Mosaic evolution in an asymmetrically feathered troodontid dinosaur with transitional features

Xing Xu,Philip Currie,Qingjin Meng,Michael Pittman,Dongyu Hu,Congyu Yu,Lida Xing,Junchang Lü

doi:10.1038/ncomms14972

Abstract

Asymmetrical feathers have been associated with flight capability but are also found in species that do not fly, and their appearance was a major event in feather evolution. Among non-avialan theropods, they are only known in microraptorine dromaeosaurids. Here we report a new troodontid, Jianianhualong tengi gen. et sp. nov., from the Lower Cretaceous Jehol Group of China, that has anatomical features that are transitional between long-armed basal troodontids and derived short-armed ones, shedding new light on troodontid character evolution. It indicates that troodontid feathering is similar to Archaeopteryx in having large arm and leg feathers as well as frond-like tail feathering, confirming that these feathering characteristics were widely present among basal paravians. Most significantly, the taxon has the earliest known asymmetrical troodontid feathers, suggesting that feather asymmetry was ancestral to Paraves. This taxon also displays a mosaic distribution of characters like Sinusonasus, another troodontid with transitional anatomical features.

Highlights

Asymmetrical feathers have been associated with flight capability but are found in species that do not fly, and their appearance was a major event in feather evolution
The Middle-Upper Jurassic and Lower Cretaceous of western Liaoning and neighbouring areas have produced spectacular fossil remains of theropod dinosaurs, of maniraptoran theropods, which are critical to our understanding of bird origins[1,2]
Previous studies indicate that Anchiornis huxleyi, Eosinopteryx brevipenna, Jinfengopteryx elegans and Xiaotingia zhengi have pennaceous feathers[6,7,13,16]

Summary

Introduction

Asymmetrical feathers have been associated with flight capability but are found in species that do not fly, and their appearance was a major event in feather evolution. Nov., from the Lower Cretaceous Jehol Group of China, that has anatomical features that are transitional between long-armed basal troodontids and derived short-armed ones, shedding new light on troodontid character evolution. It indicates that troodontid feathering is similar to Archaeopteryx in having large arm and leg feathers as well as frond-like tail feathering, confirming that these feathering characteristics were widely present among basal paravians. The taxon has the earliest known asymmetrical troodontid feathers, suggesting that feather asymmetry was ancestral to Paraves This taxon displays a mosaic distribution of characters like Sinusonasus, another troodontid with transitional anatomical features. Its discovery is highly significant in reconstructing both the skeletal and integumentary evolution of troodontids, and the more inclusive paravians

Methods

Results

Conclusion