恐龍的長尾巴去哪了？福建出土1.5億年前鳥類化石破解謎題

當看到鳥兒翹起扇形的短尾巴在空中調整飛行方向時，很難想象，它們的恐龍祖先曾拖著由30多節尾椎組成、長達一兩米的大尾巴，在侏羅紀的原始森林里快速狂奔。

從“長尾龍”到“短尾鳥”，中間經歷了什么？

不虞政和鳥（前）和奇異福建龍（后）生態復原圖（張宗達繪制）

過去，化石記錄留下了一道巨大的“演化鴻溝”。長尾鳥和短尾鳥幾乎同時出現，也就是說現代鳥類的短尾巴（由4—9塊尾椎和一塊尾綜骨構成）似乎是憑空冒出來的，瞬間取代了恐龍標志性的長尾巴，缺乏中間的過渡環節。

這讓許多生物學家認為，那種“尾巴變短但缺少尾綜骨”的過渡物種，在演化上從未出現過，尾巴變短不過是少數基因突變的結果，而非漸進演化。

Because long-tailed and short-tailed birds appear almost simultaneously in the fossil record, without intermediate forms, many evolutionary biologists argued that a transitional species with an abbreviated but no unfused pygostyle — the bony structure that characterizes the tails of modern birds — was unlikely present in bird evolutionary history.

pygostyle /?pa?.ɡ?.sta?l/ 尾綜骨

They suggested that tail shortening could result from just a few genetic mutations — a hypothesis seemingly supported by the abrupt appearance of the pygostyle in the Late Jurassic.

mutation /mju??te?.??n/ 基因突變

不虞政和鳥正型標本、骨骼復原圖和“小虞”卡通復原圖（王敏供圖）

如今，一件從福建出土的距今約1.5億年的鳥類化石推翻了這一猜想。

However, the discovery of a 150-million-year-old bird fossil unearthed in Fujian province challenges that long-held assumption by providing a long-sought transitional form.

中科院古脊椎所和福建地科院聯合考察隊發現不虞政和鳥正型標本

近日，中國科學院古脊椎動物與古人類研究所和福建省地質科學研究院聯合團隊經過累計400余天的野外發掘，在福建政和動物群發現了一件保存精美的鳥類化石。

The fossil was discovered by a joint research team from the Institute of Vertebrate Paleontology and Paleoanthropology of the Chinese Academy of Sciences and the Fujian Geological Science Research Institute. The discovery followed more than 400 days of fieldwork at the Zhenghe Fauna, a Late Jurassic fossil locality in Zhenghe county, Nanping, Fujian province, renowned for yielding exquisitely preserved vertebrate fossils.

他們將其命名為“不虞政和鳥”。其種名“不虞”出自《國語·周語》，意為“意料之外”，因為它獨特的尾部結構完全顛覆學界過往認知。

Researchers named the new species Zhengheornis buyu. The genus name refers to the discovery site, while the species name is derived from Discourses of the States, or Guoyu, an ancient Chinese book, meaning "unexpected" — a tribute to the specimen’s surprising tail anatomy.

不虞政和鳥3D復原視頻（王敏提供）

不虞政和鳥的尾部僅由15塊變短的尾椎組成，且其末端并沒有愈合成為尾綜骨。相比之下，其他長尾鳥類（如始祖鳥）尾椎數超過23塊；而與鳥類親緣關系更近的多數獸腳類恐龍，尾椎數通常超過30塊，尾巴長度接近甚至超過體長。

Dating to the Tithonian stage of the Late Jurassic, about 148 million to 150 million years ago, the well-preserved articulated skeleton has a tail composed of only 15 shortened caudal vertebrae and lacks a pygostyle. That is significantly fewer than in other long-tailed birds, such as Archaeopteryx, which possessed more than 23 caudal vertebrae, and other early bird-like dinosaurs, which typically exceeded 30.

Tithonian /ta??θ??.ni.?n/ 提通期

skeleton /?skel.?.t?n/ 骨骼

vertebrae /?v??.t?.bri?/ 椎骨、脊椎骨

caudal /?k??.d?l/ 尾部的

中生代獸腳類恐龍（包括鳥類）后肢形態多樣性比較（王敏供圖）

論文通訊作者、第一作者、古脊椎所研究員王敏表示：這一尾骨形態結構有力地證明了在鳥類尾部的演化歷史中，尾椎數量的減少和變短發生在尾椎愈合并形成尾綜骨之前。這種“分步走”的演化模式，填補了鳥類尾部演化缺失的關鍵拼圖。

"This tail morphology provides critical evidence for the stepwise evolution of the bird tail: vertebral reduction and tail shortening preceded pygostyle fusion in early bird evolution," said Wang Min, the study's lead and corresponding author and a professor at the Institute of Vertebrate Paleontology and Paleoanthropology.

"This landmark discovery not only reconciles long-standing academic debates regarding the timing of early avian diversification but also adds a crucial piece to the puzzle across the dinosaur-bird transition," Wang said.

morphology/m???f?l.?.d?i/ 形態學

此外，這種縮短且沒有過度僵化的短尾巴，能夠有效減輕體重，使身體重心和升力中心向前移動。同時，較少的尾椎關節提升了尾部的剛性，更利于飛行控制；較短的力臂也讓政和鳥能更輕松地操控尾羽，從而獲得了比始祖鳥等更好的飛行穩定性和機動性。

The researchers said the shortened but flexible tail likely offered important functional advantages. By reducing body weight, shifting the center of gravity forward, and making the tail less rigid, Zhengheornis buyu could move its tail feathers more effectively. This would have improved its flight stability and control compared with its longer-tailed contemporaries like Archaeopteryx.

rigid /r??d??d/ 剛硬的

所以，下次看到鳥兒收攏尾羽俯沖而下，不妨想想1.5億年前——恐龍祖先的古老印記，早已在那只小“意外鳥”未完成的尾巴里，悄然蛻變成了如今的輕盈。

記者：李夢涵

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