Friday, July 21, 2017

[Paleontology • 2017] Aepyornithomimus tugrikinensis • First Ornithomimid (Theropoda, Ornithomimosauria) from the Upper Cretaceous Djadokhta Formation of Tögrögiin Shiree, Mongolia


Aepyornithomimus tugrikinensis
Tsogtbaatar, Kobayashi, Khishigjav, Currie, Watabe & Rinchen, 2017

Illustration by Masato Hattori

Abstract
The Upper Cretaceous Djadokhta Formation has been intensively surveyed for its fossil vertebrate fauna for nearly a century. Amongst other theropods, dromaeosaurids and parvicursorines are common in the formation, but ornithomimosaurs are extremely rare. A new ornithomimosaur material was discovered from the Djadokhta Formation, represented by eolian deposits, of the Tögrögiin Shiree locality, Mongolia. This is only the third ornithomimosaur specimen reported from this formation, and includes the astragalus, the calcaneum, the third distal tarsal, and a complete pes. The new material is clearly belonged to Ornithomimidae by its arctometatarsalian foot condition and has the following unique characters; unevenly developed pair of concavities of the third distal tarsal, curved contacts between the proximal ends of second and fourth metatarsals, the elongate fourth digit, and a laterally inclined medial condyle on phalanx IV-1. These diagnostic characters of the Djadokhtan ornithomimosaur indicate that this is a new taxon. Our phylogenetic analysis supports three clades within derived ornithomimosaurs, and the new taxon is placed a member of the derived ornithomimosaurs. The present specimen is the first ornithomimid record from eolian Tögrögiin Shiree locality, and is indicative of their capability to adapt to arid environments.



Systematic paleontology
Dinosauria Owen, 184224.
Theropoda Marsh, 188125.

Ornithomimosauria Barsbold, 197626.
Ornithomimidae Marsh, 189027.

Aepyornithomimus tugrikinensis gen. et sp. nov.

Etymology: The generic name refers to the largest ratite bird Aepyornis~, which has similar pes structure; in Latin, ~mimus = ‘as’ or ‘like’; the species name tugrikinensis refers to the locality where the specimen was found.

Holotype: MPC-D 100/130, articulated left pes preserved with an astragalus that is missing the ascending process, a complete calcaneum, and distal tarsal III (DT-III) (Figs 2, 3 and 4). The original specimen is now housed in the Institute of Paleontology and Geology of the Mongolian Academy of Sciences (IPG-MAS).


Type locality and horizon: Central Sayr of Tögrögiin Shiree locality, Upper Cretaceous Djadokhta Formation (Campanian) (Fig. 1). This locality is interpreted as semi-arid eolian sediments28 with up to 52 m of light gray, cross-bedded, structureless sands and sandstones17.

Diagnosis: An ornithomimid dinosaur with the following unique characters; unevenly developed pair concavities on the posterior margin of the DT-III; robust distal articular caput of second metatarsal (Mt II) in dorsal view; proximoventrally rounded ridge of phalanx II-1 (II-1); the elongate fourth digit; laterally inclined medial condyle of phalanx IV-1 (IV-1); elongated pedal unguals.

Illustration by Masato Hattori 

Figure 8: Comparative graph and restoration drawing of Aepyornithomimus tugrikinensis.
 (a), Different proportions of the three metatarsals is represented by ternary diagram, (b), Illustration is drawn by Mr. Masato Hattori.
Abbreviations: (Mt II), the metatarsal II, (Mt III), the metatarsal III, and (Mt III), the metatarsal III, (Ω), Aepyornithomimus tugrikinensis, (Δ), basal ornithomimosaurs, (Π), deinocheirids, (†), ornithomimids. 

Chinzorig Tsogtbaatar, Yoshitsugu Kobayashi, Tsogtbaatar Khishigjav, Philip J. Currie, Mahito Watabe and Barsbold Rinchen. 2017. First Ornithomimid (Theropoda, Ornithomimosauria) from the Upper Cretaceous Djadokhta Formation of Tögrögiin Shiree, Mongolia.  Scientific Reports. 7, Article number: 5835. DOI:  10.1038/s41598-017-05272-6
  

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