Publication: Age of the Early Triassic ichthyopterygian Thaisaurus inferred from ammonoid biostratigraphy
Issued Date
2020-10-05
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13428144
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2-s2.0-85093850328
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Mahidol University
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SCOPUS
Bibliographic Citation
Paleontological Research. Vol.24, No.4 (2020), 276-284
Suggested Citation
Kittichai Tongtherm, Yasunari Shigeta, Apsorn Sardsud, Katsuo Sashida, Sachiko Agematsu Age of the Early Triassic ichthyopterygian Thaisaurus inferred from ammonoid biostratigraphy. Paleontological Research. Vol.24, No.4 (2020), 276-284. doi:10.2517/2019PR022 Retrieved from: https://repository.li.mahidol.ac.th/handle/20.500.14594/59808
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Age of the Early Triassic ichthyopterygian Thaisaurus inferred from ammonoid biostratigraphy
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Abstract
© by the Palaeontological Society of Japan The age of the primitive ichthyopterygian Thaisaurus is more accurately defined due to the discovery of a new species of the ammonoid genus Marcouxia from beds about 2.4 m below the horizon from which the holotype of Thaisaurus chonglakmanii was collected in the Phukhaothong Dolomite Member of the Chaiburi Formation in the Phatthalung area, southern Thailand. The shell of Marcouxia chaiburiensis sp. nov. is characterized by a quadrate whorl section, an arched venter with a sub-acute keel-like elevation, and spiny tubercles on the ventrolateral shoulders as well as numerous regularly spaced, radial or slightly prorsiradiate ribs. Because the range of Marcouxia is limited to the Columbites parisianus Subzone of the lower Spathian (upper Olenekian, Lower Triassic) in the western USA, the age of Thaisaurus is likely constrained to the early Spathian, thus suggesting it is one of the oldest known ichthyopterygians.