The western reaches of Abu Dhabi, particularly the areas known as Jebel Barakah and the Baynunah Formation, are particularly rich in fossils dating to the so-called Tertiary period. Yet to understand the significance of the UAE's fossil record, we must first have a grasp of what the geology, climate and environment of that period were like, for the UAE of the Tertiary period certainly did not resemble the UAE of the twenty-first century!
First introduced in 1760, the term Tertiary (following on from Primary and Secondary, which have been replaced by Paleozoic and Mesozoic) is applied to the period between c. 66.4 and 1.6 million years ago and denotes the youngest of the three divisions of the Earth's rocks. Some scholars now prefer to use the terms Paleogene (66.40-23.7 million years ago) and Neogene (23.7-1.6 million years ago) Periods in place of Tertiary. Tertiary rocks are generally found in the Earth's lower elevations, but the eighteenth century view that the Primary, Secondary and Tertiary rock groups were formed before, during and after the flood associated with Noah has long since been abandoned.
The Tertiary period is itself divided into a number of epochs, beginning with the Palaeocene and running through the Eocene, Oligocene, Miocene and Pliocene. These terms originally identified so-called 'biostratigraphic units', i.e. associations of rock and particular types of fossils.
The world was a very different place during the Tertiary period! The oceans and continents as we know them were constantly evolving, changing shape, becoming linked or unlinked, throughout this long era. The rearrangement of the continents and oceans which began around 200 million years ago continued throughout the Tertiary. In the late Palaeocene Australia broke off from Antarctica, which only saw the onset of glaciation about 34 million years ago. Norway was separated from Greenland about 56-55 million years ago, and India joined Asia around 45 million years ago. Between 6 and 5 million years ago the Mediterranean basin became cut off from that part of Tethys which we today recognise as the Atlantic Ocean. Eurasia and North America remained joined by the Bering Land Bridge until 2.5 million years ago
Nor was the climate any less static. The northern part of Norway was tropical, as shown by the recovery there of various types of molluscs (shellfish) and sharks, while London and Hampshire experienced sub-tropical conditions. Conditions began to cool during the middle and late Eocene, as jungle gave way to savannah-like grassland, increasing in intensity into the Oligocene when glaciation began in Antarctica.
Mammalian evolution was a hallmark of the Tertiary, as over 20 orders became established by the early Eocene. These included the earliest artiodactyls (e.g. camels and deer), perissodactyls (e.g. horses, rhinoceroses and tapirs), rabbits and rodents.