Spencer, Lee A. and Kennedy, Elaine G.
The primary difficulty in accurately identifying dinosaur nest sites and behaviors has been the lack of defining criteria, both paleontological and sedimentological. If eggs are found, especially associated eggs or abundant eggshell fragments, they are almost always assumed to be nests. Sedimentological data has been minimized or ignored.
The Allen Formation in the Rio Negro Province, Argentina, preserves numerous localities with either whole eggs or abundant eggshell fragments, which have been interpreted as representing nesting areas. A 4 m2 quarry was excavated through part of a layer containing abundant eggshell fragments utilizing both paleontological and sedimentological techniques. The eggshell fragments were randomly oriented throughout a 1.5 m thick mudstone; the mudstone lacked depositional structures; and the layer was exposed over 1.5 km. The fragments were taxonomically diverse and were mixed with other biota, including fish and turtle fragments as well as plant debris. We interpreted the depositional environment as a storm surge deposit.
Sedimentological structures were also noted at the site of whole eggs. The eggs were found at the toe of a cross-bedded sandstone. The cross-beds draped across the eggs and were not cut by any parental digging activity. Rip-ups, mud lenses and mud stringers were noted in the basal portion of the sandstone.
The sedimentological context of all sites examined involved transport. No nest structures were seen. Preliminary studies in North America and Europe have yielded data suggesting that nesting behavioral interpretations there could also benefit from additional sedimentological research.
Published in 2001 in Paleobios 21(Supplement to No. 2):119.