Unique maniraptoran egg clutch from the Upper Cretaceous Two Medicine Formation of Montana reveals theropod nesting behaviour

51 6 November 1253 1259 10.1111/j.1475-4983.2008.00815.x

ZELENITSKY, D. K., THERRIEN, F. 2008. Unique maniraptoran egg clutch from the Upper Cretaceous Two Medicine Formation of Montana reveals theropod nesting behaviour. Palaeontology, 51, 6, 1253–1259.

Darla K. Zelenitsky and François Therrien Egg clutches of non-avian maniraptoran theropods (Dinosauria) are rare, particularly in North America where those of Troodon formosus are the only maniraptoran clutches known. Here we describe a new partial maniraptoran clutch and nesting trace referred to Montanoolithus strongorum oogen. et oosp. nov. (Montanoolithidae oofam. nov.), from the Upper Cretaceous Two Medicine Formation of Montana. Based on a cladistic analysis of reproductive traits, we infer that this clutch belonged either to a caenagnathid or to a dromaeosaurid, which makes it the first clutch known of either taxon. This specimen preserves impressions and eggshell fragments of at least five eggs on a nest structure. The eggs are asymmetrical, paired, and lay radially in a ring configuration on the sloped sides of a bioturbated, flat-topped sandstone mound. Geology of the locality indicates the female nested in a poorly-vegetated area of freshly deposited sand, possibly near an active river channel. This clutch reveals that the egg-layer of Montanoolithus strongorum had a unique suite of reproductive characteristics and nesting behaviours among maniraptorans.
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