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Two newly discovered dinosaurs may be missing links in an unusual lineage of predators that lived between 160 million and 90 million years ago, new research suggests.

The two species, Xiyunykus and Bannykus, were theropods a group of bipedal, largely carnivorous dinosaurs. Some theropods eventually gave rise to birds, while another branch, the alvarezsauroids, evolved into strange-looking insectivores with short arms and hands with an enlarged finger for digging into nests.

But until now, little was understood about how this change happened because of the 70-million-year evolutionary gap separating the insect-eating alvarezsauroids from the earliest known member of the group, Haplocheirus.

"The significance of Xiyunykus and Bannykus is that they fall within that gap and shed light on patterns of evolution within Alvarezsauroidea," explained Corwin Sullivan, a University of Alberta paleontologist who participated in the international study.

"These specimens greatly improve the scientific community's understanding of the early stages of alvarezsauroid evolution and give us a better idea of what early alvarezsauroids were like."

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