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鳥(niǎo)類(lèi)具有與靈長(zhǎng)類(lèi)動(dòng)物相近的相對(duì)大腦尺寸，但是造成這一現(xiàn)象的驅(qū)動(dòng)力和大尺度模式尚未得到解答。結(jié)合鳥(niǎo)類(lèi)的起源和進(jìn)化過(guò)程，本研究探索了鳥(niǎo)類(lèi)基本的腦-體比例關(guān)系的演變模式。通過(guò)一份包含超過(guò)2,000種現(xiàn)代鳥(niǎo)類(lèi)、化石鳥(niǎo)類(lèi)和獸腳亞目恐龍的綜合數(shù)據(jù)，我們得以從長(zhǎng)時(shí)間跨度對(duì)鳥(niǎo)類(lèi)腦-體共變模式進(jìn)行了推斷。研究證實(shí)，在獸腳亞目恐龍-鳥(niǎo)類(lèi)過(guò)渡期間，伴隨小型化或適應(yīng)飛行進(jìn)化的趨勢(shì)，鳥(niǎo)類(lèi)的相對(duì)大腦尺寸沒(méi)有顯著增加。不過(guò)，關(guān)鍵的是，獸腳類(lèi)和基干鳥(niǎo)類(lèi)的大腦大小與體型之間的整合較弱，允許腦-體比例關(guān)系發(fā)生快速改變，這為早期冠群鳥(niǎo)類(lèi)發(fā)生急劇轉(zhuǎn)變奠定了基礎(chǔ)。研究推斷，在白堊紀(jì)-古近紀(jì)大滅絕后，新鳥(niǎo)類(lèi)快速的產(chǎn)生了重大轉(zhuǎn)變，表現(xiàn)為多個(gè)進(jìn)化支系發(fā)生了由于體型減小而獲得了相對(duì)較高的大腦大小的現(xiàn)象。鸚鵡和烏鴉具有鳥(niǎo)類(lèi)中的最大大腦，但是其產(chǎn)生模式完全不同。鸚鵡主要是通過(guò)減小它們的體型來(lái)實(shí)現(xiàn)，而烏鴉雖然同時(shí)增加身體和大腦大小，但是其大腦尺寸的進(jìn)化速度要超過(guò)其身體。總的來(lái)說(shuō)，這些模式表明早期在大腦尺寸上發(fā)生的適應(yīng)性輻射為隨后的選擇和穩(wěn)定提供了基礎(chǔ)。

[中文內(nèi)容僅供參考，請(qǐng)以英文原文為準(zhǔn)]

Relative brain sizes in birds can rival those of primates, but large-scale patterns and drivers of avian brain evolution remain elusive. Here, we explore the evolution of the fundamental brain-body scaling relationship across the origin and evolution of birds. Using a comprehensive dataset sampling> 2,000 modern birds, fossil birds, and theropod dinosaurs, we infer patterns of brain-body co-variation in deep time. Our study confirms that no significant increase in relative brain size accompanied the trend toward miniaturization or evolution of flight during the theropod-bird transition. Critically, however, theropods and basal birds show weaker integration between brain size and body size, allowing for rapid changes in the brain-body relationship that set the stage for dramatic shifts in early crown birds. We infer that major shifts occurred rapidly in the aftermath of the Cretaceous-Paleogene mass extinction within Neoaves, in which multiple clades achieved higher relative brain sizes because of a reduction in body size. Parrots and corvids achieved the largest brains observed in birds via markedly different patterns. Parrots primarily reduced their body size, whereas corvids increased body and brain size simultaneously (with rates of brain size evolution outpacing rates of body size evolution). Collectively, these patterns suggest that an early adaptive radiation in brain size laid the foundation for subsequent selection and stabilization.