A new species of pengornithidae (aves: enantiornithes) from the lower cretaceous of China suggests a specialized scansorial habitat previously unknown in early birds.

Han Hu,Jingmai K O’Connor,Zhonghe Zhou,Andrew A Farke

doi:10.1371/journal.pone.0126791

Abstract

We describe a new enantiornithine bird, Parapengornis eurycaudatus gen. et sp. nov. from the Lower Cretaceous Jiufotang Formation of Liaoning, China. Although morphologically similar to previously described pengornithids Pengornis houi, Pengornis IVPP V18632, and Eopengornis martini, morphological differences indicate it represents a new taxon of the Pengornithidae. Based on new information from this specimen we reassign IVPP V18632 to Parapengornis sp. The well preserved pygostyle of the new specimen elucidates the morphology of this element for the clade, which is unique in pengornithids among Mesozoic birds. Similarities with modern scansores such as woodpeckers may indicate a specialized vertical climbing and clinging behavior that has not previously been inferred for early birds. The new specimen preserves a pair of fully pennaceous rachis-dominated feathers like those in the holotype of Eopengornis martini; together with the unique morphology of the pygostyle, this discovery lends evidence to early hypotheses that rachis-dominated feathers may have had a functional significance. This discovery adds to the diversity of ecological niches occupied by enantiornithines and if correct reveals are remarkable amount of locomotive differentiation among Enantiornithes.

Highlights

Enantiornithes (Aves: Ornithothoraces) represents the dominant Cretaceous clade both in terms of the overall number of specimens and species diversity [1]
Parapengornis eurycaudatus shares several diagnostic features with previously known pengornithids Pengornis houi [7], ‘Pengornis’ IVPP V18632 [10], and Eopengornis martini [6], that readily allow its referral to the Pengornithidae: premaxillae relatively short and entirely unfused; teeth extremely small and numerous; pygostyle short and broad; tip of the scapular acromion hooked; sternum with a V-shaped caudal margin and intermediate trabeculae absent; ulna 110–115% length of the humerus; femur approximately equal to tibia in length; elongated fibula nearly reaching the distal end of the tibia; and elongated metatarsal I and digit I-1
Apart from the strong resemblance between Parapengornis eurycaudatus and other pengornithids, there exist substantial morphological differences that indicate despite its ontogenetic immaturity IVPP V18687 cannot be referred to any previously known pengornithid species and represents a new member of this clade

Summary

Introduction

Enantiornithes (Aves: Ornithothoraces) represents the dominant Cretaceous clade both in terms of the overall number of specimens and species diversity [1]. More than half this diversity belongs to the Early Cretaceous Jehol Biota in northeastern China [2]. The Huajiying Formation, the first stage of the Jehol Biota [3], is the oldest known enantiornithine bearing deposit in the world [4]. Three avian fossils have been described, all from the “Protopteryx-horizon”: Eoconfuciusornis (Confuciusornithiformes), Protopteryx (Enantiornithes), and Eopengornis, a member of the Pengornithidae [4,5,6]. The Pengornithidae was considered to be a primitive. PLOS ONE | DOI:10.1371/journal.pone.0126791 June 3, 2015

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