網路城邦
上一篇 回創作列表 下一篇   字體:
古代魚類化石揭示了人類手部的演化源頭
2020/03/29 11:35:22瀏覽44|回應0|推薦0

古代魚類化石揭示了人類手部的演化起源

在加拿大發現的古代化石揭示了人類的手如何從魚鰭進化而來的新見識。

在加拿大米瓜沙發現的古老Elpistostege魚化石揭示了人類手如何從魚鰭進化的新見解。

來自澳大利亞弗林德斯大學和加拿大魁北克大學Rimouski的一支古生物學家國際團隊發現,該魚標本已如《自然》雜誌所述,隨著魚類開始進食而在魚類與四足動物的過渡中缺失了進化聯繫。泥盆紀晚期數百萬年前的淺水和土地等棲息地。

這種完整的1.57米長的魚首次出現在任何腕骨魚類中的完整臂(胸鰭)骨骼。使用高能CT掃描,胸鰭的骨骼顯示出肱骨(臂),radius骨和尺骨(前臂),腕骨(腕)行和指骨以手指組織(手指)的存在。

完整的沃森尼標本

在背面查看完整的標本。比例尺,1 m。b,標本的顱後解剖學的照相機lucida圖;儘管僅在腹側可見,但已說明了胸鰭的位置。c,重建。an.fi,肛門鰭;cau.fi,尾鰭;運算符 pec.fi,胸鰭;pel.fi,骨盆鰭。信用:自然

“今天,我們在《自然》雜誌上宣布,我們發現了完整的四足類魚標本,稱為Elpistostege,它揭示了脊椎動物手進化的非凡新信息,”弗林德斯大學古生物學戰略教授約翰·朗說。

“這是我們首次明確發現在任何已知魚類中,手指都被鰭條鎖在鰭中。” 鰭中的可發音手指就像大多數動物手中的指骨一樣。”

“這一發現將脊椎動物中數字的起源推回了魚類的水平,並告訴我們,在魚類離開水面之前,脊椎動物手的圖案首先在進化中得到了深深的發展。

魚類進化為四足動物(人類屬於四足脊椎動物)是生命史上最重要的事件之一。

脊椎動物(背骨動物)便能夠離開水面並征服土地。為了完成此過渡,最重大的變化之一是手腳的演變。

為了了解從魚鰭到四足動物肢體的進化,古生物學家研究了中泥盆紀和上足泥盆紀(393-359百萬年前)的鰭鰭魚和四足動物的化石,這些化石被稱為“ elstestostegalians”。

其中包括加拿大北極地區的著名Tiktaalik,僅從不完整的標本中才知道。

比較解剖莖四足動物和早期四足動物

比較四足動物(Panderichthys,Tiktaalik和Elpistostege)和早期四足動物(Tulerpeton)的胸肢內骨骼(a)和肱骨(b)的解剖結構。徑向或數字的近端行顯示為根據圖4的方案進行了顏色編碼。b中的紅色箭頭表示外胚層。Panderichthys的數據來自參考文獻。13; Tiktaalik數據來自參考文獻。4; Acanthostega的數據來自參考文獻。26; Tulerpeton數據來自參考文獻。31. b中的圖像是從ref修改的。49. art.sf,鉸接表面;lat.dor,背闊肌的附著脊;旋後脊 rd.ext,徑向伸展器的固定區域;肩cap骨,肩骨和肱骨的附著區域。信用:自然

Rimouski魁北克大學的合著者Richard Cloutier說,在過去的十年中,化石為魚類向四足動物的過渡提供了幫助,從而更好地了解了與呼吸,聽力和進食有關的解剖學變化,因為棲息地從水變成了土地在地球上。

“數字的起源與開發魚類在淺水中支撐體重或短期出海的能力有關。鰭中小骨頭數量的增加允許更多的柔性平面通過鰭分散其重量。

該研究揭示的其他特徵與上臂骨或肱骨的結構有關,也顯示了與早期兩棲動物共有的特徵。Elpistostege不一定是我們的祖先,但它最接近我們可以找到真正的“過渡化石”,即魚類和四足動物之間的中間人。”

Elpistostege是生活在魁北克約3.8億年前的淺海至河口棲息地的最大捕食者。它的嘴中有強大的尖牙,因此可以捕食在同一礦床中化石的幾條較大的已滅絕的鰭鰭魚。

背景

Elpistostege最初僅取自頭骨屋頂的一小部分,位于魁北克省Miguasha國家公園的化石峭壁上,1938年被描述為屬於早期的四足動物。

1985年發現並描述了這只神秘動物的頭骨的另一部分,這表明它確實是一種高級的鰭鰭魚。Elpistostege的非凡新完整標本於2010年被發現。

新標本的精心準備和化石的CT掃描於2010年在魁北克進行,Cloutier教授與Isabelle Bechard共同對掃描數據進行了初步解釋,Vincent Roy和Roxanne Noel分析了骨架和鰭結構。

參考文獻:“ Elpistostege和脊椎動物手的起源”由理查德·克盧捷,愛麗絲M.克萊門特,邁克爾SY李,羅克珊諾埃爾,伊莎貝爾Béchard,文森特·羅伊和John A.龍年,2020年3月18日,自然
DOI:10.1038 / s41586-020-2100-8

2014年開始與John Long教授和Flinders University團隊合作。AliceClement博士繼續進行CT工作,該工作揭示了鰭中手指的細節。Mike Lee教授分析了系統發育數據,以證明Elpistostege現在是已知最進化的“高級”魚,位於進化樹上所有四足動物的下一個節點。該研究於2019年完成,當時Richard Cloutier教授作為弗林德斯大學訪問國際學者在休假期間工作了6個月。

這項研究由UQAR(電力公司)的古生物學和進化生物學研究實驗室資助。我們感謝米瓜沙國家公園(MHNM)借來的標本以及為研究該材料提供的特殊機會

Evolutionary Origin of the Human Hand Revealed by Ancient Fish Fossil

An ancient fossil found in Canada reveals new insights into how the human hand evolved from fish fins.

An ancient Elpistostege fish fossil found in Miguasha, Canada has revealed new insights into how the human hand evolved from fish fins.

An international team of paleontologists from Flinders University in Australia and Universite du Quebec a Rimouski in Canada have revealed the fish specimen, as described in the journal Nature, has yielded the missing evolutionary link in the fish to tetrapod transition, as fish began to foray in habitats such as shallow water and land during the Late Devonian period millions of years ago.

This complete 1.57 meter long fish shows the complete arm (pectoral fin) skeleton for the first time in any elpistostegalian fish. Using high energy CT-scans, the skeleton of the pectoral fin revealed the presence of a humerus (arm), radius and ulna (forearm), rows of carpus (wrist) and phalanges organized in digits (fingers).

Complete E. watsoni Specimen

Complete specimen in dorsal view. Scale bar, 1 m. b, Camera lucida drawing of the postcranial anatomy of the specimen; pectoral fins have been illustrated in their position, although they are only visible ventrally. c, Reconstruction. an.fi, anal fin; cau.fi, caudal fin; op, opercular; pec.fi, pectoral fin; pel.fi, pelvic fin. Credit: Nature

“Today we announce in the journal Nature our discovery of a complete specimen of a tetrapod-like fish, called Elpistostege, which reveals extraordinary new information about the evolution of the vertebrate hand,” says Strategic Professor in Palaeontology at Flinders University Professor John Long.

“This is the first time that we have unequivocally discovered fingers locked in a fin with fin-rays in any known fish. The articulating digits in the fin are like the finger bones found in the hands of most animals.”

“This finding pushes back the origin of digits in vertebrates to the fish level, and tells us that the patterning for the vertebrate hand was first developed deep in evolution, just before fishes left the water.”

The evolution of fishes into tetrapods — four-legged vertebrates of which humans belong — was one of the most significant events in the history of life.

Vertebrates (back-boned animals) were then able to leave the water and conquer land. In order to complete this transition, one of the most significant changes was the evolution of hands and feet.

In order to understand the evolution from a fish fin to a tetrapod limb, paleontologists study the fossils of lobe-finned fish and tetrapods from the Middle and Upper Devonian (393-359 million years ago) known as ‘elpistostegalians.’

These include the well-known Tiktaalik from Arctic Canada, known only from incomplete specimens.

Comparative Anatomy Stem-Tetrapod Fish and Early Tetrapod

Comparison of the anatomy of the pectoral limb endoskeleton (a) and humerus (b) of stem-tetrapod fish (Panderichthys, Tiktaalik and Elpistostege) and an early tetrapod (Tulerpeton). Proximodistal rows of radials or digits are shown color-coded according to the scheme in Fig. 4. Red arrows in b indicate the ectepicondyle. Panderichthys data are from ref. 13; Tiktaalik data are from ref. 4; Acanthostega data are from ref. 26; Tulerpeton data are from ref. 31. Images in b are modified from ref. 49. art.sf, articulation surfaces; lat.dor, attachment ridges for latissimus dorsi muscles; sup.rid, supinator ridge; rd.ext, attachment area for radial extensors; scap- hum., attachment area for scapula and humeral muscles. Credit: Nature

Co-author Richard Cloutier from Universite du Quebec a Rimouski says over the past decade, fossils informing the fish-to-tetrapod transition have helped to better understand anatomical transformations associated with breathing, hearing, and feeding, as the habitat changed from water to land on Earth.

“The origin of digits relates to developing the capability for the fish to support its weight in shallow water or for short trips out on land. The increased number of small bones in the fin allows more planes of flexibility to spread out its weight through the fin. ”

“The other features the study revealed concerning the structure of the upper arm bone or humerus, which also shows features present that are shared with early amphibians. Elpistostege is not necessarily our ancestor, but it is closest we can get to a true ‘transitional fossil,’ an intermediate between fishes and tetrapods.”

Elpistostege was the largest predator living in a shallow marine to estuarine habitat of Quebec about 380 million years ago. It had powerful sharp fangs in its mouth so could have fed upon several of the larger extinct lobe-finned fishes found fossilized in the same deposits.

Background

Elpistostege was originally named from just a small part of the skull roof, found in the fossiliferous cliffs of Miguasha National Park, Quebec, and described in 1938 as belonging to an early tetrapod.

Another part of the skull of this enigmatic beast was found and described in 1985, demonstrating it was really an advanced lobe-finned fish. The remarkable new complete specimen of Elpistostege was discovered in 2010.

Meticulous preparation of the new specimen and CT scanning of the fossil took place in Quebec in 2010 with Prof Cloutier working with Isabelle Bechard to do the initial interpretation of the scan data, and Vincent Roy and Roxanne Noel to analyze the backbone and fin structures.

Reference: “Elpistostege and the origin of the vertebrate hand” by Richard Cloutier, Alice M. Clement, Michael S. Y. Lee, Roxanne Noël, Isabelle Béchard, Vincent Roy and John A. Long, 18 March 2020, Nature.
DOI: 10.1038/s41586-020-2100-8

Collaboration with Prof John Long and the Flinders University team began in 2014. Dr Alice Clement continued the CT work which revealed details of the digits in the fin. Prof Mike Lee analysed the phylogenetic data to demonstrate that Elpistostege is now the most evolutionary ‘advanced’ fish known, one node down on the evolutionary tree to all tetrapods. The research was completed in 2019 when Prof Richard Cloutier spent 6 months on sabbatical working as a Flinders University Visiting International Fellow.

This study was funded by a Research Laboratory in Palaeontology and Evolutionary Biology at UQAR (Power Corporation Inc.). We thank the Parc national de Miguasha (MHNM) for the loan of the specimen and the special opportunity to work on this material.

( 不分類不分類 )
列印 加入我的文摘
上一篇 回創作列表 下一篇

引用
引用網址:http://classic-blog.udn.com/article/trackback.jsp?uid=acewang3005&aid=132263224