normal ones would, but directly upward, through the top of the skull bone and out through the muzzle skin.
* It is pretty hard to imagine a mouse or its relatives with bony headgear, but a genus of extinct rodents really did have horns, including the foot-long Ceratogaulus rhinoceros. These burrowing relatives of the living mountain beaver might have used their horns to woo mates, or perhaps they frequently foraged for food above ground and evolved horns to protect themselves from predators.
* Like living elephants, extinct mammoths had six sets of grinding teeth during their lifetimes, each one larger than the last. The largest molar could weigh four pounds. These ridged teeth helped the animals chew tough grasses, shrubs, and twigs.
* A male narwhal's strong, eight- to 10-foot-long spiral tusk is more flexible than it looks: in live animals, it can bend a foot in any direction. By studying narwhals' tusks under an electron microscope, scientists found that they are pierced by channels for extremely sensitive nerves. These nerves may help the whales detect subtly changing ocean conditions and locate prey. Tusks usually are found in males only, so narwhals also may use them to attract females.
* Despite having the largest absolute brain weight of any animal--up to 20 pounds--sperm whales have small brains for their body size of up to 110,000 pounds.
* Aye-ayes have much larger brains than their closest primate relatives, other lemurs, possibly to allow for their complex food-hunting strategies. With their two wiry, very long middle fingers, aye-ayes patiently tap tree branches and listen to the pitch of the taps to locate the bugs inside. Then, with their skinny, flexible middle digits, they pull out the catch.
* When aye-ayes bore through branches with their sharp front teeth, sawdust can fly. However, their eyes have built-in third eyelids--almost like a carpenter's goggles--that moisten the eyes and protect them as they work.
* A tiny nocturnal primate, the tarsier has eyeballs that bulge too tightly against the skull to pivot. To see around itself, a tarsier must swivel its entire head, which can rotate nearly 180[degrees] in each direction.