Post by creature386 on May 22, 2020 18:26:16 GMT 5
Bannykus wulatensis
Size comparison between B. wulatensis and H. sapiens by Tomopteryx
Temporal range: Aptian (Lower Cretaceous; 125–113 Ma)
Location: Bayin-Gobi Formation (Inner Mongolia, China)
Scientific classification:
Dinosauria
Saurischia
Theropoda
Alvarezsauroidea
Bannykus
B. wulatensis
Description:
Bannykus wulatensis a small alvarezsaur from the Lower Cretaceous of China. It is known from a holotype that had an estimated mass of 24 kg in life. Based on a histological analysis, the age of the holotype is estimated at eight years, implying it was in the subadult stage. The material includes the majority of the skeleton. The preserved skeletal features have more in common with later alvarezsaurids like Shuvuuia than with older genera like Haplocheirus or Xiyunykus.[1]
Bannykus as well as Xiyunykus (who was described in the same paper) represent important transitional forms in the evolution of alvarezsaurs. Older genera, like the Late Jurassic Haplocheirus, possess long arms with claws that were suitable for grasping. Later genera from the Cretaceous, however, show more specialized forelimbs which are shorter and possess only a single claw. The forelimbs of Bannykus are shorter than those of Late Jurassic alvarezsaurs, but longer than those of alvarezsaurs from the Late Cretaceous. Its forelimbs possess an elongated thumb whilst all other fingers are reduced in length, showing that the grasping function had already been lost at that point.[2]
Locality:
Fossil material of the B. wulatensis was found in the Bayin-Gobi Formation which is part of Inner Mongolia (China).[1] Thus, Bannykus, like all other known Late Jurassic or Early Cretaceous alvarezsaurs, lived in Asia which strongly implies that the group as a whole evolved there. According to a phylogenetic analysis, the appearance of alvarezsaurs in other contents was the result of dispersal rather than vicariance (as had been earlier suggested).[3]
Phylogenetic position:
The description paper of Bannykus and Xiyunykus contains a phylogenetic analysis. Their status as transitional species is supported by the inclusion of Haplocheirus into the group Alvarezsauria. Within the group, Xiyunykus is most closely related to Tugulusaurus while Bannykus is closer related to alvarezsaurids than to Xiyunykus. The analysis also supports a basal position of Alvarezsauria within maniraptora.[4]
The analysis, however, also shows that the evolution of alvarezsaurs took place in a modular manner which means that the anterior parts of the skeleton were modified earlier than the posterior ones.[2]
Literature:
Xu et al. (2018) Two Early Cretaceous Fossils Document Transitional Stages in Alvarezsaurian Dinosaur Evolution. Current Biology. 28, pp. 1–8, doi:10.1016/j.cub.2018.07.057.
Citations:
[1] Xu et al. (2018), p. 3
[2] Xu et al. (2018), p. 5
[3] Xu et al. (2018), p. 4-5
[4] Xu et al. (2018), p. 4
Size comparison between B. wulatensis and H. sapiens by Tomopteryx
Temporal range: Aptian (Lower Cretaceous; 125–113 Ma)
Location: Bayin-Gobi Formation (Inner Mongolia, China)
Scientific classification:
Dinosauria
Saurischia
Theropoda
Alvarezsauroidea
Bannykus
B. wulatensis
Description:
Bannykus wulatensis a small alvarezsaur from the Lower Cretaceous of China. It is known from a holotype that had an estimated mass of 24 kg in life. Based on a histological analysis, the age of the holotype is estimated at eight years, implying it was in the subadult stage. The material includes the majority of the skeleton. The preserved skeletal features have more in common with later alvarezsaurids like Shuvuuia than with older genera like Haplocheirus or Xiyunykus.[1]
Bannykus as well as Xiyunykus (who was described in the same paper) represent important transitional forms in the evolution of alvarezsaurs. Older genera, like the Late Jurassic Haplocheirus, possess long arms with claws that were suitable for grasping. Later genera from the Cretaceous, however, show more specialized forelimbs which are shorter and possess only a single claw. The forelimbs of Bannykus are shorter than those of Late Jurassic alvarezsaurs, but longer than those of alvarezsaurs from the Late Cretaceous. Its forelimbs possess an elongated thumb whilst all other fingers are reduced in length, showing that the grasping function had already been lost at that point.[2]
Locality:
Fossil material of the B. wulatensis was found in the Bayin-Gobi Formation which is part of Inner Mongolia (China).[1] Thus, Bannykus, like all other known Late Jurassic or Early Cretaceous alvarezsaurs, lived in Asia which strongly implies that the group as a whole evolved there. According to a phylogenetic analysis, the appearance of alvarezsaurs in other contents was the result of dispersal rather than vicariance (as had been earlier suggested).[3]
Phylogenetic position:
The description paper of Bannykus and Xiyunykus contains a phylogenetic analysis. Their status as transitional species is supported by the inclusion of Haplocheirus into the group Alvarezsauria. Within the group, Xiyunykus is most closely related to Tugulusaurus while Bannykus is closer related to alvarezsaurids than to Xiyunykus. The analysis also supports a basal position of Alvarezsauria within maniraptora.[4]
The analysis, however, also shows that the evolution of alvarezsaurs took place in a modular manner which means that the anterior parts of the skeleton were modified earlier than the posterior ones.[2]
Literature:
Xu et al. (2018) Two Early Cretaceous Fossils Document Transitional Stages in Alvarezsaurian Dinosaur Evolution. Current Biology. 28, pp. 1–8, doi:10.1016/j.cub.2018.07.057.
Citations:
[1] Xu et al. (2018), p. 3
[2] Xu et al. (2018), p. 5
[3] Xu et al. (2018), p. 4-5
[4] Xu et al. (2018), p. 4