Montanoolithusis anoogenusof fossil egg found inMontanaandAlberta.They were probably laid by adromaeosauror acaenagnathid.[1]
| Montanoolithus Temporal range:
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|---|---|
Egg fossil classification
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| Basic shell type: | Ornithoid |
| Morphotype: | Ornithoid-ratite |
| Oofamily: | †Montanoolithidae Zelenitsky and Therrien, 2008 |
| Oogenus: | †Montanoolithus Zelenitsky and Therrien, 2008 |
| Oospecies | |
Distribution
editThe type specimen ofMontanoolithuswas found in theTwo Medicine Formationon theBlackfeet Reservation.Other specimens are known from theOldman Formationin Alberta. AllMontanoolithusfossils yet discovered date to theLate Cretaceous.[1]
Description
editMontanoolithus strongorumis known from several eggshell fragments and a partialegg clutch(with five preserved eggs). When complete, this clutch likely had at least twelve eggs, arrayed in pairs in a ring, similar to the Asianoviraptorid clutches.The most complete egg is elongated, measuring 125 mm (4.9 in) long by 60 mm (2.4 in) wide, and slightly asymmetrical. The outer surface of its shell is ornamented withanastomosingridges.[1]
Montanoolithus's eggshell ranges from 0.70 to 0.85 mm thick, and is composed of two layers. The outer layer, called the columnar layer (or squamatic zone, so named because of the peculiar texture of the layer),[2]is twice as thick as the inner mammillary layer.[1]The two layers are divided by a gradual boundary. The mammillae (the cone-shaped structures in the mammillary layer which make up the base of each eggshell unit) are formed by wedge-shaped crystals.[1]
Palaeobiology
editCladistic analysisshowsMontanoolithusto bemaniraptoraneggs, more basal thantroodontids,but more derived thanoviraptorids.[1][3]Maniraptorans are only represented at the Two Medicine formation byTroodon(whose eggs are already known),dromaeosaurs,andcaenagnathids.Therefore, the parent ofMontanoolithuswas probably a dromaeosaur or a caenagnathid.[1]
The mother of theMontanoolithuseggs made a mound-shaped nest out of sand, and laid the eggs in a ring around the top. The nest was made from freshly deposited sand (perhaps near to a river), or in a poorly vegetated area. Even though no parent was found with the eggs, it is likely based on its identification as a maniraptoran that the eggs were incubated, since this behavior has been observed in both troodontids and oviraptorids.[1]The pairing of the eggs suggests that, like other maniraptorans, the egg-layer ofMontanoolithushad two functioningoviductswhich would each form an egg simultaneously.[1]
Parataxonomy
editMontanoolithusis classified in its ownoofamily,Montanoolithidae,which is related to the eggs of oviraptorids, troodontids, and birds. It contains a single oospecies:M. strongorum.[1]
References
edit- ^abcdefghijD. K. Zelenitsky and F. Therrien. (2008) "Unique maniraptoran egg clutch from the Upper Cretaceous Two Medicine Formation of Montana reveals theropod nesting behaviour."Palaeontology51(6):1253–1259
- ^Laura E. Wilson, Karen Chin, Frankie D. Jackson, and Emily S. Bray.II. Eggshell morphology and structure.UCMP Online Exhibits: Fossil Eggshell
- ^López-Martínez, Nieves; Vicens, Enric (2012)."A new peculiar dinosaur egg, Sankofa pyrenaica oogen. nov. oosp. nov. from the Upper Cretaceous coastal deposits of the Aren Formation, south-central Pyrenees, Lleida, Catalonia, Spain".Palaeontology.55(2): 325–339.doi:10.1111/j.1475-4983.2011.01114.x.ISSN1475-4983.