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Saurolophus Perinatal Specimens from Mongolia



Ben Creisler
bcreisler@gmail.com

New in PLoS ONE:

Leonard Dewaele,  Khishigjav Tsogtbaatar, Rinchen Barsbold, Géraldine
Garcia, Koen Stein, François Escuillié & Pascal Godefroit (2015)
Perinatal Specimens of Saurolophus angustirostris (Dinosauria:
Hadrosauridae), from the Upper Cretaceous of Mongolia.
PLoS ONE 10(10): e0138806.
doi:10.1371/journal.pone.0138806
http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0138806


Background

The Late Cretaceous Nemegt Formation, Gobi Desert, Mongolia has
already yielded abundant and complete skeletons of the hadrosaur
Saurolophus angustirostris, from half-grown to adult individuals.

Methodology/Principal Findings

Herein we describe perinatal specimens of Saurolophus angustirostris,
associated with fragmentary eggshell fragments. The skull length of
these babies is around 5% that of the largest known S. angustirostris
specimens, so these specimens document the earliest development stages
of this giant hadrosaur and bridge a large hiatus in our knowledge of
the ontogeny of S. angustirostris.

Conclusions/Significance

The studied specimens are likely part of a nest originally located on
a riverbank point bar. The perinatal specimens were buried by sediment
carried by the river current presumably during the wet summer season.
Perinatal bones already displayed diagnostic characters for
Saurolophus angustirostris, including premaxillae with a strongly
reflected oral margin and upturned premaxillary body in lateral
aspect. The absence of a supracranial crest and unfused halves of the
cervical neural arches characterize the earliest stages in the
ontogeny of S. angustirostris. The eggshell fragments associated with
the perinatal individuals can be referred to the Spheroolithus oogenus
and closely resemble those found in older formations (e.g. Barun Goyot
Fm in Mongolia) or associated with more basal hadrosauroids
(Bactrosaurus-Gilmoreosaurus in the Iren Dabasu Fm, Inner Mongolia,
China). This observation suggests that the egg microstructure was
similar in basal hadrosauroids and more advanced saurolophines.