Yuanlin Sun

First record of Placodontoidea (Reptilia, Sauropterygia, Placodontia) from the Eastern Tethys

DA-YONG JIANG, RYOSUKE MOTANI, WEI-CHENG HAO, OLIVIER RIEPPEL, YUAN-LIN SUN, LARS SCHMITZ, and ZUO-YU SUN Department of Geology and Geological Museum, Peking University, Beijing 100871, P. R. China, djiang@pku.edu.cn; Department of Geology, University of California, Davis, California 95616-8605, U.S.A; Department of Geology, The Field Museum, Chicago, Illinois 60605-2496, U.S.A., rieppel@fieldmuseum.org.

A NEW MIXOSAURID ICHTHYOSAUR FROM THE MIDDLE TRIASSIC OF CHINA

Abstract We describe the new ichthyosaur taxon Mixosaurus panxianensis, sp. nov., from the Middle Triassic of Guizhou Province, China. Diagnostic characters of the new species include a short posteroventral jugal process and the absence of external contact between jugal and quadratojugal. The morphologic description of the type specimens amends the knowledge of the postorbital region and the postcranium of the Mixosauridae. The holotype of Mixosaurus maotaiensis, which is very fragmentary and has no taxonomic value at the species level, is found to be undiagnostic, and hence the lately introduced, monospecific genus name for this species needs to be abandoned. Phylogenetic analysis strongly supports the monophyly of the family Mixosauridae. Furthermore, the analysis shows a bifurcation of the family into two sister groups, suggesting the presence of two genera, Mixosaurus and Phalarodon. Mixosaurus, characterized by a relatively short and wide humerus, includes M. panxianensis sp. nov., M. cornalianus, and M. kuhnschnyderi. Synapomorphies of Phalarodon, which contains P. fraasi, P. callawayi, and P. atavus, are a narial shelf and the absence of a maxillary dental groove.

A new species of Xinpusaurus (Thalattosauria) from the Upper Triassic of China

Abstract A new species of Xinpusaurus Yin in Yin et al., 2000 (Thalattosauria, Thalattosauridae), is described from the Wayao Member of the Falang Formation (Tuvalian, Carnian, Upper Triassic) of Guanling County in Guizhou, southwestern China. It is the third thalattosaur species known from the Guanling faunal assemblage of marine reptiles. The type and only specimen consists of an entire skeleton, including a complete skull. It differs from the type species, X. suni, by its smaller adult size, the larger nasal, the more slender angular and low retroarticular process, the shape of the cervical neural spines, the number of presacral vertebrae, the large size of the scapula, the shape of the radius, the presence of a well ossified carpus, the more slender femur, the smaller hindfin, the presence of a complete row of distal tarsal ossifications, and the proportions of the metatarsals. It is consequently referred to a new species, Xinpusaurus kohi. A new analysis of thalattosaur interrelationships based on 30 cranial and postcranial characters corroborates a sister-group relationship between Xinpusaurus and Nectosaurus from the Carnian of California.

A New Middle Triassic Eosauropterygian (Reptilia, Sauropterygia) from Southwestern China

Abstract A new eosauropterygian genus and species is described from the middle Anisian (Middle Triassic) of Panxian (Guizhou Province, southwestern China). The new taxon is characterized by an unique specialization of the jaws that form an elongate pointed rostrum furnished with numerous small, monocuspid and vertically oriented teeth with a basally expanded crown and pointed tip, which is quite unlike any other sauropterygian known. Other diagnostic characters include: frontals paired; parietal unpaired; pineal foramen located centrally in broad parietal skull table; two carpal ossification; ilium with distinct preacetabular process at the base of the dorsally extending iliac blade; pubis plate-like and of rounded contours; two tarsal ossifications. The curved and distally expanded humerus, the reversed topological relationship of the clavicle and scapula, and the presence of three sacral ribs indicate sauropterygian affinities of the new taxon, whereas the ‘butterfly-shaped’ or ‘cruciform’ facet for the neural arch on the dorsal centrum surface indicate its eosauropterygian status.

Tanystropheus cf. T. longobardicus from the Early Late Triassic of Guizhou Province, Southwestern China

ABSTRACT The protorosaur Tanystropheus longobardicus is well known from the Middle Triassic of alpine Europe. It has been described on the basis of a number of specimens that apparently range from juvenile to adult. The largest specimens have a total body length of approximately 3 m. Here we report on the first occurrence of a large tanystropheid from the Middle or early Late Triassic of southwestern China. The new specimen is indistinguishable from the largest specimens of T. longobardicus from Europe, although it lacks a skull. Both the Chinese specimen here described and the European specimens of T. longobardicus are characterized by 13 cervical vertebrae (not 12 as had previously been assumed). The new find, together with a recent specimen of Macrocnemus from Yunnan Province, highlight shared elements of the vertebrate fauna around the coastline of western and eastern Tethys during Middle to Late Triassic times.

Horizons and Assemblages of Middle Triassic Marine Reptiles from Panxian, Guizhou, China

RYOSUKE MOTANI, DA-YONG JIANG, ANDREA TINTORI, YUAN-LIN SUN, WEI-CHENG HAO, ALEC BOYD, SANJA HINIC-FRLOG, LARS SCHMITZ, JI-YEON SHIN, and ZUO-YU SUN; Department of Geology, University of California, Davis, California 95616, U.S.A., montani@geology.ucdavis.edu; Department of Geology and Geological Museum, Peking University, Beijing 100871, China; Dipartimento di Scienze della Terra, Università degli Studi di Milano, Via Mangiagalli 34 I-20133 Milano, Italy

THE MIXOSAURID ICHTHYOSAUR PHALARODON CF. P. FRAASI FROM THE MIDDLE TRIASSIC OF GUIZHOU PROVINCE, CHINA

The family Mixosauridae Baur, 1887 is a dominant group of Middle Triassic ichthyosaurs. Its generic composition has been controversial, but recent findings from southern China enabled Jiang et al. (2006) to recognize two monophyletic taxa within the clade, suggesting the presence of two genera within the family, namely Mixosaurus Baur, 1887 and Phalarodon Merriam, 1910. The latter genus, which was invalidated at one point (Nicholls et al., 1999; McGowan and Motani, 2003), was recently resurrected by Schmitz (2005) by validating its type species. Mixosaurus is Tethyan in distribution, whereas Phalarodon had been known mostly from North America and Spitsbergen, apart from a possible juvenile from Switzerland (Brinkmann, 1997, 1998). More recently, Jiang et al. (2003) reported a largely complete, yet poorly preserved skeleton as the first record of the genus Phalarodon from Asia and referred it to Phalarodon sp. However, important synapomorphies were not clearly identified, and evidence has since emerged that the specimen had been tampered with by farmers after it was collected. In the light of the cladistic analysis by Jiang et al. (2006), the referral of the specimen to the genus Phalarodon is questionable. A new specimen was excavated in Panxian County, near the western border of Guizhou Province, by the Geological Museum and Department of Geology of Peking University. The new material, the authenticity of which is unquestionable, is from the same stratigraphic horizon as the specimen of Jiang et al. (2003). It contains a well-preserved skull and some postcranial bones, and for the first time firmly establishes the presence of the genus Phalarodon in the western Pacific. Also, the skull is preserved in a very unusual condition: it had been split near the sagittal plane, enabling examination of the poorly known interior suture pattern. This illustrates that mixosaurids had extensive …

A NEW BASAL NEOPTERYGIAN FROM THE MIDDLE TRIASSIC OF LUOPING COUNTY (SOUTH CHINA)

A new taxon belonging to Neopterygians is described, based on very nicely preserved specimens from the rich vertebrate levels recently discovered in Luoping County, Yunnan Province, South China. This new assemblage dates to Pelsonian (Anisian, Middle Triassic), about the same age of the Panxian Fauna from the nearby Guizhou Province. The Luoping Fauna, yielding this new taxon, is turning out to be one of the most important fish faunas of the whole Middle Triassic and the oldest evidence of the fish radiation of this time span. This new genus of basal neopterygian shows unique derived characters, especially for the almost naked body, with a single row of urodermals covering the body lobe in the tail and a row of very small and thin scales bearing the lateral line canal along the flank. Also in the axial skeleton the new taxon shows peculiar characters such as the neural spines perfectly aligned to each paired neural arches and abdominal ribs well developed. Concerning skull bones, no suborbitals have been detected.

Traces of marine nematodes from 470 million years old Early Ordovician rocks in China

Summary – Cylindrical, mostly horizontal, burrows of 20-60 μm diam. and sinusoidal course, found in the middle part of the Early Ordovician (early Floian) Fenxiang Formation in the Hubei Province of China, represent the oldest record of activity by marine nematodes, preceding known nematode body fossils by 70 million years. The burrows are filled with secondarily oxidised pyrite framboids and clay mineral flakes, indicating low oxygen content in the mud and proving that the animals lined their burrows with organic matter, being bacteriovores and mud-eaters. The marine bottom environment enabling such a mode of life originated no earlier than the mid Early Cambrian (approximately 535 million years ago) owing to peristaltic bioturbation, mostly by nemathelminthans of priapulid affinities. Before the so-called ‘Agricultural Revolution’, the bottoms of shallow seas were covered with microbial mats preventing within-sediment animal life. This event imposes the lower time limit on the possible date of origin of nematodes.

Germanium/silicon of the Ediacaran‐Cambrian Laobao cherts: Implications for the bedded chert formation and paleoenvironment interpretations

Sedimentary strata of the terminal Ediacaran (635–542 Ma) to early Cambrian (542–488 Ma) Laobao-Liuchapo bedded cherts in the South China Block include the Ediacaran Oxidation Event and the Cambrian explosion. Understanding the origin and depositional environment of the bedded cherts may provide insight into how the Earths surface environment changed between the Proterozoic and Phanerozoic. We measured major and trace element compositions and Ge/Si ratios of the Laobao cherts from northern Guangxi province. The Laobao cherts were deposited in the deep basinal environment of the South China Block. We show that the composition of the Laobao cherts is determined by a mixture of four components: quartz, clay, carbonate, and pyrite/iron-oxide. The quartz component is the dominant component of the Laobao cherts. The maximum estimated Ge/Si of the quartz component is between 0.4 and 0.5 μmol/mol, which is close to the Ge/Si of modern seawater and biogenic silica but 1 order of magnitude lower than that of hydrothermal fluids. These Ge/Si systematics suggest that normal seawater rather than mid-ocean ridge hydrothermal fluids is the primary Si source for the Laobao cherts. The Ge/Si of the clay component varies between 1 and 10 μmol/mol, which is comparable to the Ge/Si of typical marine clays, but 10–100 times lower than that of chert nodules from early Ediacaran beds (the Doushantuo Formation) predating the terminal Ediacaran Laobao cherts studied here. Our observations indicate that the clay component Ge/Si ratio decreased from the early Ediacaran to the late Ediacaran. We speculate that high Ge/Si ratios in clays reflect the preferential chelation of Ge by dissolved organic compounds adsorbed onto clays. If so, this suggests that the decrease in Ge/Si ratio of the clay component in the Ediacaran signifies a decrease in the total dissolved organic carbon content of seawater toward the Ediacaran-Cambrian transition, consistent with oxidation of the oceans during the late Ediacaran. Finally, the seawater origin of the Laobao cherts also suggests that replacement of carbonate may not be the primary cause for bedded chert formation. Instead, direct precipitation from seawater or early diagenetic silicification of calcareous sediments, perhaps due to the emergence of Si-accumulation bacteria, may have been responsible for the bedded Laobao-Liuchapo chert formation in South China Block.