The eyes of Tullimonstrum reveal a vertebrate affinity
The eyes of Tullimonstrum reveal a vertebrate affinity
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DOI：
10.1038/nature17647
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发表时间：
2016-04-28
期刊：
影响因子：
64.8
通讯作者：
Gabbott, Sarah E.
中科院分区：
文献类型：
--
作者：
Clements, Thomas;Dolocan, Andrei;Gabbott, Sarah E.
Tullimonstrum gregarium是一种标志性的软体化石，来自美国伊利诺斯州石炭纪的亚马逊河流域（mason Creek lagerstate）。尽管有大量的标本和不同的解剖结构，在过去的五十年中，各种分析都未能确定“塔利怪物”的系统发育亲缘关系，尽管它与软体动物(2)、环节动物(3)、(4)或脊索动物(5)等不同的门有关，但它仍然是一个谜（1-5）。Tullimonstrum的性质和系统发育亲缘关系已经对系统定位提出了质疑，因为没有保存下来的解剖结构提供明确的同源性证据，没有这些证据，比较分析就失败了。在这里，我们证明了兔眼具有超微结构细节，表明与脊椎动物的眼睛同源。利用扫描电子显微镜的解剖分析显示，Tullimonstrum的眼睛保存着一个由不同层的球状和圆柱形黑素体组成的厚层视网膜。时间飞行二次离子质谱分析和多元统计进一步证明了这些微体是黑素体。许多动物的眼睛里都有黑色素，但拥有两种不同形态的黑素体，它们成层排列，形成视网膜色素上皮，这是脊椎动物的一种突触形态。我们的分析表明，除了颜色图案(6)、生态学(7)和体温调节(8)的证据外，化石黑素体还可以携带系统发育信号。在兔足中发现形成视网膜色素上皮残余的球状和圆柱形黑素体，表明它是脊椎动物；从新的角度来看它的身体部位
Tullimonstrum gregarium is an iconic soft-bodied fossil from the Carboniferous Mazon Creek Lagerstatte ( Illinois, USA)(1). Despite a large number of specimens and distinct anatomy, various analyses over the past five decades have failed to determine the phylogenetic affinities of the 'Tully monster', and although it has been allied to such disparate phyla as the Mollusca(2), Annelida(3),(4) or Chordata(5), it remains enigmatic(1-5). The nature and phylogenetic affinities of Tullimonstrum have defied confident systematic placement because none of its preserved anatomy provides unequivocal evidence of homology, without which comparative analysis fails. Here we show that the eyes of Tullimonstrum possess ultrastructural details indicating homology with vertebrate eyes. Anatomical analysis using scanning electron microscopy reveals that the eyes of Tullimonstrum preserve a retina defined by a thick sheet comprising distinct layers of spheroidal and cylindrical melanosomes. Time-offlight secondary ion mass spectrometry and multivariate statistics provide further evidence that these microbodies are melanosomes. A range of animals have melanin in their eyes, but the possession of melanosomes of two distinct morphologies arranged in layers, forming retinal pigment epithelium, is a synapomorphy of vertebrates. Our analysis indicates that in addition to evidence of colour patterning(6), ecology(7) and thermoregulation(8), fossil melanosomes can also carry a phylogenetic signal. Identification in Tullimonstrum of spheroidal and cylindrical melanosomes forming the remains of retinal pigment epithelium indicates that it is a vertebrate; considering its body parts in this new light suggests