A new ankylosaurid skeleton from the Upper Cretaceous Baruungoyot Formation of Mongolia: its implications for ankylosaurid postcranial evolution

A new articulated postcranial specimen of an indeterminate ankylosaurid dinosaur from the Upper Cretaceous (middle-upper Campanian) Baruungoyot Formation from Hermiin Tsav, southern Gobi Desert, Mongolia includes twelve dorsal vertebrae, ribs, pectoral girdles, forelimbs, pelvic girdles, hind limbs, and free osteoderms. The new specimen shows that Asian ankylosaurids evolved rigid bodies with a decreased number of pedal phalanges. It also implies that there were at least two forms of fank armor within Ankylosauridae, one with spine-like osteoderms and the other with keeled rhomboidal osteoderms. Unique anatomical features related to digging are present in Ankylosauridae, such as dorsoventrally fattened and fusiform body shapes, extensively fused series of vertebrae, anteroposteriorly broadened dorsal ribs, a robust humerus with a well-developed deltopectoral crest, a short robust ulna with a well-developed olecranon process, a trowel-like manus, and decreased numbers of pedal phalanges. Although not fossorial, ankylosaurids were likely able to dig the substrate, taking advantage of it for self-defence and survival

Reexamination of a primitive ornithomimosaur, Garudimimus brevipes Barsbold, 1981 (Dinosauria: Theropoda), from the Late Cretaceous of Mongolia

The holotype of Garudimimus brevipes, discovered from the Upper Cretaceous sediments of Mongolia and named by Barsbold in 1981, is redescribed in detail in this paper. Reexamination of the holotype reveals a great deal of anatomical information, which allows us to revise the original diagnosis of this taxon and make comparisons with other ornithomimosaur taxa to understand the evolution of ornithomimosaurs. This paper suggests that characters used to differentiate this taxon in the original paper (short ilia, short metatarsals, exposure of the proximal end of metatarsal III, presence of pedal digit I, and absence of pleurocoels) are not apomorphies but represent the primitive conditions in ornithomimosaurs and are symplesiomorphies. Revised diagnoses are assigned for G. brevipes (posteriorly positioned jaw articulation, fossae at base of dorsal process of supraoccipital, paired depressions on neural spines of proximal caudal vertebra, and deep groove on lateral surface of pedal phalanges III-1 and III-2). Metatarsals of Garudimimus display a non-arctometatarsalian condition as in an Early Cretaceous form, Harpymimus, but the constriction of metatarsal III in Garudimimus is intermediate between Harpymimus and the arctometatarsalian condition in Gallimimus and other derived ornithomimosaurs (ornithomimids). Garudimimus is the only non-ornithomimid ornithomimosaur with edentulous jaws, which were probably covered by rhamphothecae. The loss of teeth with evolution of rhamphothecae and development of a cutting edge in the dentary of Garudimimus suggest the acquisition of feeding habits that included plucking food at the anterior portion of the jaw and cutting at the middle portion, similar to ornithomimids

A new baby oviraptorid dinosaur (Dinosauria: Theropoda) from the Upper Cretaceous Nemegt Formation of Mongolia.

Recent discoveries of new oviraptorosaurs revealed their high diversity from the Cretaceous Period in Asia and North America. Particularly, at the family level, oviraptorids are among the most diverse theropod dinosaurs in the Late Cretaceous of Mongolia and China. A new oviraptorid dinosaur Gobiraptor minutus gen. et sp. nov. from the Upper Cretaceous Nemegt Formation is described here based on a single holotype specimen that includes incomplete cranial and postcranial elements. The most prominent characters of Gobiraptor are its thickened rostrodorsal end of the mandibular symphysis and a rudimentary lingual shelf on each side of the dentary. Each lingual shelf is lined with small occlusal foramina and demarcated by a weakly developed lingual ridge. This mandibular morphology of Gobiraptor is unique among oviraptorids and likely to be linked to a specialized diet that probably included hard materials, such as seeds or bivalves. The osteohistology of the femur of the holotype specimen indicates that the individual was fairly young at the time of its death. Phylogenetic analysis recovers Gobiraptor as a derived oviraptorid close to three taxa from the Ganzhou region in southern China, but rather distantly related to other Nemegt oviraptorids which, as the results of recent studies, are also not closely related to each other. Gobiraptor increases diversity of oviraptorids in the Nemegt Formation and its presence confirms the successful adaptation of oviraptorids to a mesic environment

A new specimen of Shuvuuia deserti Chiappe et al., 1998, from the Mongolian Late Cretaceous with a discussion of the relationships of alvarezsaurids to other theropod dinosaurs

Volume: 494Start Page: 1End Page: 1

Skeletal morphology of Mononykus olecranus (Theropoda, Avialae) from the late Cretaceous of Mongolia. American Museum novitates ; no.3105

29 p. : ill. ; 26 cm.Includes bibliographical references (p. 27-29