Primordial ocean floor concept (stock image). 原始海底概念圖（庫存圖像）。
Credit: © AnnaPa / Adobe Stock 圖片來源：©AnnaPa / Adobe Stock
A team led by UC Riverside geologists has discovered the first ancestor on the family tree that contains most familiar animals today, including humans.
由加州大學裡弗賽德分校的地質學家帶領的一個團隊發現了當今最熟悉的動物，包括人類家譜中的第一個祖先。
The tiny, wormlike creature, named Ikaria wariootia, is the earliest bilaterian, or organism with a front and back, two symmetrical sides, and openings at either end connected by a gut. The paper is published today in Proceedings of the National Academy of Sciences.
這種微小的蠕蟲狀生物，稱為Ikaria wariootia，是最早的雙側對稱生物，即具有正面和背面，兩個對稱側面以及兩端通過腸胃相連的開口的生物。該論文今天發表在《Proceedings of the National Academy of Sciences》上。
The earliest multicellular organisms, such as sponges and algal mats, had variable shapes. Collectively known as the Ediacaran Biota, this group contains the oldest fossils of complex, multicellular organisms. However, most of these are not directly related to animals around today, including lily pad-shaped creatures known as Dickinsonia that lack basic features of most animals, such as a mouth or gut.
最早的多細胞生物，例如海綿和海藻墊，形狀各異。這一組統稱為Ediacaran生物群，包含最複雜的多細胞生物化石。但是，其中大多數與當今的動物沒有直接關係，包括稱為狄金森氏菌的睡蓮狀生物，缺乏大多數動物的基本特徵，例如嘴或腸。
The development of bilateral symmetry was a critical step in the evolution of animal life, giving organisms the ability to move purposefully and a common, yet successful way to organize their bodies. A multitude of animals, from worms to insects to dinosaurs to humans, are organized around this same basic bilaterian body plan.
雙邊對稱性的發展是動物生命進化的關鍵步驟，使有機體能夠有目的地移動，並且是一種常見但成功的組織身體的方式。圍繞著相同的基本雙側對稱生物人體計劃，組織了從蠕蟲到昆蟲再到恐龍再到人類的眾多動物。
Evolutionary biologists studying the genetics of modern animals predicted the oldest ancestor of all bilaterians would have been simple and small, with rudimentary sensory organs. Preserving and identifying the fossilized remains of such an animal was thought to be difficult, if not impossible.
研究現代動物遺傳學的進化生物學家預測，所有雙側對稱生物中最古老的祖先將是簡單而小巧的，具有基本的感覺器官。保存和鑑定這種動物的化石遺骸被認為是困難的，即使不是不可能的。
For 15 years, scientists agreed that fossilized burrows found in 555 million-year-old Ediacaran Period deposits in Nilpena, South Australia, were made by bilaterians. But there was no sign of the creature that made the burrows, leaving scientists with nothing but speculation.
在15年的時間裡，科學家們一致認為，在南澳大利亞州Nilpena擁有5.55億年歷史的Ediacaran時期沉積物中發現的化石洞穴是雙側對稱生物製造的。但是沒有跡象表明這種生物能夠挖洞，科學家們除了猜測外別無他法。
Scott Evans, a recent doctoral graduate from UC Riverside; and Mary Droser, a professor of geology, noticed miniscule, oval impressions near some of these burrows. With funding from a NASA exobiology grant, they used a three-dimensional laser scanner that revealed the regular, consistent shape of a cylindrical body with a distinct head and tail and faintly grooved musculature. The animal ranged between 2-7 millimeters long and about 1-2.5 millimeters wide, with the largest the size and shape of a grain of rice -- just the right size to have made the burrows.
斯科特·埃文斯（Scott Evans），最近從加州大學河濱分校獲得博士學位。地質學教授瑪麗·德羅斯（Mary Droser）注意到其中一些洞穴附近有微小的橢圓形印象。在美國國家航空航天局（NASA）外生生物學資助的資助下，他們使用了三維雷射掃描儀，該掃描儀揭示了圓柱體的規則，一致的形狀，具有明顯的頭尾和略微凹陷的肌肉組織。這種動物的長度在2-7毫米之間，寬在1-2.5毫米之間，最大的大小和形狀是米粒-恰好適合製作洞穴。
"We thought these animals should have existed during this interval, but always understood they would be difficult to recognize," Evans said. "Once we had the 3D scans, we knew that we had made an important discovery."
埃文斯說：「我們認為這些動物應該在這段時間內就已經存在了，但一直都知道它們將難以識別。」 「一旦進行了3D掃描，我們就知道我們已經做出了重要發現。」
The researchers, who include Ian Hughes of UC San Diego and James Gehling of the South Australia Museum, describe Ikaria wariootia, named to acknowledge the original custodians of the land. The genus name comes from Ikara, which means "meeting place" in the Adnyamathanha language. It's the Adnyamathanha name for a grouping of mountains known in English as Wilpena Pound. The species name comes from Warioota Creek, which runs from the Flinders Ranges to Nilpena Station.
研究人員包括加州大學聖地牙哥分校的伊恩·休斯（Ian Hughes）和南澳大利亞博物館的詹姆斯·蓋林（James Gehling），對伊卡裡亞（Ikaria wariootia）進行了命名，以表彰該土地的原始保管人。屬名稱來自Ikara，在Adnyamathanha語言中意為「聚會場所」。這是Adnyamathanha的名稱，是由英語中的Wilpena Pound組成的一組山脈的名稱。物種名稱來自Warioota Creek，該河從弗林德斯山脈到Nilpena站。
"Burrows of Ikaria occur lower than anything else. It's the oldest fossil we get with this type of complexity," Droser said. "Dickinsonia and other big things were probably evolutionary dead ends. We knew that we also had lots of little things and thought these might have been the early bilaterians that we were looking for."
德羅斯（Droser）說：「伊卡裡亞（Ikaria）洞穴的發生率比其他任何物種都低。這是我們獲得的最古老的化石。「狄金森病和其他大事情可能是進化的死胡同。我們知道我們也有很多小事情，並認為這些可能是我們一直在尋找的早期雙側對稱生物。」
In spite of its relatively simple shape, Ikaria was complex compared to other fossils from this period. It burrowed in thin layers of well-oxygenated sand on the ocean floor in search of organic matter, indicating rudimentary sensory abilities. The depth and curvature of Ikaria represent clearly distinct front and rear ends, supporting the directed movement found in the burrows.
儘管其形狀相對簡單，但與該時期的其他化石相比，依卡裡亞還是複雜的。它鑽入海底的一層充氧良好的薄沙中以尋找有機物，表明基本的感官能力。伊卡裡亞的深度和曲率代表了明顯不同的前端和後端，支持了洞穴中的定向運動。
The burrows also preserve crosswise, "V"-shaped ridges, suggesting Ikaria moved by contracting muscles across its body like a worm, known as peristaltic locomotion. Evidence of sediment displacement in the burrows and signs the organism fed on buried organic matter reveal Ikaria probably had a mouth, anus, and gut.
洞穴還保留了橫向的「 V」形山脊，表明伊卡裡亞人的身體像蠕蟲一樣通過收縮肌肉而蠕動，這被稱為蠕動。洞穴中沉積物移位的跡象和以地下有機物為食的生物體跡象表明，伊卡裡亞人可能有嘴，肛門和腸。
"This is what evolutionary biologists predicted," Droser said. "It's really exciting that what we have found lines up so neatly with their prediction."
「這是進化生物學家預言的，」德羅斯說。 「我們發現的結果與他們的預測如此巧妙地結合在一起，真是令人興奮。」
Ancestor 祖先
Animal 動物
Primordial原始的
Riverside 河畔
Geologist 地質學家
Human 人類
Wormlike 蠕蟲狀
Creature 生物
Sponge 海綿
Algal 藻類
Mat 墊
Symmetry 對稱
Rudimentary 基本的
Burrow 洞穴
Curvature 彎曲
本期：迷你數獨
每個謎題都由一個在不同位置給與提示數字的4x4或6x6網格組成。遊戲的目的是將空方格填上數字1到4（對於4x4大小的謎題）或者1到6（對於6x6的謎題），使得每一行，每一列以及每一個宮都沒有重複的數字出現。
本期難度：Moderate
註：數獨是一種源自 18 世紀末的瑞士數學家歐拉所創造的拉丁方塊遊戲。傳數獨源起於拉丁方陣（ Latin Square ）， 1970 年代在美國發展，改名為數字拼圖（ Number Place ）、之後流傳至日本並發揚光大，以數學智力遊戲智力拼圖遊戲發表。在 1984 年一本遊戲雜誌《パズル通信ニコリ》正式把它命名為數獨，意思是「在每一格只有一個數字」。後來一位前任香港高等法院的紐西蘭籍法官高樂德（ Wayne Gould ）在 1997 年 3 月到日本東京旅遊時，無意中發現了。他首先在英國的《泰晤士報》上發表，不久其他報紙也發表，很快便風靡全英國，之後他用了6年時間編寫了電腦程式，並將它放在網站上，使這個遊戲很快在全世界流行