A New Sapeornithid Bird from China and Its Implication for Early Avian Evolution

Recent discoveries of basal birds have greatly improved our understanding of early bird evolution, yet the evolution of several important features such as cranial kinesis and arboreality remain debated. A new sapeornithid bird, Shenshiornis primita gen. et sp. nov., based on an articulated skeleton from the Early Cretaceous Jehol Group of western Liaoning, China, sheds new light on these issues. Shenshiornis possesses a skull as primitive as or even more primitive than that of Archaeopteryx and hind limbs modified for an improved arboreal capability. A cladistic analysis shows that: 1) presence of a diapsid skull is a plesiomorphy of the Aves and a kinetic skull evolved incrementally later in avian evolution; and 2) cursorial capability significantly weakens at the base of the Pygostylia due to a change in locomotor system.