''Triprismatoolithus'' is an

oogenus Egg fossils are the fossilized remains of eggs laid by ancient animals. As evidence of the physiological processes of an animal, egg fossils are considered a type of trace fossil. Under rare circumstances a fossil egg may preserve the remains ...

dinosaur egg Dinosaur eggs are the organic vessels in which a dinosaurs, dinosaur embryo develops. When the first scientifically documented remains of non-avian dinosaurs were being described in England during the 1820s, it was presumed that dinosaurs had la ...

native to Teton County, Montana. It is classified in the oofamily Arriagadoolithidae, the eggs of alvarezsaurs.

Distribution

''Triprismatoolithus'' is known exclusively from Sevenmile Hill, a fossil site at the

Two Medicine Formation The Two Medicine Formation is a geological formation, or rock body, in northwestern Montana and southern Alberta that was deposited between 82.4 Ma and 74.4 Ma, during Campanian (Late Cretaceous) time. It crops out to the east of the Rocky Mountai ...

in Teton County,

Montana Montana ( ) is a landlocked U.S. state, state in the Mountain states, Mountain West subregion of the Western United States. It is bordered by Idaho to the west, North Dakota to the east, South Dakota to the southeast, Wyoming to the south, an ...

. It is the oldest known fossil egg site at that formation, dating to 80 million years ago, the early part of the

Campanian The Campanian is the fifth of six ages of the Late Cretaceous epoch on the geologic timescale of the International Commission on Stratigraphy (ICS). In chronostratigraphy, it is the fifth of six stages in the Upper Cretaceous Series. Campa ...

History

Fossil eggs are common from the upper part of the Two Medicine formation, but it was not until

2010 The year saw a multitude of natural and environmental disasters such as the 2010 Haiti earthquake, the Deepwater Horizon oil spill, and the 2010 Chile earthquake. The 2009 swine flu pandemic, swine flu pandemic which began the previous year ...

that paleontologists discovered eggs in the lower part, including ''Triprismatoolithus''. They were discovered by two paleontologists from the

University of Montana The University of Montana (UM) is a public research university in Missoula, Montana, United States. UM is a flagship institution of the Montana University System and its second largest campus. Fall 2024 saw total enrollment hit 10,811, marki ...

: Frankie D. Jackson and David J. Varricchio. It remained of uncertain classification (because no similar eggs were known) until

2012 2012 was designated as: *International Year of Cooperatives *International Year of Sustainable Energy for All Events January *January 4 – The Cicada 3301 internet hunt begins. * January 12 – Peaceful protests begin in the R ...

when Agnolin ''

et al. References Notes References Further reading * * External links * {{Latin phrases E ...

'' discovered similar eggs associated with ''

Bonapartenykus ''Bonapartenykus'' (meaning "José Bonaparte, José F. Bonaparte's claw") is a monospecific genus of alvarezsauroidea, alvarezsauroid dinosaur from Argentina that lived during the Late Cretaceous (Campanian-Maastrichtian) in what is now the uppe ...

'', which they classified with ''Triprismatoolithus'' in a new oofamily, Arriagadoolithidae.

Description

The

type specimen In biology, a type is a particular wikt:en:specimen, specimen (or in some cases a group of specimens) of an organism to which the scientific name of that organism is formally associated. In other words, a type is an example that serves to ancho ...

of ''Triprismatoolithus'' is a complete egg measuring 30 mm by 75 mm, but several other incomplete eggs and eggshell fragments are known. The eggs were paired, similar to '' Continuoolithus''. The eggshell is between ranges from 525 to 850 μm thick. ''Triprismatoolithus'' is notable for having three structural layers, similar to birds and unlike most other non- avian

dinosaur Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic Geological period, period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the #Evolutio ...

eggs.Laura E. Wilson, Karen Chin, Frankie D. Jackson, and Emily S. Bray. (2012).
Fossil eggshell: Fragments from the past
UCMP's online fossil egg exhibit. The second layer, known as the prismatic layer, is made up of closely packed calcite crystals, and exhibits irregular squamatic texture.F. L. Agnolin, J. E. Powell, F. E. Novas and M. Kundrát. 2012. "New alvarezsaurid (Dinosauria, Theropoda) from uppermost Cretaceous of north-western Patagonia with associated eggs." ''Cretaceous Research'' 35(1):33–56 It is five times thicker than the mammillary layer. The surface of the eggshell of ''Triprismatoolithus'' is covered with low, rounded tubercles, similar to ''

Arriagadoolithus ''Arriagadoolithus'' is the oogenus of fossil eggs which includes the eggs of the alvarezsaurid ''Bonapartenykus''. Fossils of the creature were found in Patagonia; it may have brooded on its eggs. Description ''Arriagadoolithus patagoniensis'' i ...

''.

Classification

''Triprismatoolithus'' shares many unique characteristics with ''Arriagadoolithus'', so they are classified together in the oofamily Arriagadoolithidae. ''Triprismatoolithus'' contains a single oospecies: ''T. stephensi''.

Paleobiology

''Triprismatoolithus'' has not been found associated with embryos or adult remains, so it is unknown precisely what kind of dinosaur laid the eggs. However, the closely related oogenus, ''Arriagadoolithus'', was discovered closely associated with the

alvarezsaurid Alvarezsauridae is a family of small, long-legged dinosaurs. Although originally thought to represent the earliest known flightless birds, they are now thought to be an early diverging branch of maniraptoran theropods. Alvarezsaurids were highly ...

''Bonapartenykus'', so it is likely that ''T. stephensi'' was also laid by an unknown alvarezaur or a closely related dinosaur. Arriagadoolithids, like elongatoolithids, prismatoolithids, and '' Continuoolithus'', are laid in pairs, which is interpreted as evidence that

oviraptorosaurs Oviraptorosaurs ("egg thief lizards") are a group of feathered maniraptoran dinosaurs from the Cretaceous Period of what are now Asia and North America. They are distinct for their characteristically short, beaked, parrot-like skulls, with or wi ...

troodontids Troodontidae is a clade of bird-like theropod dinosaurs from the Late Jurassic to Late Cretaceous. During most of the 20th century, troodontid fossils were few and incomplete and they have therefore been allied, at various times, with many dinos ...

, and alvarezsaurs had two functioning

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

, unlike birds which have only one.

References

{{Taxonbar, from=Q24913691 Fossil parataxa described in 2010 Arriagadoolithidae Two Medicine Formation