The fossil record of two dinosaur species from the alvaressauroid subfamily has filled a gap in the evolutionary history of their forelimbs, which were intended to prey on insects. Previously, paleontologists have not found the remains of these dinosaurs between 160 and 90 million years old, so they could not draw conclusions about how these limbs evolved. The results of the work are presented in the journal Current Biology.
Alvaressauroids descended from one of the evolutionary lines of dinosaur dinosaurs, the ancestors of modern birds. Paleontologists speculate that alvaressauroids ate insects, which is why they had short forelimbs with an elongated toe, which the animal needed to find prey. Paleontologists did not know how these limbs evolved, since until a certain moment they could not find intermediate species between the earliest known representative of the alvaressaurid family, which includes the alvaressauroids, Haplocheirus sollers, who lived about 160 million years ago, and later, which existed in Cretaceous period (about 90 million years ago).
In the new work, Chinese scientists describe the fossils of the transitional species of alvaressauroids - Xiyunykus and Bannykus, who lived 131-113 million years ago. “The significance of Xiyunykus and Bannykus is that they hit the gap and shed light on the evolution of alvaressauroids,” says co-author Corwin Sullivan of the University of Alberta, Canada. "These species allow us to better understand how this subfamily of dinosaurs developed in the early stages, and allow us to better understand what the early alvaressauroids looked like."
The forelimbs of new species are adapted for digging, in later species they will become much larger.
Some of the features of the skull structure of the found dinosaurs also resemble the late insectivorous alvaressauroids. However, the hind limbs have changed significantly less than the ancestors. The authors note that despite the importance of the discovery and the value of the information received, in order to fully understand how this group of dinosaurs evolved, additional finds will be needed.