Friday, September 14, 2018

[Paleontology • 2018] Yizhousaurus sunae • A New Sauropodiform Dinosaur with A ‘Sauropodan’ Skull from the Lower Jurassic Lufeng Formation of Yunnan Province, China

Yizhousaurus sunae 
Zhang, You, Wang & Chatterjee, 2018

The Early Jurassic Lufeng Formation of Yunnan Province in southwestern China is one of the best fossil localities in the world for understanding the early radiation of sauropodomorph dinosaurs. It has yielded a rich assemblage of complete and three-dimensionally preserved skeletons of herbivorous dinosaurs that provide crucial morphological information for systematic and evolutionary studies. Here we describe a new taxonYizhousaurus sunae gen. et sp. nov., represented by a nearly complete skeleton with an exquisitely preserved skull and mandible. Yizhousaurus is distinguished from other non-sauropodan sauropodomorphs by a unique combination of plesiomorphic and apomorphic features, which increases our understanding of the anatomical variation on the relatively conservative ‘prosauropod’ cranial plan. Phylogenetic analysis resolves Yizhousaurus as a sauropodiform, showcasing a mosaic character suite combining plesiomorphic states in the postcranial skeleton with some more ‘sauropodan’-like features in the skull. Furthermore, Yizhousaurus is placed closer to the base of Sauropoda than other non-sauropodan sauropodomorphs currently known from the Lufeng Formation, adding another taxon to enrich the Lower Jurassic Lufeng dinosaur fauna.

Figure 2 Status of preservation of Yizhousaurus sunae gen. et sp. nov.
 (A) The reconstruction in sketch of Yizhousaurus in left lateral view (drawn by Xiao-Cong Guo), regions in red rim represent absent elements; (B), the original burial map of Yizhousaurus 
(drawn by Qian-Nan Zhang).

Systematic Paleontology

Dinosauria Owen, 1842
Saurischia Seeley, 1887
Sauropodomorpha von Huene, 1932
Massopoda Yates, 2007

Sauropodiformes Sereno, 2007 

Yizhousaurus sunae gen. et sp. nov.

Holotype: LFGT (Bureau of Land and Resources of Lufeng County, Yunnan, China) -ZLJ0033. An undistorted skeleton about 7 meters long, including a well-preserved skull and mandible, a mostly complete vertebral series (9 cervicals, 14 dorsals, 3 sacrals and 5 anterior caudals), pectoral and pelvic girdles, forelimbs (lacking both carpi) and both femora (Fig. 2A).

Type locality and horizon: The specimen was collected near Duwafang Village, Chuanjie Town, Lufeng County, Chuxiong Yi Autonomous Prefecture, Yunnan Province, China (Fig. 1); the skeleton was excavated in the uppermost layer of the Zhangjiaao Member of the Lower Jurassic Lufeng Formation.

Etymology: The generic name Yizhou refers to the Chuxiong Yi Autonomous Prefecture of Yunnan Province. The specific name is in honor of Professor Ai-Ling Sun, for her great contribution to Chinese vertebrate fossils, including those from Lufeng.

Differential Diagnosis: A medium-sized sauropodiform distinguished from other non-sauropodan sauropodomorphs with respect to the following unique combination of character states (autapomorphies marked with *): lateral plates appressed to the labial sides of the premaxillary and maxillary teeth but not the dentary teeth*; anteroposterior expansion at the dorsal end of the maxillary ascending ramus; antorbital fenestra anteroposteriorly narrow and pipe-shaped in outline*; lacrimal shaft vertical with respect to the maxillary ramus*; transverse width of the ventral process of the postorbital greater than its anteroposterior width at midshaft; anterior tip of the dentary anterodosally curved over the alveolar margin*; tiny external mandibular fenestra (about 5% of the mandibular length)*; broad axial intercentrum wider than its centrum; deep depressions on the lateral surfaces of centra of dorsal vertebrae 3–6; hyposphenes of the anterior dorsals equal to their neural canals in height; and subelliptical cross-section of the midshaft of the femur.

Comment: Yizhousaurus sunae was briefly reported as a basal sauropod at the Geological Society of America Conference in 2010, but has never received formal study. In addition, its fourth and fifth caudal vertebrae are fused together, which is considered pathological in nature.

Qian-Nan Zhang, Hai-Lu You, Tao Wang and Sankar Chatterjee. 2018. A New Sauropodiform Dinosaur with A ‘Sauropodan’ Skull from the Lower Jurassic Lufeng Formation of Yunnan Province, China. Scientific Reports.  8,  13464.  DOI:  10.1038/s41598-018-31874-9

 Chatterjee, Sankar; Wang, T.; Pan, S.G.; Dong, Z.; Wu, X.C.; Upchurch, P. 2010. A Complete Skeleton of A Basal Sauropod Dinosaur from the early Jurassic of China and the Origin of Sauropoda. Geological Society of America Abstracts with Programs. 42 (5): 26.

Found: First complete remains of early sauropod dinosaur via @physorg_com

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