Here we are, at the end of the alphabet. You might have noticed that every letter has had an entry except one: W. Wintonotitan sometimes ends up in Titanosauria, but it's not a consensus titanosaur. This means, of course, that those of us who are describing new titanosaurs should consider generic names starting with "W" (as well as adding a couple more to those letters represented by single names). We aren't at the end of the series, though; for one thing, there is still one rather significant genus and species that hasn't yet taken its turn in the spotlight...
Anyway, the four titanosaurs at the end of the alphabet include some of the most recently described genera and species, which isn't really surprising; it wasn't until the past couple of decades that genera beginning with letters after "T" became more than a novelty. Three of the four postdate 2016, leaving Xianshanosaurus as the relative oldster with a 2009 name. This means there isn't a lot of literature for them, so having four in one post seems reasonable. The four are also alike in that each name is a double geographic reference.
Volgatitan simbirskiensis is the current holder of the coveted "oldest named titanosaur" position. It is also one of the more geographically unusual taxa, being the one and only form named from European Russia. (If you've perused The Compact Thescelosaurus, you may have noticed a scarcity of dinosaurs from European Russia in general, although if you like dubious marine reptiles there's plenty of those.)
V. simbirskiensis was described in Averianov and Efimov (2018) based on fossils collected by Efimov during the 1980s, from 1982 to 1987. The specimens came from a site on the west bank of the Volga River about 0.5 km (0.3 mi) south of Slantsevy Rudnik and 5 km (3 mi) north of Ulyanovsk, in Ulyanovsk Oblast. The bones were found in pyritic limestone concretions eroding out of an unnamed Lower Cretaceous marine unit predominantly composed of dark gray shale, dating to the late Hauterivian (Speetoniceras versicolor ammonite zone) (Averianov and Efimov 2018). Efimov briefly mentioned the bones as far back as 1987 (Efimov 1987), although at the time did not classify them. Later consultation with L. A. Nesov introduced the possibility of sauropod affinities, which first appeared in Efimov (1997), albeit as a potential brachiosaurid. A potential titanosaur affiliation didn't appear until Efimov (2001) (a different Efimov).
The name Volgatitan simbirskiensis refers to the Volga River and to Simbirsk, the former name of Ulyanovsk, giving us something like "Volga River titan from Simbirsk (=Ulyanovsk)". The holotype and only known material is UPM 976/1–7 (Ulyanovsk Paleontological Museum), a group of seven anterior and middle caudals interpreted as representing a single individual. Based on the size of the caudals, it was probably somewhat smaller than Opisthocoelicaudia skarzynskii, but in the general vicinity. As is typical of titanosaurs in general, the caudals are strongly procoelous and have neural arches perched on the anterior half of the centra, and the bone texture is camellate (many small internal spaces rather than few large spaces, which is described as camerate). The vertebrae have a single ventral ridge, rather than a groove or multiple ventro-lateral ridges. Unusually, there is also what is interpreted as a hyposphene–hypantrum articulation present on at least one anterior caudal (Averianov and Efimov 2018). As discussed way back with Andesaurus delgadoi, this feature is found in the dorsals of non-titanosaurian sauropods. It is much rarer in caudals, otherwise only present in the obscure titanosauriform Astrophocaudia and true titanosaur Epachthosaurus sciuttoi (Averianov and Efimov 2018).
The presence of strongly procoelous middle caudals is one of the features that indicates Volgatitan simbirskiensis is indeed a true titanosaur, and not an imitator with procoelous anterior caudals (particularly mamenchisaurs). In fact, the middle caudals indicate V. simbirskiensis was not in the crowd of basal titanosaurs either. Averianov and Efimov (2018) presented a phylogenetic analysis that placed their new sauropod near the base of the line leading to the lognkosaurs, past the split with the line leading to the saltasaurs. This would imply that we are missing a fair chunk of titanosaur evolution and diversification, if the oldest known example is relatively derived.
Xianshanosaurus shijiagouensis began its scientific existence as a sauropod of unknown affinities from the Ruyang Basin of Henan, east-central China (Lü et al. 2009). One of our previous guests, Ruyangosaurus giganteus, also hails from the same unit, albeit with somewhat greater notoriety. X. shijiagouensis was described by Lü et al. (2009) for a handful of bones, including ten articulated anterior caudals with a chevron (KLR-07-62-6), a right coracoid (KLR-07-62-59), a left femur (KLR-07-62-15), and dorsal ribs (KLR-07-62-3a and KLR-07-62-59-1), all of which are grouped as the holotype. The type is reposited at the Henan Geological Museum (Lü et al. 2009). A spatulate sauropod tooth similar to those of Brachiosaurus was also found at the quarry, and Lü et al. described it with the holotype, but did not included it in the holotype. Mannion et al. (2013) excluded the tooth from X. shijiagouensis as not being found in association with the type.
These bones came from the Shijiagou quarry at Liudian, which is otherwise noted for small theropods, among them at least seven ornithomimosaurs and the type specimen of the oviraptorid Luoyanggia liudianensis (Lü et al. 2009). The quarry is recognized in the animal's name, which also refers to nearby Xian Mountain (Xianshan), giving us something like "Xianshan lizard from Shijiagou Quarry". The stratigraphy of the quarry was originally described as the Mangchuan Formation, but as mentioned in the Ruyangosaurus entry, Xu et al. (2012) revised the stratigraphy and placed the dinosaur-bearing beds in the Aptian–Albian Haoling Formation.
The caudals are mildly procoelous, and each centrum is about 12 cm long (4.7 in), but it should be noted that the caudals are markedly short and broad. The sutures are not completely fused, indicating the animal was not mature at the time of death. The neural spines are expanded laterally into plate-like surfaces which are roughened, which Lü et al. (2009) interpreted as evidence of strong muscles. The femur is 126 cm long (49.6 in) (Lü et al. 2009).
Lü et al. (2009) could not classify X. shijiagouensis beyond Neosauropoda. They noted that although the caudals are procoelous, other titanosaur features are missing in the caudals, ribs, and femur. However, a series of later phylogenetic analyses found it to be within Titanosauria (Mannion et al. 2013, 2017; Upchurch et al. 2015) or even Lithostrotia (D'Emic 2012; Averianov and Sues 2017). It was even retained as a titanosaur in Mannion et al. (2019), in which several other putative titanosaurs were banished to the euhelopodids. However, this relative stability was challenged by Moore et al. (2020), in which X. shijiagouensis showed signs of succumbing to the magnetic attraction of Euhelopus (itself in the processes of making up with Mamenchisaurus and Omeisaurus).
Xianshanosaurus is another one of those sauropods with an inexplicable skeletal mount commemorating all 16 or so known bones. Is someone sitting on more complete material? Was there some groundswell of support to fill a Xianshanosaurus-shaped void in the public's heart? Argentinosaurus, I can see; "world's largest sauropod" and all that. What about "third largest sauropod from the Haoling Formation"?
Yamanasaurus lojaensis comes with a geopolitical claim to fame: it is the first non-avian dinosaur named from Ecuador. It is also the northernmost "core" saltasaur currently known, although that could change at any time. This species is otherwise not especially well known, being based on fragmentary remains. It was described in Apesteguía et al. (2020, or 2019 depending on your feelings toward online availability). The specimens were discovered near Yamana in Loja Province of southwestern Ecuador, with both locality and province mentioned in the name ("Yamana lizard from Loja", or something like that).
The bones were collected circa 1995 by Tarquino Efraín Celi Bravo and ended up in the collections of two institutions, the Instituto Nacional de Patrimonio Cultural (INPC) and the Universidad Técnica Particular de Loja (UTPL). They are thought to represent one individual, and taken together include two fused sacrals (YM-UTPL_002), the posterior half of a caudal (YM-INPC-014), the proximal half of the left humerus (YM-INPC-016), the proximal half of a radius (YM-INPC-015), and a fragment that might be a proximal tibia (YM-INPC-017). This entire group of specimens is the holotype (Apesteguía et al. 2020). Stratigraphically, the specimens are from yellowish sandstones of the Río Playas Formation, in the Alamor-Lancones Basin (Apesteguía et al. 2020). Based on a 66.9 Ma date for an underlying unit elsewhere, the site presumably dates to near the end of the Cretaceous.
Anatomically, there is not a great deal to say about Y. lojaensis based on the limited material. As a titanosaur it was small with short stout limbs. The bones resemble those of Neuquensaurus australis, with the notable exception of an odd constriction just below the proximal end of the radius (Apesteguía et al. 2020).
Zhuchengtitan zangjiazhuangensis at the end of the alphabet makes for another short entry: there's only one publication that discusses it in any detail (Mo et al. 2017), and it happens to be in a language I can't read, leaving me at the tender mercies of Google Translate and a notably detailed Wikipedia entry.
Both the genus and species names refer to geography, in this case the city Zhucheng and village Zangjiazhuang, giving us something like "Zhucheng City titan from Zangjiazhuang" (Mo et al. 2017). Zhucheng is not quite up there with Fukui yet, but we also have Zhuchengceratops, Zhuchengosaurus (=Shantungosaurus), and Zhuchengtyrannus.
The holotype and only known specimen is ZJZ-57 (Zhucheng Dinosaur Culture Research Center), a mostly complete left humerus. As restored (slightly wonky), it is 108.0 cm long (42.5 in). This bone was discovered in 2008 at Zangjiazhuang along with other, less diagnostic sauropod remains. (The site is otherwise almost wall-to-wall hadrosaurs.) Stratigraphically, the site is in the Wangshi Group, which includes the Xingezhuang Formation (fine-grained floodplain deposits) and overlying Hongtuya Formation (coarser, with basalt at the top dated to 73.5 million years old) (Mo et al. 2017). The humerus is noted for its robust build, comparable to Opisthocoelicaudia skarzynskii and Saltasaurus loricatus, with a very wide proximal end (55% the length of the bone). Mo et al. (2017) described Z. zangjiazhuangensis as a saltasaurid titanosaur. Mannion et al. (2019) kept it in Titanosauria without comment.
Apesteguía, S., J. E. Soto Luzuriaga, P. A. Gallina, J. Tamay Granda, and G. A. Guamán Jaramillo. 2020 (available online in 2019). The first dinosaur remains from the Cretaceous of Ecuador. Cretaceous Research 108:104345. doi:10.1016/j.cretres.2019.104345.
Averianov, A., and V. Efimov. 2018. The oldest titanosaurian sauropod of the Northern Hemisphere. Biological Communications 63(6):145–162. doi:10.21638/spbu03.2018.301.
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.
D'Emic, M. D. 2012. The early evolution of titanosauriform sauropod dinosaurs. Zoological Journal of the Linnean Society 166(3):624–671.
Efimov, D. V. 2001. [Dinosaur remains in Lower Cretaceous deposits of Ulyanovsk Province]. Page 111 in [Geologists of XXI Century. Abstracts of regional scientific conference of students, aspirants, and young specialists. Saratov, March 26–28, 2001]. Saratov, Russia.
Efimov, V. M. 1987. [Marine reptiles in Mesozoic deposits of Ulyanovsk Province]. Kraevedcheskie Zapiski 7:60–66.
Efimov, V. M. 1997. On a find of a fossil sauropod from the marine Hauterivian of the middle Volga Region. Paleontological Journal 31(6):653–654.
Lü, J., L. Xu, X. Jiang, S. Jia, M. Li, C. Yuan, X. Zhang, and Q. Ji. 2009. A preliminary report on the new dinosaurian fauna from the Cretaceous of the Ruyang Basin, Henan Province of central China. Journal of the Paleontological Society of Korea 25:43–56.
Mannion, P. D., P. Upchurch, R. N. Barnes, and O. Mateus. 2013. Osteology of the Late Jurassic Portuguese sauropod dinosaur Lusotitan atalaiensis (Macronaria) and the evolutionary history of basal titanosauriforms. Zoological Journal of the Linnean Society 168:98–206. doi:10.1111/zoj.12029.
Mannion, P. D., R. Allain, and O. Moine. 2017. The earliest known titanosauriform sauropod dinosaur and the evolution of Brachiosauridae. PeerJ 5:e3217. doi:10.7717/peerj.3217.
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.
Mo, J., K. Wang, S. Chen, P. Wang, and X. Xu. 2017. A new titanosaurian sauropod from the Late Cretaceous strata of Shandong Province. Geological Bulletin of China 36(9):1501–1505.
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.
Upchurch P., P. D. Mannion, and M. P. Taylor. 2015. The anatomy and phylogenetic relationships of "Pelorosaurus" becklesii (Neosauropoda, Macronaria) from the Early Cretaceous of England. PLoS ONE 10(6):e0125819. doi:10.1371/journal.pone.0125819.
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.