Yen-Nien Cheng

An unusual archosaurian from the marine Triassic of China

A new Triassic archosaurian from China shows a number of aquatic specializations, of which the most striking is the extreme lateral compression of the long tail. Others that may also reflect aquatic adaptations include platelike scapula and coracoid, elongate neck with extremely long and slender ribs, and reduction of osteoderms. In contrast, its pelvic girdle and hind limb have no aquatic modifications. Anatomic features, taphonomy, and local geological data suggest that it may have lived in a coastal–island environment. This lifestyle, convergent with some Jurassic marine crocodyliforms that lived at least 40 million years later and the saltwater species of extant Crocodylus, contradicts with the prevailing view that Triassic archosaurians were restricted to nonmarine ecosystems. Its mosaic anatomy represents a previously unknown ecomorph within primitive archosaurians.

FIRST COMPLETE PISTOSAUROID FROM THE TRIASSIC OF CHINA

Triassic pistosauroids (Reptilia: Sauropterygia) are the closest relatives of the Plesiosauria, a group that achieved considerable taxonomic diversity and cosmopolitan distribution during the Mesozoic. Despite their importance for the understanding of the origin of the Plesiosauria, however, our knowledge on the Triassic pistosauroids (Augustasaurus Sander et al, 1997; Chinchenia Young, 1965; Corosaurus Case, 1936; Cymatosaurus Fritsch, 1894; Kwangsisaurus Young, 1959; Pistosaurus Meyer, 1939; Edinger, 1935; Rieppel, 1997, 1998, 1999; Storrs, 1991) has been limited due to the lack of well-preserved specimens. We report a new pistosauroid, Yunguisaurus liae gen. et sp. nov., from the Triassic of southern China. This taxon is represented by a virtually complete and articulated skeleton embedded in a limestone slab from the Falang Formation (upper Middle to lower Upper Triassic). Previously described Triassic pistosauroids are known from the upper Lower to lower Middle Triassic (Rieppel, 1999, 2000; Wang et al., 2001), and Y. liae is the youngest pistosauroid (excluding the Plesiosauria). Because of the rarity of pistosauroids, we are providing this preliminary report while the postcranial skeleton waits for further preparation and subsequent full description. A unique combination of primitive and derived traits is observed in this specimen, and a phylogentic analysis confirms its close relationship with derived pistosauroids.

Osteology of Yunguisaurus Cheng et al., 2006 (Reptilia; Sauropterygia), a Triassic Pistosauroid from China

Abstract. Triassic pistosauroids are closely related to the Plesiosauria which flourished later in the Mesozoic, but their fossil record has been poor due to the fragmentary nature of the known specimens. Yunguisaurus liae Cheng et al. (2006) (Reptilia, Sauropterygia) from China was the first Triassic pistosauroid represented by an almost complete skeleton, and we provide a full description of the holotype specimen based on the result of complete preparation of the skull and postcranium. A revised diagnosis characterizes Y. liae by a mixture of primitive and derived features for sauropterygians, such as the high number of cervical vertebrae (similar to the Plesiosauria) with large zygapophyses (shared with basal sauropterygians). The holotype skeleton likely represents a juvenile individual. In a revised phylogeny, relationships among the Triassic pistosauroids are fully resolved but weakly supported; the revised phylogeny differs from the existing hypothesis on a sauropterygian relationship, likely due to the previous reliance on fragmentary taxa. The long neck and hyperphalangy give an impression that Yunguisaurus is very “plesiosaurian,” but detailed comparison revealed morphological differences in various parts of the postcranial. These differences, in combination with the revised phylogenetic hypothesis, suggest that Yunguisaurus was not necessarily comparable to the Plesiosauria in terms of body plan and mode of swimming.

NEW INFORMATION ON WUMENGOSAURUS DELICATOMANDIBULARIS JIANG ET AL., 2008 (DIAPSIDA: SAUROPTERYGIA), WITH A REVISION OF THE OSTEOLOGY AND PHYLOGENY OF THE TAXON

ABSTRACT Wumengosaurus delicatomandibularis Jiang et al., 2008, is restudied on the basis of three new specimens. Many elements of the skeleton that were either briefly or not described at all in the original study are detailed. With the additional information derived from the new specimens, we have revised the diagnosis of W. delicatomandibularis. A phylogenetic analysis further demonstrates that the Pachypleurosauria is not a monophyletic group and questions that W. delicatomandibularis is closely related to the Pachypleurosauria. W. delicatomandibularis might represent the basal-most member of a monophyletic clade that includes the Nothosauroidea and those taxa assigned to the ‘Pachypleurosauria.’ The five known specimens show morphological variation in W. delicatomandibularis, as in Keichousaurus and in pachypleurosaurs such as Neusticosaurus and Serpianosaurus.

A new eosauropterygian (Diapsida, Sauropterygia) from the Triassic of China

ABSTRACT A new Middle Triassic sauropterygian, Qianxisaurus chajiangensis, gen. et sp. nov., is described on the basis of a skeleton from the Zhuganpo Member (Ladinian) of the Falang Formation, Xingyi, southwestern Guizhou Province, China. It is primarily characterized by a premaxilla with eight teeth, marginal teeth with a slightly constricted peduncle and short conical crown, snout longer than the rest of skull, postorbital with a truncated dorsal process and forked posterior process, a very small supratemporal fenestra, a short retroarticular process posteriorly truncated and lacking a dorsal concavity, an elongate trunk with 28 vertebrae, a stout sacrum with four vertebrae, a longitudinal groove on proximodorsal surface of the dorsal ribs, and a coracoid with a narrow lateral portion and a foot-shaped medial portion. Q. chajiangensis appears similar to the European pachypleurosaurs, but a global phylogenetic analysis failed to support close relationships with these taxa. Instead, Q. chajiangensis is an eosauropterygian and most probably the sister group of a clade consisting of the European pachypleurosaurs and the Nothosauroidea. The discovery of Q. chajiangensis certainly enriches our knowledge of the early history of the Eosauropterygia and leads to a better understanding of the phylogenetic relationships among known eosauropterygians.

A new tomistomine (Crocodylia) from the Miocene of Taiwan

Penghusuchus pani gen. et sp. nov. is described on the basis of a skeleton from the upper Miocene of Penghu Island. It is the most complete vertebrate fossil from Taiwan. Penghusuchus pani is distinguished from other tomistomines mainly in features of the skull and mandible. The most diagnostic characters for the taxon are that the prefrontal and anterior process of the jugal extend as anteriorly as the lacrimal does; the seventh maxillary tooth is the largest; the choana is sharply triangular in outline; and the floor of the nasopharyngeal canal and choanal borders strongly drop downward to form a Y-shaped prominence on the ventral surface of the pterygoids. Our phylogenetic analysis indicates that the new form is closely related to two other Asian fossil tomistomines, Tomistoma petrolica from southeastern China and Toyotamaphimeia machikanensis from Japan. The discovery of P. pani certainly enriches our knowledge of the paleogeography and the phylogenetic relationships amongst tomistomines.

Diandongosaurus acutidentatus Shang, Wu & Li, 2011 (Diapsida: Sauropterygia) and the relationships of Chinese eosauropterygians

Diandongosaurus acutidentatus Shang, Wu & Li, 2011 is restudied on the basis of a new specimen. The new specimen provides further information on the palate of the skull, the shoulder girdle, the gastralia and hind limbs, and permits revision of the diagnosis. Newly added or modified diagnostic characters include the presence of a few small vomerine teeth, the presence of an ectopterygoid, lateral elements of gastralia distally swollen and curving dorsally, boomerang-shaped interclavicle and clavicle with a distinct anterolateral process. Slight variations in the vertebral counts, girdle morphology, and phalangeal formulae are attributed to the intraspecific variations. A revised phylogenetic analysis demonstrates that Diandongosaurus is closely related to the Nothosauroidea and that certain Chinese taxa (e.g. Keichousaurus ) previously affiliated with the Pachypleurosauridae are more closely related to the Nothosauroidea. The effect of inclusion or exclusion of fragmentary taxa in the phylogenetic analysis is observed in the branching pattern of the cladogram, but it has little effect on the morphological characterization of the major clades.