A fully feathered enantiornithine foot and wing fragment preserved in mid-Cretaceous Burmese amber

Lida Xing,Ryan C Mckellar,Ming Bai,Kuowei Tseng,Luis M Chiappe,Jingmai K O’Connor

doi:10.1038/s41598-018-37427-4

Abstract

Over the last three years, Burmese amber (~99 Ma, from Myanmar) has provided a series of immature enantiornithine skeletal remains preserved in varying developmental stages and degrees of completeness. These specimens have improved our knowledge based on compression fossils in Cretaceous sedimentary rocks, adding details of three-dimensional structure and soft tissues that are rarely preserved elsewhere. Here we describe a remarkably well-preserved foot, accompanied by part of the wing plumage. These body parts were likely dismembered, entering the resin due to predatory or scavenging behaviour by a larger animal. The new specimen preserves contour feathers on the pedal phalanges together with enigmatic scutellae scale filament (SSF) feathers on the foot, providing direct analogies to the plumage patterns observed in modern birds, and those cultivated through developmental manipulation studies. Ultimately, this connection may allow researchers to observe how filamentous dinosaur ‘protofeathers’ developed—testing theories using evolutionary holdovers in modern birds.

Highlights

Burmese amber has been studied extensively for its arthropod and botanical inclusions[1,2], but has only recently been recognized as a valuable source of diverse vertebrate material living during the beginning of the Cenomanian (98.8 ± 0.6 Ma)[3,4,5,6,7]
Metatarsals II and III are subequal in mediolateral width, whereas metatarsal IV is thinner and its distal trochlea is reduced to a single condyle, both features characteristic of many enantiornithines
Their relative prominence may be attributable to interspecific variation, or their enlargement may suggest that scutellae scale filament (SSF) become more pronounced with increasing maturity, given that DIP-V-15105a does not appear to be a very young juvenile

Summary

Introduction

Burmese amber has been studied extensively for its arthropod and botanical inclusions[1,2], but has only recently been recognized as a valuable source of diverse vertebrate material living during the beginning of the Cenomanian (98.8 ± 0.6 Ma)[3,4,5,6,7]. Amber inclusions of enantiornithines with both skeletal material and feathers have been recovered for a pair of juvenile wing fragments[5]; a partial hatchling[8]; and the compacted skeleton of a juvenile[9]. Most pedal elements; the individual bones have not been distorted by compaction[6,8,9]; and traces of a network of haversian canals are visible within the exposed bone ends (Figs 1, 3C) Feathers from both the foot and wing fragment (Fig. 2) provide some insight into their developmental stage, with the extensive contour plumage of the foot providing some clues about the overall appearance of the individual, including the first documentation of feathered pedal digits in a stem bird. The foot inclusion demonstrates a new plumage pattern for enantiornithines—one that has similarities to both modern birds and theropods basal to the Enantiornithes[18,19]

Methods

Results

Conclusion