The largely stagnant marine ecosystem following the Permian–Triassic mass extinction (PTME) was superseded by the appearance of marine reptiles. One of the most abundant Early Triassic (Spathian) marine reptile faunas occurs in the Nanzhang‐Yuan'an area of Hubei Province, South China, and provides remarkable information for understanding biotic recovery after the PTME. Situated on the north edge of the Middle Yangtze Platform in South China, the well‐exposed Zhangjiawan stratigraphic succession in Yuan'an County represents one of the most productive sections, yielding abundant marine reptiles. Intensive sampling of this section reveals a unique conodont community both before and during the emergence of the Nanzhang‐Yuan'an Fauna (NYF). Occurrences of Neostrachanognathus tahoensis below the NYF and deposition of ʻGreen Bean Rock (GBR)ʼ above the NYF restricted this fauna to the latest Early Triassic. Except for the coniform Neostrachanognathus, this conodont community consists of abundant Ellisoniidae characterized by ramiform P1 elements. Foraminifers and fish found together with the conodont elements form other low‐level parts of the local food web. Other temporally coincident sections nearby, for example, the Yanduhe section of western Hubei Province, yield only rare conodonts. Hence, the unique conodont community from the Zhangjiawan section suggests that the Nanzhang‐Yuan'an area might be a “refuge area” for the Early Triassic marine ecosystem, or at least for the marine reptiles and the conodont communities. Although the direct connection between conodonts and marine reptiles is still uncertain, low‐level consumers—conodont animals‐played important roles in the food webs of NYF. The collision of the South China and North China blocks removed this “refuge area” and witnessed the disappearance of endemic Hupeisuchians.
No abstract
Modern baleen whales are unique as large-sized filter feeders, but their roles were replicated much earlier by diverse marine reptiles of the Mesozoic. Here, we investigate convergence in skull morphology between modern baleen whales and one of the earliest marine reptiles, the basal ichthyosauromorph Hupehsuchus nanchangensis, from the Early Triassic, a time of rapid recovery of life following profound mass extinction. Two new specimens reveal the skull morphology especially in dorsal view. The snout of Hupehsuchus is highly convergent with modern baleen whales, as shown in a morphometric analysis including 130 modern aquatic amniotes. Convergences in the snout include the unfused upper jaw, specialized intermediate space in the divided premaxilla and grooves around the labial margin. Hupehsuchus had enlarged its buccal cavity to enable efficient filter feeding and probably used soft tissues like baleen to expel the water from the oral cavity. Coordinated with the rigid trunk and pachyostotic ribs suggests low speeds of aquatic locomotion, Hupehsuchus probably employed continuous ram filter feeding as in extant bowhead and right whales. The Early Triassic palaeoenvironment of a restrictive lagoon with low productivity drove Hupehsuchus to feed on zooplankton, which facilitated ecosystem recovery in the Nanzhang-Yuan’an Fauna at the beginning of the Mesozoic.
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