[Paleontology • 2017] Xingxiulong chengi • A New Basal Sauropodiform Dinosaur from the Lower Jurassic of Yunnan Province, China

Xingxiulong chengi 

Wang, You & Wang, 2017 

   DOI: 10.1038/srep41881 

Abstract

The Lufeng Formation in Lufeng Basin of Yunnan Province, southwestern China preserves one of the richest terrestrial Lower Jurassic vertebrate faunas globally, especially for its basal sauropodomorphs, such as Lufengosaurus and Yunnanosaurus. Here we report a new taxon, Xingxiulong chengi gen. et sp. nov. represented by three partial skeletons with overlapping elements. Xingxiulong possesses a number of autapomorphies, such as transversely expanded plate-like summit on top of the neural spine of posterior dorsal vertebrae, four sacral vertebrae, robust scapula, and elongated pubic plate approximately 40% of the total length of the pubis. Phylogenetic analysis resolves Xingxiulong as a basal member of Sauropodiformes, and together with another two Lufeng basal sauropodiforms Jingshanosaurus and Yunnanosaurus, they represent the basalmost lineages of this clade, indicating its Asian origin. Although being relatively primitive, Xingxiulong displays some derived features normally occurred in advanced sauropodiforms including sauropods, such as a four sacral-sacrum, a robust scapula, and a pubis with elongated pubic plate. The discovery of Xingxiulong increases the diversity of basal sauropodomorphs from the Lufeng Formation and indicates a more complicated scenario in the early evolution of sauropodiforms.

Figure 2: Representative elements of Xingxiulong chengi gen. et sp. nov. and reconstruction of the skeleton.
 (a) Cervical vertebrae of LFGT-D0001 (3–10); (b) articulated posterior dorsal vertebrae (10–14) and dorsosacral of LFGT-D0001 in lateral and dorsal views; (c) scapula with articulated dorsal vertebrae of LFGT-D0003 in left lateral view; (d) left humerus of LFGT-D0003 in posterior and anterior views; (e) left forelimb of LFGT-D0003 in medial view; (f) right articulated humerus, ulna and radius in medial view, and detail of the proximal end of ulna and radius; (g) left ilium of LFGT-D0002 (photograph and line drawing) in lateral view; (h) right ilium of LFGT-D0003 in lateral view; (i) right ischium of LFGT-D0002 in lateral view; (j) left femur of LFGT-D0002 in anterior, lateral, posterior and medial views; (k) distal end of left tibia of LFGT-D0003 in anterior and distal views; (l) left astragalus of LFGT-D0002 in posterior view; (m) left pes of LFGT-D0002 in lateral and ventral views; (n) right pes of LFGT-D0002 in dorsal and ventral views, with detailed metatarsal I in dorsal view; (o) reconstruction of the skeleton of Xingxiulong chengi gen. et sp. nov. (scaled to the size of the holotype). Abbreviations: 4t, fourth trochanter; alp, anterolateral process; ds, dorsosacral; epls, expanded plate-like summit; it, internal tuberosity; ls, longitudinal sulcus; lt, lesser trochanter; mt I, metatarsal I; mt V, metatarsal V; plp, posterolateral process; pmb, posterior median bulge; pop, postacetabular process; prp, preacetabular process. Dashed lines represent highlighting (c,b, and f) or reconstruction (g and h). Scale bars equal 10 cm in (a–n) and 1 m in (o). 

SYSTEMATIC PALAEONTOLOGY

Dinosauria Owen, 1842
Saurischia Seeley, 1887

Sauropodomorpha Huene, 1932
Massopoda Yates, 2007

Sauropodiformes Sereno, 2007

Xingxiulong chengi gen. et sp. nov.


Type locality and horizon: The specimens were excavated near Sankeshu (Three Trees) Village, Jinshan Town, Lufeng County, Chuxiong Yi Autonomous Prefecture, Yunnan Province, southwestern China (Fig. 1). The specimens were from the base of the Shawan Member of the Lower Jurassic Lufeng Formation, composed of dark purple silty mudstones.

Etymology: The generic name “Xingxiu”, meaning constellation in Chinese, is derived from the name of the ancient “Xingxiu Bridge” in Lufeng County, which was built during the Ming Dynasty (1368–1644). The specific name is dedicated to Prof. Zheng-Wu Cheng (1931–2015), for his lifetime contribution to Chinese terrestrial biostratigraphy, including the Lufeng Basin.

Diagnosis: A medium-sized basal sauropodiform with the following unique combination of character states (autapomorphies are marked by *): both surangular and angular extended more anteriorly with respect to the external mandibular fenestra; transversely expanded plate-like summit on top of posterior dorsal vertebrae* (convergent in basal saurischians); four sacral vertebrae, with two primordial sacrals bounded by a dorsosacral and a caudosacral* (convergent in derived sauropodiforms); robust scapula with both ends extremely expanded; ilium with ventral margin of postacetabular process strongly concave*; pubis with elongated proximal pubic plate relative to the pubic apron, with pubic plate approximately 40% of the total length of the pubis*(convergent in basal sauropods); posterolateral process of distal tibia much narrower anteroposteriorly and extended more laterally and distally than anterolateral process*; a median bulge present on the dorsoposterior margin of the astragalus; metatarsal V with strongly expanded proximal end with a proportion of proximal width/total length 0.85*.

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Ya-Ming Wang, Hai-Lu You & Tao Wang. 2017. A New Basal Sauropodiform Dinosaur from the Lower Jurassic of Yunnan Province, China. Scientific Reports 7, 41881. DOI: 10.1038/srep41881