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| Paralitherizinosaurus japonicus Kobayashi, Takasaki, Fiorillo, Chinzorig & Hikida, 2022 Life reconstruction by Masato Hattori. twitter.com/dgdt2425 |
Abstract
The record of therizinosaurs is rich in Asian countries such as Mongolia and China. Fragmentary therizinosaur specimens have been reported from the Lower and Upper Cretaceous deposits in Japan. One of these specimens, from the lower Campanian Osoushinai Formation in Nakagawa Town of Hokkaido Prefecture, was previously identified as a maniraptoran theropod dinosaur, possibly therizinosaur, but its taxonomic status remained unresolved. This study re-examines the specimen and provides a more detailed description and attempts to resolve its taxonomic status. Our study demonstrates that it is a new taxon, Paralitherizinosaurus japonicus gen. et sp. nov., because it shows a unique combination of characters in the metacarpal I and unguals. Our phylogenetic analysis places this new taxon within an unresolved clade of Therizinosauridae in the strict consensus tree. The 50% majority-rule consensus tree shows better resolution within Therizinosauridae, showing an unresolved monophyletic clade of Paralitherizinosaurus, Therizinosaurus, Suzhousaurus, and the Bissekty form. Geometric morphometric analysis suggests that Paralitherizinosaurus unguals most closely resemble Therizinosaurus unguals in being slender and has weak flexor tubercles. This study also shows an evolutionary trend in ungual shape, which associates a decrease in mechanical advantage, development of flexor tubercle, and hypothesized output (product of mechanical advantage and development of flexor tubercle) in derived therizinosaurs, supporting the hook-and-pull function of claws to bring vegetation to its mouth. Paralitherizinosaurus is the youngest therizinosaur from Japan and the first recovered from the marine deposits in Asia. This suggests a long temporal existence of therizinosaurs at the eastern edge of the Asian continent and adaptation of therizinosaurs to coastal environments.
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| Life reconstruction of Paralitherizinosaurus japonicus (Courtesy of Masato Hattori). |
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| Map of Japan, showing the location of Nakagawa Town and other dinosaur localities (a). Two other names in red are locations of other therizinosaur materials. This figure was created by using Adobe Photoshop 21.2.0 and Adobe Illustrator 24.2.1 (https://www.adobe.com/). A photo of the concretion containing materials of Paralitherizinosaurus japonicus gen. et sp. nov. before preparation (b). Dark parts in the concretion are exposed bones of Paralitherizinosaurus, showing that all elements were preserved in this block. See Murakami et al.1 for stratigraphic column of the Oshoushinai Formation and the horizon of the specimen. Manual unguals and silhouette of Paralitherizinosaurus japonicus, showing recovered skeletal elements in white (c) (Courtesy of Genya Masukawa). Life reconstruction of Paralitherizinosaurus japonicus (d) (Courtesy of Masato Hattori). |
Theropoda Marsh, 1881
Coelurosauria von Huene, 1920
Therizinosauria Russell, 1997
Therizinosauridae Maleev, 1954
Paralitherizinosaurus japonicus gen. et sp. nov.
Etymology: “Paralos” means by or near the sea in Greek, “therizo” means reap in Greek, and “sauros” means reptile in Latin. Specific name, “japon” refers to Japan.
Holotype: NMV-52 (NMV, Nakagawa Museum of Natural History, Japan), a partial vertebra and a partial right hand, including metacarpal I, proximal ends of unguals I and II, and nearly complete ungual III (Fig. 1c).
Horizon and locality: The Osoushinai Formation (early Campanian) of the Yezo Group in Nakagawa Town in Hokkaido Prefecture, Japan.
Diagnosis: A therizinosaurid with the following unique characters: dorsoventrally flattened metacarpal I (dorsoventral height less than half of transverse width) with no rotation of the axis of the distal end; presence of proximodorsally projecting dorsal lip in digits I and III; a shallow depression at the proximal portion of ungual III-4, connecting to the collateral groove; the presence of proximally extending ventral process; a weak flexor tubercle expressed as a small ridge.
Yoshitsugu Kobayashi, Ryuji Takasaki, Anthony R. Fiorillo, Tsogtbaatar Chinzorig and Yoshinori Hikida. 2022. New Therizinosaurid Dinosaur from the marine Osoushinai Formation (Upper Cretaceous, Japan) provides insight for Function and Evolution of Therizinosaur Claws. Scientific Reports. 12: 7207. DOI: 10.1038/s41598-022-11063-5
