Lufengosaurus huenei Young, 1941

Xing, Lida, Rothschild, Bruce M., Ran, Hao, Miyashita, Tetsuto, Iv, W. Scott Persons, Sekiya, Toru, Zhang, Jianping, Wang, Tao & Dong, Zhiming, 2015, Vertebral fusion in two Early Jurassic sauropodomorph dinosaurs from the Lufeng Formation of Yunnan, China, Acta Palaeontologica Polonica 60 (3), pp. 643-649 : 644-645

Lufengosaurus huenei Young, 1941

Fig. 2 .

Type material: IVPP V15 , a complete skeleton with skull .

Type locality: Shawan Member of Lufeng Formation (Hettangian), Shawan village , Lufeng County, Yunnan Province .

Material.—ZLJ T001 an articulated, but incomplete, skeleton from the Dalishu bonebed, Shawan Member of Lufeng Formation, Lufeng County, Yunnan Provence, China. ZLJ T001 and ZLJ 0013 can be referred to Lufengosaurus huenei based on the manus longer than the ulna and the pubis-illium length ratio of 1.1 ( Young 1941, 1951; Galton and Upchurch 2004; Barrett et al. 2005).

Description.—ZLJ T001. The posterior cervical vertebrae (6 th –10 th) of Lufengosaurus ( Young 1941, 1947) are weakly amphicoelous and lack pleurocoels ( Figs. 2–4 ). The parapophysis develops just below the neurocentral suture to the mid-height of the centrum. There is no bony lamina connecting the parapophysis and the neural arch. The centrum is approximately twice longer anteroposteriorly than tall dorsoventrally, but the height/length ratio gets progressively high- er posteriorly within the series. The centrum is constricted ventrally into a gentle hourglass shape in lateral view, and a longitudinal keel develops on the ventral surface between the intervertebral joints. The neural arch is not markedly taller dorsoventrally than the centrum. As a result, the neural spine is a low rectangle in lateral view, anteroposteriorly longer than dorsoventrally tall. The dorsal margin of the neural spine is straight horizontally or slightly posterodorsally inclined. Both pre- and postzygapophysis are robust, round in cross section and projected for less than 20% the length of the centrum beyond the intervertebral joint.The prezygapophysis has a weak ridge along the lateroventral margin in lateral view, whereas the postzygapophysis has a medial wall along all its length below the level of the zygapophyseal articulation.

The pathologic vertebrae of ZLJ T001 are the 7 th and 8 th cervical vertebrae ( Figs. 2 , 3 ), which are fused at the intervertebral joint (contrast with the normal 7 th and 8 th cervical vertebrae of Lufengosaurus huenei ZLJ 0013; Fig. 4). This region is swollen with anomalous ossification. Like normal posterior cervical vertebrae, the anterior surface of the 7 th centrum and the posterior surface of the 8 th centrum are both gently concave. A pleurocoel is absent. The ventral keel is present on both centra but splits into two parallel ridges in the pathological region in ventral view. Unlike normal posterior cervical vertebrae, the neural spines are anteroposteriorly shorter than dorsoventrally tall in lateral view. The posterior surface of the neural spines is rugose, with numerous pits and tubercles developed over the normal, smooth texture, which indicates ossification of the interspinous tendons at the site of attachment ( Fig. 3 ).

The 7 th cervical vertebra (centrum length: 265 mm; centrum width [anterior]: 125 mm; centrum height [anterior]: 130 mm) has an incompletely closed, visible neurocentral suture. The parapophysis is normal on the right side and poorly preserved on the left. The broken right prezygapophysis shows no abnormal internal structure within that part of the neural arch. The 8 th cervical vertebra (centrum length: 190 mm; centrum width [posterior]: 135 mm; centrum height [posterior]: 150 mm) is shorter anteroposteriorly than the 7 th cervical vertebra. The parapophysis is just behind the pathological region on both right and left sides.

The centrum fusion between the 7 th and 8 th cervical vertebrae is due to proliferation and ossification of annulus fibrosus, not by the ossification of the intervertebral ligaments. The surface of the fused region is generally smooth. At the border of the proliferation, some exostoses are visible. No infection holes or bone density changes are apparent, and the surfaces of each vertebra are free of tooth marks. Inconsistent with infection, the pathology is highly localized and appears only at and around the intervertebral zone, with both the posterior end of the 7 th cervical and the posterior end of the 8 th cervical having altogether normal appearances.

Stratigraphic and geographic range.— ZLJ T001 and ZLJ 0013 are from Dalishu bonebed, Shawan Member of Lufeng Formation , Lufeng County, Yunnan Provence, China .

Figures

Fig. 2. The 7th and 8th cervical vertebrae of spondyloarthropathy dinosaur Lufengosaurus huenei Young, 1941 (ZLJ T001) from Dalishu bonebed, Lower Jurassic, in right lateral (A), left lateral (B), posterior (C), dorsal (D), ventral (E), and anterior (F) views.

Fig. 3. Details of the rugose surfaces of the posterior neural-spine faces of the 7th (A) and 8th (B) cervical vertebra of spondyloarthropathy dinosaur Lufengosaurus huenei Young, 1941 (ZLJ T001) from Dalishu bonebed, Lower Jurassic.