Triprismatoolithusis anoogenusofdinosaur eggnative toTeton County, Montana.[1]It is classified in the oofamilyArriagadoolithidae,the eggs ofalvarezsaurs.[2]
| Triprismatoolithus Temporal range:
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|---|---|
Egg fossil classification
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| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Clade: | Dinosauria |
| Clade: | Saurischia |
| Clade: | Theropoda |
| Family: | †Alvarezsauridae |
| Oofamily: | †Arriagadoolithidae |
| Oogenus: | †Triprismatoolithus Jackson and Varricchio, 2010 |
| Oospecies | |
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Distribution
editTriprismatoolithusis known exclusively from Sevenmile Hill, a fossil site at theTwo Medicine Formationin Teton County,Montana.It is the oldest known fossil egg site at that formation, dating to 80 million years ago, the early part of theCampanian.[1]
History
editFossil eggs are common from the upper part of the Two Medicine formation, but it was not until2010that paleontologists discovered eggs in the lower part, includingTriprismatoolithus.They were discovered by two paleontologists from theUniversity of Montana:Frankie D. Jackson and David J. Varricchio.[1]It remained of uncertain classification (because no similar eggs were known) until2012when Agnolinet al.discovered similar eggs associated withBonapartenykus,which they classified withTriprismatoolithusin a new oofamily,Arriagadoolithidae.
Description
editThetype specimenofTriprismatoolithusis a complete egg measuring 30 mm by 75 mm, but several other incomplete eggs and eggshell fragments are known. The eggs were paired, similar toContinuoolithus.The eggshell is between ranges from 525 to 850 μm thick.[1]
Triprismatoolithusis notable for having three structural layers,[1]similar to birds and unlike most other non-aviandinosaureggs.[3]The second layer, known as the prismatic layer, is made up of closely packed calcite crystals, and exhibits irregular squamatic texture.[1][2]It is five times thicker than the mammillary layer.[1]
The surface of the eggshell ofTriprismatoolithusis covered with low, rounded tubercles, similar toArriagadoolithus.[1][2]
Classification
editTriprismatoolithusshares many unique characteristics withArriagadoolithus,so they are classified together in the oofamily Arriagadoolithidae.[2]Triprismatoolithuscontains asingle oospecies:T. stephensi.[1]
Paleobiology
editTriprismatoolithushas 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 thealvarezsauridBonapartenykus,so it is likely thatT. stephensiwas also laid by an unknown alvarezaur or a closely related dinosaur.[2]
Arriagadoolithids, likeelongatoolithids,prismatoolithids,andContinuoolithus,[1]are laid in pairs, which is interpreted as evidence thatoviraptorosaurs,troodontids,and alvarezsaurs had two functioningoviducts,unlike birds which have only one.[2]
References
edit- ^abcdefghijJackson, Frankie; Varricchio, David (2010)."Fossil eggs and eggshell from the lowermost Two Medicine Formation of western Montana, Sevenmile Hill locality".Journal of Vertebrate Paleontology.30(4): 1142–1156.doi:10.1111/j.1475-4983.2011.01114.x.
- ^abcdefF. 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 Research35(1):33–56
- ^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.