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A Fossilized Egg from the Middle Jurassic Tiouraren Formation of Niger

Jenna Bures and Dr. David J. Varricchio (both co-author and mentor), Earth Sciences, Montana State University, Bozeman MT 59717; Dr. Paul C. Sereno, Organismal Biology & Anatomy, U. Chicago, 1027 E. 57th St. A405, Chicago IL 60637

Fossilized Mesozoic egg specimens in Africa come from two major sources, the Lower Jurassic-age Elliot Formation of South Africa and Upper Cretaceous-age localities in Morocco. This includes the discovery of eggs containing dinosaur embryos in the Elliot Formation. In the late 1990s, an expedition led by Paul Sereno of the University of Chicago discovered a fossilized egg specimen in the Tawachi locality of the Tiouraren Formation in Niger. The Tiouraren Formation is generally interpreted as a terrestrial depositional environment and is of disputed age. Originally considered Early Cretaceous in age, reexamination of primarily the fossil evidence suggests a Middle Jurassic age instead. Here we describe this first Middle Jurassic egg of Africa in order to taxonomically identify it or otherwise assign it according to ootaxonomy, the standard classification scheme for fossilized eggs. It was studied using x-ray scans and a scanning electron microscope (SEM) to perform imaging and elemental analyses. The specimen is a small (31.3 x 34.1 mm), dark brown egg that is spherical and not crushed. The interior has been infilled with a light gray, calcitic matrix. X-ray scans indicate that there are no skeletal remains inside. They also imply a strong similarity between the composition of the specimen and that of the infilling matrix. SEM imaging and elemental dot analyses suggest diagenetic alteration has occurred within the specimen. The SEM images reveal little about the morphology and microstructure of the eggshell. Thin sectioning imaging through a petrographic microscope, however, does reveal microstructure that suggests it is a turtle egg. Turtles, while known from other formations of this age, are not known from this particular locality. Furthermore, the fossil record for turtle eggs is noted to be poorly represented on Gondwanan continents and begins in the Middle Jurassic, making this potentially one of the oldest to be recovered.

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