地球上最古老的動(dòng)物或許可以追溯到距今5.85億年前,，比原先認(rèn)為的5.55億年前要早3000萬(wàn)年。
來(lái)自加拿大艾伯塔大學(xué)等機(jī)構(gòu)的研究人員在新一期《科學(xué)》雜志上報(bào)告說(shuō),，他們?cè)谀厦绹?guó)家烏拉圭發(fā)現(xiàn)了有動(dòng)物爬行痕跡的化石,，經(jīng)年代測(cè)定，留下痕跡的動(dòng)物應(yīng)生活在距今5.85億年前。
這種動(dòng)物在堆積物上留下了寬2毫米至3毫米的爬行痕跡,。研究人員據(jù)此推斷這種動(dòng)物是一種類(lèi)似蛞蝓的動(dòng)物,，擁有左右對(duì)稱(chēng)的身體，體長(zhǎng)1厘米左右,。
細(xì)菌等原核生物在地球上存在的時(shí)間超過(guò)30億年,，而此前科學(xué)家找到的證據(jù)顯示，最古老動(dòng)物生活在距今5.55億年前,。（生物谷Bioon.com)
doi:10.1126/science.1216295
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Bilaterian Burrows and Grazing Behavior at >585 Million Years Ago
Ernesto Pecoits1,，*， Kurt O. Konhauser1,， Natalie R. Aubet1,，2， Larry M. Heaman1,， Gerardo Veroslavsky2,， Richard A. Stern1， Murray K. Gingras1
Based on molecular clocks and biomarker studies,， it is possible that bilaterian life emerged early in the Ediacaran,， but atpresent， no fossils or trace fossils from this time have been reported. Here we report the discovery of the oldest bilaterianburrows in shallow-water glaciomarine sediments from the Tacuarí Formation,， Uruguay. Uranium-lead dating of zircons in cross-cuttinggranite dykes constrains the age of these burrows to be at least 585 million years old. Their features indicate infaunal grazingactivity by early eumetazoans. Active backfill within the burrow,， an ability to wander upward and downward to exploit shallowlysituated sedimentary laminae， and sinuous meandering suggest advanced behavioral adaptations. These findings unite the paleontologicaland molecular data pertaining to the evolution of bilaterians,， and link bilaterian origins to the environmental changes thattook place during the Neoproterozoic glaciations.
