Chaohusaurus zhangjiawanensis (Triassic ichthyosauriform) dentition + Middle Triassic marine Luoping biota preservation

[Ben Creisler]

Ben Creisler

bcre...@gmail.com

Recent papers:

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Li-Ang Gu, Andrzej S. Wolniewicz & Jun Liu (2024)
New information on the dentition of Chaohusaurus zhangjiawanensis (Reptilia, Ichthyosauriformes) from the Early Triassic of Yuan’an, Hubei Province, China
Swiss Journal of Palaeontology (advance online publication)
doi: https://doi.org/10.1186/s13358-024-00331-8
https://link.springer.com/article/10.1186/s13358-024-00331-8

Chaohusaurus is an early ichthyosauriform represented by three species known from the Early Triassic of Chaohu, Anhui Province, China, with a fourth species—Chaohusaurus zhangjiawanensis—known from the Nanzhang-Yuan’an region of Hubei Province. In contrast to the Chaohusaurus species from Chaohu, Chaohusaurus zhangjiawanensis remains poorly known, hindering our understanding of early ichthyosauriform evolution. Here, we report a new specimen of Chaohusaurus zhangjiawanensis, which provides new information on its dentition. The new specimen confirms that Chaohusaurus zhangjiawanensis had heterodont dentition consisting of pointed anterior teeth and robust, rounded posterior teeth, indicating a generalist diet. The posterior teeth of Chaohusaurus zhangjiawanensis are more robust (broader and larger) than the posterior dentition of Chaohusaurus chaoxianensis and Chaohusaurus brevifemoralis from Chaohu. This suggests differences in hard-shelled prey preference between species of Chaohusaurus from Chaohu and Nanzhang-Yuan’an, with Chaohusaurus zhangjiawanensis likely capable of feeding on harder and larger prey than Chaohusaurus brevifemoralis and Chaohusaurus chaoxianensis. In turn, this probably reflects differences in durophagous prey availability between the shallow-marine palaeoecosystem of Nanzhang-Yuan’an and the deeper, slope-basin palaeoecosystem of Chaohu. The posterior dentition and forefin of Chaohusaurus zhangjiawanensis are strikingly similar to those of Chaohusaurus geishanensis, the rarest species of Chaohusaurus from the Chaohu fauna. The scarcity of Chaohusaurus geishanensis in the Chaohu fauna, and its morphological similarity to Chaohusaurus zhangjiawanensis, possibly indicate that Chaohusaurus geishanensis was closely related with Chaohusaurus zhangjiawanensis and that it was also a shallow-marine species that was not a typical component of the Chaohu fauna. It probably occasionally wandered out into the deeper waters of Chaohu from a nearby coastal environment.

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Zhongzhao Ding, Zhixin Ma, Shixue Hu, Shuang Dai, Qiyue Zhang, Xiao Min, Jinyuan Huang, Wen Wen, Changyong Zhou, Xinnan Fang, Tianqi Ji & Lingfeng Qin (2024)
Paleoclimate evolution of the Middle Triassic Guanling Formation from South China and its significance for the preservation of the Luoping biota
Global and Planetary Change 104588
doi: https://doi.org/10.1016/j.gloplacha.2024.104588
https://www.sciencedirect.com/science/article/abs/pii/S0921818124002352

Highlights
Five stages of sedimentary and climate evolution have been identified in a middle Anisian marine succession at South China.

The mid-Anisian warming and sea-level rising event occurred during the interval yielding the Luoping biota based on microfacies and paleoclimate analysis.

Intermittent marine anoxia induced by mid-Anisian warming climate, enhanced continental weathering and nutrient inputs is a main cause of death and preservation of Luoping biota.

Abstract

The Middle Triassic is regarded as an important period of biotic recovery after the end-Permian mass extinction, of which the Middle Triassic Luoping biota represents a full recovery of marine ecosystem. However, the research on the relationship between biotic recovery and environmental evolution in the Middle Triassic remains poorly understood. To investigate this issue, microfacies analysis and multiple geochemical proxies (Al, Ti, Th, Sc, and ∑REY) of an Anisian (Middle Triassic) succession (the Member II of the Guanling Formation, Leniduo section, South China) yielding the Luoping biota are carried out. Five sedimentary facies are identified through field investigation and microfacies analysis: open platform, restricted platform, tidal flat, shoal and intra-platform depression. According to the changes of multiple geochemical proxies, this section can be divided into five stages. A sudden facies transition from open platform to intra-platform depression, and high contents of Al, Ti, Sc, Th, and ∑REY in stage IV indicate a rapid sea-level rise and detrital input increase, coinciding with the preservation of the Luoping biota. This evidence suggest that enhanced continental weathering caused by global warming, global sea level rise, and frequent regional volcanic activities promoted the death and preservation of the Luoping biota.

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