Dinosaurs and other fossil vertebrates from fluvial deposits in the Lower Cretaceous of southern Tunisia
Introduction
The Cretaceous vertebrate faunas of Africa are of considerable importance in terms of palaeobiogeography and evolution. Africa was linked to South America and Euramerica during most of the Early Cretaceous, but these land connections were severed in the Late Cretaceous. Detailed faunal studies, and precise dating of faunas, show that African continental vertebrate faunas were essentially of cosmopolitan character until the Late Jurassic and earliest Cretaceous, but they developed ever more specialized features as land connections broke down (Buffetaut and Rage, 1993, Russell, 1996, Sampson et al., 1998, Sereno et al., 1994, Sereno et al., 1996): Madagascar broke away from the main African landmass by 120 Ma, and South America finally separated from Africa by 100 Ma, although those two land masses may have retained a connection with each other via Antarctica. A major transgression in the late Cenomanian then flooded most of North Africa and the Sahara, and a seaway extended from Algeria southwards across the Sahara, separating the northwestern portion of Africa from the rest of the continent
Dinosaurs and other vertebrates have been found extensively over North Africa and the Sahara, in Morocco, Algeria, Tunisia, Libya, Egypt, Sudan, Mali, and Niger in a sequence of rocks termed the ‘continental intercalaire’ by de Lapparent (1960). More recent work (e.g. Bouaziz et al., 1989, Lefranc and Guiraud, 1990, Taquet, 1976) has shown that the ‘continental intercalaire’ is a very loose term that includes rocks of latest Jurassic to Late Cretaceous (Cenomanian) age, and that there is a succession of faunas. These faunas show similarities with South America, especially in comparisons between Morocco and Brazil (Buffetaut and Rage, 1993, Sereno et al., 1994, Sereno et al., 1998), and with Euramerican faunas (Buffetaut and Rage, 1993, Sereno et al., 1994, Sereno et al., 1996). In the Late Cretaceous, the dinosaurs of Madagascar, India, and South America still retained resemblances, but those of Africa were somewhat different since Africa had become essentially an island by this time (Sampson et al., 1998).
Abundant bones of dinosaurs and other vertebrates have been reported from the mid-Cretaceous of the Tataouine region, southern Tunisia. The earlier reports were, however, either brief accounts that noted the presence of vertebrate remains as part of a broader-scale survey of the north African region (e.g. de Lapparent, 1951, de Lapparent, 1960, Pervinquière, 1912) or reports of limited sampling operations (Bouaziz et al., 1988, Schlüter and Schwarzhans, 1978). The bones were found in Tunisian equivalents of the continental intercalaire. Short Tunisian–British–French expeditions in 1997 and 1998 have provided additional information on the setting of the bone beds and on the vertebrate faunas. A new find, reported here, is the first evidence of a pterosaur, identified as an ornithocheirid.
The aims of this paper are to introduce the little-studied mid-Cretaceous vertebrate faunas of southern Tunisia, to describe the geological setting, dating, palaeogeography, and environment of the dinosaurs, and to provide comparisons with other North African and Saharan localities of similar age.
Section snippets
Geological setting
The fossil vertebrates occur in units of presumed early Albian age (latest Early Cretaceous, ca 100 Myr) within a succession of rocks dating from the Late Permian to latest Cretaceous (Fig. 1, Fig. 2). These deposits are located on the northern edge of the Saharan platform, and south of the Atlas Mountains, the Chott Range, a fold belt that forms an east–west-trending structural unit across North Africa from Morocco to Tunisia. Southern Tunisia is divided into two domains, based on tectonics and
Palaeogeography of North Africa in the mid-Cretaceous
During the Jurassic, Africa and South America were in close contact. The North Atlantic was opening southwards, and the South Atlantic northwards, as Africa and South America rotated apart. Sea levels were higher in much of the Late Jurassic, and North Africa and the Sahara were largely under shallow epicontinental seas, as indicated by the extensive deposition of marine units. In south Tunisia, a major marine transgression occurred in the Callovian, and this extended southwards to the
Biostratigraphic setting
The Chenini Formation is generally dated as early Albian (Burollet et al., 1983; Ben Ismaı̈l et al., 1989, Bouaziz et al., 1988), a determination based partly on indirect evidence. The upper part of the underlying Merbah el Asfer Group, the Douiret Formation, has yielded palynomorphs that suggest an early Aptian age (Ben Ismaı̈l, 1991). Palynomorphs have suggested a late Aptian to early Albian age for the Aı̈n el Guettar Group, which includes the Chenini Formation (Pons, in Barale et al., 1998,
Vertebrate fauna
The vertebrate fauna of the Chenini sandstones has been reported by several authors (Bouaziz et al., 1988, de Lapparent, 1951, de Lapparent, 1960, Pervinquière, 1912, Schlüter and Schwarzhans, 1978). These authors noted the presence of teeth of sharks, teeth and scales of actinopterygian fishes, turtle carapace fragments, skull fragments, scutes, jaw elements, and teeth of crocodilians, bones and teeth of large theropod dinosaurs (including the teeth classically assigned to Spinosaurus and
Biogeographical implications
The dinosaur beds of Saharan Africa range in age from Hauterivian or Barremian to Cenomanian. All these vertebrate-bearing units lie below the late Cenomanian marine transgression layer, represented in most regions by massive Cenomanian–Turonian limestones. The oldest dinosaur localities may be in the Tiourarén beds of In Gall in Niger, where Sereno et al. (1994) reported the theropod Afrovenator and a sauropod in units that lie stratigraphically below the ?Aptian Gadoufaoua beds. Associated
Acknowledgments
We thank the Cité des Sciences, Tunis for introducing M.J.B. and E.B. to the Chenini Formation dinosaurs during a conference in November, 1997. We thank Bob Loveridge and Jill Martill for assistance in the field. In addition, we thank Wall-to-Wall TV, the Discovery Channel, Musée des Dinosaures (Espéraza), Université de Sfax, University of Bristol, and University of Portsmouth for funding our expedition in May, 1998. The Office National des Mines (Tunis) provided funding for an additional visit
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