UNIQUE MANIRAPTORAN EGG CLUTCH FROM THE UPPER CRETACEOUS TWO MEDICINE FORMATION OF MONTANA REVEALS THEROPOD NESTING BEHAVIOUR |
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Authors: | DARLA K ZELENITSKY FRANÇOIS THERRIEN |
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Institution: | 1. Department of Geoscience, University of Calgary, Calgary, Alberta T2N 1N4, Canada;2. e‐mail: dkzeleni@ucalgary.ca;3. Royal Tyrrell Museum of Palaeontology, Box 7500, Drumheller, Alberta T0J 0Y0, Canada;4. e‐mail: francois.therrien@gov.ab.ca |
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Abstract: | Abstract: 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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Keywords: | Theropoda Maniraptora eggs eggshell nesting trace Montanoolithus Two Medicine Formation |
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