Scientists have named a new species of therizinosaur based on fragmentary remains found on the Japanese island of Hokkaido. The dinosaur has been named Paralitherizinosaurus japonicus, it is the first recovered from Asian marine deposits and the third example of a therizinosaur to be found in Japan.

The fossil material, recovered from the lower Campanian Osoushinai Formation near to the town of Nakagawa in the Hokkaido Prefecture, was previously identified as a maniraptoran theropod dinosaur, possibly therizinosaur, but its taxonomic status remained uncertain. A group of scientists including Yoshitsugu Kobayashi and Anthony R. Fiorillo from the Hokkaido University Museum re-examined the fossils and erected a new taxon confirming the fossil material did represent a Late Cretaceous member of the Therizinosauridae.

Evolution of Claw Shape in the Therizinosauridae

Writing in the academic journal “Scientific Reports”, the researchers reassessed the fossil material consisting of a single vertebra plus bones and claws (unguals) from the right hand. As well as concluding that the fossils represent a therizinosaur, they confirmed that it is the geologically youngest therizinosaur known from Japan described to date.

Important Implications for Claw (Ungual) Evolution in the Therizinosauridae

The scientists compared the shape of the hand claws from Paralitherizinosaurus japonicus with the claws from geologically older therizinosaurs and they postulated that that primitive therizinosaurs had claws with generalist functionalities and that the claws of more derived, later therizinosaurs such as P. japonicus were more suited to the hook-and-pull feeding function. Hook-and-pull feeding involves the use of the claws to help gather vegetation and bring it closer to the mouth.

What’s in a Name?

The fossils were found in a concretion associated with the Campanian-aged Osoushinai Formation of the Yezo Group on Hokkaido Island. The Yezo Group mostly consists of marine deposits and many vertebrate fossils such as plesiosaurs, sharks, mosasaurs and turtles have been discovered. Fragmentary dinosaur fossils are also associated with these strata including hadrosaurids, an armoured dinosaur (nodosaurid) and a potential tyrannosaur. A therizinosaur taxon can now be added to this Late Cretaceous dinosaur biota.

To view replicas of feathered theropods including therizinosaurus (whilst stocks last): PNSO Age of Dinosaurs Figures.

The discovery of the bones and claw elements in marine deposits helped to inspire this dinosaur’s scientific name. The genus name translates as “scythe reptile by the sea”, whilst the species name honours Japan.

The scientific paper: “New therizinosaurid dinosaur from the marine Osoushinai Formation (Upper Cretaceous, Japan) provides insight for function and evolution of therizinosaur claws” by Yoshitsugu Kobayashi, Ryuji Takasaki, Anthony R. Fiorillo, Tsogtbaatar Chinzorig and Yoshinori Hikida published in Scientific Reports.

Fragmentary bones excavated from Santa Cruz Province, Patagonia (Argentina), have revealed the presence of a super-sized megaraptorid theropod in the Late Cretaceous (Maastrichtian faunal stage). The new dinosaur, named Maip macrothorax is estimated to have been at least 9.5 metres long. It represents the biggest member of the Megaraptoridae described to date and its discovery lends support to the theory that these types of dinosaurs were not members of the Allosauria clade, but they were coelurosaurs and therefore related to the dinosaur lineage that gave rise to the birds.

Silhouette of Maip macrothorax showing the preserved bones in white (A). Reconstruction of the thoracic cavity of Maip (B) at the level of dorsal vertebra 6 (D6). Drawing of the excavation of Maip showing the original disposition of the bones (C). Abbreviations: a, axis; c, coracoid; ind, indeterminate bone; g, gastralia; r, rib; v, vertebrae. Picture credit: Rolando et al. Note scale bar in (A) = 1 metre, and (B,C) 50 cm.

Picture credit: Rolando et al

The fossil material was collected from exposures of the Chorrillo Formation approximately eighteen miles southwest of the city of El Calafate (southwestern Santa Cruz Province, Patagonia, Argentina).

The “Shadow of the Death” which “Kills with Cold Wind”

The Megaraptora clade are mostly known from fragmentary and very incomplete specimens. The fossils of Maip macrothorax (pronounced my-eep mac-row-thor-ax), although representing only a small portion of the overall skeleton, consist of a single cervical vertebra (C2 the axis), several dorsal vertebrae, ribs, the left coracoid, a partial toe bone, fragments of the scapula and caudal vertebrae.

By studying these bones the researchers, that included Alexis M. Aranciaga Rolando from the Museo Argentino de Ciencias Naturales “Bernardino Rivadavia” (Buenos Aires, Argentina) and Makoto Manabe from the National Museum of Nature and Science (Japan), postulate that the Megaraptora are not archaic members of the Allosauroidea but members of the Coelurosauria clade, that group of theropods more closely related to birds than they are to other members of the Avetheropoda lineage.

Maip macrothorax

The genus name is from the native Aónikenk people of Patagonia (known as the Tehuelche in western culture). Maip is an evil spirit said to roam the Andes and its name means “the shadow of death” which “kills with cold wind”. The specific name derives from the Latin for big thorax. The rib bones indicate that this dinosaur was deep chested with a large thoracic cavity more than 1.2 metres in width.

The second neck bone of Maip macrothorax (axis – C2) shown in lateral (A), anterior (B), posterior (C) and dorsal (D) with accompanying line drawings. Note scale bar = 5 cm. Picture credit: Rolando et al.

Picture credit: Rolando et al

The researchers propose that with the extinction of the carcharodontosaurids, many of which were apex predators on the southern continents, the megaraptorids evolved becoming larger, heavier and more robust, eventually filling the niche of top predator in many parts of the Southern Hemisphere during the Late Cretaceous.

Evolutionary trends of the Megaraptora. Evolutionary trends of Megaraptora. Temporal scale and bars depicting currently known temporal distributions of Megaraptora and Carcharodontosauridae (A). Time-calibrated phylogeny of megaraptoran taxa (B), showing most relevant genera from Asia (black bars), Australia (red bars) and South America (blue bars). Main synapomorphies supporting each node are indicated by arrows. Tree topology follows the results of the present work. Curve showing the increasing in average body size of megaraptorans during Barremian faunal stage through to the Maastrichtian (C). Picture credit: Rolando et al.

Picture credit: Rolando et al

The Rise of the Megaraptorids

Around 94 million years ago (Cenomanian faunal stage of the Late Cretaceous), there was a global extinction event which led to the demise of the Carcharodontosauridae. As far as Everything Dinosaur team members are aware, there are no reliable fossil records for the presence of carcharodontosaurids in South America beyond the Turonian faunal stage (the stage that followed the Cenomanian). An absence of apex predators permitted the megaraptorids and the abelisaurids to evolve to fill this niche in the Southern Hemisphere, whilst the tyrannosaurids become bigger and occupied the apex predator role in Asia and North America.

Maip macrothorax estimated at around 9.5 metres in length, lived some sixteen million years after the next largest megaraptorid (Aerosteon – A. riocoloradense). The body size of megaraptorids during the Early Cretaceous when the carcharodontosaurids still roamed seems to have been limited to around six metres in length, suggesting that these theropods were secondary predators. However, with the extinction of the carcharodontosaurids, body size in the Megaraptoridae increased and by the very end of the Cretaceous (Maastrichtian faunal stage), a body length in excess of ten metres seems plausible.

To read the Everything Dinosaur blog post that reported the discovery of these bones in 2020: Scientists Discover Giant Megaraptor.

Helping to Resolve the Phylogeny of these Enigmatic Theropods

Although the bones only represent a small part of the total skeleton and no cranial material has been identified, Maip macrothorax is the most informative megaraptoran known from the Maastrichtian stage. Phylogenetic analysis has placed this new taxon together with other South American megaraptorans in a monophyletic clade (they shared a single, common ancestor), whereas Australian and Asian members constitute successive stem groups.

A leggy, Late Cretaceous carnivore (Murusraptor).  Picture credit: Jan Slovak (University of Alberta).

Picture credit: Jan Sovak (University of Alberta).

For models and replicas of theropods and other prehistoric animals: Wild Safari Prehistoric World Models and Figures.

The researchers propose that the South American megaraptorids differ from more basal megaraptorans such as Fukuiraptor from Japan and Australovenator from Queensland, Australia in several anatomical features and the South American lineage evolved into much bigger, more robust and powerful predators.

The scientific paper: “A large Megaraptoridae (Theropoda: Coelurosauria) from Upper Cretaceous (Maastrichtian) of Patagonia, Argentina” by Alexis M. Aranciaga Rolando, Matias J. Motta, Federico L. Agnolín, Makoto Manabe, Takanobu Tsuihiji and Fernando E. Novas published in Scientific Reports.

The Everything Dinosaur website: Dinosaur Toys.