英國研究人員報(bào)告最新成果說,，在約2．5億年前一次生物大滅絕事件以前,，所有爬行動(dòng)物都是腿在身體兩側(cè)“趴”著行走,，而在此之后，大中型爬行動(dòng)物大都“站”了起來,。
英國布里斯托爾大學(xué)15日發(fā)布新聞公報(bào)稱,，該校研究人員和日本同行分析了大滅絕事件前后的460件爬行動(dòng)物足跡化石。結(jié)果發(fā)現(xiàn)大滅絕事件之前所有爬行動(dòng)物的腿腳都是長在身體兩側(cè),，而之后大中型爬行動(dòng)物的腿腳幾乎都長到身體正下方的位置,，從“趴”進(jìn)化到“直立”。
研究人員說,，“直立”與“趴”相比有非常大的生理優(yōu)勢,。直立行走時(shí)膝關(guān)節(jié)等處所受的壓力較小，且步幅較大,。更關(guān)鍵的是，腿腳在身體正下方,，就可以像柱子一樣支撐起更重的身體,，如恐龍和大象。
此前人們認(rèn)為生物從“趴”到“直立”的進(jìn)化經(jīng)歷了很長時(shí)間,，但這次研究顯示大滅絕事件可能促使動(dòng)物在短時(shí)間內(nèi)迅速完成了這種進(jìn)化過程,，后來出現(xiàn)的許多爬行動(dòng)物都直立行走，如此后不久出現(xiàn)的恐龍,。
有研究稱,，在約2．5億年前地球上發(fā)生了最大一次生物滅絕事件，地球上超過90％的物種消失,。一般認(rèn)為這次大滅絕是環(huán)境突變造成的,，但具體原因尚不明確。
相關(guān)研究報(bào)告發(fā)表在《古生物學(xué)》雜志上,。（生物谷Bioon.com）
生物谷推薦原始出處：
Palaeontology Volume 52 Issue 5, Pages 1029 - 1037
Tetrapod postural shift estimated from Permian and Triassic trackways
by TAI KUBO* and MICHAEL J. BENTON
*Department of Earth and Planetary Science, University of Tokyo, 7-3-1, Hongo, Bunkyouku, Tokyo 113-0033, Japan
Abstract: The end-Permian mass extinction, 252 million years (myr) ago, marks a major shift in the posture of tetrapods. Before the mass extinction, terrestrial tetrapods were sprawlers, walking with their limbs extended to the sides; after the event, most large tetrapods had adopted an erect posture with their limbs tucked under the body. This shift had been suspected from the study of skeletal fossils, but had been documented as a long process that occupied some 15–20 myr of the Triassic. This study reads posture directly from fossil tracks, using a clear criterion for sprawling vs erect posture. The track record is richer than the skeletal record, especially for the Early and Middle Triassic intervals, the critical 20 myr during which period the postural shift occurred. The shift to erect posture was completed within the 6 myr of the Early Triassic and affected both lineages of medium to large tetrapods of the time, the diapsids and synapsids.
