Stromatolite is a rock formed by small cyanobacteria, shaped like a paraphysis. The aggregate of cyanobacteria secretes a mucus, which forms limestone of a stripe-like structure by catching accumulated particles and depositing calcium carbonate. Naturally formed stromatolites are found in Australia and Africa.
Excavation in shale layers formed during the Cambrian period (the first of the Palaeozoic era) has yielded fossils far greater in number than in older beds. This phenomenon is ascribed to the rapid evolution of marine invertebrates (called the Cambrian explosion), which took place during the earlier Palaeozoic era.
Burgess shale fauna, comprising the fossils of animals belonging to about 150 exotic species, are among the typical fossils dating back to the Cambrian period; the fauna were discovered in the U.S. in 1909 by C. D. Walcott. Among these animals, which swam over the sea bottom, are Opabinia, a creature with five eyes and a long nose, resembling that of an elephant; and Anomalocaris, a carnivorous animal whose name means “strange lobster.” It is thought that most of the ancestors of present-day animals and plants appeared during the Cambrian period.
Dimetrodon is a reptile with features resembling those of a mammal. Appearing in the Carboniferous period, it is one of the most well-known of its kind. With long spinal processes, protruding from the spinal column, a Dimetrodon looks like a ship with a sail on its back.
Various theories have been proposed to explain the function of this sail-like feature. A widely accepted theory holds that it served to adjust body heat. The exhibit was made by putting together actual fossils.
This exhibit illustrates the excavation of a Triceratops in South Dakota, U.S. Triceratops, a Ceratopsia, is characterized by three large horns. The exhibit shows actual fossils of the Triceratops in actual arrangement, except for the head, which is not suitable for exhibition due to instability.
Shown above the bone bed is the entire frame of the Triceratops, designed using a cast modeled after the actual fossils.
Visitors can enjoy a thrilling, bird’s-eye view of the bone bed (placed about three meters under the floor), through reinforced glass.
This exhibit is part of the actual skeleton of a Camarasaurus―a dinosaur of the late Jurassic period. The skeleton was excavated in Bonecabin quarry, Wyoming ,and restored in 1993. Studies have found that the excavated skeleton represents about 65% of the original skeleton. Its size, the degree of cranial cohesion and the form of the spinal process on the caudal vertebra indicate that the skeleton is that of an old female dinosaur. The skeleton clearly shows the marks of a bone disease and predator’s bitemark.
Paleoparadoxia, and Desmostylus, their kin, were marine mammals that lived on the northern Pacific Rim during the Miocene epoch. Fossils of Paleoparadoxia have been found in Gunma Prefecture. A unique feature of Paleoparadoxia is its teeth, resembling bound pillars. Presumably, Paleoparadoxia ate roots of water plants, shellfish and lugworms in mud, using their shovel-like jaws.
Fossils of Paleoparadoxia found in Gunma are much larger than those excavated in other places. Presumably, Paleoparadoxia consisted of two types―smaller ones and larger ones.
The Kabutoiwa Layer is a layer at the bottom of a lake near Mt. Kabutoiwa in Nanmoku Village. This layer consists of multiple thin tuff sub-layers. The layer is assumed to have been formed during the late Miocene epoch. Excavated from the layer are fossils of frogs, tadpoles, and birds and other vertebrates (e.g. fossils of bird feathers).
This exhibit is the fossil of a frog excavated from the Kabutoiwa Layer. It shows the shapes of the frog bones, as well as the color pattern of the frog’s spotted skin. The fossil is one of the few frog fossils showing the skin color patterns. It is highly valuable, given the fact that frog fossils showing the impressions of skin are rare.
Yabe’s Giant Fallow Deer, now extinct, were a variety of deer far larger than recent deer. The exhibited skeleton of a Yabe’s Giant Fallow Deer comprises six fossils of roughly the same size, found separately at different sites in Japan. The antler is a replica of a fossil found in 1797 in Kamikuroiwa, Tomioka City, Japan, the oldest ever recorded in Japan. The actual fossil, as well as a record and minute illustration of the fossil, made at the time of excavation, are still kept in the collection of Jagu Jinja shrine in Tomioka city.