Thoughts on paper by D'Emic (2023) regarding evolution of huge body size in sauropods

For generations, sauropod dinosaurs have starred in the popular imagination as the biggest land animals to ever walk the Earth, with interest in giant sauropods going back to the 1970s and 1980s with the discovery of the derived titanosaur Argentinosaurus and the diplodocids Diplodocus (=Seismosaurus) hallorum and Supersaurus (the giant rebbachisaurid Maraapunisaurus was seen in some publications as possibly the biggest-ever sauropod, although the missing nature of the holotype dorsal vertebra made size estimates of 190 feet guesswork, but Carpenter [2018] revised the size estimate of this genus to 105 feet, which makes sense because the initial size estimates of 170 feet for Diplodocus  hallorum was later revised to 110 feet). While children and adults alike marvel at the immense size of sauropods compared to elephants, rhinoceroses, and the extinct paraceratheres, I have not forgotten the fact that some sauropods living on island arcs in southern Europe during the Late Cretaceous which today are part of France, Spain, and Romania exhibited insular dwarfism, and that not all sauropods approached the body sizes attained by Apatosaurus, Brachiosaurus, Brontosaurus, Diplodocus, Galeamopus, Giraffatitan, and Supersaurus. Recently, D'Emic (2023) published a new paper illuminating the evolution of body size among sauropod taxa, relying on measurements of the circumferences of sauropod limb bones to propose that massive body size evolved convergently in multiple sauropod clades, while noting that select taxa of sauropods showed decreasing trends in body size. Having had the chance to read this paper, there are some noteworthy observations from the study that I wish to emphasize in detail. 

As admitted by D'Emic (2023), the patchy sauropod fossil record has constrained the focus on sauropod body size evolution to less than half of the approximately 250 described sauropod taxa, but the fact that Franz Nopcsa's interpretation of Magyarosaurus as a dwarf taxon has been vindicated by several studies (e.g. Benton et al. 2010; Stein et al. 2010) along with the small size of the short-necked dicraeosaurid Brachytrachelopan and the dwarf brachiosaurid Europasaurus shows that diminutive body size was present in more than one eusauropod clade. Although Cope's rule says that tetrapod lineages tend to increase in body size over time, it should be noted that when Edward Drinker Cope and Othniel Charles Marsh described to science the sauropod fauna of the Morrison Formation in western North America, they did not foresee that a few sauropod taxa of diminutive body size would be named in a handful of publications long after their deaths, and Magyarosaurus would be the first sauropod to be described that deviates from Cope's rule when it comes to body size in sauropods. With respect to the argument by D'Emic that the evolutionary cascade hypothesis put forward by Sander (2013) to interpret gigantism in some sauropods as being driven by anatomical and physiological innovations stemming from a nested array of historical prerequisites is best explained by ecological and life-history factors rather than any shared morphological traits, I should emphasize that the co-existence of dwarf and gigantic titanosaurs in the Late Cretaceous of Romania, Spain, and France (Stein et al. 2010; Vila et al. 2022) lends support to D'Emic's conclusion that ecological and life-history factors influenced the degree of dwarfism or gigantism among sauropod clades by showing that the insular nature of the ecosystems of the Ibero-Armorican island and Hațeg Island didn't necessarily translate into uniform dwarfism among titanosaur taxa from the Late Ceretaceous of Europe. For instance, Vila et al. (2022) note that the holotype of Abditosaurus kuehnei is substantially larger than specimens of other titanosaur taxa from the Ibero-Armorican Island as well as titanosaur specimens from the Hațeg Island, indicating that Cope's rule might apply to the evolution of body size in titanosaurs over the course of the Maastrichtian in southern Europe.

Phenogram of sauropod body size evolution over the course of the Mesozoic (from D'Emic 2023). Note that the lineages of the six eusauropod lineages that surpassed the maximum mammalian body mass are denoted by longitudinal lines highlighted in different colors (light green=non-neosauropod eusauropods; dark green=turiasaurians; blue=diplodocoids; orange=basal macronarians and non-titanosaur somphospondyls; purple=brachiosaurids; red=titanosaurs).

According to D'Emic, a total of 36 sauropod lineages independently evolved huge body sizes greater than those of other terrestrial tetrapods from the Mesozoic and Cenozoic, 32 of them belonging to the clade Neosauropoda. The discovery of isolated postcranial remains from the Bajocian-Callovian age Dongdaqiao Formation of Tibet belonging to a eusauropod over 66 feet (20 meters) long (Wei et al. 2023), two gigantic eusauropod cervical vertebrae from the Shishugou Formation of Xinjiang indicating a eusauropod 115 feet (35 meters) in length (which are referred to Mamenchisaurus sinocanadorum by Paul [2019] but considered to be of indeterminate taxonomic placement by Moore et al. [2023]), and a maximum size estimate of 105 feet (32 meters) for the Middle Jurassic mamenchisaurid Xinjiangtitan given by Wu et al. (2013), indicate that gigantic body size evolved in more than one clade of non-turiasaurian, non-neosauropod eusauropods during the Middle Jurassic, although the limited amount of material known for Mamenchisaurus sinocanadorum renders the exact size of this taxon unclear. The gigantic size of Turiasaurus relative to that of other turiasaurs makes me feel tempted to suggest that the rate of body size evolution in Turiasauria is inconsistent with Cope's rule because of the medium body size of the Early Cretaceous turiasaurs Mierasaurus and Moabosaurus and small body size of the Late Jurassic form Amanzia from Switzerland (Schwarz et al. 2020), the minor age difference between  Turiasaurus and the Yellow Cat Member of the Cedar Mountain Formation yielding Mierasaurus and Moabosaurus could suggest large-bodied turiasaurs might survived into the Valanginian-Barremian interval and that the small size of Amanzia can be best explained as a result of insular dwarfism given that much of western and central Europe was covered by seas during the Late Jurassic.

References:

Benton, M.J., Csiki, Z., Grigorescu, D., Redelstorff, R., Sander, P.M., Stein, K., and Weishampel, D.B., 2010. Dinosaurs and the island rule: The dwarfed dinosaurs from Haţeg Island. Palaeogeography, Palaeoclimatology, Palaeoecology 293 (3): 438–454. doi:10.1016/j.palaeo.2010.01.026

Carpenter, K, 2018. Maraapunisaurus fragillimus, N.G. (formerly Amphicoelias fragillimus), a basal Rebbachisaurid from the Morrison Formation (Upper Jurassic) of Colorado. Geology of the Intermountain West 5: 227–244.

D'Emic, M. D., 2023. The evolution of maximum terrestrial body mass in sauropod dinosaurs. Current Biology 33 (9): R349–R350. doi:10.1016/j.cub.2023.02.067

Paul, G.S., 2019. Determining the largest known land animal: A critical comparison of differing methods for restoring the volume and mass of extinct animals. Annals of the Carnegie Museum 85 (4): 335–358. doi:10.2992/007.085.0403

Sander, P.M., 2013. An Evolutionary Cascade Model for Sauropod Dinosaur Gigantism - Overview, Update and Tests. PLoS ONE 8(10): e78573. https://doi.org/10.1371/journal.pone.0078573

Schwarz, D., Mannion, P.D., Wings, O., and Meyer, C.A., 2020. Re-description of the sauropod dinosaur Amanzia (‘Ornithopsis/Cetiosauriscus’) greppini n. gen. and other vertebrate remains from the Kimmeridgian (Late Jurassic) Reuchenette Formation of Moutier, Switzerland. Swiss Journal of Geosciences 113: 2. https://doi.org/10.1186/s00015-020-00355-5

Stein, K., Csiki, Z., Curry Rogers, K., Weishampel, D.B., Redelstorff, R., Carballidoa, J.L., and Sander, P.M., 2010. Small body size and extreme cortical bone remodeling indicate phyletic dwarfism in Magyarosaurus dacus (Sauropoda: Titanosauria). Proceedings of the National Academy of Sciences of the United States of America 107 (20): 9258–9263. doi:10.1073/pnas.1000781107

Vila, B., Sellés, A., Moreno-Azanza, M., Razzolini, N.L., Gil-Delgado, A., Canudo, J.I., and Galobart, A., 2022. A titanosaurian sauropod with Gondwanan affinities in the latest Cretaceous of Europe. Nature Ecology & Evolution 6: 288-296. doi:10.1038/s41559-021-01651-5.

Wei, X.-F.; Wang, Q.-Y., An, X.-Y., Wang, B.-D., Zhang, Y.-J., Mou, C.-L., Li, Y., Wang, D.-B., Ma, W., and Kundrát, M., 2023. New sauropod remains from the Middle Jurassic Dongdaqiao Formation of Qamdo, eastern Tibet. Palaeoworld: in press. doi:10.1016/j.palwor.2023.02.002

Wu, W.H., Zhou, C.F., Wings, O., Sekiya, T., and Dong, Z.M., 2013. A new gigantic sauropod dinosaur from the Middle Jurassic of Shanshan, Xinjiang. Global Geology 32: 437–446.

Did early titanosaurs have non-procoelous anterior caudals and broad-crowned teeth? My thoughts on Poropat et al. 2023 paper

I remember that the description of  Rapetosaurus from Madagascar in the early 2000s demonstrated that the supposed late-surviving diplodocoids Nemegtosaurus and Quaesitosaurus are derived titanosaurs, the morphological similarities of the skulls of these taxa to diplodocids stemming from convergent evolution. Ironically, very few non-lithostrotian somphospondyl taxa preserve cranial remains, namely Diamantinasaurus, Euhelopus, Liaoningotitan, Ligabuesaurus, Mongolosaurus,  Phuwiangosaurus, Sarmientosaurus, and Tambatitanis, and the dearth of cranial remains for both basal titanosaurs and basal somphospondyls has been an obstacle to better understanding the ancestral cranial Bauplan of the most primitive titanosaurs, although Sarmientosaurus has a skull morphologically intermediate between that of basal titanosauriforms and derived titanosaurs. Recently, Poropat et al. (2023) have described a new specimen of Diamantinasaurus matildae (recovered by Poropat et al. [2021] as the sister taxon of Sarmientosaurus and Savannasaurus in the new titanosaur clade Diamantinasauria) preserving a nearly complete skull, AODF 906, illuminating aspects of the skull anatomy of this genus not preserved in referred Diamantinasaurus matildae specimen AODF 836 (described in detail by Poropat et al. 2021). Since AODF 906 reveals that Diamantinasaurus had a Sarmientosaurus-like skull and non-procoelous anterior caudal vertebrae, I have an opportunity to investigate whether the most primitive titanosaurs had broad, spatulate teeth and non-procoelous anterior caudals.

Equal-weights cladistic analysis of Diamantinasaurus matildae based on new morphological information from referred specimen AODF 906 (after Poropat et al. 2023). The figure drawings of Diamantinasaurus and Sarmientosaurus in the cladogram highlight the greater height of the rear skull relative to the snout distinguishing diamantinasaurians from lithrostrotian taxa for which skull material is known.  

In their paper erecting the name Diamantinasauria for the non-lithostrotian titanosaur clade formed by Diamantinasaurus, Sarmientosaurus, and Savannasaurus, Poropat et al. (2021) listed amphicoelous anterior caudal vertebrae as one of the distinguishing features of Diamantinasauria, but stressed that amphicoelous anterior caudals could only be assessed in Savannasaurus in contrast to the holotypes of Diamantinasaurus matildae and Sarmientosaurus musacchioi as well as referred D. matildae specimen AODF 836 lacking caudal remains even though Andesaurus has been consistently recovered as a basal titanosaur, raising the question of whether the presence of slight procoely in the anterior caudals of Andesaurus represents an independent morphological acquisition from lithostrotian titanosaurs. As Carballido et al. (2022) point out, Andesaurus has been consistently recovered as a basal titanosaur in nearly all titanosaur phylogenies, but its phylogenetic instability in some recent cladistic studies renders its role as a phylogenetic exemplar for basal Titanosauria labile, and it should be noted that the holotype of Andesaurus delgadoi is incomplete, which raises the possibility that future discoveries could render Andesaurus less basal within Titanosauria but still outside Lithostrotia. Indeed, the cladistic analysis of the titanosaur Ruixinia by Mo et al. (2023) places Andesaurus in a basal titanosaur clade that also includes Dongyangosaurus, Huabeisaurus, and Tambatitanis in a basal clade of Titan, and because Baotianmansaurus, Dongyangosaurus, Huabeisaurus and Tambatitanis share with Diamantinasaurus and Savannasaurus the presence of amphicoelous anterior caudals, it is possible that slightly procoelous in the anterior caudals of Andesaurus constitutes an autapomorphy among non-lithostrotian titanosaurs, since Poropat et al. (2023) recover Baotianmansaurus, Dongyangosaurus, and Huabeisaurus basally within Titanosauria outside Lithostrotia, like the clade Diamantinasauria. Although Hamititan from the Early Cretaceous of Xinjiang (Wang et al. 2021) is much older than Andesaurus and Diamantinasaurus, it differs from diamantinasaurians in having strongly procoelous caudal vertebrae, suggesting that some early titanosaurs had strongly procoelous anterior caudals and that others had either amphicoelous or opisthocoelous anterior caudal vertebrae because the anterior caudal vertebrae of Ninjatitan from the earliest Cretaceous of Argentina is slightly procoelous like Andesaurus (Gallina at al. 2021).

As noted by Poropat et al. (2021), the cranial material of the Diamantinasaurus matildae specimen AODF 836 is similar to the holotype of Sarmientosaurus musacchioi in having a quadratojugal with a posterior tongue-like process, a braincase with more than one ossified exit for cranial nerve V, and compressed and conical chisel-shaped teeth, but the new D. matildae specimen described by Poropat et al. (2023) demonstrates that the skull of diamantinasaurian titanosaurs was taller and acutely elevated relative to the snout, and that members of Diamantinasauria have robust dentigerous elements. I earlier mentioned that Euhelopus, Liaoningotitan, Mongolosaurus, Phuwiangosaurus, and Tambatitanis are the only non-lithostrotian somphospondyls besides diamantinasaurians that preserve extensive cranial remains, but the skulls of Diamantinasaurus and Sarmientosaurus are similar in every respect to those of brachiosaurids and differ from Euhelopus in having narrower tooth crowns, although they are not as slender as that of the basal somphospondylan Phuwiangosaurus (for which one referred specimen containing cranial and dental elements is known) or derived titanosaurs (Poropat et al. 2022, 2023). The occurrence of a relatively broad-crowned titanosauriform tooth in Santonian-age deposits in Hungary (Ősi et al. 2017) and the presence of broad-crowned teeth in the lithostrotian titanosaur Ampelosaurus (Le Loeuff 2005), in tandem with the spatulate teeth of Euhelopus and the fairly narrow tooth crowns of Diamantinasaurus, Huabeisaurus, Sarmientosaurus, and Tambatitanis, could indicate that the tooth crowns of the earliest and most primitive titanosaurs were more similar to those of Camarasaurus and Euhelopus, especially considering that the teeth of Diamantinasaurus, Huabeisaurus, Sarmientosaurus, and Tambatitanis are not as slender as those of lithostrotians such as Nemegtosaurus, Quaesitosaurus, Rapetosaurus, and Tapuiasaurus. Although the holotype of the basal somphospondyl Yongjinglong datangi does not preserve any cranial remains, it does include three teeth, all of which are somewhat similar to Euhelopus, and the basal somphospondyl Sibirotitan also had broad tooth crowns (Poropat et al. 2022). Therefore, broad-crowned teeth are most probably symplesiomorphic for the most primitive titanosaurs and a few derived titanosaurs, with conical chisel-shaped teeth and slender pencil-shaped teeth being derived states for Titanosauria. 

References:

Carballido, J.L., Otero, A., Mannion, P.D., Salgado, L., and Moreno, A.P., 2022. Titanosauria: A Critical Reappraisal of Its Systematics and the Relevance of the South American Record. pp. 269–298. In: Otero, A., Carballido, J.L., and Pol, D. (eds.). South American Sauropodomorph Dinosaurs. Record, Diversity and Evolution. Cham, Switzerland: Springer. ISBN 978-3-030-95958-6

Gallina, P. A., Canale, J. I., and Carballido, J. L., 2021. The Earliest Known Titanosaur Sauropod Dinosaur. Ameghiniana 58 (1): 35–51. doi:10.5710/AMGH.20.08.2020.3376.

Le Loeuff, J., 2005. Osteology of Ampelosaurus atacis (Titanosauria) from Southern France. pp. 115–137. In: Tidwell, V., and Carpenter, K. (eds.). Thunder-Lizards: The Sauropodomorph Dinosaurs. Bloomington: Indiana University Press. ISBN 978-0-253-34542-4.

Mo, J., Ma, F., Yu, Y., and Xu, X., 2023. A new titanosauriform sauropod with an unusual tail from the Lower Cretaceous of northeastern China. Cretaceous Research 144: 105449.  doi:10.1016/j.cretres.2022.105449.

Ősi, A., Csiki-Sava, Z., and Prondvai, E., 2017. A sauropod tooth from the Santonian of Hungary and the European Late Cretaceous 'Sauropod Hiatus.' Scientific Reports 7: 3261. https://doi.org/10.1038/s41598-017-03602-2 

Poropat, S. F., Kundrát, M., Mannion, P. D., Upchurch, P., Tischler, T. R., and Elliott, D. A., 2021. Second specimen of the Late Cretaceous Australian sauropod dinosaur Diamantinasaurus matildae  provides new anatomical information on the skull and neck of early titanosaurs. Zoological Journal of the Linnean Society 192 (2): 610-674. doi:10.1093/zoolinnean/zlaa173 

Poropat, S.F., Frauenfelder, T.G., Mannion, P.D., Rigby, S.L., Pentland, A.H., Sloan, T. and Elliott, D.A., 2022. Sauropod dinosaur teeth from the lower Upper Cretaceous Winton Formation of Queensland, Australia and the global record of early titanosauriforms. Royal Society Open Science 9: 220381.

Poropat, S. F., Mannion, P. D., Rigby, S. L., Duncan, R. J., Pentland, A. H., Bevitt, J. J., Sloan, T., and Elliott, D. A., 2023. A nearly complete skull of the sauropod dinosaur Diamantinasaurus matildae from the Upper Cretaceous Winton Formation of Australia and implications for the early evolution of titanosaurs. Royal Society Open Science 10(4): 221618. https://doi.org/10.1098/rsos.221618   

Wang, X., Bandeira, K. L. N., Qiu, R., Jiang, S., Cheng, X., Ma, Y., and Kellner, A.W.A., 2021. The first dinosaurs from the Early Cretaceous Hami Pterosaur Fauna, China. Scientific Reports 11:14962. doi:10.1038/s41598-021-94273-7.

Ruixinia and convergences in vertebral morphology among East Asian mamenchisaurids and titanosauriforms

The past decade or so has seen a considerable increase in the number of titanosauriform taxa known from the Early Cretaceous (Berriasian-early Aptian) of East Asia (e.g. Wang et al. 2007; You et al. 2008; Azuma and Shibata 2010; Zhou et al. 2018; Wang et al. 2021), shedding light on the evolution of both titanosaurs and non-titanosaurian titanosauriforms in this region during the Berriasian-early Aptian. However, most of those taxa are based on fragmentary and/or incomplete holotypes, in some cases preserving minimal vertebral material, and although D'Emic (2012) and Mannion et al. (2019) recovered Euhelopus and some non-titanosaur somphospondyls from the Berriasian to Aptian of East Asia in a monophyletic Euhelopodidae, the recovery of Daxiatitan, Dongbetitan, Euhelopus, and Xianshanosaurus outside Titanosauriformes in some cladistic analyses of Klamelisaurus by Moore et al. (2020) combined with the fact that no caudals are preserved for Euhelopus raise questions about the degree of the convergence of cervical and caudal vertebral characters among different lineages of eusauropods which have been found in East Asia. Mo et al. (2023) have recently described a new titanosaur from the Yixian Formation of Liaoning in northeastern China, Ruixinia zhangi, on the basis of a partial articulated postcranial skeleton, constituting the first East Asian titanosauriform of the Early Cretaceous to preserve a complete caudal series. Thus, a discussion of the implications of Ruixinia for the degree of convergent evolution in the morphology of the cervical and caudal vertebrae among East Asian eusauropods found in strata from the Aalenian-Albian interval is warranted.

Elements of the holotype of Ruixinia zhangi (ELDM EL-J009) (from Mo et al. 2023)

As I have noted elsewhere, D'Emic (2012) considered bifurcated cervical neural spines and the presence of thick, subhorizontal epipophyseal–prezygapophyseal laminae on the cervical vertebrae as diagnostic for Euhelopodidae, but those characters are either homoplastic among derived eusauropods or are not exclusively shared by the taxa included by D'Emic (2012) in Euhelopodidae. When describing the cervical vertebrae of Ruixinia, Mo et al. emphasize that the preservation of the cervicals in ELDM EL-J009 make it uncertain whether the neural spines of the middle and posterior cervicals for this taxon are bifurcated, and it should be noted that very few cervical vertebrate are known for Phuwiangosaurus and Tangvayosaurus, making it uncertain if the Southeast Asian taxa assigned to Euhelopodidae by D'Emic (2012) had bifurcated neural spines or not. Also, unpublished cladistic results reported in an abstract by D'Angelo (2022) recover Erketu as a basal titanosaur closely related to Huabeisaurus, indicating that whether or not Ruixinia had bifurcated cervical neural spines, the presence or absence of bifurcation of the neural spines of the cervical vertebrae varies among basal somphospondyls and some members of  Titanosauria. The occurrence of strongly procoelous anterior caudal vertebrae in Ruixinia that was once used to diagnose derived titanosaurs but is now recognized as being present in mamenchisaurids (e.g. the holotype of Wamweracaudia keranjei was once used to assign Janenschia to Titanosauridae before being recognized as a mamenchisaurid), turiasaurians (Royo-Torres et al. 2017; Mannion et al. 2019), the basal titanosaur Hamititan (Wang et al. 2021) and the basal macronarian Bellusaurus (Jacobs et al. 1993) may suggest that strongly procoelous anterior and middle caudal vertebrae evolved convergently among different clades of derived eusauropods by the Tithonian-Berriasian. Considering that Wang et al. (2021) recover Hamititan as more derived than the basal titanosaur Andesaurus despite the younger age of the latter, it is possible that Hamititan might be closely related to Ruixinia because both taxa possess marked ventrolateral ridges on the second caudal vertebrae (compare Mo et al. 2023, fig. 6 with Wang et al. 2021, fig. 4), and Wang et al. note that the well-marked ventrolateral ridges of the anterior caudals of Hamititan are comparable to those of Xianshanosaurus. The fusion of the last six caudals of Ruixinia also deserves attention because Mo et al. point out that this morphological feature has been previously described from mamenchisaurids and the basal eusauropod Shunosaurus, but since the distal end of the tail of Ruixinia is distinct from Shunosaurus and mamenchisaurids in being rod-shaped, the fusion of the distalmost caudal vertebrae constitutes yet another caudal vertebral feature that evolved convergently in Titanosauria and non-neosauropod eusauropods.

    

Reduced consensus cladistic analysis of Ruixinia zhangi (after Mo et al. 2023).

The cladistic analysis of Ruixinia by Mo et al. provides some very important insights into the degree of convergence in the vertebral morphologies of titanosauriforms and non-neosauropod eusauropods found in East Asia. In this phylogeny, Ruixinia is recovered as a derived titanosaur closely related to the taxa Daxiatitan and Xianshanosaurus, while Dongbeititan is placed as a non-titanosaur somphospondylan, whereas Liaoningotitan is clustered with Baotianmansaurus and Diamantinasaurus in the majority of he most parsimonious trees created by the Ruixinia phylogenetic analysis. It is interesting to note that Daxiatitan, Dongbeititan, and Xianshanosaurus are recovered along with Euhelopus within the "Core Mamenchisaurus-like Taxa" clade of Mamenchisauridae in some phylogenetic analyses by Moore et al. (2020) because Dongbeititan and Euhelopus are both similar to mamenchisaurids in having more than 15 cervical vertebrae, and the anterior and middle caudal vertebrae of Daxiatitan, Dongbeititan, and Ruixinia are strongly procoelous like those of mamenchisaurids and the basal titanosaur Hamititan. Since no cervical vertebrae are preserved for Xianshanosaurus, and the Daxiatitan holotype preserves 10 cervicals, the placement of Dongbeititan outside Titanosauria in contrast to Daxititan, Ruixinia, and Xianshanosaurus being recovered as derived titanosaurs suggests that vertebral characters shared with mamenchisaurids by Daxiatitan, Dongbeititan, Ruixinia, and Xianshanosaurus are best regarded as being convergent because Mo et al. (2023) note morphological differences between Ruixinia and other titanosauriforms found in Liaoning and a few titanosaur taxa have been described as having more than 15 cervical vertebrae. For instance, although Ruixinia and Dongbeititan have a cervical vertebral count exceeding 15 and strongly procoelous anterior caudals, the presence of bifid anterior caudal neural spines in both Ruixinia and mamenchisaurids in contrast to the undivided neural spines of the anterior caudals of Dongbeititan indicates that some early-branching somphospondylan titanosauriform taxa from the Early Cretaceous of East Asia evolved strong procoelous anterior caudals convergent with those of derived titanosaurs. Additionally, the anterior caudals of the basal macronarian Bellusaurus are also strongly procoelous and were used to suggest titanosaurian affinities for this taxon by Jacobs et al. (1993), and the lithostrotian titanosaur Rapetosaurus has a total of 17 cervicals (Rogers 2009), in which case the presence of more than 15 cervical vertebrae occurs not just in mamenchisaurids, Euhelopus,  Dongbeititan, and Ruixinia but also in lithostrotian titanosaurs. Considering that Euhelopus is recovered as a basal macronarian by Dai et al. (2022), and Moore et al. (2020) note that the anterior margin of the neural spine in posterior dorsal vertebrae being level with or posterior to the rear margin of the neural arch is shared by Dongbeititan with some mamenchisaurids, it is highly probable that the anterior margin of the neural spine in posterior dorsal vertebrae being level with or posterior to the rear margin of the neural arch evolved convergently in Ruixinia and some mamenchisaurids because Daxiatitan and Euhelopus lack this character as pointed out by Moore et al. (2020).

In summary, Ruixinia is not only the third titanosauriform to be described from the Early Cretaceous of Liaoning, China, but is also the first titanosaur from the Early Cretaceous of East Asia to preserve a complete caudal vertebral series. Although several morphological features of this taxon are also found in non-titanosauriform taxa, including a high cervical vertebral count and strongly procoelous anterior and middle caudal vertebrae, the titanosaurian placement of Ruixinia indicates that the most primitive derived titanosaurs and non-titanosaurian somphospondylans from East Asia convergently evolved those characters with mamenchisaurids, turiasaurians, basal macronarians, and even some titanosaurs. By displaying an unusual combination of autapomorphic characters of the caudal region, Ruixiana itself promises to shed additional light on the presence or absence of strong procoely of the anterior and middle caudals among derived eusauropods, including somphospondylans and mamenchisaurids.

References:

Azuma, Y., and Shibata, M., 2010. Fukuititan nipponensis, a new titanosauriform sauropod from the Early Cretaceous Tetori Group of Fukui Prefecture, Japan. Acta Geologica Sinica – English Edition 84 (3): 454–462. doi:10.1111/j.1755-6724.2010.00268.x.

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.

D'Angelo, J., 2022. A re-evaluation of the phylogenetic relationships of the controversial Central Asian sauropod Dzharatitanis kingi. Society of Vertebrate Paleontology 82th Annual Meeting Program & Abstracts: 119. (link here)

D’Emic, M. D., 2012. Early evolution of titanosauriform sauropod dinosaurs. Zoological Journal of the Linnean Society 166: 624–671.

Jacobs, L., Winkler, D. A., Downs, W. R., and Gomani, E. M., 1993. New material of an Early Cretaceous titanosaurid saurepod dinosaur from Malawi. Palaeontology 36: 523-523.

Mannion, P. D., Upchurch, P., Schwarz, D., and Wings, O., 2019. Taxonomic affinities of the putative titanosaurs from the Late Jurassic Tendaguru Formation of Tanzania: phylogenetic and biogeographic implications for eusauropod dinosaur evolution. Zoological Journal of the Linnean Society 185: 784–909. 

Mo, J., Ma, F., Yu, Y., and Xu, X., 2023. A new titanosauriform sauropod with an unusual tail from the Lower Cretaceous of northeastern China. Cretaceous Research: in press.  doi:10.1016/j.cretres.2022.105449

Moore, A. J., P. Upchurch, P. M. Barrett, J. M. Clark, and Xu, X., 2020. Osteology of Klamelisaurus gobiensis (Dinosauria: Eusauropoda) and the evolutionary history of Middle–Late Jurassic Chinese sauropods. Journal of Systematic Palaeontology 18 (16):1299–1393.

Rogers, K. C., 2009. The Postcranial Osteology of Rapetosaurus krausei (Sauropoda: Titanosauria) from the Late Cretaceous of Madagascar. Journal of Vertebrate Paleontology 29 (4): 1046–1086. 

Royo-Torres, R., Upchurch, P., Kirkland, J.I., DeBlieux, D.D., Foster, J.R., Cobos, A., and Alcalá, L., 2017. Descendants of the Jurassic turiasaurs from Iberia found refuge in the Early Cretaceous of western USA. Scientific Reports 7 (1): 14311. doi:10.1038/s41598-017-14677-2

Wang, X., You, H., Meng, Q., Gao, C., Cheng, X., and Liu, J., 2007. Dongbeititan dongi, the first sauropod dinosaur from the Lower Cretaceous Jehol Group of Western Liaoning Province, China. Acta Geologica Sinica 81: 911–916.

Wang, X., Bandeira, K. L. N.,  Qiu, R., Jiang, S., Cheng, X., Ma, Y., and Kellner, A.W.A., 2021. The first dinosaurs from the Early Cretaceous Hami Pterosaur Fauna, China. Scientific Reports 11:14962. doi:10.1038/s41598-021-94273-7.

You, H., Li, D., Zhou, L., and Ji, Q., 2008. Daxiatitan binglingi: a giant sauropod dinosaur from the Early Cretaceous of China. Gansu Geology 17: 1–17.

Zhou, C., Wu, W., Sekiya, T., and Dong, Z., 2018. A new Titanosauriformes dinosaur from Jehol Biota of western Liaoning, China. Global Geology 37: 327–333.

Thoughts on Peterson et al. (2022) paper regarding diplodocid feeding mechanisms

Many scientific papers have published regarding the degree of tooth replacement and wear in diplodocoid and macronarian sauropods, namely diplodocids, Camarasaurus, brachiosaurids, and select titanosaurs for which skull material is known. However, very little attention until recently was paid the patterns of tooth replacement and wear in apatosaurine diplodocids, in no small part because the Apatosaurus louisae skull CM 11162, the undescribed Apatosaurus ajax specimen CMC VP-7180, and the apatosaurine specimen TATE 099 found at the Nail Quarry in Como Bluff, Wyoming in 1996, constitute the only apatosaurine skulls that preserve complete teeth (known cranial material for the Apatosaurus ajax holotype includes a braincase and two quadrates, but that's another story). Recently, Peterson et al. (2022) published a paper describing in detail for the first time TATE 099 from Nail Quarry, offering a comprehensive analysis of patterns of tooth wear and replacement for this specimen and further illuminating the nature of feeding mechanisms among flagellicaudatan diplodocoids. 

The history of the systematic placement of TATE 099 within Diplodocidae is rather interesting. It was first referred to as Apatosaurus sp. when first reported in an abstract by Connely and Hawley (1998), who suggested that Apatosaurus used its jaws in front to back sliding motion to aid in cropping and biting when eating plants. For his part, Bakker (1998) referred TATE 099 to Brontosaurus excelsus and used this specimen to claim that B. excelsus differed from Apatosaurus in having the basitubera situated far behind the occipital condyle, but provided no justification as to why TATE 099 was conspecific with B. excelsus, and due to a lack of overlapping material between TATE 099 and B. excelsus holotype, this taxonomic referral was basically ignored by many authors (e.g. Upchurch et al. 2004; Tschopp et al. 2015). In any case, Peterson et al. point out that the basitubera of Apatosaurus louisiae are positioned anterior to the occipital condyle, similar to the condition in TATE 099, and I'm heartened that the authors recognized Bakker's (1998) referral of TATE 099 to Brontosaurus excelsus as lacking basis, and instead assign it to Apatosaurus sp. based on a widely diverging basipterygoid process greater than 60 degrees and the absence of a basisphenoid/basipterygoid recess, both of which are listed as diagnostic characters for Apatosaurus by Tschopp et al. (2015).

CT scans of the maxillae and premaxillae (left) and dentary (right) of Apatosaurus specimen TATE 099 showing unerupted teeth (from Peterson et al. 2022). 3D scans of the unerupted premaxillary/maxillary and dentary teeth shown at the bottom of figures 10 and 11 in Peterson et al. (2022) are included for convenience.

The discussion section of the paper by Peterson et al. (2022) constitutes the real focus on deciphering the rate of tooth wear and replacement among diplodocids. The unerupted tooth counts for TATE 099 reported by the authors in their description of TATE 099 are 5-8 unerupted tooth crowns per alveolus in the premaxilla, 3-5 unerupted tooth crowns per alveolus in the maxilla, and 1-3 unerupted crowns per alveolus in the dentary. Even though Peterson et al. observe differences between diplodocoids and macronarians in the number of replacement teeth as well as tooth volume, shape, and replacement rate, it is quite noteworthy how the authors point out that the rebbachisaurid Nigersaurus lacks alveolar septae and has smaller replacement teeth than those of diplodocid taxa despite the both Nigersaurus and TATE 099 being comparable in the maximum number of replacement teeth. However, the authors don't comment on how the number of replacement teeth of the dentary in TATE 099 compares with that of the holotype of the rebbachisaurid Lavocatisaurus from late Aptian-early Albian deposits in Patagonia, because the latter taxon has several replacement teeth preserved in the dentary. When noting that the numbers of premaxillary/maxillary replacement teeth for TATE 099 as well as Apatosaurus premaxilla MWC 8430 and maxilla MWC 6002 described from Mygatt-Moore Quarry in Colorado by McHugh (2018) are similar, but that dentary of TATE 099 has a number of replacement teeth comparable to those of Dicraeosaurus and the macronarian Brachiosaurus, Peterson et al. (2022) propose that diplodocid taxa retained similar numbers of replacement teeth in the dentary, and interpret the higher numbers of replacement teeth in the upper jaw of Apatosaurus compared to those of diplodocines as supporting the hypothesis by McHugh (2018) that the upper jaw of Apatosaurus was more accustomed to crushing tough plant leaves than that of Diplodocus. In retrospect, the difference between apatosaurines and diplodocines in how they used their upper jaw to chew on plant material may provide another hint at morphological differences between these two diplodocid clades, because some distinguishing features between Apatosaurinae and Diplodocinae can be found in the cervical vertebrae (see Tschopp et al. 2015). Although the erupted tooth row of TATE 099 was unavailable for study by Peterson et al., the authors provide a succinct analysis of the degree of tooth replacement in this specimen based on examination of high-fidelity casts of the erupted tooth row and comparisons with the tooth rows of other sauropods because they note that the row-set tooth replacement patterns in diplodocid taxa like  Apatosaurus, Diplodocus, and Galeamopus contrast with the alternating tooth replacement patterns of the basal macronarian Camarasaurus, since the tooth row of TATE 099 has an uneven occlusal margin that creates an uneven distribution of wear facets on the teeth. 

References:

Bakker, R.T. 1998. Dinosaur mid-life crisis: The Jurassic-Cretaceous transition In Wyoming and Colorado. New Mexico Museum of Natural History and Science Bulletin 14:67-76.

Connely, M.V. and Hawley, R. 1998. A proposed reconstruction of the jaw musculature and other soft cranial tissues of Apatosaurus. Journal of Vertebrate Paleontology 18 (suppl. to volume 3): 35A.

McHugh, J.B. 2018. Evidence for niche partitioning among ground-height browsing sauropods from the Upper Jurassic Morrison Formation of North America. Geology of the Intermountain West 5:95-103.  https://doi.org/10.31711/giw.v5.pp95-103

Peterson, J. E., Lovelace, D., Connely, M., and McHugh, J.B., 2022. A novel feeding mechanism of diplodocid sauropods revealed in an Apatosaurine skull from the Upper Jurassic Nail Quarry (Morrison Formation) at Como Bluff, Wyoming, USA. Palaeontologia Electronica 25(2):a21. https://doi.org/10.26879/1216. palaeo-electronica.org/content/2022/3653-apatosaurine-feeding-mechanism

Tschopp, E., Mateus, O., and Benson, R.B.J. 2015. A specimen-level phylogenetic analysis and taxonomic revision of Diplodocidae (Dinosauria, Sauropoda). PeerJ 3:e857.  https://doi.org/10.7717/peerj.857

Upchurch, 

P., 

Tomida, 

Y., and 

Barrett, 

P.M., 2004. 

A new specimen of Apatosaurus ajax (Sauropoda: Diplodocidae) from the Morrison Formation (Upper Jurassic) of Wyoming, USA. 

National Science Museum Monographs 

26: 

1–

107

.

Perijasaurus and implications for Early-Middle Jurassic eusauropod paleobiogeography in the Western Hemisphere

The South American country of Colombia has received some attention in some media outlets because its government beginning in the mid-2010s engaged in peace talks with the Marxist insurgent groups FARC (Revolutionary Armed Forces of Colombia) and ELN (National Liberation Army), leading to a peace agreement with FARC in 2016 under President Juan Manuel Santos that led to FARC abandoning its guerrilla activities and disbanding to allow many of its members to take part in the Colombian political process. Somewhat lost in talk about Colombia, however, is the fact that it has yielded its own Mesozoic tetrapods, including plesiosaurs, marine turtles, ichthyosaurs, and even a titanosauriform sauropod, Padillasaurus. Recently, Rincón et al. (2022) erected the new genus and species Perijasaurus lapaz for a sauropod dorsal vertebra (UCMP 37689) described from the Early to Middle Jurassic La Quinta Formation of eastern Colombia by Langston and Durham (1955), the species name referring to the town of La Paz near which this specimen was excavated and the fact that the 2016 peace agreement between Bogota and FARC made it possible to relocate the site in Colombia that yielded the holotype of P. lapaz. Given that Patagonia has yielded almost all Jurassic sauropod taxa from South America,  and Perijasaurus is quite significant as the first eusauropod from the Hettangian-Callovian interval to described from a locality in the Western Hemisphere north of Patagonia, I am dedicating this post to giving a synopsis of how Perijasaurus affects knowledge of eusauropod paleobiogeography in the Western Hemisphere during the Early-Middle Jurassic interval.

To give an introductory preview of how Perijasaurus affects state-of-the art knowledge of eusauropod paleobiogeography in the Western Hemisphere, it should be noted that the fossil record of Early-Middle Jurassic eusauropods from this region of the world is mostly concentrated in Patagonia, Argentina, with an extreme dearth of sauropod body and trace fossils in localities in the Western Hemisphere outside Patagonia, in contrast to the abundance of eusauropod taxa unearthed in Hettangian-Callovian deposits of East Asia, Europe, Niger, and Madagascar. For instance, fragmentary sauropod remains described from the Toarcian-age La Boca Formation of southwestern Mexico by Fastovsky et al. (1995) and an isolated caudal vertebra from the Summerville Formation of New Mexico (Lucas and Heckert 2000) constituted the only evidence for sauropod body fossils from the Hettangian-Callovian interval in North American until Rivera-Sylva and Espinosa-Arrubarrena (2020) described fragmentary diplodocid remains collected from the Bathonian-Callovian age Otlaltepec Formation in east-central Mexico in the late 1980s. I have always suspected that sampling biases are mostly responsible for the patchy record of sauropod in western North America from the Toarcian-Callovian interval because sauropod trackways are known from Bajocian-Bathonian deposits in Mexico (Ferrusquía-Villafranca et al. 1978, 1995, 1996). Outside Patagonia, dinosaur trackways have been described from Early-Middle Jurassic deposits in southeastern Brazil and northern Chile (see Weishampel et al. 2004), and together with Perijasaurus show that there maybe additional sauropod fossils from fossiliferous Early-Middle Jurassic deposits in South America outside Patagonia waiting to be unearthed or described to science.

Select views of the holotype of Perijasaurus lapaz (UCMP 37689) (after Rincón et al. 2022) 

When placing the phylogenetic position of Perijasaurus obtained by Rincón et al. (2022) in the broader context of eusauropod biogeography during the Toarcian-Callovian interval, it should be pointed out that the recovery of Perijasaurus in a polytomy with Cetiosaurus, Mamenchisauridae, Neosauropoda, Turiasauria, Jobaria, and a non-neosauropod clade formed by Bagualia, Nebulasaurus, Patagosaurus, and Spinophorosaurus raises questions about the timing of the paleogeographical dispersal of some derived eusauropod lineages from Patagonia to the northern Andes, Africa, Australia, and other regions of the worlds from which sauropod taxa dating to the Toarcian-Callovian have been recorded. For instance, the upper unit of the La Quinta Formation that yielded the Perijasaurus lapaz holotype spans the Toarcian-Aalenian boundary, whereas the Cañadón Asfalto Formation that has yielded Bagualia, Patagosaurus, and Volkheimeria plus a few unnamed taxa has been dated to the middle-late Toarcian based on radiometric dating (Pol et al. 2022). Despite the P. lapaz holotype comprising only a single dorsal vertebra, the late Toarcian-early Aalenian age of Perijasaurus combined with the revised age of the Cañadón Asfalto Formation, but also the fact that the mamenchisaurid Tonganosaurus hails from deposits dating to the Pliensbachian, could indicate that eusauropods had immigrated to northern South America and western North America (e.g. Mexico) by the end of the Early Jurassic. In support of this hypothesis, the North American landmass, including present-day Mexico, was mostly attached to South America until the eve of the Middle Jurassic, by which time Pangaea had begun to break up and the Caribbean Seaway started to form, and East Asia was mostly isolated from the Western Hemisphere (Iturralde-Vinent 2003, fig. 1). Moreover, the Bathonian-Callovian age of the Otlaltepec Formation  makes it probable that eusauropods began migrating to Mexico and eventually most of western North America beginning in the Toarcian because the unit of the the La Quinta Formation that has yielded Perijasaurus lapaz is comparable in age to the La Boca Formation, and present-day Mexico and Central America are adjacent to northwestern South America and therefore must have served as a land bridge for tetrapods to disperse into western North America prior to North America breaking away from South America in the Middle Jurassic. Although Rincón et al. (2022) recover a eusauropod clade comprising  Bagualia, Nebulasaurus, Patagosaurus, and Spinophorosaurus, the cladistic analysis by Holwerda et al. (2021) places Patagosaurus as the sister taxon of Cetiosaurus in a monophyletic Cetiosauridae, and the recovery of Spinophorosaurus as a member of Mamenchisauridae by Ren et al. (2023) combined with the Pliensbachian age of Tonganosaurus indicates that more derived eusauropods began achieving a global distribution by the Toarcian-Aalenian. Alternate placements of Perijasaurus within Eusauropoda as sister to either Haplocanthosaurus or the Turiasauria+Neosauropoda clade hinted at by Rincón et al. could hold water in future studies not only due to the P. lapaz holotype comprising a single element but also because the co-existence of the early-diverging eusauropod Archaeodontosaurus and turiasaurian  Narindasaurus in the Bathonian of Madagascar suggests that both basal and derived eusauropods were also coeval in western North America by the late Toarcian/early Aalenian.  

In summary, Perijasaurus is a chronologically important eusauropod taxon for providing new data on the biogeography of basal and derived eusauropods not only because it the oldest eusauropod from a Western Hemispheric locality outside Patagonia but also in that its discovery in northwestern South America provides hints at the timing of the dispersal of eusauropods into western North America given the current dearth of sauropod body fossils in the Hettangian-Callovian interval. Despite the limited amount of material known for the holotype, it demonstrates that eusauropods began spreading into areas of South America and eventually Mexico at lower latitudes over the course of the Toarcian stage of the Early Jurassic due to the presence of sauropod remains from Toarcian and Bathonian-Callovian deposits in Mexico and New Mexico, and thus constitutes the first non-Patagonian eusauropod genus from the Early to Middle Jurassic of the Western Hemisphere. Given that no sauropod body fossils were reported from the Early to Middle Jurassic of western North America until the 1980s, not to mention dinosaur tracks from deposits of Hettangian-Toarcian and Callovian age in Brazil and Chile, Perijasaurus lapaz itself will be of use in helping track the early evolution and paleobiogeography of eusauropods in areas of the Western Hemisphere north of Patagonia, namely the vicinity of the northern Andes and western North America.

Referennces: 

Fastovsky, D.E., Clark, J.M., Strater, N.H., Montellano, M., Hernandez, R., and Hopson, J.A., 1995, Depositional environments of a Middle Jurassic Terrestrial Vertebrate Assemblage, Huizachal Canyon, Mexico. Journal of Vertebrate Paleontology 15(3): 561–575.

Ferrusquía-Villafranca, I., Applegate., S.P., and Espinosa-Arrubarrena, L., 1978. Rocas volcanosedimentarias mesozoicas y huellas de dinosaurios en la región suroccidental pacífica de México. Revista Mexicana de Ciencias Geológicas 2 (2): 150-162.

Ferrusquía-Villafranca, I., Jiménez-Hidalgo, E., and Bravo-Cuevas, V. M., 1995, Jurassic and Cretaceous dinosaur footprints from México: additions and revisions, Journal of Vertebrate Paleontology 15 (Suppl. to No. 3):28A.

Ferrusquía-Villafranca, I., Jiménez-Hidalgo, E., and Bravo-Cuevas, V.M., 1996, Footprints of small sauropods from the Middle Jurassic of Oaxaca, southeastern Mexico. pp. 119-126. In: Morales, M. (ed.), The Continental Jurassic. Museum of Northern Arizona Bulletin 60.

Iturralde-Vinent, M.A., 2003. The conflicting paleontologic versus stratigraphic record of the formation of the Caribbean Seaway. pp. 75–88. In: Bartolini, C.R., Buffler, B.J., and Blickwede, J.F., (eds.), The Circum-Gulf of Mexico and the Caribbean: Hydrocarbon Habitats, Basin Formation, and Plate Tectonics. American Association of Petroleum Geologists Memoir 79: Tulsa, Oklahoma.

Holwerda, F. M., Rauhut, O. W. M., and Pol, D., 2021. Osteological revision of the holotype of the Middle Jurassic sauropod dinosaur Patagosaurus fariasi Bonaparte, 1979 (Sauropoda: Cetiosauridae). Geodiversitas 43 (16): 575-643. https://doi.org/10.5252/geodiversitas2021v43a16. 

Langston, W., Jr., and Durham, J.W., 1955. A sauropod dinosaur from Colombia. Journal of Paleontology 29 (6):1047–1051.

Lucas, S.G., and Heckert, A.B., 2000. Jurassic dinosaurs in New Mexico. New Mexico Museum Of Natural History and Science Bulletin 17:43-46.

Pol, D., Gomez, K., Holwerda, F.H., Rauhut, O.W.M., and Carballido, J.L., 2022. Sauropods from the Early Jurassic of South America and the Radiation of Eusauropoda. pp. 131-136. In: Otero, A., Carballido, J.L., and Pol, D. (eds.), South American Sauropodomorph Dinosaurs. Record, Diversity and Evolution. Cham, Switzerland: Springer. ISBN 978-3-030-95958-6.

Ren, X.X, Jiang, S., Wang, X.R., Peng, G.Z., Ye, Y., Jia, L., and You, H.L., 2023. Re-examination of  Dashanpusaurus dongi (Sauropoda: Macronaria) supports an early Middle Jurassic global distribution of neosauropod dinosaurs. Palaeogeography, Palaeoclimatology, Palaeoecology 610: 111318. doi:10.1016/j.palaeo.2022.111318.

Rincón, A.F., Raad Pájaro, D.A., Jiménez Velandia, H.F., Ezcurra, M.D., and Wilson Mantilla, J.A., 2022. A sauropod from the Lower Jurassic La Quinta Formation (Dept. Cesar, Colombia) and the initial diversification of eusauropods at low latitudes. Journal of Vertebrate Paleontology 42 (1): e2077112. doi:10.1080/02724634.2021.2077112

Rivera-Sylva, H. E., and Espinosa-Arrubarena, L., 2020, Remains of a diplodocid (Sauropoda: Flagellicaudata) from the Otlaltepec Formation Middle Jurassic (Bathonian-Callovian) from Puebla, Mexico. Paleontologia Mexicana 9 (3): 145-150.

Weishampel, D.B., Barrett, P.M., Coria, R.A., Le Loeuff, J., Xu, X., Zhao, X., Sahni, A., Gomani, E.M.P., and Noto, C.R., 2004, Dinosaur distribution. pp. 517-606. In: Weishampel D.B., Dodson, P., and Osmólska, H., (eds.), The Dinosauria, second edition. Berkeley, CA: University of California Press.

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.