Inauguration by His Excellency Sheikh Nahayan bin Mubarak Al-Nahayan, Minister for Higher Education and Scientific Research, United Arab Emirates (fifth from left) of the first International Conference on the Fossil Vertebrates of Arabia held at the Dhafra Beach Hotel, Western Region, Emirate of Abu Dhabi, United Arab Emirates in March 1995. Back row, from the left are Hans de Bruijn, Jes de Bruijn, guest, Herbert Thomas, Peter Friend, Vera Eisenmann, Peter Forey, Norman MacLeod, Pascal Tassy, Andrew Hill, John Kingston, Peter Ditchfield, Walid Yasin, Fred Rögl and Peter Andrews. Front row, from the left, guest, Saif Rashed al Swedi, Finance and Administration Manager, Ministry of Higher Education and Scientific Research, United Arab Emirates, Peter J. Whybrow, His Excellency Yousef Omair Bin Yousef, Chairman Abu Dhabi National Oil Company, His Excellency Sheikh Nahayan bin Mubarak al Nahayan, Minister for Higher Education and Scientific Research, United Arab Emirates, Kevin Dunne, General Manager, Abu Dhabi Company for Onshore Oil Operations, Sally McBrearty, and other guests. Photograph courtesy of Sah el Baz, Emirates News.
The fossil animals of the 6 to 8 million years old Baynunah Formation were deposited in a large river system that once drained an area in the interior of the Arabian peninsula to the northwest of modern Abu Dhabi. This river may have been part of a larger system that includes the modern Tigris and Euphrates Rivers. At this time sea level was substantially lower than today, and the marine coastline was about 300 km to the east of its present location.
The Baynunah river itself had a low gradient and was made up of numerous small channels separated by low sand banks. The channels were probably no more than 3 meters deep, but the entire braided river network was tens to hundreds of meters wide. A permanent flow of water in this river is clear from the presence of large freshwater turtles and crocodiles, including the gariel, but the presence of catfish suggests that flow was sluggish or intermittent in some of the channels. Occasional flow of a higher velocity is indicated by coarser conglomerates in some of the channels and by the disarticulated and fragmented state of some of the fossil bones.
Temperatures were warm during Baynunah times, and calcretes preserved in the sediments indicate that the climate was semiarid, with an annual rainfall of no more than 75 millimeters. The vegetation consisted of a mixture of grass, shrubs, and trees, including palm and Acacia. Trees and shrubs were probably concentrated near the river banks, while a more open grassy vegetation grew farther away from the river itself.
This habitat supported a rich and diverse group of land animals, including ancient forms of elephant, hippopotamus, horse, antelope, wolverine, hyaena, and sabre tooth cat. Some of the animals, such as the hyaena, were twice as big as their modern relatives. The Baynunah Formation fossils most closely resemble animals known from this time period from North Africa, East Africa, Pakistan, and perhaps China, while relationships with European fossil animals are less close. This suggests that during Baynunah times animals could migrate freely in an east-west direction, but that north-south movement may have been restricted by barriers presented by ancient deserts, mountains, or river systems.
Summarized from the conference discussion of the afternoon of March 8, 1995, by Sally McBrearty.
All the fossils of the Baynunah area occur in rocks that formed when a large river system flowed across the area and deposited fine grained sands. It consisted of a belt of channels and sand bars. The belt as a whole may have been about 1 km across, and its channels and bars were tens to hundreds of meters across. During much of the year flow in the main channels was low, and in some other channels dry stretches separated more or less stagnant ponds. When floods occurred the channels and sand bars moved, and soil pebbles and bones were eroded out of the banks and moved into the channel beds. The bank of the channels and the tops of some of the sand bars often became covered by grasses and bushes, and the more stable sand bars became cemented by soil formation. The river often flowed to the east and southeast across Abu Dhabi, although it meandered locally.
Rocks of the Baynunah Formation have never been buried very deeply, but have been changed by contact with ground water in the past. Microscopic and chemical analysis shows that although rocks at the top and the bottom of the section were deposited in a shallow sea, the middle part of the section was deposited in a large river system with abundant vegetation on the banks. Chemical analysis of eggshell from Miocene ostrich living near the ancient river system indicates a mixed grass/woodland environment.
Six to seven million years ago the Emirate of Abu Dhabi was crossed by a slowly flowing river system in which lived at least three kinds of fishes which fell prey to crocodiles and scavenging carnivores. There were two species of catfishes - an airbreathing catfish (Clarias) and Bagrus - and one species of carp-like fish (Barbus). Air breathing catfishes may have been widespread in Africa and Asia by this time but Bagrus moved into the area at about the time that Afro-Arabia met Asia during continental movements. Abu Dhabi may therefore have been an important gateway. The absence of the hardy catfishes from the modern Arabian peninsular may suggest that increasing aridity sterilised this part of the world and the modern carp-like fishes living here now were reinvasions from the Horn of Africa, Asia and the Middle East.
Three fossil turtles were found in Abu Dhabi. One of them, a very big herbivorous and terrestrial species, resembles the gigantic turtle living today in the semi-arid environment of Sahel, in Africa. It also enjoys taking a bath when possible. The two others were freshwater and carnivorous. One, a very agressive and good swimming turtle, was the cousin of the Nile soft-shelled turtle. The second, shy and smaller, was like the turtle living today on the border of the Arabian Gulf.
The rodent fauna of the Baynunah Formation shows strong affinities with that of the Ethiopian faunal province and some similarity with south Adriatic assemblages, but does not show a single genus common to faunas of a similar age in Anatolia. The Baynunah assemblage contains a small generalized rat. This suggests that it cannot be older than Late Turolian of the latest Miocene. One form is an entirley new species of gerbil, which has been named Abudhabia baynunensis, in honour of the Emirate and the region in which it occurs.
Elephant-like remains found at Abu Dhabi belong to three species. Two of them are well identified. The most common is called Stegotetrabeledon syrticus, while the rarest is a Deinotherium (only one fragment). A rare and invaluable discovery of Stegotetrabeledon syrticus is an individual composed of skull and lower jaw with tusks, and postcranial remains such as vertebrae, limbones and ribs. It was found on the island of Shuwaihat. This animal was a young adult, of about 20 to 30 years in age. The last species found at Jebel Barakah, just one or perhaps two specimens, is an enigmatic one. We need more discoveries for it to be identified.
Two species of primitive horses, with three digits on each leg, are represented in Abu Dhabi. The larger one is not yet well known. The smaller one, less than one metre high, was probably living in open grasslands at some distance from the river where it came to drink. It ate mostly grasses, just as modern horses do nowadays.
Six species of antelopes, as well as two or three species of giraffes have been found in the Baynunah Formation, and testify to the former presence of a varied ruminant fauna in this part of the world. They include relatives of the present day Indian nilgai and blackbuck. However none of theses fossil animals belong to species still alive today. Their closest relationships are to other extinct giraffes and antelopes in North Africa and the Indian subcontinent. They lived in a lightly wooded environment and there could not have been any substantial development of aridity at this period. No deer were present in the fauna.
A species of early hippopotamus is present in the Miocene rocks of Abu Dhabi. This animal is smaller and more primitive than the living hippopotamus of Africa. Its most notable feature is a mouth opening no wider than that of a modern horse or cow, in contrast to the wide gape of the living hippopotamus. It also showed relatively longer and more slender legs, so it would have been a more lightly built animal. Its closest relationship is with an extinct hippopotamus from Libya, described in 1987.
The fossil community of Abu Dhabi includes suids, which are very interesting animals. From the seventeen suid fossils found we can tell that there were two kinds of suids that lived in Abu Dhabi when the Baynunah Formation was being deposited. Before these important discoveries, we knew one of these species only from Pakistan, and the other only from Africa. The presence of these animals confirms that Abu Dhabi was an important and unique place where mammals from several continents met.
Carnivores are the meat-eating order of mammals. A small collection of their remains from Abu Dhabi adds to our otherwise totally lacking knowledge of the carnivores of the Arabian peninsular between 8 and 6 million years ago. The remains, which are all from kinds of animals that are now extinct, includes a very large hyaena, a second rather small hyaena, a lion-sized sabre toothed cat, and a distant relative of the wolverines. Similar kinds of carnivores are known from areas as distant as northern China.
Different types of plants have distinctive carbon isotopic signatures that are retained by the soils in which they grow and also in the teeth of animals that eat the plants. We have retrieved these isotopic signals from ancient soils and fossil teeth from the Baynunah Formation and used these data to reconstruct the past vegetation. Carbon isotopes from the ancient soils indicate a grassy woodland environment along the major river system with which they are associated. The carbon isotopic composition of a variety of fossil herbivore tooth enamel, including that of ancient horses, antelopes, elephants, hippopotami, and giraffes also indicate that they fed in a mixed habitat made up of trees, shrubs, and grass.
During the last ten years, Omani-French expeditions under the aegis of the Ministry of Petroleum and Minerals, discovered several fossil sites in the Sultanate of Oman, in the Dhofar Province, as well as near the Oman Mountains. Although older than the Abu Dhabi localities, the Oman discoveries indicate the existence of a very large diversity of terrestrial mammals 30 million years ago, comparable to those found in Abu Dhabi's western region. These faunas, obviously with African affinities, confirms the key role of the Arabian Peninsula in the development of Eurasian faunas at the time that Arabia collided with Asia around 18 million years ago.
There are few fossiliferous localities in Africa south of the Sahara that are the same age as the Abu Dhabi sites. The best occur in the Tugen Hills, Kenya, where a series of sites provide fossils ranging in age from 9 to 4 million years ago. Over this time we can see changes in the communities of animals, resulting in the beginnings of the characteristic modern African fauna by about 6 million years. The Red Sea has obviously limited animal movement between sub-Saharan Africa and Arabia in the past. But it is also possible that an early Sahara desert restricted the movement of animals between north Africa, Arabia and Asia, and the more southern regions.
Years of research with the Geological Survey of Pakistan have reconstructed a fossil record that shows past links between the U.A.E. and Pakistan. Our work in northern Pakistan rocks of Miocene age (23 to 5 million years ago) shows how the mammal fauna developed through time, and can be used as a framework for judging the age of the Baynunah fossils. In turn, the Baynunah fossils shed light on Pakistani Siwalik rodents. The small mammals from the Baynunah Formation are particularly informative because they are so diverse. The Abu Dhabi species are similar to those from Pakistan, and they indicate a partly moist environment. The new gerbil species Abudhabia of U.A.E. finds a close relative in the Siwaliks, which has been named Abudhabia pakistanensis.
OF WORK ON FOSSIL VERTEBRATES IN THE WESTERN REGION OF ABU DHABI
The history of work on fossils in the western region of Abu Dhabi began with the early explorations of oil company geologists. This was followed up by Peter Whybrow (The Natural History Museum, London) working at Jebel Barakah from 1979 onwards. In 1983 an archeological survey involving Walid Yasin of the Abu Dhabi Department of Antiquities and a german group discovered fossils at localities further east. These fossils and sites were examined by Andrew Hill (Yale University, USA) in 1984 at the invitation of the Department. Whybrow, Hill and Yasin subsequently collaborated in further research, at first funded by the Department, and since 1991 by ADCO. Since then, other experts became involved in investigating the fossils and associated features of the area; a region now proving so important for understanding the geography and biology of the Old World as a whole.
Stone tools of undoubted human manufacture have been found at four sites on the coast of western Abu Dhabi. While they cannot be dated precisely, their technique of manufacture may indicate the earliest human presence that has yet been detected in the Emirates.
Geochemical analysis of the Miocene rocks that outcrop along the Abu Dhabi coast and on the offshore islands, provide information on how and when these rocks were formed. The stable isotope ratios of oxygen, carbon, sulphur and strontium preserved in these rocks can be compared to values from around the world, to determine how old the rocks are. They can also provide clues to the type of environment in which they were deposited. Rocks of the Gachsaran Formation, which occur near the city of Abu Dhabi, were deposited 19-16 million years ago in a setting similar to the current Abu Dhabi coast, but with large saline lakes and lagoons. Stable isotope analysis was not able to determine the age of the fossil-bearing Baynunah Formation of western Abu Dhabi, as these rocks have been altered over time.
The Baynunah Formation elephant excavated in 1992-1994 at the site of Shuwaihat was found to consist of much of the animal's head, legs, and back bone. The bones were mostly complete, indicating absence of surface decay and carnivore action. All of the bones were found within an area of 153 square metres, and their scatter is due to water flow over the body. There is every indication that the elephant died on the same spot where it was found.
The age of the rocks containing the vertebrate fossils has been investigated by studying the magnetism of these sediments. Rocks become magnetized parallel with the Earth's magnetic field when they are formed and knowledge of the changes in direction of the field with time can be used to date them. Results from the fossil-bearing Baynunah Formation are consistent with an age of 6-8 million years. Furthermore, the river sediments of the Baynunah Formation were laid down during a period when the earth's magnetic field pointed on average toward the south pole, whereas the underlying wind-blown deposits of the Shuwaihat Formation were formed when the field pointed dominantly toward the north pole (as at present). This indicates a significant difference in the ages of the two formations.
Todays Old World climatic belts, lessening rainfall from the tropics to the Equator, of which the Sahara-Sahel belt is an example, may have been present 6 to 8 million years ago. Although the climate far away from the river habitat of the Abu Dhabi faunas may have been very different, it is now possible to test the idea of climatic belts in the Old World using the new data from Abu Dhabi.
Appreciation of several palaeoceanographic factors is necessary to understand Miocene environmental and climate change. Isolation of Antarctica (between 40 and 20 million years ago) cooled the southern high latitudes, increased latitudinal temperature differences, and increased seasonality world-wide. Submergence of the Iceland-Faeroe ridge between Greenland and Europe (between 21 and 18 million years ago) reorganised deep-water circulation in the Atlantic and caused relatively warm water to appear off the Antarctic coast. Evaporation of this water enhanced precipitation in the southern high latitudes and, over the course of the Miocene, produced the Antarctic ice sheet. Development of this ice sheet lowered sea level, increased average wind velocity, and further increased temperature differences. Finally, isolation of the Mediterranean Ocean Basin lowered marine salinity levels, led to increased ice production, and lowered sea level, resulting in the temporary drying up of the Arabian Gulf.
Moving continents constantly change the face of the Earth through geological time. The distribution of continents and oceans, and occasional connecting landbridges between the continents are responsible for the animal assemblages on different areas of the Earth. The Oligocene and Miocene epochs of younger Earth history covers the time between 34 and 5 million years before the present. At the beginning of the Oligocene the African-Arabian continent was separated from Eurasia. India had already crashed into Asia. Distinct faunas inhabited the different continents. Around 18 million years ago the broad seaway between the Mediterranean Sea and the Indian Ocean closed. The Arabian peninsular for the first time formed a bridge between Africa and Asia. Elephant like animals and primates moved northwards, rhinos came in from Eurasia. Such exchanges occured repeatedly during the Miocene. Sometimes the land bridge was blocked by short-lived marine connections between the Indian Ocean and the Mediterranean or the Black Sea. Consequently, the Arabian Peninsula has been the important cross-roads for faunal exchanges between Africa and Asia, as is shown in the fossil record.
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