Age of the Early Triassic Ichthyopterygian Thaisaurus Inferred from Ammonoid Biostratigraphy
Age of the Early Triassic Ichthyopterygian Thaisaurus Inferred from Ammonoid Biostratigraphy
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DOI：
10.2517/2019pr022
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发表时间：
2020-10
影响因子：
0.9
通讯作者：
Kittichai Tongtherm;Y. Shigeta;A. Sardsud;K. Sashida;Sachiko Agematsu
中科院分区：
文献类型：
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作者：
Kittichai Tongtherm;Y. Shigeta;A. Sardsud;K. Sashida;Sachiko Agematsu
抽象。由于在泰国南部法塔隆地区的Chaiburi组的Chaikhaothong白云岩段中发现了菊石属的一个新种，因此原始鱼鳍泰龙的年龄得到了更准确的界定。该种的壳具方形轮节、拱形腹部和近尖龙骨状隆起、腹外侧肩部有刺状瘤以及许多规则间隔的放射状或略前放射状肋。由于马库西亚龙的分布范围仅限于美国西部的下斯帕斯阶（下三叠统，上奥伦尼克阶）的哥伦比亚龙（Columbites parisianus）亚带，因此泰国龙的年龄可能局限于早期斯帕斯阶，这表明它是已知最古老的鱼龙类之一。
Abstract. 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.