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A self guided Tour of the Vertebrate Fossils
Submitted by Steven A. Sauter (inactive)
A Guide to Vertebrate Paleontology
at The Amherst College Museum of Natural History
The Amherst College Museum of Natural History has one of the most outstanding research collection of vertebrate fossils in New England, and only a portion of its holdings are on public display. To prepare for these exhibits, start with the introductory displays to the left of the main entrance. These show the main events in the evolution of plants and animals on a time scale, as well as some of the different kinds of fossils.
This handout more or less follows the exhibits, although the vertebrate fossils are not always arranged in phylogenetic (or evolutionary) order.
Some of the best vertebrate fossils in the Museum are on the center platform near the front entrance. Most of these are from relatively late in the Ice Age (Pleistocene). The largest skeletons are the mastodon and the mammoth. Of the two, the mammoth is more closely related to modern elephants. Mastodons frequented more forested areas than mammoths and had shorter, heavier limbs, lower crowned teeth, and small lower tusks. Another spectacular specimen is the Irish elk, which is neither a true elk nor restricted to Ireland. Its huge antler rack may have been useful to males competing for mates and probably was not a severe disadvantage as long as the animals frequented open country.
The dire wolf and saber-toothed cat both come from the La Brea tar pits in Los Angeles, California. These specimens probably became mired in the tar while following prey that had itself become trapped. At the far SW corner of the platform is a cave bear. These plant-eating bears are uncommon in American museums because they lived only in Europe and Asia. The moa - found in the case of extinct birds is an example of a flightless bird from New Zealand. The moa's wings are reduced to a tiny remnant of the shoulder girdle, but its hind limbs are well adapted for running.
The camel/horse walls have fine fossil skeletons. The horse sequence from early Hyracotherium to living Equus traces the loss of toes, skull changes, and size increases that characterize horse evolution. The evolution of modern horses is linked to the spread of grasslands in the late Tertiary. The evolutionary sequences, many aspects of which were first worked out in the late 1800's, provides a classic example of dramatic long-term evolutionary change within a lineage.
Oxydactylus represents an early camel. Both horses and camels had most of their evolutionary histories in North America: they radiated here, and then spread to other continents. In only the last few thousand years, however, both lines became extinct in North America. A large skeleton of a Brontothere is at the base of the Cenozoic Wall. Brontotheres are extinct relatives of the horses and rhinoceroses; note the bony protuberances on its nose above its eyes.
Dinosaurs on the lower level
On the South wall is a tall plant-eating dinosaur called Gryposaurus. This dinosaur belonged to a group called the hadrosaurs or "duckbills" and comes from the famous dinosaur fossil beds in Alberta, Canada. The shorter forelimbs probably helped in browsing for food. The front of the jaws are toothless, but there were numerous grinding teeth farther back. To the left you as you look at Gryposaurus is a skull of Triceratops. Triceratops, a ceratopsian dinosaur, had two horns over its eyes and one on its nose. The "frill" probably helped to protect the neck.
Among the specimens is a cast of the skull of Tyrannosaurus, a savage meat-eating dinosaur. The teeth are all of different sizes, as some had erupted recently and others were ready to fall out. Near Tyrannosaurus are the fore- and hind- limbs from a gigantic sauropod dinosaur, Diplodocus. These limbs resemble those of elephants in some ways, partly because of the large weight of animals, but the feet of sauropods are clawed. Nearby is a series of models showing a scheme of dinosaur evolution. There are also several other specimens, including two from the famous collection of Connecticut Valley dinosaur footprints begun by Edward Hitchcock in the 1830's. Other parts of the footprint collection can be viewed in the Hitchcock Ichnology Collection.
Birds evolved from a lineage of small meat-eating dinosaurs. The vertebrate beltway in the main hall has two casts of Archaeopteryx, one of the most famous of all fossils. The fine preservation of the best specimens of Archaeopteryx, reveals impressions of feathers. Archaeopteryx has a mosaic of reptilian and avian features: the teeth, tail, and claws are similar to those of dinosaurs, while the feathers and furcula are similar to those of birds. Recently, improved methods of fossil preparation allowed paleontologists to study details the brain case and skull of Archaeopteryx. Such new information not only contributes to understanding more about the biology of Archaeopteryx, but also allows better comparisons to dinosaurs and crocodilians.
There has been much speculation about the independent evolution of flight in birds, bats, and pterosaurs. There are two theories about the origin of bird flight.
One theory invokes intermediate forms that first took to the air by gliding, somewhat like flying squirrels. The other theory suggests that bird wings originated as stabilizers for rapidly running animals, and that flapping of these stabilizers allowed the derivation of flapping flight without an intermediate gliding form. The bird alcove also shows some of the diversity of beak and foot structures of modern birds: even within the seemingly narrow body plan of birds, there has been a great deal of structural evolution.
On the second floor mezzanine is a skeleton of a large amphibian named Eryops. This flat-headed animal was among the earliest vertebrates adapted for extensive walking on land. Its body shape is typical of members of the large radiation of Paleozoic amphibians. To its right is a "fin-backed" reptile, Edaphosaurus, probably a plant-eater. We know that the large spines on its back supported a membrane because one was broken in life and held in place by the membrane while it healed. The membrane probably helped Edaphosaurus regulate its body temperature. Edaphosaurus belongs to the lineage of reptiles which gave rise to mammals, about 100 million years later.
Above these two is the great black skull of Dunkleosteous, a bony plated fish that lived in Ohio 350 million years ago.
You can also see several other kinds of reptiles: fossil turtle eggs and shells in the vertebrate beltway , the mososaur Platecarpus (a large marine lizard), and the crocodile-like phytosaur, both down by the dinosaurs. Also present is an ichthyosaur, a porpoise-like reptile which lived in the oceans during the Age of Dinosaurs. Numerous similarities and differences between reptilian ichthyosaurs and mammalian porpoises provide a particularly elegant example of convergent evolution.
Highlights of human evolution are displayed on the second floor mezzanine. The constant discovery of new fossils and analytical techniques continue to change the details but not the basic story of our evolution.