A Mesozoic bird from Gondwana preserving feathers.

Marcelo P. Isasi,José A. Andrade,Federico L. Agnolín,Fernando E. Novas,Ismar de Souza Carvalho,Francisco I. Freitas

doi:10.1038/ncomms8141

Abstract

The fossil record of birds in the Mesozoic of Gondwana is mostly based on isolated and often poorly preserved specimens, none of which has preserved details on feather anatomy. We provide the description of a fossil bird represented by a skeleton with feathers from the Early Cretaceous of Gondwana (NE Brazil). The specimen sheds light on the homology and 3D structure of the rachis-dominated feathers, previously known from two-dimensional slabs. The rectrices exhibit a row of rounded spots, probably corresponding to some original colour pattern. The specimen supports the identification of the feather scapus as the rachis, which is notably robust and elliptical in cross-section. In spite of its juvenile nature, the tail plumage resembles the feathering of adult individuals of modern birds. Documentation of rachis-dominated tail in South American enantiornithines broadens the paleobiogeographic distribution of basal birds with this tail feather morphotype, up to now only reported from China.

Highlights

The fossil record of birds in the Mesozoic of Gondwana is mostly based on isolated and often poorly preserved specimens, none of which has preserved details on feather anatomy
Because most fossils are preserved in two dimensions, the detailed anatomy of these tail feathers still remains in debate
UFRJ-DG (Universidade Federal do Rio de Janeiro, Department of Geology collection) 031 Av, partial skeleton of a possible juvenile specimen preserved in slab and counterslab (Supplementary Fig. 1), including poorly preserved skull bones, fore- and hindlimbs, portions of vertebral column, and most of both pectoral and pelvic girdles

Summary

Introduction

The fossil record of birds in the Mesozoic of Gondwana is mostly based on isolated and often poorly preserved specimens, none of which has preserved details on feather anatomy. Most specimens and valuable information on feathers in early birds have been recovered from the Lower Cretaceous Jehol Group (Hauterivian through Aptian) in NE China (for example, see refs 1,2). Because most fossils are preserved in two dimensions, the detailed anatomy of these tail feathers still remains in debate They have been variously suggested as representing an scale-like structure intermediate in morphology between the reptilian and bird integuments, a modified pennaceous feather, or a unique type of primitive feather[2,3,8,9,10,11,12]. The specimen constitutes the most complete avian specimen of Early Cretaceous age from Gondwana; more importantly, it sheds light on the anatomical structure and probable function of the peculiar rachis-dominated tail feathers. Isolated feathers probably belonging to birds have been described from these beds[17,18], as well as succinct reports on avian skeletons associated with poorly preserved feathers 19

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