Data from: Fossil evidence of the avian vocal organ from the Mesozoic

From complex songs to simple honks, birds produce sounds using a unique vocal organ called the syrinx1, 2. Located close to the heart at the tracheobronchial junction, vocal folds or membranes attached to modified mineralized rings vibrate to produce sound1, 2, 3, 4, 5, 6, 7. Syringeal components were not thought to commonly enter the fossil record6, and the few reported fossilized parts of the syrinx are geologically young8, 9, 10, 11 (from the Pleistocene and Holocene (approximately 2.5 million years ago to the present)). The only known older syrinx is an Eocene specimen that was not described or illustrated12. Data on the relationship between soft tissue structures and syringeal three-dimensional geometry are also exceptionally limited5. Here we describe the first remains, to our knowledge, of a fossil syrinx from the Mesozoic Era, which are preserved in three dimensions in a specimen from the Late Cretaceous (approximately 66 to 69 million years ago) of Antarctica. With both cranial and postcranial remains, the new Vegavis iaai specimen is the most complete to be recovered from a part of the radiation of living birds (Aves). Enhanced-contrast X-ray computed tomography (CT) of syrinx structure in twelve extant non-passerine birds, as well as CT imaging of the Vegavis and Eocene syrinxes, informs both the reconstruction of ancestral states in birds and properties of the vocal organ in the extinct species. Fused rings in Vegavis form a well-mineralized pessulus, a derived neognath bird feature, proposed to anchor enlarged vocal folds or labia5. Left-right bronchial asymmetry, as seen in Vegavis, is only known in extant birds with two sets of vocal fold sound sources. The new data show the fossilization potential of the avian vocal organ and beg the question why these remains have not been found in other dinosaurs. The lack of other Mesozoic tracheobronchial remains, and the poorly mineralized condition in archosaurian taxa without a syrinx, may indicate that a complex syrinx was a late arising feature in the evolution of birds, well after the origin of flight and respiratory innovations.

从复杂鸣唱到简单鸣叫，鸟类均通过一种名为鸣管（syrinx）的独特发声器官产生声音¹,²。该器官位于气管支气管分叉处且贴近心脏，附着于特化矿化环的声带或薄膜通过振动发声¹,²,³,⁴,⁵,⁶,⁷。
此前学界普遍认为鸣管结构极少能形成化石记录⁶，目前仅报道过少量保存为化石的鸣管组织，且其地质年代均较新⁸,⁹,¹⁰,¹¹——均属于更新世（Pleistocene）与全新世（Holocene，约250万年前至今）。目前已知的更古老鸣管标本仅一件始新世（Eocene）样本，但该样本未被描述或配图¹²。
关于软组织结构与鸣管三维形态之间关联的研究数据也极为匮乏⁵。
本研究报道了迄今为止据我们所知的第一件中生代（Mesozoic Era）鸣管化石标本，该标本发现于南极洲晚白垩世（约6600万至6900万年前）地层中，其鸣管以三维立体形态保存完好。这件同时保存有颅骨与躯干后骨遗骸的新Vegavis iaai标本，是迄今为止从现生鸟类（Aves）辐射演化类群中发现的最为完整的化石标本。
研究团队对12种现生非雀形目鸟类的鸣管结构进行了增强对比度X射线计算机断层扫描（CT），同时对Vegavis标本与始新世鸣管标本开展CT成像，相关结果可为鸟类祖先状态重建以及已灭绝物种发声器官的特征解析提供关键支撑。
Vegavis标本中的愈合环形成了一处矿化程度良好的鸣管支架（pessulus），这是新颚鸟类（neognath）的衍生特征，被认为可用于固定增大的声带或唇状结构⁵。
Vegavis标本中所见的左右支气管不对称结构，目前仅在拥有两套声带发声结构的现生鸟类中被发现。
本次新发现的数据证实了鸟类发声器官的化石保存潜力，同时也引出了一个关键科学问题：为何这类遗骸未在其他恐龙化石中被发现？
目前尚未发现其他中生代气管支气管遗骸，且不具有鸣管的主龙类类群矿化程度普遍较低，这两点或可表明：复杂鸣管是鸟类演化后期才出现的特征，其起源时间远晚于飞行起源与呼吸革新事件。