''Montanoolithus'' is an oogenus of fossil egg found in Montana and Alberta. They were probably laid by a dromaeosaur or a

caenagnathid Caenagnathidae is a family of bird-like maniraptoran theropod dinosaurs from the Cretaceous of North America and Asia. They are a member of the Oviraptorosauria, and close relatives of the Oviraptoridae. Like other oviraptorosaurs, caenagnathids ...

.D. K. Zelenitsky and F. Therrien. (2008) "Unique maniraptoran egg clutch from the Upper Cretaceous Two Medicine Formation of Montana reveals theropod nesting behaviour." ''Palaeontology'' 51(6):1253–1259

Distribution

The type specimen of ''Montanoolithus'' was found in the Two Medicine Formation on the Blackfeet Reservation. Other specimens are known from the Oldman Formation in Alberta. All ''Montanoolithus'' fossils yet discovered date to the Late Cretaceous.

Description

''Montanoolithus strongorum'' is known from several eggshell fragments and a partial

egg clutch __NOTOC__ A clutch of eggs is the group of eggs produced by birds, amphibians, or reptiles, often at a single time, particularly those laid in a nest. In birds, destruction of a clutch by predators (or removal by humans, for example the Califor ...

(with five preserved eggs). When complete, this clutch likely had at least twelve eggs, arrayed in pairs in a ring, similar to the Asian oviraptorid clutches. The most complete egg is elongated, measuring long by wide, and slightly asymmetrical. The outer surface of its shell is ornamented with anastomosing ridges. ''Montanoolithuss 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),Laura E. Wilson, Karen Chin, Frankie D. Jackson, and Emily S. Bray
II. Eggshell morphology and structure
''UCMP Online Exhibits: Fossil Eggshell'' is twice as thick as the inner mammillary layer. 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.

Palaeobiology

Cladistic analysis shows ''Montanoolithus'' to be maniraptoran eggs, more basal than troodontids, but more derived than oviraptorids. Maniraptorans are only represented at the Two Medicine formation by '' Troodon'' (whose eggs are already known), dromaeosaurs, and

s. Therefore, the parent of ''Montanoolithus'' was probably a dromaeosaur or a caenagnathid. The mother of the ''Montanoolithus'' eggs 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. The pairing of the eggs suggests that, like other maniraptorans, the egg-layer of ''Montanoolithus'' had two functioning

oviducts The oviduct in mammals, is the passageway from an ovary. In human females this is more usually known as the Fallopian tube or uterine tube. The eggs travel along the oviduct. These eggs will either be fertilized by spermatozoa to become a zygote, ...

which would each form an egg simultaneously.

Parataxonomy

''Montanoolithus'' is classified in its own oofamily, Montanoolithidae, which is related to the eggs of oviraptorids, troodontids, and birds. It contains a single oospecies: ''M. strongorum''.

References

{{Taxonbar, from=Q16919269 Egg fossils Fossil parataxa described in 2008 Dinosaur reproduction Prehistoric maniraptorans