Sinankylosaurus zhuchengensis, the newest addition to the armored dinosaur family!
"Zhucheng's Chinese Fused Lizard"
A new member of the Ankylosauria from China, Sinankylosaurus zhuchengensis, was named in July 2020. It means "Zhucheng's Chinese Fused Lizard" and was excavated in the Zhucheng area, northeast China, in rocks approximately 75 million years old. It was named by Wang et al. 2020 based off of a single hip bone, the right ilium. Ankylosaurids are walking tanks: heavily armored, low to the ground, and adorned with spikes, scutes, and tail clubs. They would have been a difficult meal for any predator unless they could flip them onto their soft underbelly.
The Zhucheng locale in the northeast of China has produced tyrannosaurs (Zhuchengtyrannus, a close relative of Tyrannosaurus and a dream match-up in Fossil Crates' Chew-ly Chompionship), hadrosaurs (Shantungosaurus, compares favorably to Edmontosaurus, both regions have produced numerous named hadrosaurs), ceratopsians (Sinoceratops, Udanoceratops, Ischioceratops, and Zhuchengceratops in China and over a dozen named ceratopsians from the United States), sauropods (Zhuchengtitan from China, though no northern North America sauropods are yet known, Alamosaurus was present in North America), pachycephalosaurs (Micropachycephalosaurus from China, Pachycephalosaurus from North America), oviraptorosaurs (Anomalipes from China, Caenagnathus and Anzu from North America), ornithopods, small theropods, and now... more ankylosaurs! This find continues to demonstrate the startling similarity between the Late Cretaceous faunas of North America's Campanian and Maastrichtian rocks compared to those of China's Wangshi Group. Sinankylosaurus was found in the Wang's Group of the Upper Cretaceous in Zhucheng City, Shandong Province, and is 73.5 - 77.3 Ma (Campanian age).
The holotype, or name-bearing bone used to compare Sinankylosaurus to all other dinosaurs, is ZJZ-183, a right ilium housed at the Zhucheng Dinosaur Culture Research Center (image below).
Figure 1. Image of ZJZ-183, right ilium holotype of Sinankylosaurus, ~65cm long, 40 cm wide. (a) is the ventral view, (b) is the "back" view
What follows is my interpretation of a Google translation of their paper (all translation errors are mine). It gets heavy in the details but I hope you find it interesting to see how paleontologists go about making comparisons to other animals when they are trying to determine if their discovery is new or can be assigned to an existing animal.
Wang et al. 2020 list the following characters as a combination unique to Sinankylosaurus:
- The back of the ilium is smooth
- The acetabular protrusion is developed
- A wide "wing", anterior twist, acetabular protrusion posterior (distal)
- The process of extending to the proximal end strongly shrinks and narrows
- The rear end has a large gap in width
Comparison to other Chinese Ankylosauria
Pinacosaurus cf. grangeri
R 264 is the specimen number assigned to "A nearly complete sacrum and the articulated right ilium..." that was collected by T'an at Tianqiaotun in April of 1923, making it the earliest recorded ankylosaur fossil collected in China. Buffetaut called it Pinacosaurus cf. grangeri. Wang et al. 2020 state, "R264 has broad 'wings', that is, very broad ilium bones. In appearance, shape, curvature, and appearance and direction of ridges on the mid-abdominal surface."
Their comparison to a specimen they labeled Zpal MgD-II/1, a left ilium, calling it "Gu's painted dragon in Warsaw" and stating it is "very similar to Buffetaut (1995)", meaning Pinacosaurus cf. grangeri. I interpreted this section as Wang et al. 2020 are agreeing with the synonymy of P. ningshiensis with P. grangeri, and thus ZPAL MgD-II/1 and R 264 belong to the same type of animal. The presence of ridges on these specimens means they are not the same animal as ZJZ-183.
Jinyunpelta is the most primitive and oldest known true ankylosaurid and possesses a cool tail club. Wang et al. 2020 compared ZJZ-183 with Jinyunpelta. Jinyunpelta's left ilium "is wider, and the contraction of the front protrusion is weaker than Sinankylosaurus", the "...acetabular protrusion is relatively degree weaker than that of Sinankylosaurus", and "...the acetabulum width of the protrusion from the distal end to the proximal end varies more". Thus they conclude ZJZ-183 cannot be referred to Jinyunpelta which I agree with.
Crichtonsaurus is a Late Cretaceous ankylosaurid that may not be a valid taxon because of some issues with the material referred to it by previous paleontologists. However, a nearly complete left ilium (LPM 101-3) has been referred to Crichtonsaurus and, though it may belong to a different genus than Crichtonsaurus, Wang et al. 2020 rightly compared ZJZ-183 to LPM 101-3 and observed ZJZ-183 "is significantly wider than LPM 101-3, and the width shrinks when extending forward. The degree is also significantly stronger." Additionally, the "Wide distal end, raised back, narrowed forward..." make it at once different from ZJZ-183. Whatever LPM 101-3 ultimately comes to be called it clearly belongs to a different genus than ZJZ-183.
Zhejiangosaurus is a Late Cretaceous nodosaurid with both left and right ilia preserved, their "...acetabular protruding middle back. The surface is convex, there are obvious ridges, and a deep longitudinal direction is formed on the ventral surface.". Wang et al. 2020 note, "The extension direction of the dorsal ridge of the acetabular protrusion is different from that of Zhejiangosaurus. Similarly, there is no longitudinal depression on the ventral surface, and the acetabular anterior of Zhejiangosaurus, the protrusion is significantly narrower and slender than the acetabular protrusion in ZJZ-183." Their conclusion means ZJZ-183 does not belong to Zhejiangosaurus, which I agree with. However, it doesn't automatically mean ZJZ-183 is not a nodosaurid.
Taohelong is the first polacanthid discovered in China. Wang et al. 2020 compared ZJZ-183 to Taohelong and write, "Most of the surface [of Taohelong] is a long oval shallow depression, and its outer edge is backward. The ridges continue to the top of the acetabular fossa." They further compare ZJZ-183, noting a "Protrusion of the acetabulum There is a nearly circular depression on the ventral surface, which does not continue to the acetabular fossa. The square ridge, the acetabular protrusion of both contracted forward and narrowed, the latter. The degree of forward extension and contraction is more intense, and the former [Taohelong] has two acetabular protrusions. The width of the end has relatively little change.", concluding ZJZ-183 does not belong to Taohelong but does have some polacanthid similarity. Polacanthids are "halfway" between nodosaurids and ankylosaurids so it isn't surprising to me there is some resemblance in the bones with these specimens.
Wang et al. 2020 Conclusion
Their initial analysis wasn't able to determine if Sinankylosaurus belongs to the Ankylosauridae, Nodosauridae, or Polacanthidae. Ankylosaurs have wide skulls, short acetabular processes, and large tail clubs, nodosaurs have pear-shaped skulls, long acetabular processes, and no tail clubs, while polacanthids have a blend of characters between them.
The ZJZ-183 acetabular process "is distorted, but it is relative to the acetabular protrusion of the ankylosaurids", however, "The degree of forward contraction of the acetabular protrusion is more intense, which is similar to that of the polacanthids." My instincts say it belongs to the Ankylosauridae and would have had an awesome tail club, which is how I asked our artist to illustrate it for this blog. I will leave the final word with Google translate, which produced this as the final sentence in the paper regarding the family affinity of Sinankylosaurus, "It seems, therefore, Sinankylosaurus belongs to Ankylosauridae and Nodosauridae or Polacanthidae, family is still uncertain. It is determined that its ownership needs to be further confirmed by new fossil materials." The story of all paleontologists the world over and the reason we keep seeking fossils, to solve these relationship riddles!