Sphaerovum

Sphaerovum is an oogenus of dinosaur egg that has only been discovered in South America.

Sphaerovum
Temporal range: Campanian-Maastrichtian
Egg fossil classification
Basic shell type: †Dinosauroid-spherulitic
Oofamily: †Faveoloolithidae
Oogenus: †Sphaerovum
Mones, 1980
Oospecies
  • †S. erbeni Mones, 1980 (type)

History

Sphaerovum was first described, along with Tacuarembovum, in 1980 by paleontologist Alvaro Mones, following their discovery at the Asencio Formation in Uruguay. This was one of the first discoveries of fossil dinosaur eggs in South America.[1]

Distribution

Fossils of Sphaerovum and Sphaerovum-like eggs are known from the Puerto Yeruá, Allen and Colorado Formations in Argentina and the Guichón and Asencio Formations of Uruguay.[2] They are always found in Campanian- or Maastrichtian-aged rocks, leading to their use as index fossils.[3]

Description

Sphaerovum eggs are 15-20 cm in diameter, with a shell between 4.2 and 5.5 mm thick. The ornamentation is compactituberculate, i.e. the eggshell is covered with dome-like nodes formed by the tops of the shell units.[2][1] The type specimen of Sphaerovum erbeni is too silicified to make out its microstructure, however many specimens of South American fossil eggs showing superficial similarities to Sphaerovum have been found.[4] These specimens are resemble other Faveoloolithids in their filispherulitic structure and a multicanaliculate pore system. Unlike Faveoloolithids, however, Sphaerovum has compactituberculate ornamentation more similar to Megaloolithids.[3][5] The high density of pores on the eggshell surface suggests that these eggs were laid in a humid environment.[3]

At the Mercedes Formation, Sphaerovum-like eggs were found in large, closely packed groups indicating that they were buried in a shallow pit.[6]

Classification

Due to their poor preservation, classification of Sphaerovum has proven difficult.[4]

Parataxonomy

The holotype specimen of Sphaerovum is heavily silicified, making the eggshell structure unrecognizable and assignment to any oofamily difficult.[6][4] However, other specimens which have strong superficial resemblance to Sphaerovum have been found in Uruguay and Argentina. These specimens show morphology similar to members of Faveoloolithidae, supporting the referral of Sphaerovum to that oofamily.[2][3] However, it is occasionally considered to be a Megaloolithid[7] on the basis of its ornamentation.[8]

Parentage

It is unknown what kind of dinosaur laid Sphaerovum eggs because embryonic remains have not been found. However, they have long been considered to be the eggs of titanosaurs. This would be consistent with the fact that titanosaurs were extremely common in the Upper Cretaceous of South America. Also, some eggshell fragments tentatively assigned to Sphaerovum were found loosely associated with the remains of a Saltasaurid titanosaur at the Guichón Formation in Uruguay.[2]

See also

References
  1. Mones, A. (1980) "Nuevos elementos de la paleoherpetofauna del Uruguay (Crocodilia y Dinosauria)." Actas II Congreso Argentino de Paleontologia y Bioestratigrafia y I Congreso Latinoamericano, Buenos Aires 1:265-277 (in Spanish)
  2. Soto, M., Perea, D., and Cambiaso, A.V. (2012) "First sauropod (Dinosauria: Saurischia) remains from the Guichón Formation, Late Cretaceous of Uruguay" Journal of South American Earth Sciences 33(1):68-79. DOI: 10.1016/j.jsames.2011.08.003
  3. Casadío, S., Manera, T., Parras, A., & Montalvo, C. I. (2002). "Dinosaur eggs (Faveloolithidae) from the Upper Cretaceous of the Colorado Basin, La Pampa Province, Argentina". Ameghiniana, 39(3), 285-293.
  4. Simón, M.E., (2006) "Cáscaras de huevos de dinosaurios de la Formación Allen (Campaniano e Maastrichtiano), en Salitral Moreno, provincia de Río Negro, Argentina." Ameghiniana 43: 513e528.
  5. Carpenter, K. (1999) Eggs, Nests, and Baby Dinosaurs: A Look at Dinosaur Reproduction (Life of the Past). Indiana University Press, Bloomington, Indiana. p. 144
  6. Faccio, G. (1994). "Dinosaurian eggs from the Upper Cretaceous of Uruguay." in Dinosaur eggs and babies, Edited by Kenneth Carpenter, Karl F. Hirsch, John R. Cambridge University Press. pp. 47-55.
  7. Carpenter, K. (1999) Eggs, Nests, and Baby Dinosaurs: A Look at Dinosaur Reproduction (Life of the Past). Indiana University Press, Bloomington, Indiana. p. 272
  8. Batista, A. (2012). "Análisis morfológico y sistemático de Tacuarembovum oblongum Mones 1980 y otras ooformas similares (Dinosauria), cretácico tardío? de Uruguay: implicancias." Graduate Thesis for Universidad de la República (Uruguay).
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