Trigonoolithus

''Trigonoolithus'' is an oogenus of dinosaur egg, representing a basal prismatoolithid. Its eggshell, like avian eggs, is composed of three structural layers, but cladistic analysis suggests that its parent was a non-avian theropod.

History

Fossil eggshells now assigned to ''Trigonoolithus'' were first discovered in 2009 by Miguel Moreno-Azanza, José Manuel Gasca, and José Ignacio Canudo, three paleontologists from Universidad de Zaragoza.Moreno-Azanza, M., Gasca, J.M., and Canudo, J.I. (2009)
A high-diversity egg shell locality from the Hauterivian–Barremian transition of the Iberia Peninsula.
'' Journal of Vertebrate Paleontology'' 29 (Supplement to No. 3): 151A. They recognized that the fossils represented a new oogenus of prismatoolithids, but the description would not be completed until 2014, when they published a description of the new oogenus and oospecies ''Trigonoolithus amoae'' in the paleontology journal '' Acta Palaeontologica Polonica''.

Distribution

Fossils of ''Trigonoolithus'' are found in abundance at the La Cantera site of the Blesa Formation in Teruel, Spain. This site is dated to the early Barremian age.

Description

''Trigonoolithus'' is known from numerous eggshell fragments, but no complete or near-complete eggs. The whole egg of ''T. amoae'' was probably highly elongated, similar to other prismatoolithids. The shell fragments vary between 330 and 1040 μm in thickness, including the prominent triangular protuberances ornamenting their outer surface.

Its eggshell is made up of three structural layers, with gradual boundaries between them. The middle layer, known as the prismatic layer, has a squamatic texture and the prismatic structure characteristic of Prismatoolithidae. It is three to four times thicker than the innermost layer (the mammillary layer), and two to three times thicker than the external layer.

Circular pores 10 μm in diameter cut through ''Trigonoolithuss shell to allow for gas exchange. They are angusticanaliculate (meaning the pores are long, straight, and narrow), similar to the pore systems of ''Prismatoolithus'', ''Sankofa'', and ''Protoceratopsidovum''.Carpenter, K. (1999). Eggs, Nests, and Baby Dinosaurs: A Look at Dinosaur Reproduction (Life of the Past). Indiana University Press, Bloomington, Indiana.

Parataxonomy

''Trigonoolithus'' is classified in the oofamily Prismatoolithidae, alongside ''Preprismatoolithus'', ''Prismatoolithus'', ''Protoceratopsidovum'', ''Sankofa'', and '' Spheruprismatoolithus''.

Moreno-Azanza ''et al.'' performed multiple cladistic analyses to determine the phylogenetic position of ''Trigonoolithus''. Because no complete ''Trigonoolithus'' eggs are known, its position was slightly unstable, but ''Trigonoolithus'' was consistently placed as the basalmost member of Prismatoolithidae, or in a polytomy with other non-avian theropods and birds.

Paleobiology

Prismatoolithids were previously hypothesized to be eggs of hypsilophodonts or ceratopsians, but later research found that they in fact are the eggs of theropods, based on analysis of preserved embryos of '' Prismatoolithus levis'' which showed them to be '' Troodon formosus''. Therefore, ''Trigonoolithus'' was also probably laid by a theropod. Based on its phylogenetic position, Moreno-Azanza ''et al.'' concluded it was most likely a non-dromaeosaurian, non-oviraptorid coelurosaur theropod dinosaur. Of the theropods found at La Cantalera (so far represented only by teeth), only aff. '' Paronychodon'' sp. and an indeterminate maniraptoran are possible parents of ''Trigonoolithus''.

References

{{Reflist

Egg fossils
Barremian life
Early Cretaceous animals of Europe
Cretaceous Spain
Fossils of Spain
Fossil parataxa described in 2014