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The palaeontology exhibition tells about the history of life on our planet from its early beginnings until nowadays. The depths of the earth hide evidence of these remote ages in fossilized remains of ancient animals and plants preserved within rocks. The exhibition is arranged according to the division of the history of the Earth into eras and periods. Each section corresponds to a distinct span of time in the chronicle of the Earth’s history.
The exhibition begins with the Archaean and Proterozoic eras, starting 4.6 billion years ago. Upon the origin of the Earth, its outer surface cooled down gradually thus forming a solid layer – the Earth’s crust; seas and oceans formed as well – a cradle for life was ready. Bacteria and single-cellular organisms were the first and simplest beings on Earth. Usually they do not preserve as fossils; still indirect evidence of their existence has been found: carbon mineral called shungite, which is composed of the earliest organic remains, is demonstrated. Stromatolites formed by cyanobacteria or blue-green algae are more widespread. The first multicellular organisms became common by the very end of the Proterozoic – during the Ediacaran.
Next, the Palaeozoic era lasted for 335 million years. During this time, the Earth’s crust experienced remarkable events. The configuration of ocean and land areas changed while mountain ridges rose and disappeared as time passed. All of this influenced climatic conditions both globally and locally. A diverse animal world is characteristic of the Cambrian seas. Numerous trilobites crawled upon the sea floor. In contrast to Precambrian, soft-bodied creatures, animals with skeletons evolved during the Cambrian period. Their hard parts – shells and various body covers – were durable enough to be preserved over hundreds of millions of years. Still the skeleton not always protected arthropods against such furious predators as Anomalocaris.
Diverse marine animals like molluscs, brachiopods, corals, sponges and sea scorpions are characteristic for the subsequent periods of Earth history. Cephalopod molluscs, which were ancient relatives of modern squids and octopuses, were agile swimmers. Their straight or coiled shells can be found in limestone which formed during the Ordovician and the Silurian periods. The variety of trilobites was huge. Some of these animals were able to curl up when threatened thus preserving their weakly protected bellies.
The territory of what is now Latvia existed close to the equator during the Devonian period. Devonian rocks contain various fossils of brachiopods and molluscs. Some Devonian plant remains are shown as well.
Showcases arranged in the floor are allotted to the “rulers of the world” of the Devonian times – the fishes. Most of the specimens shown there have been found here in Latvia studying the rocks which formed 360 – 410 million years ago. The armoured fishes are a peculiar group of ancient fishes. The bodies of these fishes are covered with large, bony plates. The Lode clay quarry, in northeast Latvia, has yielded very well preserved fossils of the armoured fish Asterolepis ornata.
Lobe-finned fishes are of great evolutionary importance since the first four-legged (tetrapod) land animals originated from the lobe-finned fishes by the end of the Devonian period. Panderichthys is considered to be the closest ancestor to the evolutionary branch leading to tetrapods – a group that now includes amphibians, reptiles, birds and us – the mammals.
Extensive coal deposits formed during the Carboniferous period. Forests of 30 to 40- metre tall fern, horsetail, and club moss ancestors were widespread. Moist areas were inhabited by amphibians.
Permian reptiles are the first vertebrates whose existence and reproduction was not dependant upon water basins. This evolutionary adaptation enhanced the distribution of these animals all over the world since that time forward. Palaeonisic fishes are typical for that time. End-Permian mass extinction is probably most remarkable in the history of our planet – some 90% of marine invertebrates went extinct during a short period of time.
The Mesozoic era starts with the beginning of the Triassic period which was quite different from the previous ones. The climate turned dry. This influenced the distribution of forests. Reptiles spread across the Earth evolving a great diversity of forms and life strategies. Coelophysis represents the Triassic dinosaurs. This bipedal animal was some 10 feet long. It is accompanied by a mammal-like reptile – Placerias. It was the largest herbivore of those times. You are invited to compare your shoe size to the footprint of an early dinosaur (showcase in the floor).
The Mesozoic era is usually described as a time when reptiles flourished, although mammals and birds developed at the same time. The Jurassic period is well known for the wide variety of dinosaurs. Molluscs – ammonites and belemnites are no less interesting. In the past, people used to call the fossils of belemnites “devil’s toes”. The exhibition shows some Jurassic ammonites from south-west Latvia. Peloneustes is the only reptile ever found in the fossil record of the Jurassic within the territory of Latvia.
Horned dinosaurs such as Triceratops, which is shown in the floor, were quite diverse during the Cretaceous period. The biggest meat-eating land animal in the history of the Earth was the six meter tall Tyrannosaurus that was armed with a large number of huge and sharp teeth. Small fragments of these teeth are displayed in the exhibition.
At the end of the Cretaceous period, many species of reptiles and inhabitants of the sea went extinct. According to scientific opinions, an asteroid impact and intense volcanic activity are considered to have caused the mass extinction 65 million years ago. This event offered new challenges and new opportunities for the survivors. At the beginning of the Cenozoic era, groups of modern mammals developed. Proboscids, hoofed animals, carnivores, primates and many others appeared.
The Paleogene period was characterized by the diversity of molluscs; their shells are very well preserved. Warm waters favoured the development of sea urchins and modern corals. A huge, hornless rhinoceros called Indricotherium inhabited Asia. This animal was 6 meters tall and could reach a length of 9 meters.
By the Neogene period, the climate became cooler and plants that favoured a warm climate retreated to the south. Trees such as palms became rare in Europe while different types of other trees appeared (e.g. oaks, maples, chestnut trees, and coniferous trees). Animals such as moose, deer and wild boar emerged. There were proboscids as well.
The Quaternary period differs remarkably from the other periods in the Earth’s history. The Northern hemisphere experienced interchanges of several glaciations and interglacial periods. To the south of the glaciers a peculiar fauna inhabited tundra-steppe – a type of natural zone which has now disappeared. Mammoths and wooly rhinos were among the largest animals. The long fur helped them to keep themselves warm under harsh climatic conditions. Remains of these animals have been found in Latvia as well.
After the Ice Age was over, reindeer, European bison and aurochs inhabited Latvia. Their bones are preserved in the most recent deposits.