Dinosaur nesting ground from the Early Jurassic fluvial deposits, Holy Cross Mountains (Poland)

Abstract

Two different kinds of rounded structures (spherical and ellipsoid ones), filled by clayey-ferruginous sediment, occur in the fine-grained sandstone of a crevasse splay origin (meandering river environment) in the Early Hettangian Zagaje Formation, in the locality called Sołtyków, nearby little town of Odrowąż, central Poland. The structures are interpreted as dinosaur eggs, precisely as the "post-egg structures". They are strongly altered by diagenetic processes and no obvious, eggshell structure is preserved. However, faint embryo remains found inside one of the ellipsoid structures and characteristic circular clutch of the spherical structures, allows conclusion that the structures represent dinosaur eggs. This conclusion is supported by other evidences, such as regular size and shape of the structures and joint occurrence with numerous dinosaur footprints. While the circular clutch laid in a shallow depression represents an in situ nest, the smaller, ellipsoid eggs were probably transported a short distance by the current associated with a flood event. The circular clutch of unhatched egg structures most probably represents a nest of earliest sauropods; their footprints and trackways have been found nearby. The smaller ellipsoid egg structures are difficult to classify, they may represent either basal ornitishian or theropod eggs. This is the first find of dinosaur egg structures in Poland and the second known Lower Jurassic dinosaur nesting ground world-wide. It may also stimulate discussion on diagenetically altered dinosaur eggs.