The great transgressions that occurred in the mid part of the Cretaceous have had a profound influence on the geology of many parts of the world. In North America, the seas flooded the central part of the continent to produce the Western Interior Seaway, while, in northern Europe, the incoming of the Chalk seas saw much of the continent disappearing below the waves. Across the northern part of Africa, the transgression was more gradual, but on a scale as large as that seen anywhere else. In the period preceding the great marine flooding, huge coastal plains developed across a vast tract of land that extends from what is now Niger to Egypt. These coastal plains were criss-crossed by great braided river systems and provided the perfect habitat for a huge range of fresh water and terrestrial animals.
Vertebrate fossils have been known from the coastal plain, fluvial rocks of the African Cretaceous for a long time; excavations in Egypt in 1912 recovered the remains of several species, including the unusual theropod, Spinosaurus. Subsequent expeditions to other areas of north and northwest Africa have yielded many additional species of dinosaurs, as well as a host of other fossils.
In the early 1990s, the southeastern part of Morocco was just starting to open up to tourism and, with it, the great geological wealth of the region was becoming better known. In addition to the rich and diverse fossil faunas from the sandstones and limestones of the Palaeozoic, fossils were starting to be discovered in the Cretaceous rocks that unconformably overlie the older successions. This unconformable sequence is most readily seen at Hassi Begaa situated about ten miles south Taouz, where it forms the great Kem Kem escarpment.
The Cretaceous escarpments that form the north-eastern and southern margins of the Palaeozoic rocks in southeast Morocco comprise two main rock units: the fluvial sandstones of the Ifezouane and Aoufous Formations, and the marine and lagoonal limestones of the Akrabou Formation. The former are of uncertain age, but probably span the upper part of the Albian and most of the Cenomanian, while the latter contain ammonites indicative of Late Cenomanian and Turonian age. Although most of the succession along much of the escarpment is sparingly fossiliferous, there are several sites and stratigraphic levels that have produced exceptional faunas. The majority of the Akrabou Formation limestones were deposited in extremely shallow water and contain only low diversity beds of oysters and gastropods. However, some more marine intervals yield very abundant and well-preserved echinoids, while a bed of large concretions exposed near the town of Goulmima has yielded abundant large ammonites as well as skeletons of fish and marine reptiles. In addition, the recent discovery of a bed of laminated limestone with beautifully preserved fish skeletons has yielded many hundreds of small, but beautiful specimens.
However, it is the fluvial part of the succession that has become justifiably famous for its fossils. Although often obscured below fallen limestone blocks or desert sand, and sometimes seen only to expose unfossiliferous mudstones, the red beds of the lower part of the escarpment have produced vast numbers of vertebrate fossils and these now furnish museums and fossil shops across the globe. The quality of these fossils was first recognised in 1991, when the first fish bones were found by a sheep herder from the small desert village of Hassi Begaa. Later, some excellent cranial material from the dinosaur, Carcharodontosaurus (first discovered in 1927 by Charles Depéret and J Savornin in Algeria), were found in the region by Paul Sereno in 1995. As the fossils are present in rocks occurring on steep cliff faces and are largely confined to conglomerates at the base of large river channel fills, it was soon realised that only limited fossils could be found on the surface and most material could only be extracted by tunnelling into the rock face. This method of collecting fossils is hard, especially as only hand tools are used and water has to be carried to the site in this arid and extremely dangerous area, with several people having been killed by shaft collapses. (See Issues 16, Tunnelling for dinosaurs in the High Arctic, by Dr TH Rich and Issue 22, Hell and high water: the digs of Dinosaur Cove, by Robyn Molan, for more on dinosaur mining.) Despite the hazards, this is a poor part of Morocco and there is good money to be made from fossils.
The fossils within the channel lags are typically present as isolated bones and they vary from almost pristine preservation to rounded bone pebbles. There has probably been some degree of sorting within the fossil beds and the coarse grained sandstone matrix counts against the preservation and collection of small and delicate bones. Each channel appears to have a slightly different fauna, although the overall structure of the assemblage seems to be similar. There are fossils of aquatic, amphibious and terrestrial animals present, all of which are frequently found. The commonest of the aquatic fossils are the barbed rostral teeth, along with fragments from the rostrum and vertebrae, of the large sclerorhynchid sawfish, Onchopristis. Alongside these are bones, teeth and scales of a variety of fish, with teeth of lungfish being especially characteristic. More complete fish skulls and shark teeth are also known, but are rare.
Amphibious reptiles, in the form of turtles, and large and small crocodiles, are also common. These are usually found as isolated scutes and bones, but well-preserved skulls are known from both groups and shed crocodile teeth are often abundant.
Terrestrial fossils are largely limited to dinosaurs and, unlike almost all other known dinosaur sites, are almost entirely composed of the remains of carnivorous theropods, with sauropod remains being very rare in comparison. Both large and small theropods are present, with the commonest fossils being isolated teeth, but postcranial bones and parts of the skull are also recorded. The large theropod teeth are typically referred either to Carcharodontosaurus (with large serrated teeth) or Spinosaurus (with elongate, almost crocodile-like teeth), but it is possible that other genera are present, but unrecognised. Careful examination of the smaller bones and most slender teeth reveals that pterosaurs are also present within the assemblage and their teeth are not at all rare.
The bias towards carnivores shown by the Kem Kem fossils is extremely unusual and is not simply a collection bias. What were the theropods eating? It appears that the only food available to them were the aquatic forms, so was this area a place where theropods congregated to feed on fish during the dry season or during a spawning migration? There certainly is evidence that Spinosaurus could have been amphibious. However, this will probably remain unanswered until we know more about the fauna and the palaeoenvironment of the site.
Finding dinosaurs in the desert may seem like a remote possibility for many people, but, in reality, the Kem Kem is quite easy to get to, as long as you are with someone who knows what they are doing. It can easily be incorporated into a travel itinerary through eastern Morocco, taking in the mountains and sand seas of the Atlas Mountains and Merzouga, and also the Jurassic and Palaeozoic fossils of the Atlas and Anti-Atlas respectively for which this region is so famous.
For further information, go to: http://www.atlasgeotours.com.