Your Friends The Titanosaurs, part 27: Ruyangosaurus, Saltasaurus, and Sarmientosaurus

Today on "Your Friends The Titanosaurs", it's a giant enigma (Ruyangosaurus giganteus), a much smaller and much better known titanosaur that also turns out to have its enigmatic side (Saltasaurus loricatus), and a good old-fashioned titanosaur skull taxon (Sarmientosaurus musacchioi), plus special guest stars Noasaurus and the Rincón de los Sauces titanosaur! (If anything seems odd, formatting-wise, it's because this is my first structurally complex post since Blogger changed to a new interface, and I'm dealing with a couple of things.)

Ruyangosaurus giganteus

If you're working in the English language, it's a bit difficult getting information on Ruyangosaurus giganteus. There's the original description by Lü et al. (2009) and a PeerJ preprint (Sassani and Bivens 2017). There is also a later report (Lü et al. 2014) which is not the easiest thing in the world to find. It seems that the best place to find out what was in this publication is actually a post on DeviantArt by one of the authors of the preprint, which indicates that of the additional material assigned to R. giganteus in the 2014 paper, there are at least three R. giganteus individuals represented, as well as at least one other species of sauropod. For that reason, it seems best to just focus on the type specimen.

R. giganteus was named in 2009 for six partial or complete postcranial bones discovered in Ruyang County, Henan Province, China. The name is simple enough to guess, working out as "gigantic Ruyang County lizard". It was originally reported from the Mangchuan Formation (Lü et al. 2009), which has since been raised to a group and split into several formations, with the Aptian–Albian Haoling Formation getting the dinosaurs (Xu et al. 2012). The holotype is 41HIII–0002 (Henan Geological Museum), consisting of a partial possible posterior cervical vertebra (anterior dorsal per Sassani and Bivens 2017), a nearly complete posterior dorsal, a posterior cervical rib, an anterior dorsal rib, the proximal right femur, and the right tibia (Lü et al. 2009).

R. giganteus as restored by Sassani for Sassani and Bivens (2017), where it is Figure 15. The type material is white; beige elements are based on bones potentially from the type individual. CC-BY-4.0.

Let us cut right to the chase: was R. giganteus indeed "giganteus"? The dorsal centrum is 51 cm wide (20 in), slightly greater than that of Argentinosaurus, albeit with a much shorter neural spine. The tibia is 127 cm long (50 in). Yes, R. giganteus earns its species name. Is it also a titanosaur? This is trickier. It has never quite settled down. Lü et al. (2009) described it as a potential "andesauroid", in part because of the apparent hyposphene–hypantrum articulation in the dorsal vertebra, which Gunnar and Bivens (2017) considered a misinterpretation of the laminae. Several reports (e.g., Averianov and Sues 2017) have considered it outside of Titanosauria, whereas others find it just within Titanosauria (e.g., several South American papers of recent years). Mannion et al. (2019) found it to be either a basal titanosaur, or... a basal titanosaur by technicality (actually a euhelopodid, but within Titanosauria thanks to quirky resolution at the base of Titanosauria). Sassani and Bivens (2017) placed it in Lognkosauria.

So, R. giganteus is controversial, but it does permits a timely digression or two. You may have seen earlier this year a paper on Klamelisaurus, an obscure sauropod from the Jurassic of China (Moore et al. 2020). Ruyangosaurus itself does not feature in it to any great extent, apart from doing the Hokey Pokey with Titanosauria in a couple of phylogenetic analyses. The paper is more interesting for what it has to say about Euhelopus, which changes its mind every couple of decades about where it belongs. In this paper, it decides to rejoin "Omeisaurus" and "Mamenchisaurus", sometimes pulling a few putative Chinese titanosaurs with it. This, combined with the reassessments in Mannion et al. (2019), strongly suggests we have a very weak grasp on what East Asian sauropods were doing. The other thing I wanted to bring up? The newest paper is not necessarily the best paper, just the newest. This is particularly true with phylogenetics.

Saltasaurus loricatus

There is one slight, minor, infinitesimal issue with Saltasaurus loricatus, so small I hesitate to bring it up, but one which we ought to get out of the way up front. That issue is: the El Brete bonebed, the type and only known locality for S. loricatus, and described as only having one species of titanosaur, includes what appears for all the world to be a Neuquensaurus sacrum (D'Emic and Wilson 2011). The implication of this would be that, apart from sacrum and ilium specimens, we really can't be sure if we're looking at Saltasaurus bones or Neuquensaurus bones, and until such time as someone sorts the bonebed, our knowledge of Saltasaurus thus carries an inescapable question mark. (That's all. You can see why I hesitate to bring it up.) [also, see this comment below for another take]

With that behind us, we can now be properly introduced to S. loricatus, although to be fair it's already among the most familiar titanosaurs to the casual dinosaur fan. It was the titanosaur of the '80s, not that there was a great deal of competition for this slot, but Saltasaurus seized it with its combination of relatively complete material and a killer hook: the first undisputed armored sauropod (see here for the concluding post on titanosaur osteoderms, with links to the others in the series). This spawned numerous illustrations of a sauropod wearing the cloak of an ankylosaur, which strictly speaking is probably not exactly accurate. (Another issue to note in most images, toys, etc. is the neglect of breadth, a common issue for dinosaurs but particularly notable for titanosaurs. Saltasaurus may have been a "compact" in terms of length as sauropods go, but it certainly made up for it across the hips. See also this discussion, posted as I was preparing this. For the record, I have no issue with the width depicted, but I'm dubious that it was that heavily armored.)

An osteoderm from Saltasaurus loricatus (Cerda and Powell 2010:Figure 1). From the top down, the views are of the external surface, ridge-on, and ridge-side (the usual assumption is that lengthwise features like the ridge indicate the osteoderm was oriented with the ridge lengthwise on the body). CC-BY-4.0.

S. loricatus was described in 1980 by Bonaparte and Powell, from bonebed remains discovered in the Lecho Formation at El Brete in southern Salta Province, northwestern Argentina. This is also the same locality that produced the type of Noasaurus leali (Noasaurus in fact means "northwestern Argentina lizard," if you need to remember the geography). N. leali was described in the same paper and was also very famous in the 1980s before fading. In its case, it lost the "Southern Hemisphere dromaeosaur" gig by virtue of not actually being a dromaeosaur, bona fide Southern Hemisphere dromaeosaurs (or close enough) with much better fossils showed up, and it's poorly known within its own group. However, it did keep Noasauridae. Where were we again?

No prizes for guessing that Saltasaurus refers to Salta Province. "Loricatus" is a reference to mail-like armor, so we get, broadly, "armored lizard from Salta Province." The specimen selected for the holotype was PVL 4017-92 (Paleontología Vertebrados Lillo, Instituto Miguel Lillo, Tucumán, Argentina), a complete sacrum and both ilia, fused. There was a lot more in the bonebed, though. Powell (2003), the most recent list, cited three cranial fragments, an axis, 14 cervicals, 20 dorsals, three sacrals (or sacrums?), 26 caudals, four scapulae, three coracoids, four sternal plates, 10 humeri, five ulnae, four radii, five metacarpals, five ilia, four pubes, two ischia, five femora, five tibiae, four fibulae, seven metatarsals, six osteoderms, and four [patches of] associated small dermal ossicles. (This differs slightly from the count supplied in Bonaparte and Powell 1980, but I'm regarding it as more accurate because it is more recent, and yes, I am aware of the irony.) Powell interpreted these fossils as representing at least five adults and subadults (apparently at least one of which was a Neuquensaurus per D'Emic and Wilson 2011).

If you're looking for a word to sum up S. loricatus, I'd suggest something like "chunky." It didn't even put any effort into elongating its cervicals. If your ideas of aesthetically pleasing things involve slenderness, elongate forms, or essentially anything delicate, S. loricatus and its close friends Neuquensaurus and Rocasaurus are not going to appeal to you. (For those of you illustrating high-rise sauropods, if you want to do that with a saltasaur, it has to be all in the neck, because the limb proportions and shoulder girdle aren't doing you any favors.) This makes it ironic that saltasaurs had such heavily pneumatized skeletons. For S. loricatus, not only is there pneumatization of the neck, back, and tail vertebrae, there is also pneumatization of the ribs, ilium, and coracoid (Cerda et al. 2012). It's as if someone shrunk the body of a larger titanosaur but forgot to shrink the air sacs.

Tibia of various titanosaurs (Figure 8 in González Riga et al. 2019). Try to guess which one is Saltasaurus. CC-BY-4.0. (it's E)

The anatomy of S. loricatus has been discussed in a few other publications (all anatomy in Powell 1992 and 2003; osteoderms in Cerda and Powell 2010; presacral vertebrae plus pneumatic features in Zurriaguz and Powell 2015; caudal pneumaticity in Zurriaguz and Cerda 2017), although it does seem that the species gets taken for granted, and someone really ought to follow up on that "El Brete Neuquensaurus" thing. S. loricatus is notable as the only titanosaur with good remains of small ossicles as opposed to just large osteoderms; the known patches are associated with the upper rear region of the hips (Bonaparte and Powell 1980), but of course the full extent is not known. It's also noted for its small size. Being known only from a bonebed, it's difficult to put out firm numbers, but the largest humerus is 59.0 cm long (23.2 in) (Powell 2003). To put that into perspective, the humerus of Opisthocoelicaudia, an animal which generally compares favorably to Saltasaurus, is 100 cm long (39 in) (Borsuk-Białynicka 1977). The relative proportions of the other arm bones are also similar. By that rule of thumb, you can scale down Opisthocoelicaudia about 55%–60% and come up with something approximating S. loricatus.

Although the specifics of how sauropods handled being sauropods remain mysteries, the basic game plan is not too hard to figure out. They were taking in lots of fodder using a sort of rake on a crane, letting the guts deal with breaking it down, and getting huge doing it. Then you have something like the saltasaurs, which seem to have been in the process of taking the sauropod body plan and turning it into something much different when the end-Cretaceous intervened. To go back to the SVPOW post linked at the beginning of this section, Powell (1992) specifically compared S. loricatus to the hippopotamus, albeit with a long neck, living in and around lakes and rivers. If they had ten more million years, what would these relatively small, broad, squat, armored, and intensely pneumatic sauropods have become?

Sarmientosaurus musacchioi

Sarmientosaurus musacchioi may have only been described in 2016 (Martínez et al. 2016), but it had a long pre-publication existence. You my have heard about it as "Sarmientosaurus splendens", or if you go back even farther, you may recall its skull showing up in a National Geographic article (Shreeve 1997), more of which about later. It had enough of a track record to be one of the "Coming Attractions in Dinosauria". Now that it's arrived, what do we know about it?

Discovering and collecting a titanosaur skull (plus a few other bones). Figure 2 in Martínez et al. (2016). CC-BY-4.0.

S. musacchioi gets its genus name from Sarmiento, which is both a town and an administrative department in Chubut Province, Argentina. The species name honors the late scientist and educator Eduardo Musacchio of the Universidad Nacional de la Patagonia San Juan Bosco in Comodoro Rivadavia, Argentina (Martínez et al. 2016). Together we get something like "Eduardo Musacchio's Sarmiento lizard". The type and only known specimen is MDT-PV 2 (Museo Desiderio Torres-Paleovertebrados, Sarmiento), which includes a nearly complete skull with jaws, a partial axis and rib articulated with part of the following third cervical, a fragment of the fifth cervical, a nearly complete sixth cervical with a cervical rib and a rather low neural arch, part of the seventh cervical, and what is interpreted as a piece of ossified tendon (3 mm or 0.1 inch in diameter and at least 3 m or 10 ft long). This specimen was found in the upper Lower Member of the Bajo Barreal Formation at Estancia Laguna Palacios in south-central Chubut (Martínez et al. 2016).

The skull manages the interesting trick of looking like an idealized cross between a brachiosaur skull and a derived titanosaur skull. In particular, the tooth row is not confined to the front of the mouth, the teeth are not slender, and the skull is relatively broad with a pointed snout, unlike the more elongate, blunt-ended skulls of taxa such as Nemegtosaurus and Rapetosaurus. Overall, the skull is 43 cm long (17 in) from the tip of the snout to the occipital condyle, and fusion suggests it was skeletally mature (Martínez et al. 2016).

It's this one again! Sarmientosaurus musacchioi is C, in the company of Giraffatitan (A), Abydosaurus (B), Nemegtosaurus (D), Rapetosaurus (E), and Tapuiasaurus (F). Figure 33 in Martínez et al. (2016). CC-BY-4.0.

Deformation of the type skull is not substantial and is mostly confined to the dorsal-most bones (e.g., the frontals, parietals, and postorbitals). There does not appear to have been a frontal "dome" as in some other titanosaurs, though. The orbit is large, but of course the eye itself was not as big, and at any rate could not have been because the orbit has an ovate shape rather than being a circle. There is the typical hitch in the ventral margin of the skull posterior to the teeth, although not as strongly developed as in some other titanosaurs. An endocast and reconstruction of the internal ear were provided by Martínez et al. (2016), who suggested that the ear structure indicated more reliance on airborne sounds and lower frequency hearing compared to other titanosaurs. The jaws have a U-shape and the lower jaws have no "guillotine crest" as in Bonitasaura and some other titanosaurs. There are four teeth per premaxilla and 13 per dentary; the right maxilla has 12 teeth and the left has 11. The premax teeth are vertical, while the maxillary teeth are angled anteriorly and the dentary teeth are angled posteriorly, which may have something to do with the odd wear facets. They are elliptical in cross-section and anatomically fall between the heavy teeth of something like Camarasaurus and the pencil-like teeth seen in many titanosaurs (Martínez et al. 2016).

The skull of S. musacchioi in right lateral (A), left lateral (B), anterior (C), posterior (D), dorsal (E), and ventral (F) views. Figure 6 in Martínez et al. (2016). CC-BY-4.0.

Martínez et al. (2016) considered the possibility that S. musacchioi represents the heretofore unknown skull of Epachthosaurus sciuttoi. However appealing the idea may be to those of us who like our sauropods tidy, the two appear in distinct positions in Martínez et al.'s phylogeny, and, as usual, where you get one titanosaur, you're seemingly guaranteed another three or four species. Indeed, there are plenty of titanosaur fossils in the lower Bajo Barreal Formation that cannot be attributed to either species, including isolated skull material (Martínez et al. 2016). Therefore, there's no reason to jump onto the Synonym Train yet.

Sarmientosaurus will judge you with disembodied googly eyes for leaping to conclusions. Figure 13 in Martínez et al. (2016). CC-BY-4.0.

Despite the undoubted value of a basal titanosaur skull, S. musacchioi has not translated to many phylogenetic analyses beyond that in the original description, where it ended up near Malawisaurus. (I haven't included this one in my compendium because no Andesaurus, therefore no Titanosauria.)

This seems like a good place to mention the *other* titanosaur skull mentioned in Shreeve (1997). Although the photo in the article is that of Sarmientosaurus, the find described in the article is an entirely different specimen. How can I be sure? The photo caption describes the Sarmientosaurus skull as a specimen found by paleontologist Rubén Martinez in Chubut Province, while the article describes a specimen found by Daniel Eseisa in the Rincón de los Sauces area, and while both locations are in Patagonia, they aren't exactly next to each other. Furthermore, the titanosaur specimen described in the text includes a vertebral column and pelvis, which Sarmientosaurus does not have. Finally, and most prosaically, the description of Sarmientosaurus cites an undescribed titanosaur skull from Rincón de los Sauces. If you are curious, there are at least two conference abstracts relating to it (Calvo et al. 1997; Calvo and Salgado 1998), and it sounds quite a bit like the find described here.

References

Averianov, A., and H.-D. Sues. 2017. Review of Cretaceous sauropod dinosaurs from central Asia. Cretaceous Research 69:184–197. doi:10.1016/j.cretres.2016.09.006.

Bonaparte, J. F., and J. E. Powell. 1980. A continental assemblage of tetrapods from the Upper Cretaceous beds of El Brete, northwestern Argentina (Sauropoda-Coelurosauria-Carnosauria-Aves). Mémoires de la Société Géologique de France 139:19–28.

Borsuk-Białynicka, M. M. 1977. A new camarasaurid sauropod Opisthocoelicaudia skarzynskii gen. n., sp. n. from the Upper Cretaceous of Mongolia. Palaeontologia Polonica 37(5):5–64.

Cerda, I. A., and J. E. Powell. 2010. Dermal armor histology of Saltasaurus loricatus, an Upper Cretaceous sauropod dinosaur from northwest Argentina. Acta Palaeontologica Polonica 55:389–398.

Cerda, I. A., L. Salgado, and J. E. Powell. 2012. Extreme postcranial pneumaticity in sauropod dinosaurs from South America. Paläontologische Zeitschrift 86:441–449.

Calvo, J. O., R. A. Coria, and L. Salgado. 1997. Uno de los más completos titanosáuridos (Dinosauria-Sauropoda) registrados en el mundo. Ameghiniana 34:534.

Coria, R. A., and L. Salgado. 1998. Nuevos aportes a la anatomía craneana de los saurópodos titanosáuridos. Ameghiniana 36:98.

D'Emic, M. D., and J. A. Wilson. 2011. New remains attributable to the holotype of the sauropod dinosaur Neuquensaurus australis, with implications for saltasaurine systematics. Acta Paleontologica Polonica 56(1):61–73.

González Riga, B. J., M. C. Lamanna, A. Otero, L. D. Ortiz David, A. W. A. Kellner, and L. M. Ibiricu. 2019. An overview of the appendicular skeletal anatomy of South American titanosaurian sauropods, with definition of a newly recognized clade. Academia Brasileira de Ciências 91(Supp. 2): e20180374. doi:10.1590/0001-3765201920180374.

Lü, J., L. Xu, S. Jia, X. Zhang, J. Zhang, L. Yang, H. You, and Q. Ji. 2009. A new gigantic sauropod dinosaur from the Cretaceous of Ruyang, Henan, China. Geological Bulletin of China 28(1):1–10.

Lü, J., H. Pu, L. Xu, S. Jia, J. Zhang, and C. Shen. 2014. Osteology of the giant sauropod dinosaur Ruyangosaurus giganteus Lü et al., 2009. Geological Publishing House, Beijing, China.

Mannion, P. D., P. Upchurch, X. Jin, and W. Zheng. 2019. New information on the Cretaceous sauropods of Zhejiang Province, China: impact on Laurasian titanosauriform phylogeny and biogeography. Royal Society Open Science 6(8):191057. doi:10.1098/rsos.191057.

Martínez, R. D. F., M. C. Lamanna, F. E. Novas, R. C. Ridgely, G. A. Casal, J. E. Martínez, J. R. Vita, and L. M. Witmer. 2016. A basal lithostrotian titanosaur (Dinosauria: Sauropoda) with a complete skull: implications for the evolution and paleobiology of Titanosauria. PLoS ONE 11(4):e0151661. doi:10.1371/journal.pone.0151661.

Moore, A. J., P. Upchurch, P. M. Barrett, J. M. Clark, and X. Xing. 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. doi:10.1080/14772019.2020.1759706.

Powell, J. E. 1980. Sobre la presencia de armadura dérmica en algunos dinosaurios titanosáuridos. Acta Geológica Lilloana 15:41–47.

Powell, J. E. 1992. Osteologia de Saltasaurus loricatus (Sauropoda—Titanosauridae) del Cretácico Superior del noroeste Argentino. Pages 165–230 in J. L. Sanz and A. D. Buscalioni, editors. Los dinosaurios y su entorno biotico: actas del segundo curso de paleontologia in Cuenca. Institutio "Juan de Valdes", Cuenca, Argentina.

Sassani, N., and G. T. Bivens. 2017. The Chinese colossus: an evaluation of the phylogeny of Ruyangosaurus giganteus and its implications for titanosaur evolution. PeerJ Preprints 5:e2988v1. doi:10.7287/peerj.preprints.2988v1.

Shreeve, J. 1997. Uncovering Patagonia's lost world. National Geographic 192(6):120–137.

Xu, L., Z. C. Pan, Z. H. Wang, X. L. Zhang, S. H. Jia, J. C. Lü, and B. L. Jiang. 2012. Discovery and significance of the Cretaceous system in Ruyang Basin, Henan Province. Geological Review 58:601–613.

Zurriaguz, V. L., and I. A. Cerda. 2017. Caudal pneumaticity in derived titanosaurs (Dinosauria: Sauropoda). Cretaceous Research 17:14–24. doi:10.1016/j.cretres.2017.01.001.

Zurriaguz, V. L., and J. E. Powell. 2015. New contributions to the presacral osteology of Saltasaurus loricatus (Sauropoda, Titanosauria) from the Upper Cretaceous of northern Argentina. Cretaceous Research 54:283–300.