PALEOGENE

Paleogeography

The collision of Africa and India with Laurasia (Eurasia) was the most important tectonic event in the Paleogene. It started the uplift of the Alps, Dinaric Alps, Hellenides and Himalayans in Laurasia. The opening of the ocean and the expansion of North Atlantic continued. Greenland and Scandinavia detached, and Laurasia ceased to exist. The period was marked by substantial tectonic plate movements and the opening of oceans. Approximately 50% of present-day oceanic crust was formed in the Cenozoic period (Paleogene, Neogene, Quaternary). This pertains especially to the Atlantic and the Pacific Oceans, where tectonic plates are still diverging at a speed greater than 2.5 cm a year.

Paleoclimate

Temperatures dropped by about 10°C at the beginning of the Paleogene. After about ten million years they started to rise again, but they never again reached Cretaceous levels. Global sea levels rose, and lowlands were flooded. There were, however, some cooler periods in this period of warm climate. Global cooling occurred 35 million years ago as a result of tectonic events in the Southern Hemisphere, namely the opening of the ocean at the point where present-day Australia met Antarctica, merged with South America. The resulting ocean spread, establishing a circular clockwise cold current around Antarctica. The cold currents blocked the inflow and the impact of warm currents from the north, leaving Antarctica fully surrounded with cold currents and causing the formation of ice sheets that survive to this day. The formation of the ice sheets on Antarctica ushered in another ice age. The climate warmed again at the end of Paleogene, but it was never again as warm as in Mid-Paleogene.  Ice sheets formed again at the end of the period.

Terrestrial life

Fauna – The extinction of the dinosaurs made room for thus far small-sized mammals. The Cretaceous Prototheria, including marsupials (1), multituberculates (2) and placental mammals, continued their development. The separation of continents led to individual evolution of the mammals inhabiting them. Marsupials thus developed in Australia and South America, and placental mammals in the other continents.

The order of carnivores first appeared in the Paleogene, and their development accelerated towards the end of the period, when pinnipeds and mustelids developed, along with feliniforms such as the Dinictis (3) cat from the Oligocene. Ungulates first developed in the early Paleogene period, but underwent the strongest growth period in Mid-Paleogene, when they became dominant terrestrial fauna organisms in addition to rodents. Representatives of the Titanotheriidae family, including the Brontops (4), the Arsinotherium (5) and the Uintatherium (6), are the best known ungulates. Late Paleogene was generally a time of very large mammals. The Indrichotherium (7) was the largest mammal in Earth history. It is estimated to have been 5.5 metres tall at the shoulders and to have weighed 15-20 tonnes. This was also the time of the large carnivorous ratite birds called Diatryma (8), which could grow up to 2.5 metres in height. The first primates, including the prosimian Adapis (7), the tarsoid Tetonius (10) and the anthropoids or simians (11), appeared around this time.

Flora – The angiosperms, whose numbers were reduced by the Cretaceous extinction event, recovered quickly and once again became the dominant form of plant life on land. The vegetation changed depending on climate zones. Tropical and subtropical plants such as palms, magnolias, laurels and sequoias grew in the north, in present-day western and central Europe, while temperate zone vegetation, including oak, beech, chestnut, birch and poplar, grew in the northern regions, toward Alaska and Greenland. The first Rosae and Poaceae appeared in Mid-Paleogene, originally around wetlands. In time they spread to form vast grasslands. As the climate cooled at the end of the Paleogene, the flora changed, and steppes and savannas spread.

Marine life

Algae and foraminifera recovered quickly, the planktonic and the benthic ones alike. The extinction event in the Cretaceous benefited the corals, which again became the dominant reef builders. Echinoids and a number of other bivalves were common. Toothed whales (Odontoceti) migrated from the mainland to the oceans, where they became the apex predators. The Basilosaurus is a typical example (12). Enormous Carcharodon sharks, with a jaw span of 2 metres (13), also dwelled in the oceans. The penguins (14), a particular group of birds, developed in Mid-Paleogene.

Proto-Velebit sedimentary basin

In the Paleogene, the Adriatic Carbonate Platform came very close to the collision zone, whose tectonic movements started to affect the platform. The formation of the Velebit started with these processes. After a prolonged terrestrial phase, gradual transgression and sedimentation of limestones composed of the remains of marine animals occurred in the former Adriatic Carbonate Platform in the youngest Palaeocene. Flysch sedimented in deep sea trench conditions as a result of landscape differentiation due to tectonic causes. Flysch consists of marls and sandstones inlaid with conglomerate and breccias and is formed by the wearing of outcropping land surfaces. Powerful tectonic movements at the same time crushed the existing carbonate surface. This crushed material, which was not transported very much, formed the Velebit breccias.

Extinction

Global sea levels plummeted suddenly at the end of the Paleogene, causing many marine species to become extinct, but not as many as in the previous epochs. The cause of the sea level drop has not yet been fully clarified, but it is assumed that it was associated with global cooling.