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Therizinosauroid nesting site found in Mongolia

From: Ben Creisler

A news story about the discovery of a therizinosauroid nesting site in
Mongolia, announced at the SVP meeting. With the embargo over, I've
included the abstract as well:


SVP abstract:

KOBAYASHI, Yoshitsugu, Hokkaido University, Hokkaido, Japan; LEE, Yuong-Nam,
Korea Institute of Geoscience & Mineral Resources, Daejeon, Korea, Republic of
(South); BARSBOLD, Rinchen, Paleontological Center, Ulaanbaatar, Mongolia;
ZELENITSKY, Darla, University Of Calgary, Calgary, AB, Canada; TANAKA, Kohei,
University Of Calgary, Calgary, AB, Canada

In the western Gobi Desert of Mongolia, dinosaur eggs are commonly
discovered from the Upper Cretaceous beds and shed light on nesting
behaviors. However, dinosaur eggs from the eastern Gobi Desert are
relatively rare. In 2012, a colonial nesting ground of a theropod
dinosaur, containing at least seventeen clutches of eggs in a single
stratigraphic horizon within an area of 22 m by 52 m, was discovered
from the middle part of the Javkhlant Formation in the eastern Gobi.
The egg-bearing horizon consists of a red-brown mudstone with caliche
nodules and is interpreted as a paleosol of overbank deposits in a
proximal alluvial plain in a seasonally-arid setting. Each clutch
contains up to eight spherical eggs (13 cm in a diameter) in a single
layer. Eggs in each clutch are in contact and form a circular
structure without a central opening. The size of one clutch,
containing eight eggs, is 51 cm by 43 cm, and clutches are laid in
close proximity (shortest distance 1.4 m apart, and four clutches
within a 4 m by 4 m area). Eggshell is approximately 1.5 mm thick and
has a rough outer surface without distinct ornamentation. Microscopic
analyses of eggshells show the dendrospherulithic morphotype with a
prolatocanaliculate pore system. All these features suggest that the
Javkhlant eggs belong to the Dendroolithidae, an egg type that was
previously unreported from the eastern Gobi. Dendroolithids have
previously been ascribed to therizinosauroids based on in ovo
embryonic remains from China. Although there is no record of
therizinosauroids from the Javkhlant Formation, remains of large
therizinosaurs (Enigmosaurus, Erlikosaurus, and Segnosaurus) are
common from the underlying Bayanshiree Formation. This discovery
represents the first nesting colony of a non-avian theropod dinosaur
in Asia and the largest known non-avian theropod colony. Multiple egg
clutches indicate that some therizinosauroids were colonial nesters,
behaviors also described for hadrosaurids, prosauropods, titanosaurs,
and birds. Egg clutches within a single stratigraphic layer at the
outcrop suggests these dinosaurs nested at this site on a single
occasion, indicating no site fidelity.