Sunday, September 9, 2018

Yizhousaurus sunae

I originally had something else in mind for today, but it was heavily photo-dependent, and the photos weren't coming out very well (unresolved lighting and depth-of-field issues). I will have to try again some other time. Meanwhile, here comes Yizhousaurus sunae to the rescue! I'm not quite sure why "prosauropods" should have featured so frequently here (see also Bagualosaurus, Meroktenos, Xingxiulong, and two visits with Anchisaurus), but there you go.

Figure 3 from Zhang et al. (2018) (check the link for the lengthy caption). Note that the quadrate and associated bones are displaced from the back of the skull, which obscures the complete shape of the profile.

Genus and species: Yizhousaurus sunae; "Yizhou" refers to the Chuxiong Yi Autonomous Prefecture of Yunnan Province in China, "saurus" is of course "lizard", and "sunae" honors Professor Ai-Ling Sun. This gives us, roughly, "Professor Sun's lizard from Chuxiong Yi Autonomous Prefecture".
Citation: Zhang, Q.-N., H.-L. You, T. Wang, and S. Chatterjee. 2018. A new sauropodiform dinosaur with a "sauropodan" skull from the Lower Jurassic Lufeng Formation of Yunnan Province, China. Scientific Reports 8, article 13464. doi:10.1038/s41598-018-31874-9.
Stratigraphy and geography: uppermost Zhangjiaao Member of the ever-popular Lower Jurassic Lufeng Formation (a.k.a. the "dark red beds", thought to be of Sinemurian age), "near Duwafang Village, Chuanjie Town, Lufeng County, Chuxiong Yi Autonomous Prefecture, Yunnan Province, China" (Zhang et al. 2018).
Holotype: LFGT-ZLJ0033 [Bureau of Land and Resources of Lufeng County, Lufeng], a partial articulated skeleton including a skull and mandible, 9 cervical vertebrae, 14 dorsals, 3 sacrals, 5 anterior caudals, the shoulder and pelvic girdles, the forelimbs except for the wrist bones, and the femora. The whole animal is estimated as 7 m (23 ft) long.

Yizhousaurus sunae is an example of a name that showed up in preliminary form several years before it was was formally published. In this case, it was first used in a Geological Society of America abstract back in 2010 (Chatterjee et al. 2010). At the time, there was some additional publicity, including a GSA press release which is no longer available (unless you know how to use Internet Archive, or you query your search engine of choice using "Found: First complete remains of early sauropod dinosaur" to find other copies) and a video featuring Sankar Chatterjee discussing the teeth and cranial bones. At the time, Y. sunae was being referred to as a very early sauropod; almost eight years later, it has become a very derived not-quite-sauropod. This speaks to the inevitable difficulties of picking out the beginning of a group, and to the historical circumstances: "prosauropods" were particularly unstable in the early 2000s, and the membership of Sauropoda at some times included such names as Anchisaurus. Probably Y. sunae didn't so much change as did our understanding of the "prosauropod"–sauropod transition.

In basic form, Y. sunae looks the part of a large "prosauropod". The arms are still relatively short, especially the forearm bones. The ilium has the classic "prosauropod" look, being low with a short anterior (preacetabular, the acetabulum being the socket for the femur) process and a longer postacetabular process. The femur has a bit of a curve to it, which is also more "prosauropod" than sauropod. The hand is broad, short, and robust, suggesting (to me, at least) that it was not particularly well-adapted for grasping, nor did it have the weight-bearing adaptations seen in the hands of true sauropods. There is a pathology in the tail: the fourth and fifth caudals are fused (Zhang et al. 2018).

The skeleton of Yizhousaurus sunae; Figure 2 in Zhang et al. (2018). The full caption is: "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 Q.-N.Z)."

The head is where things get unusual. The typical "prosauropod" skull, as in Plateosaurus or Massospondylus, is relatively long, low, and narrow. The Y. sunae skull, as shown above, is short, deep, and broad. This is more like basal sauropod skulls; about the only "prosauropod" it shows much of a resemblance to is the restored skull of super-obscure Yimenosaurus youngi. It's not quite at a sauropod configuration yet, as shown by the sizes and shapes of the various openings, but it seems to be on that line. One un-sauropod-like feature is the anterior end, which comes to a blunt point; in sauropods, the bitey end of the skull is usually broadly rounded to squared-off (as with Antarctosaurus wichmannianus).

Y. sunae marks "yet another Lufeng sauropodomorph", with the profusion of Lufeng sauropodomorphs already mentioned in the Xingxiulong post. Unlike in the case of Xingxiulong, Y. sunae does not come out in phylogenetic analyses as closely related to any other well-known Lufeng sauropodomorphs (Jingshanosaurus, Lufengosaurus, Xingxiulong, Yunnanosaurus), and it appears to reasonably distinguishable from them. Zhang et al. (2018) classified it as a sauropodiform, and identified it as the most derived of the Lufeng sauropodomorphs, but did raise the point that its sauropod-like features may have been evolved independently from the sauropod line, which would make it a side branch.


Chatterjee, S., T. Wang, S. G. Pan, Z. Dong, X. C. Wu, and P. Upchurch. 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.

Zhang, Q.-N., H.-L. You, T. Wang, and S. Chatterjee. 2018. A new sauropodiform dinosaur with a "sauropodan" skull from the Lower Jurassic Lufeng Formation of Yunnan Province, China. Scientific Reports 8, article 13464. doi:10.1038/s41598-018-31874-9.


  1. Nice article. Lots of mosaic evolution going on at and around the base of Sauropoda.
    Is there yet another Lufeng sauropodomorph in the pipeline? Unnamed ("Grippisaurus") - based on a specimen referred to Gyposaurus sinensis (not the holotype specimens, now regarded as juvenile L. huenei). I don't know the specimen number.

    1. Nary a peep out of "Gripposaurus" for some time, although I would have to guess that the material in question would be among the three "G. sinensis" specimens set aside in Wang et al.'s 2017 SVP abstract as requiring further study (IVPP V43, V45, and V95).

    2. I think it's V43 which is a nearly complete skeleton described and illustrated by Young (1948). V45 is a fragmentary postcranial skeleton that's not illustrated and only briefly described, while V95 is a partial skeleton with only the scapula illustrated and no real description.

      What I found most interesting in the Yizhousaurus paper are the statements-

      "Jingshanosaurus was erected based on a complete skeleton, and was described in Chinese before the specimen was fully prepared. Morphological features proposed as the diagnostic characters of Jingshanosaurus are mostly indistinct, with the majority present in a wide variety of non-sauropodan sauropodomorphs. In fact, many cranial character codings of Jingshanosaurus are incorrect due to the restoration on its skull roof."

      "Unfortunately, most of the diagnoses of this taxon [Chuxiongosaurus] are either ambiguous or erroneous, or similar in condition to Jingshanosurus, thus its validity and distinctiveness relative to Jingshanosaurus requires reevaluation."

      Chuxiongosaurus was only differentiated from Jingshanosaurus in its description (Lu et al., 2010) by having more teeth (4/22/25 vs. 4/16/21-22) and having a smaller skull (~93% of the size), so I'm not surprised. For an entertaining cladogram, check out Lu et al.'s with both a "Neotheropoda" and a "Theropods" OTU, which are weirdly sister to Ornithischia like Baron's Ornithoscelida. I'm guessing Lu et al. accidentally used Herrerasaurus as the outgroup instead of Ornithischia, but have no idea how they got two theropod OTUs from Yates' (2004) matrix.

    3. Interestingly, the possibility that Chuxiongosaurus is Jingshanosaurus first came up in the Xingxiulong description, which shares two authors with the Yizhousaurus description (H.-L. You and T. Wang). There isn't much to glean from the earlier mention, though, which is limited to "Chuxiongosaurus was excluded from this phylogenetic analysis due to its controversial status as it is possibly synonymous with Jingshanosaurus (pers. observ.)."

  2. The profusion of Lufeng sauropodomorphs is almost certainly artificial to some degree. I'm not convinced that the odd skull of Yizhousaurus is anything other than taphonomic distortion. There is an extremely similar looking Massospondylus skull from the Elliot Formation, that has undergone the same weird compression. We nicknamed it the 'goblin' and it is figured in Gow, Kitching and Raath's paper on Masso skulls (can't remember the specimen number off hand).