A new euornithine from the Lower Cretaceous (Aptian) of China reveals the first radiation of fish-eating birds

Abstract

A new euornithine bird, Kunpengornis anhuimusei gen. et sp. nov., is described based on a nearly complete skeleton from the Lower Cretaceous (Aptian) Jehol Biota in western Liaoning, China. The new taxon is characterized by possessing the unique combination of reduced maxillary ramus of premaxilla shorter than half the buccal margin of premaxilla, coracoid having a trapezoidal procoracoid process not expanded craniocaudally at its medial margin, sternum with blunt craniolateral process, drop-shaped distal end of lateral trabecula and reduced intermediate trabecula not enclosing a caudal fenestra, pubis lacking ossified distal symphysis and with gradually expanding distal end, resulting twice longer craniocaudally than at mid-shaft, but lacking an abrupt distinction between shaft and distal foot. The macerated fish bones preserved in the abdominal cavity provides direct evidence that Kunpengornis was piscivorous. Despite overall similarity with some yanornithids and other piscivorous euornithines, the phylogenetic analysis places Kunpengornis as sister taxon of Piscivoravis and closer to the "ornithuromorph-gansuid" clade than Yanornithidae, a result which supports the hypothesis that a piscivorous "Yanornis-like" bauplan was a grade along the evolutionary sequence leading to the precursors of the modern avians. The acquisition of the fish-eating ecology and the exploitation of the aquatic environments represented key innovations for the successful radiation of the euornithine birds.