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| Harenadraco prima S. Lee, Y.-N. Lee, Park, Kim, Badamkhatan, Idersaikhan & Tsogtbaatar, 2024 artwork by Yusik Choi |
ABSTRACT
Among non-avian dinosaurs, troodontids are relatively rare but diverse. The Nemegt Basin in the Mongolian Gobi Desert, which incorporates three of the most fossiliferous beds in the world, is one such region with high troodontid diversity and has also produced eight troodontid taxa until now. The diversity of troodontids is biased towards the two formations, Nemegt and Djadochta. Despite its rich vertebrate fossil record, no troodontids have been described from the Baruungoyot Formation. This faunal absence is perplexing as the Baruungoyot Formation has often been considered intermediate between the other two units in stratigraphy and paleoenvironment, but there are no definite troodontid materials that could fill this ‘gap.’ Here, we report a new troodontid, Harenadraco prima gen. et sp. nov., from the Baruungoyot Formation in Hermiin Tsav, Mongolia. It is represented by an incomplete skeleton that mainly consists of partially articulated left hind limb elements. Harenadraco is small and lightly built like other troodontids, but its tarsometatarsus exhibits extreme slenderness comparable only to Philovenator among cursorial non-avian maniraptorans. It also implies high cursoriality that could be an adaptation of Harenadraco to its environment where potential prey animals like mammals and predators such as eudromaeosaurs were likely to be agile. The discovery of Harenadraco confirms the presence of troodontids in all three formations in the Nemegt Basin.
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| Left pedal phalanges and the skeletal reconstruction of the preserved parts in Harenadraco prima (MPC-D 110/119, holotype). A, left pedal digits II–IV in lateral view. M, skeletal reconstruction of Harenadraco prima (MPC-D 110/119, holotype) with missing parts in gray. Abbreviations: II-3, pedal phalanx II-3; III-3, pedal phalanx III-3; IV-2, pedal phalanx IV-2. |
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| Life reconstruction of Harenadraco prima (artwork by Yusik Choi). |
DINOSAURIA Owen, 1842
THEROPODA Marsh, 1881
TROODONTIDAE Gilmore, 1924
HARENADRACO PRIMA, gen. et sp. nov.
Diagnosis—A small-sized troodontid diagnosed by the following unique combination of characters (autapomorphies indicated with an asterisk): tall S-shaped medial margin of medial condyle of astragalocalcaneum in anterior view*, poorly developed flexor sulcus on the distal articular end of metatarsal II, which also lacks collateral ligament fossae*, metatarsal III excluded from the proximal end of the metatarsus in dorsal view (shared with Tochisaurus, Zanabazar, and Philovenator), metatarsal IV only slightly more robust than metatarsal II at the proximal end in ventral view (shared with Daliansaurus and Philovenator), pronounced ventral protrusion near the proximal end of metatarsal IV (shared with Liaoningvenator), extremely narrow proximal shaft of metatarsal IV*, greatly elongated flexor tubercle of pedal phalanx II-3 that reaches the shaft of the preceding phalanx when in articulation*, and the distal articular surface of pedal phalanx III-3 not ginglymoid*.
Etymology—The name of the genus is a composition of the Latin words harena (sand) and draco (dragon). The species name “prima” means first in Latin, referring to the taxon being the first troodontid from the Baruungoyot Formation.
Sungjin Lee, Yuong-Nam Lee, Jin-Young Park, Su-Hwan Kim, Zorigt Badamkhatan, Damdinsuren Idersaikhan and Khishigjav Tsogtbaatar. 2024. The first troodontid (Dinosauria: Theropoda) from the Upper Cretaceous Baruungoyot Formation of Mongolia. Journal of Vertebrate Paleontology. e2364746. DOI: doi.org/10.1080/02724634.2024.2364746
