Paper No. 187-2
Presentation Time: 1:20 PM
NON-MARINE MESOZOIC ECOSYSTEMS OF NORTHEASTERN AFRICA: NEW INSIGHTS FROM THE NORTHWEST PLATEAU OF ETHIOPIA
Triassic and Jurassic non-marine ecosystems from Africa are well-represented by fossils from southern Africa, southwestern Tanzania, and Morocco, but the bulk of the continent remains poorly sampled. The Northwest Plateau of Ethiopia preserves an extensive early Mesozoic sedimentary record that is well exposed in the Blue Nile (Abay) Gorge and its tributaries, as well as further north in Tigray Province. Our work since the 1990s in these areas has yielded several new non-marine vertebrate fossil assemblages that fill in major gaps in the early Mesozoic record of northeastern Africa. Vertebrates from the Upper Triassic-Lower Jurassic lower Adigrat Sandstone in Tigray include dipnoans, actinopterygians, temnospondyl amphibians including the capitosauroid Abiadisaurus, and fragmentary reptiles. Fossils recovered from outcrops west of Addis Ababa that were once assigned to the Adigrat Sandstone are now thought to be correlative to the Gohatsion Formation, and thus represent the first Early or Middle Jurassic vertebrate assemblage from this part of Africa, including actinopterygians, turtles, and crocodyliforms. The most extensive Mesozoic vertebrate assemblage of Ethiopia comes from the Upper Jurassic Mugher Mudstone of the Blue Nile Gorge and surrounding area. Larger fossils preserve records of at least four different turtles, including pleurodires, paracryptodires, and one of the earliest occurrences of Solemydidae, non-eusuchian mesoeucrocodylian crocodyliforms, and large theropod teeth. Microvertebrate assemblages, dominated by dental remains, are exceptionally diverse; they contain hybodont and batoid elasmobranchs, actinopterygians, dipnoans, crocodyliforms, theropod dinosaurs, at least two taxa of ornithischian dinosaurs, and a “peramuran” mammaliaform. These new records are of clades with widespread Pangaean distributions, demonstrating that the distinct Gondwanan faunas of the later Mesozoic did not appear in east Africa until after the Jurassic.