New papers:
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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.
Emily J. Swaby & Dean R. lomax (2020)
A revision of Temnodontosaurus crassimanus (Reptilia: Ichthyosauria) from the Lower Jurassic (Toarcian) of Whitby, Yorkshire, UK.
Historial Biology (advance online publication)
doi: https://doi.org/10.1080/08912963.2020.1826469
https://www.tandfonline.com/doi/full/10.1080/08912963.2020.1826469
While the holotype of Temnodontosaurus crassimanus still remains on display at the Yorkshire Museum, it has remained largely understudied and the validity of the species has long been questioned. Through re-examination, this study highlights several morphological features of the postcranial skeleton and determines that T. crassimanus is a valid species of the genus and includes several distinct characters that can be used to distinguish it from T. trigonodon, to which it was once assigned. These include a large, robust humerus that is proximodistally longer than the scapula (scapula length vs humerus length ratio: ~0.68); forefins which are significantly longer but less than twice the length of the hindfin (forefin length vs hindfin length ratio: ~1.51); the relative size of the forefins compared with the total body length; along with several other characters that may prove to be unique, such as humerus distal width almost equal to humerus length; presence of notching in at least five leading edge elements of both the fore- and hindfins; and anteroposteriorly wider fore- and hindfins compared with T. trigonodon. Additional specimens, previously tentatively assigned to T. crassimanus, were located and examined, but none could confidently be assigned to the species.
A revision of Temnodontosaurus crassimanus (Reptilia: Ichthyosauria) from the Lower Jurassic (Toarcian) of Whitby, Yorkshire, UK.
Historial Biology (advance online publication)
doi: https://doi.org/10.1080/08912963.2020.1826469
https://www.tandfonline.com/doi/full/10.1080/08912963.2020.1826469
While the holotype of Temnodontosaurus crassimanus still remains on display at the Yorkshire Museum, it has remained largely understudied and the validity of the species has long been questioned. Through re-examination, this study highlights several morphological features of the postcranial skeleton and determines that T. crassimanus is a valid species of the genus and includes several distinct characters that can be used to distinguish it from T. trigonodon, to which it was once assigned. These include a large, robust humerus that is proximodistally longer than the scapula (scapula length vs humerus length ratio: ~0.68); forefins which are significantly longer but less than twice the length of the hindfin (forefin length vs hindfin length ratio: ~1.51); the relative size of the forefins compared with the total body length; along with several other characters that may prove to be unique, such as humerus distal width almost equal to humerus length; presence of notching in at least five leading edge elements of both the fore- and hindfins; and anteroposteriorly wider fore- and hindfins compared with T. trigonodon. Additional specimens, previously tentatively assigned to T. crassimanus, were located and examined, but none could confidently be assigned to the species.
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Kittichai Tongtherm, Yasunari Shigeta, Apsorn Sardsud, Katsuo Sashida, and Sachiko Agematsu (2020)
Age of the Early Triassic Ichthyopterygian Thaisaurus Inferred from Ammonoid Biostratigraphy.
Paleontological Research 24(4): 276-284
doi: https://doi.org/10.2517/2019PR022
https://bioone.org/journals/paleontological-research/volume-24/issue-4/2019PR022/Age-of-the-Early-Triassic-Ichthyopterygian-Thaisaurus-Inferred-from-Ammonoid/10.2517/2019PR022.short
Paleontological Research 24(4): 276-284
doi: https://doi.org/10.2517/2019PR022
https://bioone.org/journals/paleontological-research/volume-24/issue-4/2019PR022/Age-of-the-Early-Triassic-Ichthyopterygian-Thaisaurus-Inferred-from-Ammonoid/10.2517/2019PR022.short
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.