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eggshells likely belong to a variety of theropods (Nipponoolithus ramosus oogen. et oosp. nov., Elongatoolithus sp., Prismatoolithus sp., and Prismatoolithidae indet.) and at least one ornithopod (Spheroolithus sp.)
illustration: M. Hattori | marchan-forest.blogspot.com |
Highlights
• We describe a diverse dinosaur eggshell assemblage from Japan.
• Five different ootaxa, assignable to theropods and ornithopods were identified.
• Nipponoolithus ramosus oogen. et oosp. nov. was erected as a new ootaxon.
• This study reveals a hidden diversity of small theropods in Lower Cretaceous Japan.
Abstract
The Lower Cretaceous (Albian) Sasayama Group in the Hyogo Prefecture of southwestern Japan has yielded various vertebrate fossils, including skeletal remains of dinosaurs, anurans, lizards, and mammals, and recently eggshell fragments. Here we report on numerous fossil eggshells from the bone-bearing Kamitaki locality in Tamba City, which represents a diverse dinosaur eggshell assemblage. Of the more than 90 eggshell fragments recovered, five different types were identified, including eggshells that likely belong to a variety of theropods (Nipponoolithus ramosus oogen. et oosp. nov., Elongatoolithus sp., Prismatoolithus sp., and Prismatoolithidae indet.) and at least one ornithopod (Spheroolithus sp.). All eggshells are relatively thin, and a new derived estimation method correlating egg mass with eggshell thickness indicates that they are among the smallest (28–135 g) theropod eggs known, likely laid by small bodied forms. The eggshell assemblage from this locality suggests that a diverse small dinosaur fauna, consisting primarily of theropods, nested in the region, a diversity yet to be evidenced from skeletal remains in Japan.
Keywords: Dinosaur; Egg mass estimation; Eggshell; Japan; Lower Cretaceous; Sasayama Group
Systematic paleontology
Dinosauria Owen 1842 sensu Padian and May, 1993.
Theropoda Marsh 1881b sensu Gauthier, 1986.
Oofamily. Incertae sedis.
Oogenus. Nipponoolithus, oogen. nov.
Type oospecies. Nipponoolithus ramosus oosp. nov.
Diagnosis. As for the type and only oospecies.
Etymology. Nipponoolithus refers to Japan (Nippon), and form 'oo' meaning egg and 'lithos' meaning stone in Greek.
Type locality and horizon. As for type and only oospecies.
Oospecies. Nipponoolithus ramosus oosp. nov.
urn:lsid:zoobank.org:act:8C146325-2D50-4F82-B62E-A382145FDE76.
Etymology. The specific name means branching in Latin, referring to the branching ridges on the outer surface of the eggshell.
Holotype. MNHAH D1-040057, an eggshell fragment.
Referred specimens. Isolated eggshell fragments (n = 7) (MNHAH D1-040058 to D1-040063).
Type locality and horizon. The holotype and all referred specimens come from the lower part of the 'Lower Formation' of the Sasayama Group in Kamitaki, southeastern Tamba City, Hyogo, Japan.
Diagnosis. Nipponoolithus ramosus differs from all other ootaxa in the following unique combination of traits: low-relief, branching ridges on the outer surface; eggshell thickness ranges from 0.37 to 0.53 mm (average 0.44 mm); eggshell consists of a mammillary layer and a continuous layer delimited by an abrupt boundary; mammillae composed of acicular or wedge-like crystals; mammillae wider than high; mammillary layer to continuous layer thickness ratio of 1:2 to 1:4.
Kohei Tanaka, Darla K. Zelenitsky, Haruo Saegusa, Tadahiro Ikeda, Christopher L. DeBuhr and François Therrien. 2015. Dinosaur Eggshell Assemblage from Japan reveals unknown Diversity of Small Theropods. Cretaceous Research. doi: 10.1016/j.cretres.2015.06.002
世界最小クラスの新種の恐竜の卵の化石が見つかる ニッポノウーリサス・ラモーサス 兵庫県丹波市山南町
http://animal-channel.net/?p=4885
http://animal-channel.net/?p=4885
兵庫県丹波市で新種の恐竜卵化石を発見 - カルガリー大など（マイナビニュース） - goo ニュース http://news.goo.ne.jp/article/mycom/life/mycom_1227244.html
兵庫県丹波市で新種の恐竜卵化石を発見 - カルガリー大など #ldnews http://news.livedoor.com/article/detail/10291386/
