In this hall of the American Museum of Natural History are skeletons of fossil dinosaurs, reptiles and fishes belonging to an older geological period than do the specimens in the hall previously visited. The dinosaurs were the great terrestrial vertebrates of their day, the Age of Reptiles (3,000,000 to 10,000,000 years ago), and there was a great variety of forms, but all had long hind limbs and long and generally massive tail.
Dominant over other specimens of dinosaurs is the amphibious dinosaur Brontosaurus, mounted in the center of the hall. This specimen is sixty-six feet eight inches in length, sixteen feet in height, and the animal is estimated to have weighed thirty-five tons. Beside it is a fossilized tree trunk, part of it carbonized or turned into coal, while the rest is silicified or turned into stone.
At the right is the large carnivorous dinosaur Allosaurus, mounted to represent the animal feeding on the carcass of a Brontosaurus. At the left of Brontosaurus stand two specimens of the duck-bill dinosaur Trachodon, and immediately in front of them is an extraordinary "mummified" specimen of the same species, in which a large part of the skin, showing its texture, is preserved. Near-by are specimens of Pterodactyls, or flying reptiles, and a mounted specimen of a peculiar marine bird, Hesperornis regalis, from the Cretaceous of Kansas. This bird, like the more ancient Archaeopteryx, which is the earliest bird known, had a row of small teeth in the jaws, a reminiscence of its reptilian ancestry, but it had lost the long reptilian tail which Archceopteryx still preserved.
Immediately at the right of the entrance to the dinousar hall of the American Museum of Natural History are the newly discovered and recently mounted dinosaurs skeletons from the Cretaceous of Alberta, Canada, of the crested duck-bill dinosaur Saurolophus, a herbivorous reptile, the helmet duck-bill dinosaur Corythosaurus, with its crested head similar to that of a cassowary, the horned dinosaur Monoclonius and the bird-like dinosaur Ornithomimus.
On the south side of the hall is the finest collection of fossil turtles in any museum, also specimens of finback lizards (Naosaurus and Dimetrodon), a specimen of Diadectes, a reptile with a solid-roofed skull, and one of Eryops, a primitive amphibian which inhabited the great swamps of the coal period and was one of the earliest land vertebrates. The latter represents the primitive amphibians, which are regarded as the ancestors of reptiles, birds and mammals as well as of the modern amphibians (frogs, etc.). These and other smaller specimens in the adjoining wall case are more ancient than the dinosaurs and lived at the time when the coal measures of Pennsylvania were being formed.
At the eastern end of the hall are skeletons of smaller dinosaurs and several fine skulls of horned dinosaurs, Ceratopsia, from the Upper Cretaceous of Wyoming and Alberta, the most interesting example being that of Triceratops, seven feet in length, with its three large horns and heavy bony frill extending back and over the neck. In other sections will be seen a portion of a skeleton of Tyrannosaurus rex (king of tyrant saurians) and the remains of an armored dinosaur, Ankylosaurus.
Above the entrance to the Tower Room of the Southeast Pavilion, are the reconstructed jaws of a huge fossil shark in which the actual teeth are arranged as in the sharks of to-day, in banks or rows. This is the largest and most formidable fish, living or extinct, of which there is any record. The teeth were found in the phosphate beds of North Carolina, and after the jaws of live species were carefully measured, the model was prepared according to scale. It is known that a specimen, in which the largest tooth was one and one half inches in height, measured twenty feet in length, and that another, having teeth three inches in height, had a total length of forty feet. It therefore follows that the length of this Carolina shark, whose teeth measured six inches, was approximately eighty feet, comparing with the largest modern whales in size.
In cases at the right and left of the entrance are exhibits illustrating the forms, structure and development of typical recent fishes.
The exhibits in the Tower Room comprise the remains of fossil fishes illustrating the rise and differentiation of the lowest vertebrates from the earliest (Upper Silurian) time (ending 20,000,000 years ago) to recent (Quaternary) time (ending 3,000,000 years ago). Most of the forms represented are North American and belong to five great divisions.
The first three cases confronting the visitor contain specimens of the armored fish-like forms, some of which were of huge size and armed with powerful teeth, or sharpened jaw blades. This form is best represented by the fish-like animal Dinichthys, displayed in the center of the room. Dinichthys lived about 20,000,000 years ago in the sea that existed on the site of the present State of Ohio, and was one of the most destructive and ferocious animals that ever lived in the sea. Although fish-like in appearance, it is regarded as belonging to a more primitive class of vertebrate animals. The head and front half of the body were protected by heavy plates of bone, and it had powerful jaws with "fangs" in front of and behind them, knife-like cutters which chopped against each other.
In the first alcove to the left is a "fossil aquarium," de-signed as an aid in interpreting the fossils in the adjoining cases, and it undoubtedly gives an accurate picture, since all the fishes shown were found in a single locality and in a single layer of Old Red Sandstone.
Proceeding to the right the visitor finds the sharks, rays and chimaroids, which are the earliest true vertebrates with cartilaginous skeletons and jaws, followed by the lung-fishes, the fringe-finned fishes, shark-like in form and fins but with dermal bones and bony skeleton, and finally the spiny-finned fishes, or teleosts, which constitute the multitudinous forms of the present time and which include sturgeon, garpike, cod, herring, perch and the other common bony fishes. Return to the East Corridor and enter the
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