The identity of Bashunosaurus revealed

In a few online sources and publications, there is a taxon of eusauropod from the Chinese Jurassic that has been for the most part unnoticed by the paleontological community, Bashunosaurus kaijiangensis. I first heard of Bashunosaurus when I saw this name in the alphabetical index of Justin Tweet's now defunct website Thescelosaurus! (replaced by the Microsoft Excel document Compact Thescelosaurus in 2015) as a nomen nudum, and in his list of non-avian dinosaur species, Olshevsky (2000) noted that Li et al. (1999) attributed the name Bashunosaurus kaijiangensis to "Kuang, 1996" and classified it as being a camarasaurid, but listed it as nomen nudum because of the lack of a description or diagnosis in Li et al. (1999). Oddly, Bashunosaurus is first mentioned in the paper by Ouyang (1989) describing the Middle Jurassic basal macronarian Abrosaurus dongpoi, again without a description or diagnosis. While reading a paper published earlier this month by Dai et al. (2022) describing the new basal macronarian  Yuzhoulong qurensis from the Middle Jurassic Xiashaximiao Formation of Sichuan, I noticed that Bashunosaurus is mentioned a few times in the paper, particularly the description section whereby Yuzhoulong is compared to other eusauropods from the Xiashaximiao Formation, while happening to come upon an overlooked paper by Kuang (2004) in the references list for the Yuzhoulong paper. Since Dai et al. cite Kuang (2004) when they compare Yuzhoulong with Bashunosaurus, I strongly suspected that it formally describes Bashunosaurus kaijiangensis as a new genus and species given the title of the paper. Thanks to a copy of  Kuang (2004) paper kindly provided to me by Ren Xinxin (one of the co-authors of the Yuzhoulong paper), I can confirm that Kuang (2004) officially names Bashunosaurus kaijiangensis as a new taxon, in which case Bashunosaurus is no longer a nomen nudum. Given that many eusauropod taxa from the Middle-Late Jurassic of East Asia are undergoing re-appraisal, this post will re-appraise the systematic placement and diagnosis of Bashunosaurus by Kuang (2004) as a first step to assessing the true systematic relationships of this taxon.

Kuang (2004) assigns the genus Bashunosaurus to the subfamily Camarasaurinae within the family Camarasauridae, making the partial postcranial skeleton KM 20100 the holotype and designating as the paratype a right ilium and caudal segment (KM 20103). The following characters are given by Kuang in his diagnosis for Bashunosaurus kaijiangensis: 12-13 short opisthocoelous cervical vertebrae; well-developing lateral and ventral keels on the cervicals; low neural arch and parapophysis of the cervicals; posterior cervical vertebrae with greater height/length ratios than anterior and middle cervicals; neural spines of the posterior cervicals bifurcated; anterior and middle dorsals robust and opisthocoelous with well-developed lateral and ventral keels; anterior dorsals with low neural spines, neural spines of the first anterior dorsal vertebra with shallow bifurcation; middle dorsals with elongated centra and high neural spines; deep, extremely robust prezygapophysis, postzygapophysis, and diapophysis of the dorsal vertebrae with prominent laminae; pair of suprazygapophyseal lamina projecting upwards into the transverse processes of the dorsal neural spines; middle and posterior dorsal vertebral centra platycoelous with wide, shallow pleurocoels and less prominent lamina; four sacral vertebrae; robust fan-like sacral rib; anterior caudal vertebrae amphicoelous; broad scapula with a narrow cross-section; humerus with well-developed deltopectoral crest; ilium high with a long, robust pubic peduncle; humerus/femur ratio 0.7; tibia/femur ratio 0.6; femur relatively slender.

Anterior dorsal vertebrae of Bashunosaurus, Dashanpusaurus, and Yuzhoulong showing differences between the three taxa in bifurcation of neural spines of first dorsal vertebrae. Clockwise from left to right - Bashunosaurus kaijiangensis holotype (KM 20100) (after Kuang 2004); Dashanpusaurus dongi holotype (ZDM 5028) (after Ren et al. 2022); Yuzhoulong qurensis holotype (CLGRP V00013) (after Dai et al. 2022)

As with the original diagnoses provided for most Chinese sauropods from the Middle and Late Jurassic, the diagnosis of Bashunosaurus by Kuang (2004) offers little in the way of autapomorphic characters as the cited morphological features are widespread among various eusauropod taxa. For instance, almost all eusauropod taxa have opisthocoelous cervical vertebrae, and the bifurcated neural spine of the first dorsal vertebra occurs in the basal macronarians Bellusaurus, Camarasaurus,  Lourinhasaurus, and Yuzhoulong, but also the mamenchisaurid Mamenchisaurus hochuanensis (Young and Zhao 1972; Mocho et al. 2014; Woodruff and Foster 2017; Dai et al. 2022). Opisthocoely in the anterior dorsal vertebrae and amphicoely in the middle dorsal vertebrae is present among diplodocoids, early-diverging basal eusauropods, and the basal macronarian Yuzhoulong (Dai et al. 2022), whereas platycoelous posterior dorsal vertebrae are shared with all non-macronarian eusauropods (Wilson and Sereno 1998). The humerus/femur ratio is similar to that reported for the basal eusauropod Shunosaurus and basal macronarian Camarasaurus, while the tibia/femur ratio is a characteristic of neosauropod clades (Rose 2007, appendix 1). Although not explicitly mentioned in the diagnosis for Bashunosaurus, the degree of bifurcation of the neural spines of the posterior cervical and anterior dorsal vertebrae tends to be more shallow than that of Camarasaurus, and the shallow bifurcation of the first dorsal vertebra is also found in Bellusaurus, Dashanpusaurus, and Yuzhoulong (Dai et al., 2022; Ren et al. 2022). The pleurocoels of the anterior cervicals of Camarasaurus possess sub-dividing accessory septa (='little lamina' of Kuang 2004), in contrast to the absence of accessory septa on the pleurocoels of the anterior cervicals of Bashunosaurus. As noted by Ren et al. (2022), unlike Camarasaurus and Dashanpusaurus, the middle dorsal vertebrae of Bashunosaurus have laterally oriented diapophyses of the middle dorsal vertebrae, and the first anterior dorsal vertebrae possesses dorsal and lateral margins with a sub-rounded outline in anterior view and two slightly dorsolaterally projecting metapophyses with an open ‘V’-shaped outline in anterior view. The shallow bifurcation of the neural spines of the middle dorsal vertebrae also helps distinguish Bashunosaurus from the contemporaneous basal macronarian Yuzhoulong, which lacks any bifurcation of all dorsal neural spines besides that of the first dorsal vertebra, and the middle dorsal neural spine also differs in having a prominently convex distal end (Dai et al. 2022). Therefore, the abovementioned vertebral characteristics cited by Dai et al. and Ren et al. to distinguish this taxon from some eusauropods from the Xiashaximiao Formation indicate that Bashunosaurus kaijiangensis is most probably a valid neosauropod taxon in its own right.

In an attempt to constrain the systematic placement of Bashunosaurus within Eusauropoda, Kuang (2004) distinguishes Bashunosaurus from taxa he assigns to Cetiosauridae by the more complex and robust laminae of the dorsal vertebrae, bifurcated neural spines of the posterior cervical and anterior dorsal vertebrae, and opisthocoelous centra of the anterior dorsal vertebrae, and he excludes this taxon from Brachiosauridae and Mamenchisauridae due to the cervical vertebrae being proportionally shorter and the presence of 13 short cervical vertebrae. The following characters are cited by Kuang (2004) to assign Bashunosaurus to Camarasaurinae: (1) similar number of presacral vertebrae; (2) proportionally short presacral vertebrae; (3) ventral and lateral keels on the posterior cervical centra; and (4) neural spines of posterior cervical and anterior dorsal vertebrae bifurcated. The first character is difficult to evaluate because the neck and dorsal regions of the B. kaijiangensis holotype are incomplete, whereas character 2 is present in other basal macronarians and many non-neosauropod eusauropods, including Shunosaurus, Mamenchisaurus youngi, and Omeisaurus tianfuensis (Ren et al. 2022). Because there are no cervical vertebrae preserved for Yuzhoulong, the presence of ventral and lateral keels on the posterior cervical vertebrae may be tentatively regarded as a localized autapomorphy for Bashunosaurus within basal Macronaria because Kuang (2004) notes that an undescribed referred specimen of the basal macronarian Abrosaurus lacks ventral and lateral keels on the posterior cervicals. On the other hand, the presence of low neural arches on the cervical centra is also found in Dashanpusaurus (Ren et al. 2022), and bifurcated neural spines on the posterior cervical and anterior dorsal vertebrae are widespread among mamenchisaurids and basal macronarians (Dai et al. 2022; Ren et al. 2022). Although the referred specimen of Abrosaurus is yet to be described, Kuang (2004) regards Bashunosaurus as more derived than Abrosaurus but less advanced than Camarasaurus based on features of the presacral vertebrae, including the degree of bifurcation of the posterior cervical and anterior dorsal vertebrae. However, Camarasauridae as used by Kuang (2004) has not been recovered as monophyletic in any phylogenetic context, although Upchurch et al. (2004) consider Abrosaurus a basal macronarian.  Moreover, Dai et al. (2022) and Ren et al. (2022) caution that a re-appraisal of Bashunosaurus and inclusion of this taxon in a cladistic context is necessary to confirm a potential macronarian placement for B. kaijiangensis.

With the revelation that Bashunosaurus kaijiangensis was officially described as a new genus and species in an overlooked 2004 publication, Bashunosaurus joins the list of putative Chinese dinosaur  nomina nuda that were revealed to have been described as new taxa in hitherto-overlooked papers, which includes the stegosaurs Gigantspinosaurus and Yingshanosaurus, but also increases the overall biodiversity of sauropods from the Xiashaximiao Formation to about a dozen species. As is typical with many original descriptions of new Asian sauropod taxa from the Middle to Late Jurassic, the paper describing Bashunosaurus was quite brief and gave little in the way of autapomorphies or unique character combinations,   

References:

Dai, H., Tan, C., Xiong, C., Ma, Q., Li, N., Yu, H., Wei, Z., Wang, P., Yi, J., Wei, G., You, H., and Ren, X., 2022. New macronarian from the Middle Jurassic of Chongqing, China: phylogenetic and biogeographic implications for neosauropod dinosaur evolution. Royal Society Open Science 9 (11). 220794. doi:10.1098/rsos.220794.

Kuang, X.W., 2004. A new Sauropoda from Kaijiang dinosaur fauna in middle Jurassic beds of North-Eastern Sichuan. pp. 40-46. In: Sun, J.W. (eds), Collection of the 90th anniversary of Tianjin museum of natural history. Tianjin, China: Tianjin Science and Technology Press.

Li K., Zhang, Y., and Cai K., 1999. The Characteristics of the Composition of the Trace Elements in Jurassic Dinosaur Bones and Red Beds in Sichuan Basin. Geological Publishing House, Beijing.

Mocho, P., Royo-Torres, R. and Ortega, F., 2014, Phylogenetic reassessment of Lourinhasaurus alenquerensis, a basal Macronaria (Sauropoda) from the Upper Jurassic of Portugal. Zoological Journal of the Linnean Society 170: 875–916

Olshevsky, G., 2000. An annotated checklist of dinosaur species by continent. Mesozoic Meanderings 3:1-157.

Ouyang H., 1989. A new sauropod from Dashanpu, Zigong Co., Sichuan Province (Abrosaurus dongpoensis gen. et sp. nov.). Zigong Dinosaur Museum Newsletter 2: 10-14.

Ren, X.X., Jiang, S., Wang, X.R., Peng, G.Z., Ye, Y., King, L., and You, H.L., 2022. Osteology of Dashanpusaurus dongi (Sauropoda: Macronaria) and new evolutionary evidence from Middle Jurassic Chinese sauropods. Journal of Systematic Palaeontology. 20 (1). 2132886. doi:10.1080/14772019.2022.2132886.

Rose, P.J., 2007. A new titanosauriform sauropod (Dinosauria: Saurischia) from the Early Cretaceous of central Texas and its phylogenetic relationships. Palaeontologia Electronica 10.2.8A: 1-65.

Upchurch, P., Barrett, P.M. and Dodson, P. 2004. Sauropoda. pp. 259-322. In: Weishampel, D., Dodson, P., and Osmólska, H. (eds.), The Dinosauria, 2nd edition. University of California Press, Berkeley.

Wilson, J.A., and Sereno, P.C., 1998. Early Evolution and Higher-Level Phylogeny of Sauropod Dinosaurs. Journal of Vertebrate Paleontology 18 (supp. 2): 1–79.  doi:10.1080/02724634.1998.10011115

Woodruff, D.C., and Foster, J.R., 2017. The first specimen of Camarasaurus (Dinosauria: Sauropoda) from Montana: The northernmost occurrence of the genus. PLoS ONE 12(5): e0177423. https://doi.org/10.1371/journal.pone.0177423 

Young, C.C., and Zhao, X.-J., 1972. Mamenchisaurus hochuanensis sp. nov. Institute of Vertebrate Paleontology and Paleoanthropology Monographs A 8:1-30.