Dzharatitanis and implications for the biogeography of rebbachisaurids in the Northern Hemisphere

Rebbachisaurids are a clade of diplodocoids largely known from South America and Africa, with minor occurrences in western Europe and Croatia (Upchurch et al. 2004; Fernández-Baldor et al., 2011; Fanti et al. 2015; Wilson and Allian 2015; Taylor 2018). Recently, the temporal and geographical distribution of Rebbachisauridae was extended to the Late Jurassic of western North America when Carpenter (2018) reassigned the mega-sauropod Amphicoelias fragillimus Cope, 1878 to Rebbachisauridae and renamed it Maraapunisaurus. Now, however, Averianov and Sues (2021) have described a new rebbachisaurid from the Late Cretaceous (Turonian) Bissekty Formation of Uzbekistan, Dzharatitanis kingi, on the basis of an isolated anterior caudal vertebra. The description of Dzharatitanis renders this genus the first occurrence of a rebbachisaurid from Asia, considering that diplodocoids were basically unknown from the Asian landmass until the description of the dicraeosaurid Lingwulong by Xu et al. (2018), and rebbachisaurids are known only in Laurasia from western North America, Spain, England, and Croatia.

The holotype of Dzharatitanis kingi, USNM 538217, was originally placed as Titanosauria indeterminate by Sues et al. (2015) in their discussion of titanosaur material collected from the Bissekty Formation of Uzbekistan. Subsequently, Averianov and Sues (2017) noted that USNM 538217 was most similar to the anterior caudals of Baotianmansaurus henanensis is being anteroposteriorly short but differed in being taller. They cautioned that the neural arch of the only known anterior caudal in Baotianmansaurus is incomplete, making it unclear if it had additional fossae like those present in Dongyangosaurus and USNM 538217. The decision taken by Averianov and Sues (2021) to reclassify USNM 538217 as a new taxon of rebbachisaurid thus raises a number of questions as to why it was originally classified in Titanosauria before being removed from this clade: how does Dzharatitanis differ from macronarian sauropods if it was initially interpreted as being similar to Baotianmansaurus?

In their description of USNM 538217, Sues et al. (2015) noted that this specimen possesses a transverse process (caudal rib) rising from both the centrum and the neural arch just above the mid-height of the centrum, and that it is triangular and its dorsal margin extends ventrolaterally, unlike flagellicaudatans and some rebbachisaurids. and that the neural spine of the Dzharatitanis kingi holotype has a large pneumatic cavity with a complex, internal structure comprising variously sized chambers as in the lognkosaurian titanosaur Futalognkosaurus. A prominent, deep postzygapophyseal spinodiapophyseal fossa in USNM 538217 was described as being similar to that of Dongyangosaurus in possessing four foramina on the left and three openings on the right side, with two of the foramina being situated at the base of the fossa just dorsal to the postzygodiapophyseal lamina. The paper by Averianov and Sues (2021) lists several characters to distinguish Dzharatitanis from titanosauriforms and support a referral to Diplodocoidea and specifically to Rebbachisauridae: (1) slightly convex or flat anterior articular surface of the first caudal centrum; (2) absence of the hyposphenal ridge; (3) absence of pleurocoels; (4) triangular lateral process on neural spine; and (5) composite lamina on the dorsal part of the lateral surface of the neural spine formed by the fusion of the SPRL and SPOL. It is highly probable that the authors took note of the varying presence or absence of pleurocoels on the first caudal vertebrae among rebbachisaurids and the presence of pleurocoels in many titanosauriforms to express second thoughts about USNM 538217 belonging to Titanosauria, because they identify the holotype as having slight opisthocoely and lacking chevron facets, which they note as being present among rebbachisaurids. The presence of opisthocoely in non-titanosauriform neosauropods is noteworthy because anterior caudal vertebrae with procoely have been documented for both titanosaurs and non-titanosaur sauropods (Wilson and Upchurch 2003).

When placing the age and location of Dzharatitanis into a broader contextual pattern of rebbachisaurid biogeography, it is important to note that almost all other rebbachisaurid taxa except Demandasaurus, Maraapunisaurus, and Xenoposeidon are present in Gondwana only, and that Katepensaurus is about the same geologic age as Dzharatitanis, hailing from the Cenomanian-Turonian Bajo Barreal Formation of Chubut Province, Argentina. All Early Cretaceous rebbachisaurids from Europe are of Valanginian to early Aptian age, and no rebbachisaurid has yet been reported from the Berriasian to Cenomanian of East Asia. Since Dzharatitanis is younger than other Cretaceous rebbachisaurids found in Laurasia, it is possible that a number of rebbachisaurids entered central Asia from Europe, or that Dzharatitanis was descended from an as-yet-undiscovered Early Cretaceous rebbachisaurid from East Asia, because a land connection existed between Europe and Asia during the Berriasian-Cenomanian (Baraboshkin et al. 2003) and the record of Laurasian rebbachisaurids is very scanty.

Update: A new paper by Lerzo et al. (2021) questions the rebbachisaurid placement of Dzharatitanis and instead re-assigns this genus to the titanosaur clade Lognkosauria based on comparisons with the caudal vertebrae of derived titanosaurs, including members of Colossosauria. In tandem with the recent paper by Averianov et al. (2021) classifying the genera Normanniasaurus and Volgatitan in the clade containing members of Colossosauria, the formal reclassification of  Dzharatitanis as a titanosaur sheds new light on the early biogeography of Colossosauria, given that this clade was long restricted to Gondwana.  

References:

Averianov, A.O., and Sues, H-D., 2017. Review of Cretaceous sauropod dinosaurs from Central Asia. Cretaceous Research 69:184–97.

Averianov, A., and Sues, H-D., 2021. First rebbachisaurid sauropod dinosaur from Asia. PLoS ONE 16(2): e0246620. 

Averianov, A. O., Sizov, A. V., and Skutschas, P. P., 2021. Gondwanan affinities of Tengrisaurus, Early Cretaceous titanosaur from Transbaikalia, Russia (Dinosauria, Sauropoda). Cretaceous Research 122: 104731. doi:10.1016/j.cretres.2020.104731.

Baraboshkin, E.Y., Alekseev, A.S., and Kopaevich, L.F., 2003. Cretaceous palaeogeography of the North-Eastern Peri-Tethys. Palaeogeography, Palaeoclimatology, Palaeoecology 196(1–2):177–208.

Carpenter, K., 2018. Maraapunisaurus fragillimus, N.G. (formerly Amphicoelias fragillimus), a basal Rebbachisaurid from the Morrison Formation (Upper Jurassic) of Colorado. Geology of the Intermountain West. 5: 227–244. doi:10.31711/giw.v5i0.28.

Fanti, F., Cau, A., Cantelli, L., Hassine, M., and Auditore, M., 2015. New Information on Tataouinea hannibalis from the Early Cretaceous of Tunisia and Implications for the Tempo and Mode of Rebbachisaurid Sauropod Evolution. PLoS ONE 10(4): e0123475. 

Lerzo, N.L., Carballido, J.L., and Gallina, P.A., 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

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

Taylor, M.P., 2018. Xenoposeidon is the earliest known rebbachisaurid sauropod dinosaur. PeerJ 6:e5212 https://doi.org/10.7717/peerj.5212

Torcida Fernández−Baldor, F., Canudo, J.I., Huerta, P., Montero, D., Pereda Suberbiola, X., and Salgado, L. 2011. Demandasaurus darwini, a new rebbachisaurid sauropod from the Early Cretaceous of the Iberian Peninsula. Acta Palaeontologica Polonica 56 (3): 535–552.

Upchurch, P., Barrett, P.M. and Dodson, P. 2004. Sauropoda. pp. 259-322. In: The Dinosauria, 2nd edition. Weishampel, Dodson, and Osmólska (eds.). University of California Press, Berkeley.

Wilson, J.A. and Upchurch, P., 2003. A revision of Titanosaurus Lydekker (Dinosauria – Sauropoda), the first dinosaur genus with a “Gondwanan” distribution. Journal of Systematic Palaeontology 1(3): 125-160.

Wilson, J.A., Allain, R., 2015. Osteology of Rebbachisaurus garasbae Lavocat, 1954, a diplodocoid (Dinosauria, Sauropoda) from the early Late Cretaceous–aged Kem Kem beds of southeastern Morocco. Journal of Vertebrate Paleontology 35(4):e1000701.

Xu, X., Upchurch, P., Mannion, P. D., Barrett, P. M., Regalado-Fernandez, O.R., Mo, J., Ma, J. and Liu, H., 2018. A new Middle Jurassic diplodocoid suggests an earlier dispersal and diversification of sauropod dinosaurs. Nature Communications 9, 2700. doi:10.1038/s41467-018-05128-1

anterior caudal in Baotianmansaurus henanensis is poorly preserved

and thus it is unclear if it had additional fossae like those pres

Reflections on the Whitlock and Wilson Mantilla (2020) paper on Smitanosaurus

Whitlock and Wilson Mantilla (2020) recently published a redescription of the diplodocoid sauropod "Morosaurus" agilis Marsh, 1889, erecting the new genus Smitanosaurus for it and assigning it to the family Dicraeosauridae based on comparisons with other flagellicaudatan diplodocoids from the Morrison Formation and phylogenetic analysis. The holotype of Smitanosaurus agilis, USNM 5384, was originally considered referable to Diplodocus longus by Othniel Charles Marsh judging from archival records, but was later described as a new species of the genus Morosaurus by Marsh (1889). Later, Gilmore (1907) believed it to be allied with either Brachiosauridae or Haplocanthosaurus; Osborn and Mook (1919, 1921) formally synonymized Morosaurus with Camarasaurus, and Gilmore (1925:352) clearly stated that M. agilis was not congeneric with other Camarasaurus species. McIntosh (1990) followed the suggestion by Gilmore (1907) that "M." agilis could be either a brachiosaurid or Haplocanthosaurus. Subsequently, an abstract by Tidwell et al. (2005) concluding that "Morosaurus" agilis represented a Diplodocus specimen as initially proposed by Marsh, and that it was a junior synonym of Diplodocus longus based on comparisons with skulls of diplodocid taxa from the Morrison Formation, including skulls referred to Diplodocus (AMNH 969, CM 3452, CM 11161, USNM 2672, USNM 2673). However, AMNH 969 and USNM 2673 were referred to Galeamopus hayi and G. pabsti respectively by Tschopp et al. (2015) and Tschopp & Mateus (2017), raising doubts about whether or not "Morosaurus" agilis is synonymous with Diplodocus. Suuwassea has been assigned to Dicraeosauridae by Whitlock (2011), but the placement of Smitanosaurus as a dicraeosaurid by Whitlock and Wilson Mantilla reveals a hitherto hidden diversity of dicraeosauids from the Morrison. The genus name Smitanosaurus is quite tongue-twisting, for it pays homage to not only J. August Smith, the discoverer of the holotype of S. agilis (USNM 5384), but also the Smithsonian Institution in which USNM 5384 was reposited.

Photograph and lateral view drawing of the holotype of Smitanosaurus agilis (after Gilmore 1907)

One anatomical aspect of Smitanosaurus agilis noted by Whitlock and Wilson Mantilla that deserves  attention is the presence of a postparietal foramen on the skull roof. Woodruff et al. (2017) considered the presence or absence of this feature in diplodocoids to be a influenced by ontogeny, with juvenile specimens possessing the postparietal foramen and adults lacking it. However, as Whitlock and Wilson Mantilla point out, the diplodocine specimen CM 3452 as well as CM 11255 (probably Barosaurus; Melstrom et al. 2016) lack a postparietal foramen despite being juvenile, while the adult apatosaurine specimen BYU 17096 has this feature, as does juvenile specimen SMM.P.84.15.3. Therefore, the presence or absence of a postparietal foramen is a non-ontogenetic trait among Morrison diplodocoid specimens. As detailed in a previous post, I did not rule out the possibility that the dicraeosaurid taxon Suuwassea could be a distinct taxon from other Morrison diplodocoids despite its holotype being a juvenile (Woodruff and Fowler 2012) because a postparietal foramen is absence in the diplodocine skull CM 11255 in spite of the juvenile nature of that specimen. The presence of a postparietal foramen in the Smitanosaurus agilis holotype and recovery of Suuwassea as derived within Dicraeosauridae by Whitlock and Wilson Mantilla (2020) confirms that despite being a juvenile, the holotype of Suuwassea emilieae (ANS 21122) is a distinct taxon in its own right rather than a Diplodocus juvenile as proposed by Woodruff and Fowler (2012). 

Cladistic analysis of Smitanosaurus from Whitlock and Wilson Mantilla (2020). Although not a diplodocid as concluded by Tidwell et al. (2005), the diplodocoid placement of Smitanosaurus as hinted as by Tidwell et al. is vindicated by the above cladogram. 

The recovery of Kaatedocus as a dicraeosaurid rather than a diplodocine diplodocid is quite surprising. This genus has been recovered as either closer to Barosaurus than to other diplodocines (Tschopp et al., 2015) or a basal diplodocine (Tschopp and Mateus 2017). Characters cited by Tschopp et al. (2015) as placing Kaatedocus in Diplodocinae include: (1) broad maxilla-quadratojugal contact (2) antorbital fenestra with concave dorsal margin; (3) ‘hooked’ prefrontal; (4) mandible without strong coronoid eminence; (5) direct crown–crown occlusion absent; (6) ‘box-like basal tubera;’ (7) 14–15 cervical vertebrae; and (8) posterior cervical neural spines with elongate lateral spine cavities. The first four of these characters are dismissed by Whitlock and Wilson Mantilla due to either the state of preservation in the holotype of Kaatedocus siberi (SMA 0004) or the fact that SMA 0004 does not preserve enough vertebrae. The concave dorsal margin of the antorbital fenestra is noted as present in the rebbachisaurid Nigersaurus, the ‘box-like’ basal tubera character is omitted by the authors from the cladistic analysis of Smitanosaurus "because the codified states conflate too many distinct morphologies in the current taxonomic scope", while a ‘hooked’ prefrontal is noted as absent in Kaatedocus and the presence of elongate cavities on the posterior cervical neural spines is inconsistently present among diplodocoid taxa. Whitlock and Wilson Mantilla (2020) assign Kaatedocus to Dicraeosauridae based on several characters, namely the presence of a postparietal foramen, an expanded crista prootica, a shelf overhanging the opening for cranial nerve V, and a flat medial margin of the prefrontal. The authors' assertion about the absence of dorsal vertebrae in the Kaatedocus siberi holotype that could provide a definite cervical/dorsal vertebral count is borne out by the fact that Apatosaurus louisae is the only apatosaurine diplocid for which 15 cervicals are preserved, while Diplodocus carnegii and Galeamopus pabsti are the only diplodocines known from specimens that preserve a complete cervical vertebral series (Tschopp et al. 2015). Moreover, given assignment of Suuwassea to Dicraeosauridae by Whitlock (2011), it is not hard to imagine four dicraeosaurid taxa in the Morrison Formation (Kaatedocus, Smitanosaurus, Suuwassea and MOR 592) because the Puesto Antigual Member of the La Amarga Formation has yielded two dicraeosaurids, Amargasaurus and Amargatitanis.

In retrospect, Othniel Charles Marsh was initially right in the first place about Smitanosaurus being a diplodocoid before changing his mind about the classification of USNM 5384, and although Tidwell et al. (2005) agree that USNM 5384 is a diplodocoid, doubts about their referral of Smitanosaurus agilis to Diplodocus longus due to the re-assignment of some putative skulls of D. longus to Galeamopus and the discovery of dicraeosaurid characters in USNM 5384 make clear that the diversity of Morrison non-diplodocid flagellicaudatans is greater than previously thought and that some traditional diplodocine synapomorphies are also present in some dicraeosaurids. 

References:

Gilmore, C.W., 1907. The type of the Jurassic reptile Morosaurus agilis redescribed, with a note on Camptosaurus. Proceedings of the United States National Museum 32: 151–165.

Gilmore, C.W., 1925.  A nearly complete articulated skeleton of Camarasaurus, a saurischian dinosaur from the Dinosaur National Monument, Utah. Memoirs of the Carnegie Museum 10:347-384.

Marsh, O.C., 1889. Notice of new American Dinosauria. The American Journal of Science and Arts, series 3 38:331-336.

McIntosh, J.S., 1990. Sauropoda. pp. 345-401. In: Weishampel DB, Dodson P, Osmólska H, eds. The Dinosauria. Berkeley: University of California Press.

Melstrom, K.M., D’Emic, M.D., Chure, D.J., and Wilson, J.A., 2016. A juvenile sauropod dinosaur from the Late Jurassic of Utah, USA, presents further evidence of an avian style air-sac system. Journal of Vertebrate Paleontology e1111898.

Osborn, H. F., and Mook, C. C., 1919. Characters and Restoration of the sauropod genus Camarasaurus Cope from type material in the Cope Collection in the American Museum of Natural History. Proceedings of the American Philosophical Society 58 (6): 386-396.

Osborn, H. F., and Mook, C. C., 1921. Camarasaurus, Amphicoelias, and other sauropods of Cope. Memoirs of the American Museum of Natural History, New Series 3 (3): 247-387.

Tidwell, V., K. Carpenter, and C. Miles. 2005. A reexamination of Morosaurus agilis (Sauropoda) from Garden Park, Colorado. Journal of Vertebrate Paleontology 25 (supplement to 3):122A.

Tschopp, E., Mateus, O., and Benson, R.B.J., 2015. A specimen-level phylogenetic analysis and taxonomic revision of Diplodocidae (Dinosauria, Sauropoda) PeerJ 3:e857 https://doi.org/10.7717/peerj.857 

Tschopp, E., and Mateus, O., 2017. Osteology of Galeamopus pabsti sp. nov. (Sauropoda: Diplodocidae), with implications for neurocentral closure timing, and the cervico-dorsal transition in diplodocids. PeerJ 5:e3179 https://doi.org/10.7717/peerj.3179

Whitlock, J. A. 2011. A phylogenetic analysis of Diplodocoidea (Saurischia: Sauropoda). Zoological Journal of the Linnean Society 161: 872–915.

Whitlock, C., and Wilson Mantilla, J., 2020. The Late Jurassic sauropod dinosaur  'Morosaurus’  agilis  Marsh, 1889 reexamined and reinterpreted as a dicraeosaurid. Journal of Vertebrate Paleontology  DOI: 10.1080/02724634.2020.1780600

Woodruff, C. & Fowler, D. W. 2012. Ontogenetic influence on neural spine bifurcation in Diplodocoidea (Dinosauria: Sauropoda): A critical phylogenetic character. Journal of Morphology 273: 754–764. 

 

Woodruff, D. C., Fowler, D. W. and Horner, J. R., 2017. A new multi-faceted framework for deciphering diplodocid ontogeny. Palaeontologia Electronica 20.3.43A: 1–53.

Takeaways from the Averianov and Lopatin (2020) paper on Abdarainurus barsboldi

In a new paper, Averianov and Lopatin (2020) describe a new sauropod, Abdarainurus barsboldi, for a series of caudal vertebrae (including one middle caudal) from the Alagteeg Formation of Abdrant Nuru in the northern Gobi Desert, Mongolia. Titanosauriforms have been recorded from the Late Cretaceous of Mongolia, including the lithostrotian titanosaurs Nemegtosaurus, Opisthocoelicauda, and Quaesitosaurus as well as the euhelopodid somphospondylan Erketu. However, Averianov and Lopatin note that the holotype of   Abdarainurus barsboldi (PIN 5669/1) is quite distinct from other Mongolian titanosaurs in having opisthocoely present in the anterior and middle caudals, longitudinal ridges on the neural canal walls, postprezygapophyseal processes, a hypertrophied postspinal fossa, mediolaterally constricted neural spines, and a deep pocket-like spinodiapophyseal fossa covered laterally by high postzygodiapophyseal lamina. Bearing in mind comparisons of the Abdarainurus caudal vertebrae with those of other Asian titanosaurs, Averianov and Lopatin (2020) conduct a cladistic analysis that places Abdarainurus as a basal titanosaur in a clade with the basal titanosaurs Andesaurus and the somphospondylan Huabeisaurus (the latter recovered as a non-titanosaur somphospondylan by Mannion et al. 2019). Based on the results of the cladistic analysis as well as comparative anatomy, Averianov and Lopatin conclude that Abdarainurus could belong to an unknown clade of basal titanosaurs.

In comparing Abdarainurus with titanosaurs and derived non-titanosaur somphospondylans, Averianov and Lopatin note that the holotype is similar to the lithostrotian titanosaur Normanniasaurus in having the dorsoventral curvature of the transverse processes and the presence of a large spinodiapophyseal fossa at the base of the neural spine perforating the spine (the latter character listed as autapomorphic for Normanniasaurus by Le Loeuff et al. 2013), but differs in lacking strongly procoelous anterior caudal vertebrae. The authors then compare Abdarainurus to the taxon Sonidosaurus from the Iren Dabasu Formation of Inner Mongolia, China, and find the two forms similar to each other in having opisthocoelous centra, possibly widely separated postzygapophyses, and ridges on the proximal ramus of the anterior chevrons. Averianov and Lopatin (2020) acknowledge that Opisthocoelicauda and Borealosaurus both possess opisthocoely in the anterior and middle caudals respectively, but they note that opisthocoely is restricted to the anterior caudals in Opisthocoelicauda and that the middle caudals of Borealosaurus have more pronounced opisthocoely, a greatly convex ventral centrum margin in lateral view, shorter prezygapophyses, and an anteroposteriorly longer neural spine. 

Although Averianov and Lopatin (2020) assert that the phylogenetic position of Sonidosaurus is unclear despite the genus being similar to Abdarainurus in its opisthocoelus centra and other caudal features, they overlook the fact that Sonidosaurus is recovered as a titanosaur more derived than Andesaurus but outside Lithostrotia (which includes Opisthocoelicauda) by Ksepka and Norell (2010; figure 4). When recovering Abdarainurus as a basal titanosaur in a clade with Andesaurus and Huabeisaurus, the authors state that this result could be attributable to the dearth of existing knowledge about the early evolution of titanosaurs in general. This conclusion appears to hold water in several respects, in terms of morphology. For instance, postzygodiapophyseal lamina on the anterior caudal vertebrae remain unknown for Andesaurus because most of the anterior caudal vertebrae for this taxon are incomplete, so more complete material of Andesaurus would be essential to determine of the anterior caudals of Andesaurus had postzygodiapophyseal lamina. Additionally, the recovery of Huabeisaurus by Mannion et al. (2019) of Huabeisaurus as a somphospondylan closer to Titanosauria than to Euhelopodidae (contra D'Emic et al. 2013, who considered it a probable euhelopodid) raises the possibility that the characters cited by Averianov and Lopatin as supporting a clade formed by Abdarainurus, Andesaurus, and Huabeisaurus could end up being reflective of convergent evolution in more than one high-ranking somphospondylan clade, considering that Abdarainurus and Huabeisaurus are much younger than Andesaurus. The Hauterivan age of the titanosaur genus Volgatitan also reinforces the possibility that future study could find Abdarainurus to be distantly related to Andesaurus within Titanosauria, as Volgatitan is closely related to the colossosaurian clade Lognkosauria (Averianov and Efimov 2018).

Judging from the available morphological evidence, but also greater similarities to the titanosaur Sonidosaurus, it could be parsimonous to conclude that instead of belonging to an unknown high-ranking somphospondylan clade, Abdarainurus could belong to an unnamed clade of basal Asian titanosaurs outside Lithostrotia along with Baotianmansaurus, Dongyangosaurus, Sonidosaurus, and an unnamed titanosaur from the Bissekty Formation of Uzbekistan, as suggested by Averianov and Sues (2017). Although Abdarainurus is indeed unusual in the tail morphology, the lack of substantial material in the holotype leaves open the possibility that this genus could be closer to Lithostrotia (like Sonidosaurus) than to Andesaurus. 

Note: The cladistic analysis of Hamititan and Siluotitan by Wang et al. (2021) demonstrates that Abdarainurus and Huabeisaurus are sister taxa to the basalmost titanosaur Andesaurus, while Dongyangosaurus and Jiangshanosaurus (both about the same age as Andesaurus) are recovered as basal titanosaurs more primitive than Diamantinasauria and Lithostrotia. Therefore, the Wang et al. paper has made me revise my earlier take on the conclusions by Averianov and Lopatin (2020) regarding the phylogenetic placement of Abdarainurus within Titanosauria by suggesting that at least some very primitive titanosaurs with slightly procoelous anterior caudal vertebrae survived into the Campanian-Maastrichtian due to the older age of Andesaurus and the earliest Cretaceous basal titanosaur Ninjatitan (Gallina et al. 2021). Moreover, the Early Cretaceous age of Hamititan makes clear than titanosaurs with strongly procoelous anterior caudals diverged from basal titanosaurs with slightly procoelous anterior caudals in the early Cretaceous, so future study could confirm that some Late Cretaceous titanosaurs from Asia with slightly procoely in the anterior caudals are closely related to Andesaurus or Ninjatitan.     

References:

Averianov, A.O., and Efimov, V., 2018. The oldest titanosaurian sauropod of the Northern Hemisphere. Biological Communications 63 (6): 145–162. DOI: 10.21638/spbu03.2018.301

Averianov, A.O., and Lopatin, A.V., 2020. An unusual new sauropod dinosaur from the Late Cretaceous of Mongolia. Journal of Systematic Palaeontology. DOI: 10.1080/14772019.2020.1716402

Averianov, A., and Sues, H.-D., 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., Mannion, P. D., Upchurch, P., Benson, R. B. J., Pang, Q. & Cheng, Z. 2013. Osteology of Huabeisaurus allocotus (Sauropoda: Titanosauriformes) from the Upper Cretaceous of China. PLoS ONE 8: e69375. doi:10.1371/journal.pone.0069375

Gallina, P. A., J. I. Canale, and J. L. Carballido, 2021. The earliest known titanosaur sauropod dinosaur. Ameghiniana 58(1):35–51. doi:10.5710/AMGH.20.08.2020.3376.

Ksepka, D. T. & Norell, M. A. 2010. The illusory evidence for Asian Brachiosauridae: new material of Erketu ellisoni and a phylogenetic reappraisal of basal Titanosauriformes. American Museum Novitates 3700: 1–27. doi:10.1206/3700.2

Le Loeuff, J., Suteethorn, S. & Buffetaut, E. 2013. A new sauropod dinosaur from the Albian of Le Havre (Normandy, France). Oryctos 10: 23–30.

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

Wang, X., K. L. N. Bandeira, R. Qiu, S. Jiang, X. Cheng, Y. Ma, and A. W. A. Kellner. 2021. The first dinosaurs from the Early Cretaceous Hami Pterosaur Fauna, China. Scientific Reports 11:14962. doi:10.1038/s41598-021-94273-7.