The Plantigrade Segnosaurians: Sloth Dinosaurs or Bear Dinosaurs?

This article considers the unusual Macropodosaurus gravis tracks from the Early Cretaceous (Albian) locality of Shirkent-1 (Tajikistan). The trackmaker was bipedal and plantigrade. Through a comparison of Macropodosaurus tracks with those of other dinosaurs and by a juxtaposition of track morphology...

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Bibliographic Details
Published in:Paleontological journal 2021-12, Vol.55 (10), p.1158-1185
Main Author: Sennikov, A. G.
Format: Article
Language:English
Subjects:
Cretaceous
Dinosaurs
Earth and Environmental Science
Earth Sciences
Functional morphology
Geographical distribution
Locomotion
Macropodosaurus gravis
Morphology
Paleontology
Stratigraphy
Therizinosauria
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Summary:This article considers the unusual Macropodosaurus gravis tracks from the Early Cretaceous (Albian) locality of Shirkent-1 (Tajikistan). The trackmaker was bipedal and plantigrade. Through a comparison of Macropodosaurus tracks with those of other dinosaurs and by a juxtaposition of track morphology and pes skeletal morphology, it is argued that they belong to an aberrant group of theropods, the segnosaurs. Data on the stratigraphic and geographical distribution of segnosaur tracks are presented. Aspects of functional morphology of the hind limbs are analyzed, as well as the locomotory mode and the possible lifestyle of this group of dinosaurs. Segnosaurs were most likely herbivorous; their possible ecological counterparts are giant ground sloths. The ancestors of segnosaurs were probably facultatively digitigrade and underwent a short-term stage as arboreal, climbing forms, and then reversed to a purely terrestrial lifestyle. Return to plantigrade locomotion in segnosaurs apparently required increased area of support during the slow obligate bipedal locomotion of these heavy theropods.
ISSN:0031-0301
1555-6174
DOI:10.1134/S0031030121100087