Abstract
The Middle Triassic Luoping Biota in south-west China represents the inception of modern marine ecosystems, with abundant and diverse arthropods, fishes and marine reptiles, indicating recovery from the Permian–Triassic mass extinction. Here we report a new specimen of the predatory marine reptile Diandongosaurus, based on a nearly complete skeleton. The specimen is larger than most other known pachypleurosaurs, and the body shape, caniniform teeth, clavicle with anterior process, and flat distal end of the anterior caudal ribs show its affinities with Diandongosaurus acutidentatus, while the new specimen is approximately three times larger than the holotype. The morphological characters indicate that the new specimen is an adult of D. acutidentatus, allowing for ontogenetic variation. The fang-like teeth and large body size confirm it was a predator, but the amputated hind limb on the right side indicate itself had been predated by an unknown hunter. Predation on such a large predator reveals that predation pressure in the early Mesozoic was intensive, a possible early hint of the Mesozoic Marine Revolution.
Highlights
The Triassic marine recovery is well documented in southern China, by a sequence of marine faunas, including the Nanzhang-Yuan’an, Chaohu, Panxian, Luoping, Xingyi and Guanling faunas
The fossil beds occur in Member II of the Guanling Formation which in the Daaozi section comprises approximately 16 m of dark-coloured micritic limestone, thin to moderately thickly bedded, indicating a semi-enclosed intraplatform setting[10,11]
The co-occurring conodont assemblages, primarily consisting of Cratognathodus sp. and Nicoraella kockeli, indicate that the Luoping Biota belongs to the Pelsonian Substage of the middle Anisian, and the U–Pb age, which is 246.6 ± 1.4 Ma, of the volcanic tuff at the bottom of Member I confirms this age[10,14]
Summary
The Triassic marine recovery is well documented in southern China, by a sequence of marine faunas, including the Nanzhang-Yuan’an, Chaohu, Panxian, Luoping, Xingyi and Guanling faunas. The Luoping Biota of the Middle Triassic, yielding nearly 20,000 macrofossils, provides extraordinary records of very early marine reptiles[8,9]. In contrast to modern marine ecosystems, hypercarnivores that fed on other tetrapods were common in Mesozoic oceans, confirming a different trophic structure at that time[1]. We report and describe a new large marine pachypleurosaur species from the Luoping Biota, decipher its role in eosauropterygian evolution, and its ecological implications in the recovery of ecosystems and megafaunal predation in the early Mesozoic oceans.
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