Paleontologists have announced the discovery of a new genus and species of troodontid theropod dinosaur, based on the fossilized remains found in Japan.
Life reconstruction of Hypnovenator matsubaraetoheorum. Image credit: Masato Hattori.
Hypnovenator matsubaraetoheorum roamed Earth during the Early Cretaceous epoch, between 112 and 106 million years ago.
The new dinosaur was a member of Troodontidae, a group of bird-like theropods that includes kiwi-size to rhea-size species.
“Troodontidae is a clade of small-bodied and gracile theropod dinosaurs,” said Dr. Katsuhiro Kubota, a paleontologist at the University of Hyogo, the Museum of Nature and Human Activities and Hokkaido University Museum, and colleagues.
“Although the phylogenetic position of Troodontidae is traditionally considered a clade with Dromaeosauridae, forming Deinonychosauria, Troodontidae is also regarded as a sister clade to Avialae.”
“Anchiornis from the Late Jurassic of China is problematic in its phylogeny and is included in Troodontidae or Avialae.”
“These active discussions significantly improve our understanding of the phylogeny and osteology of non-avian theropod and greatly influence our comprehension of early avialan evolution.”
“Since the discovery of the first troodontid Troodon in the Late Cretaceous of Canada, troodontid materials have been discovered from the Middle Jurassic to Late Cretaceous of Asia, Europe, and North America.”
“However, troodontid specimens with articulation are extremely rare.”
An articulated postcranial skeleton of Hypnovenator matsubaraetoheorum was recovered from the deposits of the Ohyamashimo Formation in Tambasasayama City, Hyogo Prefecture, Japan.
“In September 2010, a partial theropod skeleton including the forelimb and knee was discovered in crushing rocks from the Ohyamashimo Formation during the construction of a public park at Nishikosa in Tambasasayama City,” the paleontologists explained.
“This discovery was made by Mrs. Kaoru Matsubara and Takaharu Ohe, members of an amateur group ‘Research Group on the Sasayama Group’.”
“In July 2011, an articulated theropod heel was collected from the same locality during an excavation organized by the Museum of Nature and Human Activities, Hyogo.”
These specimens are an only confirmed occurrence of a troodontid dinosaur in Japan.
“Our phylogenetic analysis positions Hypnovenator matsubaraetoheorum as the oldest and one of the most basal troodontines, forming a clade with Gobivenator mongoliensis,” the researchers said.
“The discovery suggests that small-bodied maniraptoran dinosaurs with a sleeping posture were common not only in environments with volcanic and eolian events or alluvial systems but also in fluvial systems.”
“Geometric morphometric analysis of manual ungual phalanges shows that manual ungual phalanges I and III of Hypnovenator matsubaraetoheorum exhibit considerable morphological variation but are functionally similar, which differs from those of non-troodontine troodontids, reflecting the transition of manual motion within Troodontinae.”
“Hypnovenator matsubaraetoheorum also has mosaic features in the pes related to cursoriality,” they added.
“This study reveals that asymmetrical arctometatarsus occurred by the Albian age, and some morphological changes, such as shorter digit IV than digit III and non-ungual phalanges of digits III with roller joints and digit IV with weakly ginglymoid articulation, arose during the early Late Cretaceous.”
The discovery is reported in a paper in the journal Scientific Reports.
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K. Kubota et al. 2024. Early Cretaceous troodontine troodontid (Dinosauria: Theropoda) from the Ohyamashimo Formation of Japan reveals the early evolution of Troodontinae. Sci Rep 14, 16392; doi: 10.1038/s41598-024-66815-2
Source : Breaking Science News