Your Friends The Titanosaurs, part 21.5: Abdarainurus barsboldi

Abdarainurus barsboldi marks the first non-theropod dinosaur described in 2020. More importantly, it also represents an apparent titanosaur from part of the alphabet I've already covered, so I'm looping back to catch it, following the Baalsaurus mansillai precedent. It actually fits in well with last week's discussion of Opisthocoelicaudia skarzynskii, being another Mongolian sauropod with unusual caudal vertebrae, although in this case caudals (and some chevrons) are all that's there.

Genus and Species: Abdarainurus barsboldi. The genus name is a combination of the Russian spelling (Abdarain Nuru) of the type locality (Abdrant Nuru) plus the Greek for "tail" (Averianov and Lopatin 2020), while the species name is probably obvious if you've been at this for a few years. If not, "barsboldi" is a reference to the famous Mongolian paleontologist Rinchen Barsbold (Averianov and Lopatin 2020). The combination gives us something like "Barsbold's Abdrant Nuru tail".
Citation: Averianov, A. O., and A. V. Lopatin. 2020. An unusual new sauropod dinosaur from the Late Cretaceous of Mongolia. Journal of Systematic Palaeontology (advance online publication). doi:10.1080/14772019.2020.1716402.
Stratigraphy and Geography: As mentioned, the type locality is Abdrant Nuru, which is in Ömnögovǐ Province in south-central Mongolia. It is within the Ulan-Nuur Depression in the northern Gobi Desert. A fair number of reptile bones, footprints, and eggs and nests are also known from Abdrant Nuru. Stratigraphically, the specimen came from the Alagteeg Formation; a strat column indicates it came from the base of the formation at Abdrant Nuru. The age of the formation is not certain, but the overlying Djadokhta Formation and the presence of Pinacosaurus sp. indicate a Late Cretaceous age. The Alagteeg Formation is interpreted as representing a more humid setting than the more famous Djadohkta, with fluvial deposition dominant instead of eolian (wind-blown) deposition (Averianov and Lopatin 2020). A. barsboldi is the first dinosaur described to the species level from the Alagteeg Formation.
Holotype: The type and only known specimen of A. barsboldi is PIN 5669/1 (Borissiak Paleontological Institute, Russian Academy of Sciences, Moscow). It is composed of eight anterior caudal vertebrae, one middle caudal, and parts of seven chevrons (two fused to caudals and five free). The anterior caudals form a consecutive series, but do not begin with the very first caudal after the pelvis. At least one caudal (maybe more) is missing between the last anterior caudal and the first middle caudal (Averianov and Lopatin 2020).

See Dalanzadgad by itself with the open circle in the lower center? Start heading northwest; you'll run into Abdrant Nuru just before leaving the province. The Altan Ula IV and Nemegt localities from recent posts are due west of Dalanzadgad. Figure 1 from Tsogtbaatar et al. (2019). CC-BY-4.0.

A. barsboldi is another example of a taxon named from fossils collected many years before. In this case, the type material was collected during the 1970 field season of the Joint Soviet–Mongolian Geological Expedition. Later joint Japanese–Mongolian expeditions collected other fossils from the site, which have been described in several papers, but PIN 5669/1 itself had escaped press until now (Averianov and Lopatin 2020). The type individual was probably similar in size to or slightly smaller than the type specimen of Opisthocoelicaudia skarzynskii, based on comparing the measurements of the caudals provided by Averianov and Lopatin (2020) with those provided by Borsuk-Białynicka (1977). If you're curious, PIN 5669/1's caudals are similar in height but not as wide. The neural arches are fused to the centra, and as with O. skarzynskii some of the chevrons are fused to the caudals, so PIN 5669/1 was not simply half-grown. Unlike most other titanosauriforms, the neural arches of the anterior caudals are centered on the centra instead of being cheated to the anterior margin; the middle caudal is more typical, though.

Yes, both A. barsboldi and Opisthocoelicaudia skarzynskii have opisthocoelous caudals (the kind with the ball in front and socket in back). No, that doesn't mean they're closely related. In fact, none of the phylogenetic analyses reported by Averianov and Lopatin (2020) got them even particularly close, even though A. barsboldi jumped around. It found itself outside of Titanosauria, in a massive polytomy at the base of Titanosauria, in a small clade with Andesaurus delgadoi and Huabeisaurus allocotus, and an aeolosaur. This is all a long way of saying A. barsboldi is distinct and has something to do with Somphospondyli, but we could really use a little more material to help pin it down. Averianov and Lopatin (2020) decided that the "basal titanosaur with Andesaurus and Huabeisaurus" was the most plausible of the results, based on the number and type of shared characteristics. They also noticed some similarities with Normanniasaurus and the obscure Sonidosaurus (of comparable geology and potentially age as well), but discounted the former. (Could we be dealing with... [yet another] an endemic radiation of East Asian sauropods?)

References

Averianov, A. O., and A. V. Lopatin. 2020. An unusual new sauropod dinosaur from the Late Cretaceous of Mongolia. Journal of Systematic Palaeontology (advance online publication). doi:10.1080/14772019.2020.1716402.

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.

Tsogtbaatar, K., D. B. Weishampel, D. C. Evans, and M. Watabe 2019. A new hadrosauroid (Dinosauria: Ornithopoda) from the Late Cretaceous Baynshire Formation of the Gobi Desert (Mongolia). PLoS ONE 14 (4):e0208480. doi:10.1371/journal.pone.0208480.