Fossil evidence of the avian vocal organ from the Mesozoic

CLARKE, JULIA; CHATTERJEE, SANKAR; LI, ZHIHENG; AGNOLIN, FEDERICO

NATURE

NATURE PUBLISHING GROUP

Año: 2016

0028-0836

From complex songs to simple honks, birds produce sounds using aunique vocal organ called the syrinx1,2. Located close to the heart atthe tracheobronchial junction, vocal folds or membranes attached tomodified mineralized rings vibrate to produce sound1?7. Syringealcomponents were not thought to commonly enter the fossil record6,and the few reported fossilized parts of the syrinx are geologicallyyoung8?11 (from the Pleistocene and Holocene (approximately 2.5million years ago to the present)). The only known older syrinx isan Eocene specimen that was not described or illustrated12. Dataon the relationship between soft tissue structures and syringealthree-dimensional geometry are also exceptionally limited5. Herewe describe the first remains, to our knowledge, of a fossil syrinxfrom the Mesozoic Era, which are preserved in three dimensionsin a specimen from the Late Cretaceous (approximately 66 to 69million years ago) of Antarctica. With both cranial and postcranialremains, the new Vegavis iaai specimen is the most complete tobe recovered from a part of the radiation of living birds (Aves).Enhanced-contrast X-ray computed tomography (CT) of syrinxstructure in twelve extant non-passerine birds, as well as CT imagingof the Vegavis and Eocene syrinxes, informs both the reconstructionof ancestral states in birds and properties of the vocal organ in theextinct species. Fused rings in Vegavis form a well-mineralizedpessulus, a derived neognath bird feature, proposed to anchorenlarged vocal folds or labia5. Left-right bronchial asymmetry, asseen in Vegavis, is only known in extant birds with two sets of vocalfold sound sources. The new data show the fossilization potentialof the avian vocal organ and beg the question why these remainshave not been found in other dinosaurs. The lack of other Mesozoictracheobronchial remains, and the poorly mineralized conditionin archosaurian taxa without a syrinx, may indicate that a complexsyrinx was a late arising feature in the evolution of birds, well afterthe origin of flight and respiratory innovations.