近日，國(guó)際著名雜志《國(guó)家科學(xué)院院刊》PNAS刊登了美國(guó)芝加哥大學(xué)的研究人員的最新研究成果“Behavioral evidence for the evolution of walking and bounding before terrestriality in sarcopterygian fishes。”,，由于非洲肺魚可以用腹鰭行走并用肺呼吸,，因此可能是進(jìn)化環(huán)節(jié)中的一個(gè)關(guān)鍵環(huán)節(jié),。
該研究顯示,，非洲肺魚可能是早于四足動(dòng)物或者與之同一時(shí)期的魚類,。四足動(dòng)物由泥盆紀(jì)的肉鰭魚進(jìn)化而來(lái)，是最早占領(lǐng)陸地的脊椎動(dòng)物,。生物學(xué)家梅利娜·黑爾指出，研究人員在尋找“失去的環(huán)節(jié)”時(shí)發(fā)現(xiàn)有動(dòng)物能夠交替使用四肢,，這說(shuō)明“人類已經(jīng)發(fā)現(xiàn)形態(tài)完全不同的水生動(dòng)物，雖然它們的行走方式與四足動(dòng)物非常相似,，但它們并非四足動(dòng)物”,，肺魚就屬于這種情況,。
黑爾相信,，非洲肺魚“與從水中進(jìn)化到陸地上的動(dòng)物有著非常密切的關(guān)系”,。她指出,，幾乎所有那個(gè)時(shí)期的魚類都滅絕了。非洲肺魚的特征是能夠運(yùn)用腹鰭抬起身體并向前行走,。在行走過(guò)程中,，它還能夠和四足動(dòng)物一樣交替使用兩個(gè)后肢。
此項(xiàng)研究的作者指出,，雖然過(guò)去人們已對(duì)非洲肺魚的形態(tài)有所了解,，但是尚無(wú)研究表明它能夠利用腹鰭行走,。他們?cè)谝粋€(gè)水箱中復(fù)制了非洲肺魚的生活環(huán)境，并利用攝像頭從多個(gè)角度記錄下它的活動(dòng),，通過(guò)這種方式對(duì)它的移動(dòng)方式和腹鰭的活動(dòng)進(jìn)行全面研究。
結(jié)果研究人員發(fā)現(xiàn),，非洲肺魚完全能夠利用腹鰭支撐身體并向前行走,。他們還發(fā)現(xiàn),，非洲肺魚之所以能夠用纖細(xì)的兩個(gè)后肢行走是因?yàn)樗械闹亓^小,。此外,，它能通過(guò)用肺呼吸提高自身浮力，從而減輕“腿”受到的壓力,。研究人員指出,，必須利用活體動(dòng)物進(jìn)行研究,，因?yàn)橥ㄟ^(guò)化石只能確定腹鰭的形態(tài)而非功用。此外,，他們還指出,，生物從水中到陸地的進(jìn)化過(guò)程可能早在四足動(dòng)物之前就已經(jīng)發(fā)生。（生物谷Bioon.com）
doi:10.1073/pnas.1118669109
PMC:
PMID:
Behavioral evidence for the evolution of walking and bounding before terrestriality in sarcopterygian fishes
King, Heather M.; Shubin, Neil H.; Coates, Michael I.; Hale, Melina E.
Tetrapods evolved from sarcopterygian fishes in the Devonian and were the first vertebrates to colonize land. The locomotor component of this transition can be divided into four major events: terrestriality, the origins of digited limbs, solid substrate-based locomotion, and alternating gaits that use pelvic appendages as major propulsors. As the sister group to tetrapods, lungfish are a morphologically and phylogenetically relevant sarcopterygian taxon for understanding the order in which these events occurred. We found that a species of African lungfish (Protopterus annectens) uses a range of pelvic fin-driven, tetrapod-like gaits, including walking and bounding, in an aquatic environment, despite having a derived limb endoskeleton and primitively small, muscularly supported pelvis. Surprisingly, given these morphological traits, P. annectens also lifts its body clear of the substrate using its pelvic fins, an ability thought to be a tetrapod innovation. Our findings suggest that some fundamental features of tetrapod locomotion, including pelvic limb gait patterns and substrate association, probably arose in sarcopterygians before the origin of digited limbs or terrestriality. It follows that the attribution of some of the nondigited Devonian fossil trackways to limbed tetrapods may need to be revisited.
