A gigantic nothosaur (Reptilia: Sauropterygia) from the Middle Triassic of SW China and its implication for the Triassic biotic recovery
Authors:
Liu et al
Abstract:
The presence of gigantic apex predators in the eastern Panthalassic and western Tethyan oceans suggests that complex ecosystems in the sea had become re-established in these regions at least by the early Middle Triassic, after the Permian-Triassic mass extinction (PTME). However, it is not clear whether oceanic ecosystem recovery from the PTME was globally synchronous because of the apparent lack of such predators in the eastern Tethyan/western Panthalassic region prior to the Late Triassic. Here we report a gigantic nothosaur from the lower Middle Triassic of Luoping in southwest China (eastern Tethyan ocean), which possesses the largest known lower jaw among Triassic sauropterygians. Phylogenetic analysis suggests parallel evolution of gigantism in Triassic sauropterygians. Discovery of this gigantic apex predator, together with associated diverse marine reptiles and the complex food web, indicates global recovery of shallow marine ecosystems from PTME by the early Middle Triassic.
Trackways formed on an ancient seabed have shed new light on how nothosaurs, ancient marine reptiles that lived during the age of the dinosaurs, propelled themselves through water. The evidence is described by a team from Bristol and China in Nature Communications today.
During the Mesozoic, 252-66 million years ago, the seas were ruled by a variety of marine reptiles. One of the earliest groups were the nothosaurs, voracious semi-aquatic hunters with elongate bodies and paddle-like limbs. They were the top predators of the Triassic coasts, some 245 million years ago.
Their mode of swimming has long been debated: did they row themselves along with a back-and-forth motion of their limbs, or did they 'fly' underwater, sweeping their forepaddles in a figure-eight motion like a modern penguin?
Scientists from the University of Bristol and colleagues in China studied trackways formed on an ancient seabed which were recently discovered in Yunnan, southwest China. The tracks consist of slots in the mud arranged in pairs, and in long series of ten to fifty that follow straight lines and sweeping curves.
The size and spacing of the paired markings indicate that they were created by the forelimbs of nothosaurs, representing animals ranging in size from over 3 metres to less than a metre in length.
They demonstrate that that these reptiles moved over the seafloor by rowing their forelimbs in unison, the first direct evidence of how these creatures propelled themselves in the water.
Two types of nothosaurs, the large Nothosaurus and the diminutive Lariosaurus, known from complete fossil skeletons from the Triassic of southern China, are the likely trackmakers.
Professor Qiyue Zhang from Chengdu Center of China Geological Survey, leader of the research, said: "We interpret the tracks as foraging trails. The nothosaur was a predator, and this was a smart way to feed. As its paddles scooped out the soft mud, they probably disturbed fishes and shrimps, which it snapped up with needle-sharp teeth."
The tracks come from localities around Luoping in Yunnan, a well known site of exceptional fossil preservation that has yielded thousands of exquisite fossils of sea creatures, and occasional plants and small terrestrial animals blown in from the nearby islands.
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A new specimen of Nothosaurus youngi from the Middle Triassic of Guizhou, China
Authors:
Ji et al
Abstract:
The Xingyi Fauna has been known widely for yielding abundant specimens of the pachypleurosaur sauropterygian Keichousaurus hui, the first Triassic marine reptile described from China (Young, 1958). Later stratigraphic studies placed it within the Zhuganpo Member of the Falang Formation (latest Ladinian, Middle Triassic) that is exposed across a wide area ranging from Dingxiao and Wusha (Xingyi, Guizhou Province) to Luoping and Fuyuan (Yunnan Province) (Li and Jin, 2003). Despite the extensive exposure of this unit, K. hui remained the only tetrapod from this fauna until the end of the last century, when limited progress was made in both taxonomic and stratigraphic studies. The situation changed during the last decade when a significant quantity of K. hui material was described in detail, in addition to eight new taxa of Triassic marine reptiles, i.e., Lariosaurus xingyiensis, Nothosaurus youngi, Tanystropheus sp., Yunguisaurus liae, Anshunsaurus wushaensis, Macrocnemus fuyuanensis, Glyphoderma kangi, and Qianxisaurus chajiangensis (Li et al., 2002, 2007; Li and Rieppel, 2004; Cheng et al., 2006, 2012; Rieppel et al., 2006, 2008; Zhao et al., 2008a, 2008b). However, precise stratigraphic and locality information still remained unknown for these new taxa, as well as the Xingyi Fauna at large.
Nothosaurus youngi was named by Li and Rieppel (2004) based on an incomplete skeleton from the Xingyi Fauna. It was characterized by the combination of the following features: pineal foramen located in a trough near the posterior end of the parietal, and the longitudinal diameter of the upper temporal fenestra nearly twice of that of the orbit. The postcranial osteology was only briefly described from the incompletely preserved skeleton, including the vertebrae and ribs, parts of the pelvic girdle, and a forelimb. Most of the pectoral girdle was overlapped by the gastralia, and no information was available for the hind limb.
Here, we describe a new specimen of Nothosaurus youngi that we recovered during an excavation of the fossiliferous levels of the Zhuganpo Member at Nimaigu village in the Wusha Town, Xingyi, Guizhou Province, South China, in 2011. The excavation provided us with precise knowledge of the locality and stratigraphic level of Xingyi Fauna for the first time (see below). The specimen is more complete than the holotype and provides new information on the postcranial osteology of N. youngi, which was not known when the species was erected.
