Our story begins in the late Jurassic of Germany, in the area now known as Solnhofen. The Solnhofen Limestone is renowned for it's well preserved late Jurassic fossils, giving us a fantastic insight into the area at the time. 150 million years ago, in the latest Jurassic, Solnhofen was part on an archipelago that stretched across much of Western Europe. A Shallow sea covered most of the area, dotted with small atolls and other islands.
What the Solnhofen Archipelago would have looked like
These islands were home to a diverse fauna, but one which included surprisingly few dinosaurs, probably due to their insular nature, and the flying birds not having evolved yet. In turn, they were inhabited by an incredible diversity of Pterosaurs, including animals such as Rhamphorhynchus, Aerodactylus, and even Pterodactylus, the first Pterosaur to be discovered. Two dinosaurs were present in the faunas however, both of them quite famous. One was Compsognathus, and another the perhaps more surprising Archaeopteryx, which while often portrayed as living in dense jungles alongside Allosaurus and Brachiosaurus, was actually an inhabitant of the European archipelago. Also present were several species of Crocodylomorphs, such as the small and terrestrial Alligatorellus, an Atoposaurid, and Geosaurus, a marine crocodile of the Metriorhynchid family.
Archaeopteryx lithographica, from Matthew Martyniuk's fantastic book, Beasts of Antiquity: Stem-birds in the Solnhofen Limestone
During the cretaceous, even as the continents were beginning to approach their current state, Europe continued to be a series of islands and microcontinents. While the smaller islands continued to resemble the Solnhofen archipelago, many of the larger ones had faunas more similar to those of the continents. One example of this is Britain, which was one of the larger isles at the time. All of the first dinosaurs discovered were from here, including Iguanodon, Megalosaurus, and Hylaeosaurus. Other well known british dinosaurs include animals such as the Spinosaurid Baryonyx and the Ornithopod Hypsilophodon.
A map of Cretaceous Europe, projected over a modern one
Another part of Cretaceous Europe that must be mentioned is Hateg Island, located in present day Romania. This large offshore isle was home to an incredibly unique insular fauna, such as the dwarf Sauropod Magyarosaurus and the Hadrosaur Telmatosaurus. The island was also home to at least a dozen species of small Theropods, but the primary predators on Hateg were in fact giant Azdarchid Pterosaurs of the genus Hatzegopteryx. These giraffe-sized animals would have been more or less uncontested, dwarfing all other animals on the island, including the sauropods. The Hateg faunas existed in the late Cretaceous, up until the K-PG extinction event.
The small Eocene mammal Leptictidium, from Walking With Beasts
The Paleocene of Europe was a rather dim and poorly known time. Relatively few fossil remains are found from this period, but from what we know, it seems to have been populated by a very low diversity of species, a so-called recovery fauna, which slowly adapted and diversified in the time up until the Eocene. These early faunas were essentially composed of late Cretaceous species, but lacking any animals larger than a cat. For the first 10 million years, the orders of Artiodactyla and Carnivora had not yet appeared, though primitive primates were already present. When the modern groups first started to appear in the early Eocene, they would scarcely have been recognizable, as they had not yet settled into their modern roles. Hoofed, predatory Artiodactyls such as Dissacus stalked the undergrowth, along with other archaic groups such as the Condylarths. Interestingly, many of the larger animals during the Paleocene and Eocene of Europe were not in fact mammals, but instead members of multiple other lineages. Dinosaurs such as Gastornis, a large herbivorous bird, would have been some of the biggest animals in the faunas, and crocodiles would have been keystone predators.
Diatryma, a North American relative of Gastornis, by Matthew Martyniuk
The Eocene saw a great diversification of mammals, as the faunas of the world finally recovered after the K-PG extinction event. In Europe, early Carnivorans such as Parodectes became widespread, though they remained small throughout the period. Other familiar animals, such as Bats and Pangolins also appeared, becoming common parts of the Eocene faunas. Other, far stranger animals were also present, and made up most of the megafauna at the time. Creatures such as the hippo-like Coryphodon and the first Perissodactyls arrived on the continent, due to a connection to North America through a land-bridge with Greenland. These early Perissodactyls were more primitive than either horses or rhinos, possessing features ancestral to both. The early Perissodactyls such as Hallensia were only the size of dogs, but increased substantially in size over the course of the Eocene. The first true horses to arrive in Europe were members of the genus Pliolophous, which may in fact have been a descendant of Hallensia. The mid Eocene was a very peculiar time, in which Europe was home to several lineages not typically though of as European, including Marsupials and the aforementioned Pangolins.
Palaeotherium magnum, an archaeic Perissodactyl, related to tapirs and horses
By the late Eocene, the European archipelago was reaching it's end. The development of the first arctic glaciations was slowly causing the sea levels to lower, and the climate was getting colder. The dense, tropical jungles of the early to mid Eocene were gradually being replaced by more open, subtropical woods. Many surviving Paleocene lineages died out, and a faunal turnover began. Among the winners were animals such as Palaeotherium and Hyaenodon, and among the losers were groups like the Leptictids, which died out, leaving no descendants. The Gastornithid birds and terrestrial Crocodiles died out in Europe, and the Artiodactyls became one of the most successful groups. Then finally came the Oligocene, marking the end for the European archipelago, as a landbridge was established with mainland Eurasia, and masses of new species entered Europe. Many of these species had evolved in the more arid inland conditions of Asia, and were more well adapted to the drying climate than the insular faunas of Europe. Thus, a huge number of the endemic European lineages died out and were replaced by Asian immigrants, in an event sometimes called "La Grand Coupre". True Rhinos and Tapirs entered Europe, outcompeting many European herbivores, and several species of Hyaenodon went extinct, though a new species arrived from Asia, ensuring the genus' continued existence in Europe. Arboreal Primates disappeared from Europe, and the Creodonts, which had previously been top predators, steeply declined. Thus ended ocean Europe, and the continent began to take the shape we know today, though it would continue to look quite different for several million years to come.