219-9 Establishing modern marine ecosystem after the end-Permian mass extinction: evidence from the Middle Triassic Xingyi Fauna

Session: Paleontology, Diversity, Extinction, Origination (Posters)

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Abstract:

The end-Permian mass extinction is one of the largest biotic events in the Phanerozoic on Earth, along with the collapse of the Palaeozoic ecosystem followed by the establishment of the modern-type ecosystem, associated with the drastic global palaeoenvironmental and palaeoclimatic changes. It is a major transition in the life history, from the predators view, the terrestrail air-breathing tetropods became the top predators in the ecosystems after the extinction, both on lands and in the marine communities, while fishes and invertebrates also turned over to the modern groups.

The Xingyi Fauna found in southwestern China records this major transition and establishment of the new Modern-type ecosystem. This fauna yields abundant and well-articulated skeletons of Ladinian (Middle Triassic, ab. 240 Ma) marine reptiles, fishes, conodonts, crinoids, ammonoids, bivalves, arthropods, and other fossils including nannofossils and coprolites. Twenty marine reptile and 17 fish species have been reported, and the fossiliferous sequence can be subdivided into two assemblages. The Lower Assemblage are dominated by small to medium-sized pachypleurosaurid and nothosaurid sauropterygians, but in the Upper Assemblage, large body-sized shastasaurid ichthyopterygians and pistosauroid sauropterygians appeared, and flying fishes also presented in this subsequence.

The faunal composition of the Lower Assemblage is similar to that of the older Anisian Panxian Fauna and the western Tethyan Monte San Giorgio Fauna, while the Upper Assemblage is similar to that of the younger Carnian Guanling Biota as well as the Raibl and Polzberg Faunas in the Alps and California. The sequence of the Xingyi Fauna records the transition from the shallow water communities to the deep ocean communities, which were indicated by the large marine reptiles with a capability for long-distance cruising into the outer sea. These marine reptiles, as air-breathing tetropods invaded into the marine evironment, grew into large animals and were able to prey on other large reptiles, became the apex predators in the Middle Triassic marine ecosystem. Therefore, the Xingyi Fauna can be considered a hub of paleobiogeological exchange connecting the western Tethys and the eastern Pathalassa, and represents a new modern marine ecosystem fully developed after the end-Permian mass extinction.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-6332

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