Tiny Japanese dinosaur eggs help unscramble Cretaceous ecosystem

Date:
June 26, 2020
Source:
University of Tsukuba
Summary:
A research team has excavated over 1300 eggshell fossils from
the Lower Cretaceous Ohyamashimo Formation of Hyogo Prefecture,
Japan. Over 96% of these fossils, including numerous fragments, four
partial and almost complete eggs in an in situ nest, belonged to a
new ootaxon the authors named Himeoolithus murakamii, attributed
to a small non-avian theropod dinosaur. The remaining eggshell
fragments, belonging to five additional small theropod ootaxa,
showed notable biodiversity.



FULL STORY ==========================================================================
When most of us think of dinosaurs, we envision large, lumbering beasts,
but these giants shared their ecosystems with much smaller dinosaurs, the smaller skeletons of which were generally less likely to be preserved. The fossilized egg shells of these small dinosaurs can shed light on this
lost ecological diversity.


==========================================================================
Led by the University of Tsukuba, researchers scoured an exceptional
fossil egg site first discovered in 2015 in Hyogo Prefecture, southwestern Japan, and reported their findings in a new study published in Cretaceous Research.

The Kamitaki Egg Quarry, found in a red-brown mudstone layer of the
Ohyamashimo Formation, deposited in an Early Cretaceous (about 110 million years old) river flood plain, was carefully and intensively excavated
in the winter of 2019, and yielded over 1300 egg fossils. Most were
isolated fragments, but there were a few partial and almost complete eggs.

According to lead author Professor Kohei Tanaka, "our taphonomic analysis indicated that the nest we found was in situ, not transported and
redeposited, because most of the eggshell fragments were positioned
concave-up, not concave- down like we see when egg shells are
transported." Most of these fossil eggs belong to a new egg genus and
species, called Himeoolithus murakamii, and are exceptionally small,
with an estimated mass of 9.9 grams -- about the size of a modern
quail egg. However, biological classification analysis implies that the
eggs belonged not to early birds, but to their cousins, the non-avian
theropod dinosaurs (the group that includes well-known carnivores like Tyrannosaurus and Velociraptor). That puts Himeoolithus murakamii among
the smallest non-avian theropod eggs reported to date. These tiny eggs
were notably elongated in shape -- unusual for similarly small eggs
among Cretaceous birds, but typical among larger non-avian theropod eggs.

In addition to the abundant Himeoolithus murakamii egg shells, five more
ootaxa (distinct types of egg fossils) were recognized in the Kamitaki locality. All of these ootaxa belonged to small non-avian theropods.

As Professor Tanaka explains, "the high diversity of these small
theropod eggs makes this one of the most diverse Early Cretaceous egg localities known. Small theropod skeletal fossils are quite scarce in this area. Therefore, these fossil eggs provide a useful window into the hidden ecological diversity of dinosaurs in the Early Cretaceous of southwestern Japan, as well as into the nesting behavior of small non-avian theropods."

========================================================================== Story Source: Materials provided by University_of_Tsukuba. Note: Content
may be edited for style and length.


========================================================================== Journal Reference:
1. Kohei Tanaka, Darla K. Zelenitsky, Franc,ois Therrien, Tadahiro
Ikeda,
Katsuhiro Kubota, Haruo Saegusa, Tomonori Tanaka, Kenji Ikuno.

Exceptionally small theropod eggs from the Lower Cretaceous
Ohyamashimo Formation of Tamba, Hyogo Prefecture, Japan. Cretaceous
Research, 2020; 114: 104519 DOI: 10.1016/j.cretres.2020.104519 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/06/200626114821.htm

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