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.

Scientists writing in the journal “Nature” have announced the discovery of a new species of Late Cretaceous ankylosaur from southernmost Chile. The dinosaur named Stegouros elengassen evolved a large tail weapon, unlike any other tail weapon known in the Dinosauria. Stegouros had a flat, frond-like structure formed by seven pairs of laterally projecting osteoderms. This formidable tail weapon superficially resembles a macuahuitl, a frightening war club used by Aztec warriors.

A life reconstruction of the newly described Gondwana ankylosaur Stegouros elengassen. Picture credit: Mauricio Álvarez.

Picture credit: Mauricio Álvarez

A Combination of Stegosaur and Ankylosaur Anatomical Characteristics

The researchers from the University of Chile (Universidad de Chile) in Santiago report on an articulated, nearly complete fossil specimen representing a single animal that was excavated by a field team in February 2018 from sediments relating to the Dorotea Formation in the province of Ultima Esperanza in southern Chile. Stegouros was very small for an ankylosaur, measuring around two metres in length and weighing approximately 100 kilograms.

It shows ankylosaurian cranial characters, but a largely ancestral postcranial skeleton, with some stegosaur-like characters.

A phylogenetic analysis places Stegouros in the Ankylosauria and the research team postulate that it is closely related to other ankylosaurs known from southern Gondwana such as Kunbarrasaurus from Australia and Antarctopelta, fossils of which were found on James Ross Island off the Antarctic Peninsula.

Field team members jacket the fossilised remains of Stegouros. Picture credit: Universidad de Chile.

Picture credit: Universidad de Chile

The Parankylosauria Clade

The researchers propose the establishment of a new clade of ankylosaurs – the Parankylosauria which consists of basal ankylosaurs that split from the main ankylosaurian lineage during the Middle Jurassic, although the fossil evidence for this is currently lacking with Stegouros, Antarctopelta and Kunbarrasaurus forming part of a ghost lineage of basal ankylosaurs with origins back in the mid-Jurassic.

The posterior of the Stegouros specimen with the armoured tail clearly shown. Picture credit: Universidad de Chile.

A Transitional Ankylosaur

Commenting on the significance of this fossil discovery, lead author of the scientific paper, Sergio Soto, a researcher at the University of Chile stated that the fossilised remains of S. elengassen represent a “Rosetta Stone” for deciphering the fragmentary fossils of other ankylosaurs from southern Gondwana.

He added:

“Stegouros is an evolutionary link between ankylosaurs and other older lineages of armoured dinosaurs. Stegouros has only some of the features normally found in ankylosaurs, particularly the skull, but many others are absent. It also has some traits similar to stegosaurs, inherited from a common ancestor with them, but that other ankylosaurs lost in evolution.”

Picture credit: Universidad de Chile

Stegouros roamed the Chilean Patagonia around 74 million years ago. The genus name translates as “roofed tail”, whilst the species name comes from a mythical armoured monster from the folklore of the indigenous Tehuelche people.

Note

CollectA introduced a 1:6 scale figure of this remarkable dinosaur in 2023.  Safari Ltd also added a Stegouros model to their range in 2024.

The CollectA Deluxe 1:6 scale Stegouros elengassen dinosaur model – due to be available mid 2023.

To view the range of CollectA Deluxe prehistoric animal figures available from Everything Dinosaur: CollectA Deluxe Prehistoric Life Models.

The scientific paper: “Bizarre tail weaponry in a transitional ankylosaur from subantarctic Chile” by Sergio Soto-Acuña, Alexander O. Vargas, Jonatan Kaluza, Marcelo A. Leppe, Joao F. Botelho, José Palma-Liberona, Carolina Simon-Gutstein, Roy A. Fernández, Héctor Ortiz, Verónica Milla, Bárbara Aravena, Leslie M. E. Manríquez, Jhonatan Alarcón-Muñoz, Juan Pablo Pino, Cristine Trevisan, Héctor Mansilla, Luis Felipe Hinojosa, Vicente Muñoz-Walther and David Rubilar-Rogers published in the journal Nature.

The Everything Dinosaur website: Dinosaur Toys and Models,