The Baynunah Formation consists primarily of fluvial sands and clays. Its sediments have been studied thoroughly and detailed stratigraphic, sedimentological, and diagenetic information is presented in Whybrow et al. (1999), Ditchfield (1999), Friend (1999), and Peebles (1999). The Baynunah sediments are interpreted as deposits of a shallow braided stream system, with occasional playa lake formation. Fossils are typically found resting on lenses of intraformational conglomerate and are often covered by unconsolidated intermixed sands and clays or arenitic sands that probably represent bar deposits. The eggshell remains described here were all collected from outcrop surfaces and not in situ. Their fossil status was determined by their spatial distribution as restricted to outcrops of the Baynunah Formation, their association at these outcrops with remains of vertebrate fossils, and their reddish-brown color, indicative of prior burial in the Baynunah sediments.

The Baynunah Formation lacks any volcanic rocks that may be dated radioisotopically. As a result, the maximum and minimum ages assigned to the Baynunah are based on the composition of the fossil fauna recovered from within it. The presence of faunal elements in common between the Baynunah and radiometrically dated sequences in East Africa has permitted the assignment of an age of between 6 and 8 Ma for the Baynunah fauna (Whybrow and Hill 1999).

Detailed information on most localities mentioned in this paper is provided in Whybrow and Clements (1999b). Further locality data are on file with A.D.I.A.S. and are available upon request from the corresponding author.