Your Friends The Titanosaurs: Udelartitan celeste

Today's new entrant is actually a former briefly featured coming attraction coming off the board, the fourth such coming attraction to have arrived. It is also the first classic dinosaur to be named from Uruguay, which is the first new country added since Ecuador with Yamanasaurus lojaensis a few years back. (2020 if you insist on paper, 2019 if you just want to get it over with. Also, of course, that was a titanosaur too!) So, with that introduction, we welcome Udelartitan celeste.

Genus and Species: Udelartitan celeste. The genus name borrows the acronym of the Universidad de la República in Montevideo, Uruguay, where the fossils are reposited, and combines it with the popular "-titan" ending. "Celeste" comes from the Spanish word for sky blue, and refers to Uruguay as a country by way of its international sport teams (Soto et al. 2024). (A note to anyone else naming the first dinosaur of a country: isn't doing it this way more fun than just churning out "Uruguaytitan" or "uruguayensis"?)

Citation: Soto, M., J. L. Carballido, M. C. Langer, J. C. G. Silva Junior, F. Montenegro, and D. Perea. 2024. Phylogenetic relationships of a new titanosaur (Dinosauria, Sauropoda) from the Upper Cretaceous of Uruguay. Cretaceous Research 105894. doi: https://doi.org/10.1016/j.cretres.2024.105894.

(Have you ever noticed how many titanosaur papers are published in Cretaceous Research?)

Geography and Stratigraphy: The bonebed containing the known fossils of U. celeste is in the Araújo area, near Quebracho in the Paysandú Department of northwestern Uruguay. The bones were found in the Guichón Formation, which has so far defied narrow dating but is loosely considered to have been deposited during the first half of the Late Cretaceous (Soto et al. 2024).

Holotype: FC-DPV 3595 (Vertebrate Fossil Collection, Facultad de Ciencias, Universidad de la República), articulated caudal vertebrae 1 to 3 (Soto et al. 2024).

Allow me to reacquaint you with the basic story, as borrowed from the "Coming Attractions" page linked above: "Titanosaur remains are not a new thing in Uruguay; von Huene, for example, assigned various remains to better-known genera and species from Argentina (e.g., Huene 1931), but these specimens cannot be assigned to genera or species (Powell 2003). A more promising report was made in Soto et al. (2012), which described a collection of bones catalogued as FC-DVP 1900 from the Guichón Formation of western Uruguay. These bones include 48 caudal centra and fragments of at least nine more; two caudal neural arches; part of a coracoid; a fragmentary ulna; fragments of metacarpals; the proximal end of a right fibula; the distal end of a left tibia; two right astragali; metatarsals; two pedal phalanxes; and five probable discoidal osteoderms. The presence of two right astragali shows that at least two individuals are included in the collection; most of the bones are consistent with an animal about 12 to 14 m long (40 to 46 ft), similar to the anatomically comparable Baurutitan britoi (although the lack of neural arches on the centra indicates a lack of skeletal maturity to me). Eggshells compatible with titanosaurs were also found at this site (Soto et al. 2012)."

So, what's new? We can start with the referred material, FC-DVP 1900 (Soto et al. 2024 opted for the safe side, selecting the only articulated elements for the holotype). FC-DVP 1900 now includes parts of 60 caudals, a partial coracoid, proximal and distal fragments of a left tibia, proximal right fibula, two right astragali, and six metatarsals (left I, III, IV, and V, and right I and II). The eggshells are also still there, but additional work on the "discoidal osteoderms" has reduced them to concretions (Soto et al. 2012). The reader is referred to Soto et al. (2012) for additional measurements. The dinosaur has also grown slightly to an estimated 15–16 m (49–52 m) long (Soto et al. 2024), which is described as small-sized, although I would submit that this might be about in the middle as far as titanosaur lengths go (especially if you go by median rather than mean).

Anatomically, U. celeste is not particularly unusual, based on the known material. The diagnosis has just a couple of autapomorphies or potential autapomorphies ("middle caudal centra cotyles and/or condyles with an hexagonal contour" and "marked oblique ridges on the anterior face of metatarsals I and II") among the unique combination of features. The first caudal is markedly biconvex, which puts U. celeste in a small subset of titanosaurs. The limb elements are not complete enough to give a good picture of the legs, but the metatarsals are robust. U. celeste can be safely excluded from the aeolosaurs because it lacks their caudal quirks; this means that there were at least two lineages of titanosaurs in Uruguay, as Aeolosaurus sp. has been reported recently (Soto et al. 2022). Instead, among the titanosaurs it tends more to the traditional saltasaurs, although its caudals are not as pneumatic (Soto et al. 2024).

References

Huene, F. von. 1931. Verschiedene mesozoische Wirbeltierreste aus Sudamerika. Neues Jahrbuch für Mineralogie, Geologie und Palaeontologie 66:181–198.

Powell, J. E. 2003. Revision of South American titanosaurid dinosaurs: palaeobiological, palaeobiogeographical, and phylogenetic aspects. Records of the Queen Victoria Museum 111.

Soto, M., D. Perea, and A. Cambiaso. 2012. First sauropod (Dinosauria: Saurischia) remains from the Guichón Formation, Late Cretaceous of Uruguay. Journal of South American Earth Sciences 33:68–79.

Soto, M., F. Montenegro, F. Mesa, and D. Perea. 2022. Sauropod (Dinosauria: Saurischia) remains from the Mercedes and Asencio formations (sensu Bossi, 1966), Upper Cretaceous of Uruguay. Cretaceous Research 131:105072. doi: https://doi.org/10.1016/j.cretres.2021.105072.

Soto, M., J. L. Carballido, M. C. Langer, J. C. G. Silva Junior, F. Montenegro, and D. Perea. 2024. Phylogenetic relationships of a new titanosaur (Dinosauria, Sauropoda) from the Upper Cretaceous of Uruguay. Cretaceous Research 105894. doi: https://doi.org/10.1016/j.cretres.2024.105894.