Your Friends The Titanosaurs, part 35.5: Arrudatitan and Dzharatitanis?

Here's a quick update on some breaking news, with a new genus for an existing species and a putative rebbachisaur potentially hopping over from Diplodocoidea.

Arrudatitan maximus

This series has now gone on long enough that a species from one of the earliest entries has been transferred to a new genus. What we first came to know as Aeolosaurus maximus, third species of Aeolosaurus, is now Arrudatitan maximus (Silva et al. 2021). Confusingly, or conveniently, it remains A. maximus, but if you're facing a situation where using just one letter might cause confusion, the usual way to solve the problem is to go to two letters: Ar. maximus instead of the old Ae. maximus. The type specimen and provenance have not changed since Santucci and Arruda-Campos (2011) named Ae. maximus. For reference (repeating from the original entry), this species is based on a partial associated skeleton collected in 1997 and 1998 by staff of the Museu de Paleontologia de Monte Alto, Brazil, mentioned as early as Santucci and Bertini (2001). The skeleton, MPMA 12-0001-97, includes two partial posterior cervicals, fragments of several dorsals, parts of nine caudals, seven partial cervical ribs, twelve partial dorsal ribs, eight chevrons, a fragmentary scapula and arm bones, the left and partial right femur, the left ischium, and fragments. This specimen was found in sandstone at the top of the Adamantina Formation 12 km (7.5 mi) southwest of Monte Alto in São Paulo State. Croc and theropod teeth were found with the titanosaur, but no tooth marks were observed (Santucci and Arruda-Campos 2011). Brusatte et al. (2017) estimated the type individual as on the order of 14 to 15 m long (46 to 49 ft), but it seems to have grown since then: Silva et al. (2021) suggested it was 19 to 22 m long (62 to 72 ft), which is a bit more "maximus". The complete femur measures 1.55 m (5.09 ft) long, but is slender for its size (Santucci and Arruda-Campos 2011). The new genus name honors the now-deceased Professor Antonio Celso de Arruda Campos (Silva et al. 2021), one of the two authors of the original description. Originally the name would have translated as something like "greatest Aeolosaurus", but it would now be more akin to "Antonio Celso de Arruda Campos's greatest titan".

Future Arrudatitan maximus caudals, from Figure 1 in Martinelli et al. (2011). Scale bar is 5 cm (2 in). (License apparently CC, but iteration not stated.) If the second and third in sequence were articulated more closely at the centrum, more of the droop apparent farther back would be visible.

"Aeolosaurus" maximus had never been entirely comfortable in Aeolosaurus. Martinelli et al. (2011) regarded the caudal vertebrae of the type specimen (then "MPMA/without number") as more like those of other Brazilian aeolosaurinids than Aeolosaurus, a distinction observed quantitatively in Filippi et al. (2013): "A." maximus plotted with the great unwashed masses of aeolosaurinids rather than A. rionegrinus and A. colhuehuapensis in some details of placement of vertebral features. Bandeira et al. (2016), in their description of Austroposeidon magnificus, found A. maximus to plot rather distantly from the other two Aeolosaurus species in their phylogenetic analysis, and therefore referred to it as "A." maximus throughout the paper. The same result came up in Silva et al. (2019) and Hechenleitner et al. (2020) (and, it goes without saying, in Silva et al. 2021).

Given it hasn't been that long since the 2018 post, you might think that there hasn't been a lot of other news on this species. However, last year a paper was published devoted to its tail (Vidal et al. 2020). The articulated tail segment as discovered had a significant droop, as if Ar. maximus never got the memo about how dinosaurs didn't let their tails drag. This is not simply taphonomy, either; the vertebrae quite comfortably articulate in a downward curve. (This is also reportedly the only case of sauropod protony, as opposed to the well-known phenomenon of opisthotony in dinosaur skeletons leaving the neck and tail arched over the back.) Regrettably, at this point we only have a few vertebrae from one individual to work with.

(This also seems like as good a place as any to mention that the rock unit that produced Baurutitan britoi, Trigonosaurus pricei, and Uberabatitan ribeiroi has been differentiated from the Marília Formation as the Serra da Galga Formation, described in Soares et al. 2021 and alluded to in Silva et al. 2021.)

Dzharatitanis kingi

At the end of February 2021, Averianov and Sues published a description of a new sauropod, Dzharatitanis kingi, the first rebbachisaurid from Asia. At the end of April, in one of the faster turnarounds in memory, Lerzo et al. (2021) published a re-evaluation of the type and only known specimen that found it to be a titanosaur.

But we haven't been properly introduced yet. D. kingi is based on a well-preserved and nearly complete anterior caudal, USNM 538127 (U.S. National Museum of Natural History, Washington, D.C.). This fossil was found in 1997 during an URBAC (Uzbek/Russian/British/American/Canadian; think "Urbacodon") expedition in Uzbekistan. It came from the Turonian-age Bissekty Formation of Dzharakuduk in Navoiy Region. The genus name refers to Dzharakuduk and the species name honors the late Dr. Christopher King, giving us something like "Christopher King's Dzharakuduk titan" (Averianov and Sues 2021). USNM 538127 is one of a number of sauropod fossils from Upper Cretaceous rocks of central Asia, many of which are described in some detail in Sues et al. (2015) and Averianov and Sues (2017). There are two minor issues with the material that have held back greater understanding: the great majority of the specimens are teeth, and so far there isn't much in the way of associated specimens. USNM 538127 was obliquely referred to a couple of times before being unveiled in Sues et al. (2015) (Sues and Averianov 2004; Wilson 2005; you're not missing a whole lot if you don't go check them out, as the presence of USNM 538127 is only made clear by following Sues et al. 2015 back).

USNM 538127 in posterior (A), right lateral (B), and anterior (C) views. Scale bar 10 cm (4 in). Figure 1 in Averianov and Sues (2021). CC0 1.0.

USNM 538127 is kind of an odd piece, actually. It's notably short anterior-posterior for a titanosaur caudal, and notably short vertically for a rebbachisaur caudal. The centrum is advertised as opisthocoelous, but it's very modest about it. Lerzo et al. (2021) ran the rescored specimen in two data sets, including that used by Averianov and Sues (2021), with further tweaking based on whether or not the caudal is the first caudal or farther back. In all cases, they found it more likely to be a somphospondylan than a rebbachisaurid, well within Titanosauria in their first data set. The Averianov and Sues result is not illustrated, but stated to be a somphospondylan titanosauriform. This and some other information make me feel a slight twinge about diving in with a titanosaurian identification, though. Sues et al. (2015) and Averianov and Sues (2017) noted similarities between USNM 538127 and Baotianmansaurus henanensis and Dongyangosaurus sinensis, currently existing not quite in and not quite out of Titanosauria (Mannion et al. 2019). I have a sneaking suspicion that D. kingi may be something similar.

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.

Averianov, A., and H.-D. Sues. 2021. First rebbachisaurid sauropod dinosaur from Asia. PloS ONE 16(2), e0246620. doi:10.1371/journal.pone.0246620.

Bandeira, K. L. N., F. Medeiros Simbras, E. Batista Machado, D. de Almeida Campos, G. R. Oliveira, and A. W. A. Kellner. 2016. A new giant Titanosauria (Dinosauria: Sauropoda) from the Late Cretaceous Bauru Group, Brazil. PLoS ONE 11(10):e0163373.

Brusatte, S. L., C. R. A. Candeiro, and F. M. Simbras. 2017. The last dinosaurs of Brazil: the Bauru Group and its implications for the end-Cretaceous mass extinction. Anais de Academia Brasileira de Ciências 89(3):1465–1485.

Filippi, L. S., A. G. Martinelli, and A. C. Garrido. 2013. Registro de un dinosaurio Aeolosaurini (Sauropoda, Titanosauria) en el Cretácico Superior (Formación Plottier) del norte de la provincia de Neuquén, Argentina, y comentarios sobre los Aeolosaurini Sudamericanos [Record of an Aeolosaurini dinosaur (Sauropoda, Titanosauria) in the Upper Cretaceous (Plottier Formation) of northern Neuquén Province, Argentina, and comments on the South American Aeolosaurini]. Revista Brasileira de Paleontologia 16(1):147–156.

Hechenleitner, E. M., L. Leuzinger, A. G. Martinelli, S. Rocher, L. E. Fiorelli, J. R. A. Taborda, and L. Salgado. 2020. Two Late Cretaceous sauropods reveal titanosaurian dispersal across South America. Communications Biology 3:article number 622. doi:10.1038/s42003-020-01338-w.

Lerzo, L. N., J. L. Carballido, and P. A. Gallina. 2021. Rebbachisaurid sauropods in Asia? A re-evaluation of the phylogenetic position of Dzharatitanis kingi from the Late Cretaceous of Uzbekistan. Publicación Electrónica de la Asociación Paleontológica Argentina 21(1):18–27. doi:10.5710//PEAPA.24.03.2021.389.

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.

Martinelli, A. G., D. Riff, and R. P. Lopes. 2011. Discussion about the occurrence of the genus Aeolosaurus Powell 1987 (Dinosauria, Titanosauria) in the Upper Cretaceous of Brazil. Gaea 7(1):34–40.

Santucci, R. M., and R. J. Bertini. 2001. Distribuição paleogeográfica e biocronológica dos titanossauros (Saurischia, Sauropoda) do Grupo Bauru, Cretáceo Superior do sudeste brasileiro. Revista Brasileira de Geociências 31(3):307–314.

Santucci, R. M., and A. C. de Arruda-Campos. 2011. A new sauropod (Macronaria, Titanosauria) from the Adamantina Formation, Bauru Group, Upper Cretaceous of Brazil and the phylogenetic relationships of Aeolosaurini. Zootaxa 3085:1–33.

Silva, J. C. G. Jr., T. S. Marinho, A. G. Martinelli, and M. C. Langer. 2019. Osteology and systematics of Uberabatitan ribeiroi (Dinosauria; Sauropoda): a Late Cretaceous titanosaur from Minas Gerais, Brazil. Zootaxa 4577(3):401–438. doi:10.11646/zootaxa.4577.3.1.

Silva, J. C. G. Jr., A. G. Martinelli, F. V. Iori, T. S. Marinho, E. M. Hechenleitner, and M. C. Langer. 2021. Reassessment of Aeolosaurus maximus, a titanosaur dinosaur from the Late Cretaceous of southeastern Brazil. Historical Biology advance online publication. doi:10.1080/08912963.2021.1920016.

Soares, M. V. T, G. Basilici, T. S. Marinho, A. G. Martinelli, A. Marconato, N. P. Mountney, L. Colombera, A. F. Mesquita, J. T. Vasquez, F. R. Abrantes Jr., and L. C. B. Ribeiro. 2021. Sedimentology of a distributive fluvial system: the Serra da Galga Formation, a new lithostratigraphic unit (Upper Cretaceous, Bauru Basin, Brazil). Geological Journal 56(2):951–975. doi:10.1002/gj.3987.

Sues, H.-D., and A. Averianov. 2004. 2004. Dinosaurs from the Upper Cretaceous (Turonian) of Dzharakuduk, Kyzylkum Desert, Uzbekistan. Journal of Vertebrate Paleontology 24(supplement to 3):119A–120A.

Sues, H.-D., A. Averianov, R. C. Ridgely, and L. M. Witmer. 2015. Titanosauria (Dinosauria, Sauropoda) from the Upper Cretaceous (Turonian) Bissekty Formation of Uzbekistan. Journal of Vertebrate Paleontology 35(1):e889145. doi:10.1080/02724634.2014.889145.

Vidal, L. D. S., P. V. L. G. da Costa Pereira, S. Tavares, S. L. Brusatte, L. P. Bergqvist, and C. R. dos Anjos Candeiro. 2020. Investigating the enigmatic Aeolosaurini clade: the caudal biomechanics of Aeolosaurus maximus (Aeolosaurini/Sauropoda) using the neutral pose method and the first case of protonic tail condition in Sauropoda. Historical Biology advance online publication. doi:10.1080/08912963.2020.1745791.

Wilson, J. A. 2005. Redescription of the Mongolian sauropod Nemegtosaurus mongoliensis Nowinski (Dinosauria: Saurischia) and comments on Late Cretaceous sauropod diversity. Journal of Systematic Palaeontology 3(3):283–318.