Home / Science / Research reveals an exceptionally small nest of non-avian theropod egg fossils – HeritageDaily

Research reveals an exceptionally small nest of non-avian theropod egg fossils – HeritageDaily

When most of us think about dinosaurs, we imagine large and heavy animals, but these giants shared their ecosystems with much smaller dinosaurs, whose smaller skeletons 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, the researchers scoured an outstanding fossil egg site first discovered in 2015 in Hyogo Prefecture, southwest Japan, and reported their findings in a new study published in Cretaceous research.

The Kamitaki egg quarry, found in a layer of red-brown mud from the Ohyamashimo Formation, deposited in an alluvial plain of the early Cretaceous river (about 1

10 million years), was carefully and intensely excavated in the winter of 2019 and has produced over 1300 fossil eggs. Most were isolated fragments, but there were some partial and almost complete eggs.

According to the lead author, Professor Kohei Tanaka, “our taphonomic analysis indicated that the nest we found was in situ, not transported and repositioned, because most of the eggshell fragments were placed concave, not concave as we see when eggshells are carried “.

Most of these fossil eggs belong to a new genus and egg 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 did not belong to the first birds, but to their cousins, the non-avian theropod dinosaurs (the group that includes known carnivores such as the Tyrannosaurus and Velociraptor). This places Himeoolithus murakamii among the smallest non-avian theropod eggs reported so far. These tiny eggs were particularly elongated in shape, unusual for eggs equally small among the Cretaceous birds, but typical among the largest non-avian theropod eggs.

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In addition to the abundant egg shell of Himeoolithus murakamii, five other ootaxa (distinct types of egg fossils) have been recognized in Kamitaki. All 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 locations known. The skeletal fossils of small theropods are quite scarce in this area. Therefore, these fossil eggs provide a useful window on the hidden ecological diversity of dinosaurs in the early Cretaceous of southwest Japan, as well as on the nesting behavior of small non-avian theropods. “


Header Image Credit: Tsukuba University and Museum of Nature and Human Activities

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