2025

K.Kubo

Y.Kobayashi

Evolutionary patterns of cursorial traits, hindlimb proportions and arctometatarsus, were surveyed in theropod dinosaurs
Cursorial hindlimb proportions evolved independently in noasaurid ceratosaurs with antarctometatarsus and 5 coelurosaur lineages with arctometatarsus, suggesting a strong correlation between foot morphology and proportional lengths of distal hind limb segments.
The arctometatarsus evolved restricted to Coelurosauria, suggesting that a phylogenetic constraint may have prevented modifications to metatarsal arrangement at the ankle joint outside Coelurosauria.
The arctometatarsus emerged through parallel evolution during the mid-Cretaceous interval (93–120 Ma), which were likely subjected to strong ecological selection on hind limb morphology, adapted for cursoriality.

-2023-

K.Kubo

Y. Kobayashi

C. Tsogtobaatar

K. Tsogtobaatar

A nearly complete skeleton of a late-branching member of an alvarezsaurid dinosaur (Parvicursorinae) was discovered in the Upper Cretaceous deposits of Mongolia
We named this dinosaur, Jaculinykus yaruui (meaning speedy and tiny dragon's claw )
Jaculinykus yaruui possesses a beautifully preserved manus with only two fingers, which is an intermediate state between the tridactyl hand of Shuvuuia deserti and the monodactyl hand of Linhenykus monodactylus
Jaculinykus yaruui exhibits a stereotypical avian-like sleeping position, suggesting avian sleeping postures are a maniraptoran synapomorphy

Life Restoration by Seiji Yamamoto (@yamamotoyama555, X)

研究のハイライト

モンゴル上部白亜系(約7200万年前)より産出した，アルヴァレッツサウルス類（獣脚類・マニラプトル類）の新種・ヤキュリニクスヤルウイ（意: 素早い小さな竜の爪）を報告しました．
最も保存状態の良い骨格標本であるヤキュリニクスには，手の骨格に指が二本しかなく，同じ仲間である三本指のシュヴウイアと一本指のリンヘニクスの中間状態を示しています．
首を曲げることで頭部を胴体にうずめ，後肢をたたみ込んで座る鳥類に特有な寝る姿勢で保存されており，新たに鳥類のような行動の進化的起源がマニラプトル類まで遡ることを示唆しました．