近日，西北大學(xué)早期生命研究所研究人員與國際團(tuán)隊(duì)合作,，發(fā)現(xiàn)了當(dāng)前已知最古老的立方水母化石記錄。相關(guān)成果日前發(fā)表于美國《科學(xué)公共圖書館·綜合》（PLoS One）,。
我國陜南寒武紀(jì)初期的寬川鋪組以盛產(chǎn)小殼化石和微體動物胚胎化石而聞名于世,。其中，五輻對稱的動物胚胎化石比較常見,，但其生物學(xué)屬性長期以來一直是個(gè)謎,。
上述研究團(tuán)隊(duì)發(fā)現(xiàn)，這些五輻對稱的化石胚胎其實(shí)屬于立方水母,，是當(dāng)前已知最古老的立方水母化石記錄,，距今大約5.35億年,，較先前從北美猶他州中寒武世地層中發(fā)現(xiàn)的四輻對稱的立方水母化石至少早2000萬年，比著名的澄江動物群刺胞動物還早1000萬年以上,。
據(jù)了解,，這些微體胚胎化石是科研人員通過冰醋酸浸解技術(shù)獲得的。此后,，研究人員應(yīng)用掃描電鏡觀察了其外貌,，再借助微CT解析了其內(nèi)部結(jié)構(gòu)。研究結(jié)果顯示,，這些化石保存了非常精美,、細(xì)致的原生內(nèi)部結(jié)構(gòu)，極少受到微生物降解的破壞,。
論文作者之一韓健表示,，這些立方水母胚胎化石雖然直徑僅有0.6毫米左右，但不僅保存了細(xì)小觸手,、垂管,、外傘等外部形態(tài)，還保存了呈五輻射對稱排列的隔膜,、生殖腺等微觀內(nèi)部結(jié)構(gòu),，其中后三者為現(xiàn)代立方水母所特有。（生物谷Bioon.com）
生物谷推薦的英文摘要
PLoS One doi:10.1371/journal.pone.0070741
Early Cambrian Pentamerous Cubozoan Embryos from South China
Jian Han mail,， Shin Kubota,， Guoxiang Li， Xiaoyong Yao,， Xiaoguang Yang,， Degan Shu， Yong Li,， Shunichi Kinoshita,， Osamu Sasaki， Tsuyoshi Komiya,， Gang Yan
Background
Extant cubozoans are voracious predators characterized by their square shape,， four evenly spaced outstretched tentacles and well-developed eyes. A few cubozoan fossils are known from the Middle Cambrian Marjum Formation of Utah and the well-known Carboniferous Mazon Creek Formation of Illinois. Undisputed cubozoan fossils were previously unknown from the early Cambrian； by that time probably all representatives of the living marine phyla,， especially those of basal animals,， should have evolved.
Methods
Microscopic fossils were recovered from a phosphatic limestone in the Lower Cambrian Kuanchuanpu Formation of South China using traditional acetic-acid maceration. Seven of the pre-hatched pentamerous cubozoan embryos， each of which bears five pairs of subumbrellar tentacle buds,， were analyzed in detail through computed microtomography (Micro-CT) and scanning electron microscopy (SEM) without coating.
Results
The figured microscopic fossils are unequivocal pre-hatching embryos based on their spherical fertilization envelope and the enclosed soft-tissue that has preserved key anatomical features arranged in perfect pentaradial symmetry,， allowing detailed comparison with modern cnidarians， especially medusozoans. A combination of features,， such as the claustrum,， gonad-lamella,， suspensorium and velarium suspended by the frenula， occur exclusively in the gastrovascular system of extant cubozoans,， indicating a cubozoan affinity for these fossils. Additionally,， the interior anatomy of these embryonic cubozoan fossils unprecedentedly exhibits the development of many new septum-derived lamellae and well-partitioned gastric pockets unknown in living cubozoans， implying that ancestral cubozoans had already evolved highly specialized structures displaying unexpected complexity at the dawn of the Cambrian. The well-developed endodermic lamellae and gastric pockets developed in the late embryonic stages of these cubozoan fossils are comparable with extant pelagic juvenile cubomedusae rather than sessile cubopolyps,， whcih indicates a direct development in these fossil taxa,， lacking characteristic stages of a typical cnidarian metagenesis such as planktonic planula and sessile polyps.
