Scientists have re-examined fossil bones associated with the Chinese mamenchisaurid dinosaur Hudiesaurus sinojapanorum and propose that the robust limb bone associated with this sauropod represents an entirely different genus which they have named Rhomaleopakhus turpanensis.

The forelimb bones are exceptionally stout and strong, particularly the ulna. These fossils represent a giant sauropod. The researchers, who include Professor Paul Barrett of the London Natural History Museum, speculate that strong forelimbs could have helped this dinosaur to “push off” from the ground so that it could rear up onto its back legs to feed. Strong forelimbs would also have helped to resist the deceleration forces as the huge dinosaur lowered itself back onto all fours.

The robust right forelimb of Rhomaleopakhus turpanensis (specimen number IVPP V11121-1) showing the bones in approximate anatomical position (anterior view). The bones had been ascribed to Hudiesaurus sinojapanorum although they were not found at the same location as vertebrate that led to the erection of the Hudiesaurus genus. The forelimb bones demonstrate several autapomorphies that led the research team to propose a new genus R. turpanensis. Picture credit: Upchurch et al.

Picture credit: Upchurch et al.

Note – the scale bar in the picture (above) equals 20 cm. Although, only described from bones from the right forelimb, it is estimated that Rhomaleopakhus (pronounced Row-ma-lee-oh-pack-hus) could have been between 25 and 30 metres long.

Core Mamenchisaurus-like Taxa

In 1993, a joint Chinese/Japanese field team uncovered sauropod fossil material from the Jurassic-aged Kalazha Formation within Shanshan County in the Xinjiang Autonomous Region of north-western China. The fossils consisted of a single, huge vertebra, four teeth and a nearly complete right forelimb. On the basis of these fossils, a new member of the Mamenchisauridae family of long-necked dinosaurs was erected in 1997 – Hudiesaurus sinojapanorum. This dinosaur’s name translates as Chinese/Japanese butterfly lizard, in recognition of the co-operation between China and Japan in field excavations and because the vertebra had a flat butterfly-shaped process on the front base of the vertebral spine.

Posterior cervical vertebra of Hudiesaurus sinojapanorum (IVPP V11120; holotype). A, right lateral view; B, left lateral view; C, anterior view; D, posterior view. Scale bar = 10 cm. Picture credit: Upchurch et al

Picture credit: Upchurch et al

Having reassessed the fossil material ascribed to Hudiesaurus the scientists, writing in the “Journal of Vertebrate Palaeontology”, suggest that the bone from the spine, with its unique anatomical characteristics should remain the holotype material for H. sinojapanorum, but the forelimb which was found 1.1 kilometres from the vertebra and the teeth should not be assigned to Hudiesaurus. Indeed, the researchers propose that the robust forelimb with its own unique anatomical characteristics represents a new taxon. The teeth are too poorly preserved and can only be assigned to “core Mamenchisaurus-like taxa”.

Closely Related Mamenchisaurids

The researchers from the Chinese Academy of Sciences, University College London as well as the London Natural History Museum undertook a phylogenetic assessment of the Hudiesaurus and the newly assigned Rhomaleopakhus fossil material. The analysis indicates that Hudiesaurus is closely related to the “core Mamenchisaurus-like taxon” Xinjiangtitan, although differences between them indicate that they should remain separate genera for the time being. The four, poorly preserved teeth cannot be identified with any certainty, but they too probably represent a mamenchisaurid. Rhomaleopakhus too is very likely a member of the Mamenchisauridae family, albeit closely related to Chuanjiesaurus and Analong from the Middle Jurassic and found in Yunnan Province (south-western China).

A view of the giant PNSO Er-ma the Mamenchisaurus dinosaur model.  A typical mamenchisaurid sauropod, with a very long neck. Mamenchisaurids have many more cervical vertebrae (18+) when compared to most other sauropods. The evolution of an exceptionally long neck could have occurred as a way to exploit other food resources or perhaps through sexual selection.

View the extensive PNSO prehistoric animal model range: PNSO Dinosaur Figures.

The scientific paper: “Re-assessment of the Late Jurassic eusauropod dinosaur Hudiesaurus sinojapanorum Dong, 1997, from the Turpan Basin, China, and the evolution of hyper-robust antebrachia in sauropods” by Paul Upchurch, Philip D. Mannion, Xing Xu and Paul M. Barrett published in the Journal of Vertebrate Palaeontology.

The Everything Dinosaur website: Dinosaur Toys.

This year (2021), has been another bumper year for dinosaur discoveries with over forty new species of dinosaur described, including several from the British Isles such as Pendraig (P. milnerae) from Wales and four new dinosaurs described from fossil finds on the Isle of Wight (Brighstoneus, Ceratosuchops, Riparovenator and Vectiraptor).

New genera are erected based on new fossil discoveries. In addition, a new dinosaur genus or species can be established based on a revision of existing and previously studied fossil material. A new genus of Late Cretaceous, Brazilian titanosaur was announced this year, based on fragmentary remains that had previously been assigned to a titanosaur that roamed Argentina. Time for Arrudatitan maximus to step out of the shadows.

The fragmentary fossil bones previously assigned to the Argentinian titanosaur Aeolosaurus maximus and now defined as new Brazilian titanosaur taxon Arrudatitan maximus. Picture credit: Silva Junior et al.

Picture credit: Silva Junior et al

Aeolosaurus maximus

The Aeolosaurus genus was erected by the Argentinian palaeontologist Jaime Powell in 1987 when the first species was named (A. rionegrinus). It was a widespread genus known from numerous individuals collected from Upper Cretaceous deposits, most notably the Angostura Colorada Formation in Río Negro Province, but dinosaur fossils collected from the Bajo Barreal, Los Alamitos and Allen Formations of Argentina have also been assigned to this genus.

The Brazilian fossil remains that led to the erection of the species Aeolosaurus maximus in 2011, have always been regarded as somewhat of an outlier when compared to Aeolosaurus fossil remains discovered in Argentina. A. maximus was described based on vertebrae, ribs, a left ischium, a fragmentary scapula and elements from the limbs including a left femur discovered in 1997 eroding out of an outcrop of the Adamantina Formation in the state of São Paulo state south-eastern Brazil.

Researchers who included Julian Silva Junior (Universidade de São Paulo), reassessed the fossil material following a cladistic analysis in 2019 that challenged the taxonomic placement. Writing in “Historical Biology”, the scientists have confirmed the assertion expressed previously that the Brazilian fossil material represents a distinct genus and the fossils ascribed to Aeolosaurus maximus have been reassigned to the new dinosaur species Arrudatitan maximus.

Although the size of A. maximus remains uncertain, based on the femur length of 1.55 metres, palaeontologists estimate that this titanosaur may have reached a length of around 15 metres.

Commenting on the revision, lead author of the scientific paper, doctoral student Julian Silva Junior stated:

“When analysing the caudal vertebrae, we found that they were different to those assigned to Aeolosaurus and these characteristics served to establish a diagnosis to propose a new genus.”

2021 – A Good Year for Titanosaur Discoveries

Several new titanosaur genera have been erected this year including Menucocelsior (M. arriagadai) and Ninjatitan (N. zapatai), which is the oldest titanosaur known to science.

Everything Dinosaur’s list of new titanosaurs named in 2021

• Arackar licanantay a titanosaur from the Upper Cretaceous Hornitos Formation of Chile.
• Arrudatitan maximus from the Upper Cretaceous Adamantina Formation of south-eastern Brazil.
• Australotitan cooperensis a titanosaur from the Winton Formation of Queensland, Australia.
• Garrigatitan meridionalis from the Upper Cretaceous Argiles Rutilantes Formation of south-eastern France.
• Hamititan xinjiangensis from the Lower Cretaceous Shengjinkou Formation of north-western China which was coeval with the euhelopodid sauropod Silutitan (S. sinensis) which was also scientifically described in 2021.
• Menucocelsior arriagadai from the Upper Cretaceous Allen Formation of Argentina.
• Ninjatitan zapatai the earliest titanosaur known to date described from fossils found in the Lower Cretaceous Bajada Colorada Formation of Argentina.

To read blog posts about some of these newly described titanosaurs:

A new species of titanosaur from the Atacama Desert of northern Chile (Arackar licanantay): A New Titanosaur from Chile – Arackar licanantay.

Australian dinosaur “Cooper” named: “Cooper” – Australotitan cooperensis.

Our article on Hamititan xinjiangensis and Silutitan sinensis: Two New Sauropods from North-western China.

To read the Everything Dinosaur blog post about the earliest titanosaur known to science: Ninjatitan zapatai the Earliest Titanosaur.

The scientific paper: “Reassessment of Aeolosaurus maximus, a titanosaur dinosaur from the Late Cretaceous of Southeastern Brazil” by Julian C. G. Silva Junior, Agustín G. Martinelli, Fabiano V. Iori, Thiago S. Marinho, E. Martín Hechenleitner and Max C. Langer published in Historical Biology.

Visit the Everything Dinosaur website: Dinosaur Toys.

Scientists have named a new species of armoured dinosaur based on cranial and postcranial fossils collected in 2008 from the famous Nemegt Formation of the Gobi Desert, Mongolia. A detailed analysis of the fossil material consisting of a well-preserved skull, vertebrae, ribs, part of the hip and a tail club has been published in the journal “Scientific Reports”. The new ankylosaur has been named Tarchia tumanovae and it is the third species to be assigned to the Tarchia genus.

Location map (a) of the fossil discovery in Mongolia with (b) a larger scale map showing the fossil quarry. Photograph (c) shows the specimen (MPC-D 100/1353) partially excavated with (d) a line drawing of the fossils in situ. T. tumanovae illustrations show known fossil bones in white (e) dorsal view, (f) left lateral view and (g) shows a skeletal reconstruction with dermal armour. Picture credit: Park et al.

Picture credit: Park et al

Evidence of Injury and a Damaged Tail Club

A joint Korean/Mongolian expedition discovered the fossil material at Hermiin Tsav in the southern Gobi Desert. The ribs show signs of fracture healing and there are localised injuries on the pelvic bones. The researchers speculate that these injuries were probably caused by intraspecific combat. The pathology is consistent with tail club strikes. Intriguingly, the tail club of the skeleton also shows signs of injury. The tail club is asymmetrical when viewed from above (dorsal view). A badly healed ossified tendon on the tail knob handle is present, a possible injury caused as the tail was used during combat. Whether this injury occurred as a result of intraspecific combat or when deterring an attack from a theropod is unknown.

Noting a Change in the Diet of Late Cretaceous Ankylosaurids

The scientists noted wide muzzles are a character of low-level, bulk feeders, whereas those ankylosaurines with narrower muzzles such as T. tumanovae and the coeval, closely related Tarchia teresae were probably selective feeders. The researchers demonstrate that ankylosaurid diets shifted from one of low-level, relatively unfussy bulk feeders during the early Campanian to more selective diets as characterised by a narrower muzzle by the late Campanian/early Maastrichtian.

Photographs (a–d) and line drawings (e–h) of the skull of Tarchia tumanovae sp. nov. (MPC-D 100/1353). Photographs of the skull in (a) left lateral, (b) right lateral, (c) anterior, and (d) occipital views. Line drawings in (e) left lateral, (f) right lateral, (g) anterior, and (h) occipital views.

Picture credit: Park et al

It is not known why ankylosaurids show this trend towards selective feeding, although the researchers speculate that this change could have been a consequence of habitat change as the region gradually became less arid towards the very end of the Cretaceous. The research team also postulate that ankylosaurids evolved more selective browsing habits in response to the presence of bulk-feeding saurolophine hadrosaurids such as Saurolophus angustirostris and Barsboldia sicinskii.

A diagram showing (a) a phylogenetic analysis of Tarchia tumanovae, placed in the context of geological time. Ankylosaurids from this region seem to have changed feeding strategies, (b), evolving narrower muzzles that indicate a switch from low-level bulk feeding to more selective browsing. Ankylosaurid fossils from the geologically older Bayanshiree and Djadokhta Formations which represent arid habitats had broad muzzles, whilst ankylosaurids from the younger and more humid Nemegt Formation have narrower muzzles. Picture credit: Park et al.

Picture credit: Park et al

Honouring a Famous Researcher

The species name honours Tat’yana A. Tumanova of the Russian Academy of Sciences, in recognition of her contribution to the study of Mongolian armoured dinosaurs.

The scientific paper: “A new ankylosaurid from the Upper Cretaceous Nemegt Formation of Mongolia and implications for paleoecology of armoured dinosaurs” by Jin-Young Park, Yuong-Nam Lee, Yoshitsugu Kobayashi, Louis L. Jacobs, Rinchen Barsbold, Hang-Jae Lee, Namsoo Kim, Kyo-Young Song and Michael J. Polcyn published in “Scientific Reports”.

The Everything Dinosaur website: Dinosaur Models: Dinosaur Models.