Forelimb structure and function in a new Late Cretaceous parvicursorine theropod dinosaur from Mongolia

A new parvicursorine theropod, Manipulonyx reshetovi, gen. et sp. nov., is based on a fragmentary skeleton from the Upper Cretaceous (Maastrichtian) Nemegt Formation at Khermeen Tsav, Gobi Desert, Mongolia. The new taxon differs from other parvicursorines in a unique combination of characters. The skeleton of Manipulonyx preserves an articulated and complete forelimb, including rudimentary side fingers, and a complete series of proximal carpals (ulnare, intermedium, and radiale). The proximal carpals were previously unknown for Parvicursorinae. This specimen also shows for the first time the presence of additional dermal ossifications in the carpus, three spikes articulated with (medial and lateral spikes) or attached to (palmar spike) the carpometacarpus. We hypothesize that parvicursorines were egg-eating animals and they used these spikes (covered by a keratinous sheath), as well as rudimentary side fingers, to fix the forelimb on the round and elusive egg surface. After such fixation, the eggshell was punctured by the hypertrophied manual claw. This interpretation is supported by a number of morphofunctional traits of the parvicursorine forelimb discussed in the paper, including the hypertrophied deltopectoral crest of the humerus, keeled sternum, enlarged ectepicondyle of humerus, hypertrophied olecranon of ulna, and lack of the flexor tubercle on the main manual ungual phalanx.