Giant fishes from the Bahariya Formation, Bahariya Oasis, Western Desert, Egypt

The Cenomanian (early Late Cretaceous) Bahariya Formation of Egypt preserves a diverse fauna of marine and freshwater fishes. Fish remains recovered from this formation at Bahariya Oasis include a very large polypterid and a very large mawsoniid coelacanth. Generic identity of the polypterid remains unclear. The discovery of new mawsoniid material provides an opportunity to re-examine Mawsonia libyca, for which the type material has been lost. The amount of freshwater input to the Cenomanian environment at Bahariya Oasis has been variously interpreted. Histological sections of scales were used to confirm that the presumed polypterid fish from Bahariya is a polypterid. Comparative anatomy and biomechanical analysis were used to study the polypterid and mawsoniid fishes. The habitat preferences of extant relatives of the fish and other fossil taxa preserved at Bahariya Oasis were examined to provide information about the paleoenvironment in which the Cenomanian Bahariya fauna lived. Depositional environments of the Bahariya sediments, and the environments in which fossil relatives of the Bahariya taxa are preserved at other sites, were also used to gain a greater understanding of the paleoenvironment preserved at Bahariya Oasis. Histologic sections confirmed that polypterid scales from Bahariya have the four tissue layers characteristic of polypterids: ganoin, dentine, isopedine, and bone. The polypterid scales and ectopterygoid from Bahariya are morphologically distinct from those of Polypterus. The mawsoniid remains from Bahariya belong to Mawsonia libyca, a species originally described from the Oasis. Remains of his giant (three meter long) coelacanth are widespread in the Oasis, suggesting it lived in the paralic environment where its remains were buried. Mawsonia libyca was an active predator with a large gape, and could have preyed on many of the fishes known in the Bahariya fauna. Based on the presence of lungfish and large polypterids, as well as crocodilians and water plants, the Cenomanian environment at Bahariya included freshwater habitats close to the site of deposition.