Bannykus
| Bannykus | ||||||||||||
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Size comparison of B. wulatensis and a human |
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| Temporal occurrence | ||||||||||||
| Lower Cretaceous ( Aptium ) | ||||||||||||
| 126.3 to 112.9 million years | ||||||||||||
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| Scientific name | ||||||||||||
| Bannykus | ||||||||||||
| Xu et al., 2018 | ||||||||||||
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Bannykus was a Alvarezsauriden - genus from the Early Cretaceous of China . The only species is Bannykus wulatensis .
description
Bannykus wulatensis is known from a partially preserved holotype , the weight of which is estimated at 24 kg. Based on a histological analysis, the age of the specimen is estimated to be eight years, which is probably not an adult. The material encloses most of the skeleton . The surviving skull features have more in common with later Alvarezsauriden such as Shuvuuia than with older genera such as Haplocheirus or Xiyunykus . Bannykus , together with the Xiyunykus described at the same time, represents an important mosaic form in the evolution of the Alvarezsauria. Older genera such as the Upper Jurassic Haplocheirus have long arms with claws that were suitable for grasping. Later genera from the Upper Cretaceous Period have more specialized forelimbs, which are shorter to the west and only have one claw. The forearms of Bannykus are shorter than those of alvarez dinosaurs from the Upper Jurassic, but longer than those of alvarez dinosaurs from the Upper Cretaceous. The forearms have an extended thumb while all the other fingers are shortened, which shows that they have already lost their grip function.
Location
Fossil material of the holotype of B. wulatensis was found in the Bayin-Gobi Formation , which lies in Inner Mongolia ( China ). Thus, like all other known alvarez dinosaurs , Bannykus comes from the Upper Jurassic or Lower Cretaceous Asia, which suggests that the group originated there. According to a phylogenetic analysis, the appearance of Alvarezsauria species in other continents is a result of spreading rather than allopatric speciation as previously suspected.
Systematics
The description of Bannykus and Xiyunykus is accompanied by a phylogenetic analysis. Their status as mosaic forms confirms the inclusion of Haplocheirus in the Alvarezsauria group. Within the group, Xiyunykus is most closely related to Tugulusaurus , while Bannykus is more closely related to the Alvarezsauriden than to Xiyunykus . The analysis confirms a basal position of Alvarezsauria within Maniraptora .
The analysis also shows that the evolution of alvarez dinosaurs was modular. The front parts of the skeleton were modified earlier than the rear ones.
literature
- Xu et al. : Two Early Cretaceous Fossils Document Transitional Stages in Alvarezsaurian Dinosaur Evolution . In: Current Biology . tape 28 , 2018, p. 1–8 , doi : 10.1016 / j.cub.2018.07.057 .