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Home , Dong Zhiming, Omeisaurus, Shunosaurus, Zigong Dinosaur Museum

THE DISCOVERY OF THE BONY TAIL CLUB OF SAUROPODS*

Dong Zhiming Peng Guangzhao Huang Daxi ( Museum) Key words Zigong Province; ; Bony tail club

Original English Abstract There have been 15 pieces of the bony tail club of sauropods found in the Lower Shaximiao Formation of Middle in the Dinosaurian Quarry of Dashanpu, Zigong, Sichuan Province, . Both of the two groups of sauropods in the fauna of Dashanpu—Shunosaurus Iii and tianfuensis have a bony club at the end of the tail. It has never been reported that sauropods have a bony tail club. This discovery shows that sauropods are a group of terrestrial , and it proves that R. T. Bakker's theory is probably correct. The characteristics of the morphology and structure of these bony tail clubs are described in this paper. The main features of the bony clubs are as follows: The shape of the bony clubs is ellipspheroidal or spindle-shaped. The anterior and posterior parts are narrow and middle part is inflated. These clubs are fused with 3–5 distal caudal vertebrae. The fused lines between the vertebrae can be seen· on the ventral part. The neural spines of the anterior vertebrae of the bony clubs are present and low, and that of the posterior vertebrae have disappeared. The neural foramen is small, runs through the whole bony club, and forms a U-shaped trough at the end. The haemal arches and diapophysis have disappeared. The main function of the bony tail clubs of sauropods, like that of ankylosaurs, is for defense. However, the tail clubs of sauropods and ankylosaurs are analogous organs. Their origin and structure are different.

*Original reference: , Peng Guangzhao, and Huang Daxi. 1989. The discovery of the bony tail club of sauropods. Vertebrata PalAsiatica 27(3):219–224. Translated by Bian Wang. Edited by Tariq A. Kareem and Jeffrey A. Wilson University of Michigan, November 2018

Vol. 27 No. 3 VERTEBRATA PALASIATICA pp. 219–224 July 1989 figs. 1–3, Pl. I

THE DISCOVERY OF THE BONY TAIL CLUB OF SAUROPODS

Dong Zhiming Peng Guangzhao Huang Daxi () Key words Zigong Sichuan Province; Sauropoda; Bony tail club

Abstract

Spindle-shaped bony tail clubs formed by fusion and inflation of caudal vertebrae were found in Shunosaurus lii and Omeisaurus tianfuensis from the Dashanpu dinosaur site in Zigong. This is the first report of such features in sauropods. Bony tail clubs are a special structural adaptation for terrestrial lifestyle. It is primarily used as a weapon in self-defense. Its existence supports R. T. Bakker’s idea that sauropods were terrestrial dinosaurs.

In 1981, when organizing stegosaur fossils from Dashanpu, Zigong, we found two elongated, irregular ball-shaped bones, which we thought were “wrist bones” of stegosaurs. Zhou Shiwu (1984), when describing taibaii, also described CV 00720 (Chongqing Museum of Nature catalog number), an elliptical bone, as a “wrist bone.” In 1984, when organizing dinosaur fossils from Dashanpu, Zigong, we examined a few relatively large elliptical bones collected by Pi Xiaozhong. Bones this large could not have been “wrist bones,” but no other evidence was available back then to explain what taxa and what skeletal position the bones belonged to. In the same year, when describing a complete skeleton of a juvenile Shunosaurus lii T 5401 (number initially given by the Sichuan Zigong Dashanpu dinosaur fossil collecting team; the specimen has been returned to Zigong Dinosaur Museum and re-catalogued as ZDM5006), Zhang Yihong et al. reported that the tail of Shunosaurus lii consisted of club-shaped fused vertebrae. They thought it resulted from injury. In 1987, we compared the tail clubs of Shunosaurus lii, the so-called “wrist-bones” of stegosaurs, and large elliptical bones collected by Pi Xiaozhong, and we confirmed that these elliptical bones were tail clubs of sauropods.

Sauropods are a group of large herbivorous dinosaurs. Despite the diversity in their morphology and structures, such as with whip-shaped tails and with dermal plates (Powell, 1980), there has been no reports of their bony tail clubs. Discovery of the tail clubs of Dashanpu sauropods has important implications for sauropod morphology and paleoecology.

Section 1. Description Specimens: 15 pieces of complete bony tail club. Specimen number: V7661 (Institute of Vertebrate Paleontology and Paleoanthropology catalog number), V7662, ZDM5006 (Zigong Dinosaur Museum catalog number), ZDM5007, ZDM5013-a, ZDM5035, ZDM5045, ZDM5046, ZDM5047, ZDM5048, ZDM5049, ZDM5050, ZDM5051, ZDM5052, ZDM5053, ZDM5006 and ZDM5045 are the best preserved. Locality and stratigraphy: Dashanpu, Zigong, Sichuan Province; Lower Shaximiao Formation, . Description: ZDM5006 (T5401, Zhang et al., 1984) is a complete juvenile individual of Shunosaurus lii. The is preserved in articulation. The bone anterior to the bony tail club is enlarged compared to regular caudal vertebrae, showing apparent transition into the tail club. The tail club of ZDM 5006 (Fig. 1; Plate I, 4) is composed of three fused caudal vertebrae. The suture lines between vertebrae are not distinct/clear. The proximal end is thicker and bigger, the end surface is nearly circular and slightly concave, the middle is enlarged, the distal end is pointed; it is overall half- ellipsoid in shape. The surface is smooth, with no obvious pits or protrusions. The maximum length is 78 mm, and the maximum width is 54 mm, with a ratio of approximately 1.4 : 1. The neural arch is developed, wide and thick in shape. The neural spines of the first two vertebrae are low and connected into a low ridge. The neural spine of the last vertebra is absent. The neural canal is small; a tiny arc-shaped notch is visible above the anterior neural canal and between the anterior articular process. Neural arch is partially missing where the neural canal becomes larger and eventually turns into a U-shaped groove that extends to the end.

Fig. 1. Tail club of Shunosaurus lii (ZDM5006). Above, left lateral view; below, dorsal view. The bony element anterior to the tail club of ZDM5006 (Fig. 1) is composed of two fused vertebra, which are irregular and club-shaped. The healing line/suture between these two vertebrae is clearly visible from the ventral and lateral sides. Maximum length and width are 60 mm and 44 mm, respectively. The anterior vertebra is longer than the posterior one, and both have a relatively well developed, wide, thick neural arch. The neural spine of the anterior vertebra is low, whereas that of the posterior is absent. The neural canal is small and connected all the way through, eventually turning into a U-shaped groove at the end where the neural arch is partially missing. The postzygapophysis of the posterior vertebra is highly developed and nodular in shape. On the right side of this joint, the postzygapophysis of the first vertebra and the prezygapophysis of the latter vertebra are fused into an articular arch. A small circular hole is present on the articular arch, beneath the circular hole is a rectangular hole. Both holes connect to the neural canal. On the left side, the suture/healing line is comparatively intense/strong, the articular arch is enlarged and also fused with the centrum and neural arch. The two upper and lower holes are absent. The tail club of ZDM5045 (Fig. 2; plate 5–6) is composed of five fused vertebrae. Four sutures/healing lines are visible on the ventral and lateral sides. The suture zones slightly bulge into low ridges. The first vertebra of the fused tail club is similar in morphology to the free caudal vertebra, but it gradually expands from the anterior to the posterior, and the deformation becomes greater as well. The expansion continues on the second vertebra and reaches its maximum on the third. Reduction occurs on the fourth vertebra and continues on the fifth, finally tapering at the end and giving the tail club an elongated spindle shape. The surface is rugged and filled with small wrinkles, pits, and tuberculiform bumps. Maximum length and widths are 212 mm and 104 mm, respectively, with a ratio of ~2 : 1. The ventral side of the centrum is wide and flat, with relatively obvious depression on the lateral sides. The neural arch is developed, wide and thick in shape. The neural spines on the first three vertebrae are low and appear in isolated cones. The neural spine of the first vertebra has a three-sided cone shape, extending to the back, whereas those on the second and third vertebrae are conical and point forward. The neural spines on the fourth and fifth vertebrae are absent. The neural canal is small and has a posterior opening on the right posterior side of the fifth vertebra. The U-shaped groove is not obvious. The nutrient foramina are highly developed and circular; they are located on the ventral and right lateral sides of the third vertebra, both anterior sides and left rear side of the neural spine, and the left lateral side of the fourth vertebra. Both the transverse processes and the haemal arches are absent. Besides minor variations in morphology, other specimens are fundamentally similar to the two described above. In sum the tail club of Dashanpu sauropods are fusiform or ellipsoidal in shape with tapered ends and an expansion in the middle; composed of 3–5 fused and inflated vertebrae; anterior neural spines are low, posterior neural spines are absent; neural canal is small and turns into a U-shaped groove on the end part due to partial absence of neural arch on the last vertebra; transverse processes and haemal arches are absent.

Fig. 2. Tail club of Omeisaurus tianfuensis (ZDM5045) A. left lateral view; B. dorsal view; C. ventral view.

Section 2. Discussion Of the 15 bony tail club specimens reported in the study, nine are assigned to Shunosaurus lii (with ZDM 5006 being the most representative) and six are assigned to Omeisaurus tianfuensis (with ZDM 5045 being the most representative). They are distinguished in morphological features, size measurements, and speculated burial conditions. The tail clubs of Shunosaurus are relatively short and wide, spindle-shaped or elliptical, and have relatively small length-to-width ratios (Table 1). The tail clubs of Omeisaurus are more elongated. Except for one specimen (ZDM 5048), length-to-width ratios are around 1.7–2, with the maximum being 2.04. In addition, the tail clubs of Shunosaurus are composed of 3–4 fused vertebra and have a relatively smooth surface. The neural spines of the first two vertebra are fused into a short ridge. The neural spines of the last 1–2 spines are absent. Omeisaurus tail clubs are composed of 4–5 fused vertebra; the surface is rougher, with apparent depressions and protrusions. The nutrient foramen is relatively well developed. The neural spines of the first three vertebra are all present, isolated, and cone-shaped; neural spines on other (posterior) vertebra are absent. Tails clubs used to be found commonly among ankylosaurs but rarely in other dinosaurs. However, fundamental differences exist between ankylosaur tail clubs and those described in this paper. The tail club of ankylosaurs is formed by the lowering of several dermal plates on the tail, turning into a knob and attached to fused vertebrae; it contains dermal bone material and is not enlarged at the end. The tail club of sauropods is formed by the fusion and expansion of caudal vertebrae and contains no dermal bone material. The tail club has the same function in ankylosaurs and sauropods, serving as a defense weapon in both lifestyles. Some non-dinosaurian organisms have also successfully evolved similar structures, such as glyptodons. Concluding from currently available materials, there are two tail form changes in sauropods: a) elongation of caudal vertebrae into whip-shaped tails, such as the Diplodocus from North America; b) fusion and expansion of caudal vertebrae into club shapes. These changes represent adaptations to a terrestrial lifestyle. In the past, most researchers have considered sauropods aquatic reptiles. Based on his studies of , R. T. Bakker (1971) speculated that sauropods were terrestrial. Findings from the tail club of Dashanpu sauropods support this speculation. (Received on December 18, 1987)

Table 1. Measurements of tail club of Shunosaurus (in mm).

Specimen Length Width Height Length to width ratio V7661 90 72 60 1.25 V7662 86 58 50 1.48 ZDM5006 78 54 52 1.44 ZDM5007 180 112 101 1.61 ZDM5013-a 155 109 101 1.42 ZDM5035 163 120 110 1.36 ZDM5047 160 112 90 1.43 ZDM5051 144 110 90 1.31 ZDM5053 93 60 51 1.55

Table 2. Measurements of tail club of Omeisaurus (in mm).

Specimen Length Width Height Length to width ratio ZDM5045 212 104 94 2.04 ZDM5046 205 105 119 1.95 ZDM5048 173 140 121 1.24 ZDM5049 190 109 107 1.74 ZDM5050 195 125 108 1.56 ZDM5052 200 114 123 1.75

Fig. 3. The skeleton of Omeisaurus tianfuensis.

References

Zhang Yihong, Yang Daihuan, Peng Guangzhao, 1984: New Shunosaurus material from Dashanpu, Zigong, Sichuan. Papers from the Chengdu Academy of Geology, Supplement 2, 1–12.

Zhou Shiwu, 1984: Dinosaur fauna from the Middle Jurassic of Dasahnpu, Zigong, Sichuan. Chapter 2 Stegosaurus. Sichuan Science and Technology Press, 1–52.

Dong Shiming, Tang Zhilu, Zhou Shiwu, 1982: Shunosaurus fauna from Dashanpu, Zigong, Sichuan. Bulletin 1. Stegosaurus. Vertebrate Paleontology and Paleoanthropology, 20(1), 83–86.

Bakker, R. T., 1971: Ecology of the brontosaurs. Nature, 229(5281), 172–174.

_____, 1972: Anatomical and ecological evidence of endothermy in dinosaurs. Nature, 238(5359), 81–85.

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Powell, J. E., 1980: Sobre la presencia de una armadura dermica en algunos dinosaurios titanosauridos. Acta Geologica Lilloana, 15(2), 41–47.

Plate I. Bony tail clubs of: (1–3) Shunosaurus sp., 4X magnification; (4) Shunosaurus lii, 2X magnification; (5) Omeisaurus tianfuensis, dorsal view in 2.5X magnification; (6) Omeisaurus tianfuensis, ventral view in 2.5X magnification.