New fossils from north China shed light on the incremental evolution of insect-eating dinosaurs
An international research team today announces the discovery of two new Chinese dinosaurs: Bannykus and Xiyunykus. Professor Roger Benson from the University of Oxford Department of Earth Sciences was a leading member of the team and is co-author on the research.
The dinosaurs are both alvarezsaurs, an enigmatic group of theropod (meat-eating) dinosaurs which have many similarities with birds, and which show adaptations thought to be related to eating insects that live in colonies.
“Alvarezsaurs are weird animals,” said Professor Jonah Choiniere, co-author from the University of the Witwatersrand, “with their strong, clawed hands and weak jaws, they appear to be the dinosaurian analogue to today’s aardvarks and anteaters.”
But alvarezsaurs did not originally eat insects – the earliest members of the group had more typically meat-eating teeth and hands, useful for catching small prey. Only later-evolving members reduced their teeth and evolved a hand with a huge, single claw capable, perhaps, of tearing open rotting logs and anthills.
“The new fossils have long arms, and so show that alvarezsaurs evolved short arms only later in their evolutionary history, in species with small body sizes. This is quite different to what happens in the classic example of tyrannosaurs, which have short arms and giant size,” said Benson.
Bannykus and Xiyunykus are important because they show transitional steps in the process of alvarezsaurs adapting to new diets.
“The fossil record is the best source of information about how anatomical features evolve,” said James Clark, co-author and an Honorary Professor at Wits University “and like other classic examples of evolution such as the ‘horse series’, these dinosaurs show us how a lineage can make a major shift in its ecology over time.”
The specimens were discovered during collaborative international fieldwork in China. Xiyunykus was discovered in 2005 in Xinjiang, northwestern China. Bannykus was discovered a few years later in 2009 in Inner Mongolia, north-central China. Both research trips were joint expeditions co-led by Profs Xu Xing (Institute for Vertebrate Palaeontology and Palaeoanthropology, Beijing) and James Clark (George Washington University, Washington DC).
“Our international field teams have been tremendously productive over the years,” said Professor Xu Xing, leader of the research, “and this research showcases just some of our incredible discoveries.”
Paper: ‘Two Early Cretaceous Fossils Document Transitional Stages in Alvarezsaurian Dinosaur Evolution’ by Xing Xu, Jonah Choiniere, Qingwei Tan, Roger B.J. Benson, James Clark, Corwin Sullivan, Qi Zhao, Fenglu Han, Qingyu Ma, Yiming He, Shuo Wang, Hai Xing & Lin Tan, was published in Current Biology, doi.org/10.1016/j.cub.2018.07.057
Image: The left hand of Bannykus, showing the large first claw on the thumb and the smaller second and third finger. Credit Prof. Jonah Choiniere