Paratethys

At the same time the Alpine orogeny, a tectonic phase by which the Alps, Carpathians, Dinarides, Taurus, Elburz and many other mountain chains along the southern rim of Eurasia were formed.

The combination of a drop in sea level and tectonic uplift resulted in the partial disconnection of the Tethys and Paratethys domains.

Due to poor connectivity with the global ocean, the Paratethys realm became stratified and turned into a giant anoxic sea.

The western and central Paratethys basins experienced intense tectonic activity and anoxia during the Oligocene and early Miocene and became filled with sediments.

During its five-million-year lifetime, the megalake was home to many species found nowhere else, including molluscs and ostracods as well as miniature versions of whales, dolphins and seals.

[12] Near the end of the Miocene, an event known as the Khersonian crisis, marked by rapidly fluctuating environmental factors and sea levels, wiped out much of the unique fish fauna of this megalake.

During the Pliocene epoch (5.33 to 2.58 million years ago) the former Paratethys was divided into a couple of inland seas that were at times completely separated from each other.

An exceptionally-preserved record of this ecosystem is known from the Oligocene-aged Menilite Formation, a flysch containing fossils of pelagic and deep-sea fish taxa, as well as microbial mats.

[27] A Miocene-aged deepwater shark fauna from Slovakia is depauperate & mostly dominated by squaliforms, and appears to suggest a highly stressed paleoenvironment.

[28] Later fossil assemblages suggest that the increased isolation of the Paratethys by the Middle Miocene caused significant extirpation among most small-to-medium sized deepwater and pelagic sharks.

However, larger sharks, such as the megalodon and Cosmopolitodus, continued to persist in the Paratethys and did not see such extirpations, likely due to the widespread occurrence of marine mammals to feed on.

[30] The eurhinodelphinids, an unusual family of toothed whales, appear to have invaded the Paratethys via the Mediterranean during the middle Miocene, with remains of the widespread genus Xiphiacetus recovered from Austria.

[32] Over time, in response to the increased salinity in the Paratethys from its isolation, marine mammals independently evolved pachyosteosclerosis, leading to dense, bulky bones.

Palaeogeographical reorganization of the Tethys–Paratethys region during the Paleogene, from a connected Tethys configuration during the early Eocene (above) to a fragmented and restricted Paratethys region configuration during the Oligocene (below).
Palaeogeographical reorganization of the Tethys –Paratethys region during the Paleogene, from a connected Tethys configuration during the early Eocene (above) to a fragmented and restricted Paratethys region configuration during the Oligocene (below). Note the loss of deep-water connections between the Indian Ocean region and the Mediterranean , the complete loss of Indian–Arctic Ocean connections, and the closure of most of the Eocene seaways in the Oligocene time. [ 1 ]
Megafaunal diversity of the Paratethys megalake included cetaceans and pinnipeds most notably the Cetotherium riabinini went thorough a presumed insular dwarfism .