Tadahiro Ikeda

Museum of Nature & Human Activities, Hyogo · Division of Natural History

A nearly complete left dentary of a lizard was excavated from the Lower Cretaceous Ohyamashimo Formation of the Sasayama Group in Tamba City, Hyogo Prefecture, Japan. The specimen shows several characters, which suggest its allocation in Monstersauria of the superfamily Varanoidea (Squamata: Anguimorpha). However, the specimen exhibits obvious diff...

We investigated the environmental conditions that prevailed in continental ecosystems recorded in sedimentary deposits of Japan during the Cretaceous through the analysis of oxygen and carbon isotope compositions of phosphate (δ¹⁸Op) and apatite-bound carbonate (δ¹⁸Oc and δ¹³Cc) of vertebrate teeth and bones. Local surface water δ¹⁸Ow values were c...

The Kamitaki Locality in the Albian Ohyamashimo Formation in the eastern Hyogo Prefecture of southwestern Japan is among the richest Lower Cretaceous fossil egg sites in the world. So far, eggshells of five different ootaxa, one ornithopod and four theropods, have been identified from the Kamitaki Bonebed Quarry. Although previous discoveries of eg...

Asian hesperornithiforms are extremely rare in contrast to North American records; thus, their diversity in Asia during the Cretaceous is unclear. Maastrichtian hesperornithiform materials have been reported from both fluvial and marine deposits in North America but only from fluvial deposits in Asia. Asian hesperornithiforms from Maastrichtian dep...

要旨：港川人遺跡の裂罅堆積物から発見された85点のカメ化石の分類学的帰属について検討を行った．その結果，裂罅の下位から中位にかけてより沖縄諸島の固有種リュウキュウヤマガメ，セマルハコガメ属の一種，およびこれら2種とは異なるイシガメ類の一種，さらにリクガメ科の絶滅種オオヤマリクガメの計4種の化石が検出された．層準ごとのカメ類の化石の産出数は，下位で多い一方，中位では大きく減少していた．セマルハコガメ属の一種の化石は，ほかの3種とくらべて最も多く保存されていた．これらの結果は， 更新世末期の沖縄島南部には4種のカメ類が分布していたことを示すほか，この地域でセマルハコガメ属の一種が優先して分布していたことを示唆した．裂罅の中・上位の層準におけるカメ類化石の数の著しい減少または欠如は，人類による影響...

Crocodylians are ectothermic animals, and their past distribution has been greatly influenced by changing climate since their Cretaceous origin. The Pliocene-Pleistocene witnessed a contraction of the crocodylian latitudinal ranges due to rapid cooling with superimposed pronounced orbital-scale climate oscillations. However, a chronologically-conti...

A number of fossil snake vertebrae were collected from Early Pleistocene deposits exposed on a hill surface at Gogayama, Nakijin village, Okinawajima Island, along with many other vertebrate fossils. These represent the oldest fossil records of snakes for the whole Ryukyu Archipelago. We identified each of these fossil snake vertebrae to the lowest...

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 represent...

We describe two well-preserved and articulated fossil anurans excavated from the Lower Cretaceous Sasayama Group in Hyogo Prefecture, Western Honshu, Japan, as new taxa on the basis of unique combinations of character states. We performed a phylogenetic analysis that included these new taxa, as well as Mesozoic and archaic anurans. This analysis st...

ABSTRACT—A new fossil lizard of the genus Pachygenys is described on the basis of a single, partially broken right mandible excavated from an unnamed formation of the Lower Cretaceous Sasayama Group in Hyogo Prefecture, western Honshu, Japan. The mandible exclusively shares a few apparently highly specialized morphological features, such as distinc...

A new genus and species of titanosauriform sauropod is erected based on a partial skeleton found in the Lower Cretaceous Sasayama Group of Hyogo Prefecture, SW Japan. The new taxon is here named as Tambatitanis amicitiae gen. et sp. nov., which is diagnosed by the following features of the caudal vertebrae, chevrons and braincase: the postzygapophy...

We here describe a new Early Cretaceous (early Albian) eutherian mammal, Sasayamamylos kawaii gen. et sp. nov., from the 'Lower Formation' of the Sasayama Group, Hyogo Prefecture, Japan. Sasayamamylos kawaii is characterized by a robust dentary, a distinct angle on the ventral margin of the dentary at the posterior end of the mandibular symphysis,...

A comparative study was carried out on the vertebral morphology of 54 species and subspecies of snakes from Japan and a few other East and Southeast Asian countries. My purpose was to establish a character table for identification of Cenozoic fossil snake vertebrae frequently found in these regions. A total of 29 taxonomically useful characters wer...