魚嘴(fish mouth)也稱魚顎魚頜(fish jaw),是構成魚類口腔骨骼軟骨肌肉韌帶軟組織的組合結構,是魚類消化道呼吸道的開端。絕大多數硬骨魚有兩套頜骨——主要的口頜(oral jaws)負責開合嘴部併吞咬食物,而位於咽部後方的咽頜(pharyngeal jaws)則負責咀嚼吞咽食物[2][3]軟骨魚類(比如鯊魚鰩魚)只有由軟骨組成的口頜。通常情況下,魚類的頜骨由關節連接、垂直相對的上頜下頜組成,並且可以擁有規則排列的牙齒。軟骨魚的口頜則會長出數套多次從內向外移動更換的牙齒。

慈鯛頭骨中口頜(紫色)和咽頜(藍色)的側視圖[1]
展現一條幼年扁頭恐怖麗魚下咽頜和口頜中的鰓弓(咽弓)和角鰓硬組織(弓骨)的背視圖,白色星號所指的帶有牙齒的咽頜(圖中的比例尺為500微米[1]

魚類的頜骨(特別是硬骨魚)演化出了類似連杆機構的複雜結構,來適應水域生態系統中的各種競爭需求。比較明顯的是能夠迅速協調的將頜骨向前突出張開的平面四桿機構,使得魚嘴可以迅速擴大口腔體積並產生負壓獵物吸入口中。魚類的前上頜骨也配有這種結構[4],使得整個魚嘴擁有三套四桿機構可以前後、上下、左右的口腔直徑都產生擴大[4][5][6]

演化 編輯

 
魚類和其它脊椎動物演化紡錘圖[7],最早發展出頜部的是已經滅絕的盾皮魚綱棘魚綱

魚嘴的頜骨結構可能來源於支撐無頜魚類鰓部咽弓(pharyngeal arches)。最早的魚頜出現在約4億3000萬年前的志留紀的(已滅絕的)盾皮魚[8]棘魚之中[9]。擁有可積極開合的顎部最初的選擇優勢可能並不與進食有關,而是增加呼吸效率——顎部開合產生的「頰泵」(buccal pump)效應可以讓更多的新鮮水在單位時間內流過魚鰓以便增加納氧量。用開合頜骨進行吞咬很可能只是一個連帶產生的副功能,但隨後變成了許多從早期魚類演化出的脊椎動物的主要生存技能,被一些演化生物學家譽為「脊椎動物歷史上最深刻並最激進的演化步伐」[10][11]和「至關重要的創新」[12]。相比之下,無頜魚類的生存難度更高,因此大部分都在三疊紀滅絕沒能存活至今,對少數存活至今的圓口綱魚類(盲鰻七鰓鰻)的研究也沒能幫助解釋早期頜骨的演化對脊椎動物頭骨深層重塑的影響[13][14]

通常的看法是脊椎動物的頜骨與魚類的鰓弓(branchial arch或gill arches)同源[15],都來自於胚胎階段發展出的咽弓。無頜魚的鰓裂開口在嘴後方,由軟骨組織支撐,而第一組鰓弓則環繞嘴口。這第一組鰓弓在有頜魚中發生對摺彎曲變成了上下頜;第二鰓弓的上部在則變成了負責將頜骨和顱骨連接的舌頜骨(hyomandibula)[16],在真骨魚中還負責懸掛鰓蓋(operculum)[17]。現在被普遍接受的看法是有頜魚類的祖先是身上有骨質的甲板覆蓋、無頜的甲冑魚[18][19]

另見 編輯

參考 編輯

  1. ^ 1.0 1.1 Fraser, G. J.; Hulsey, C. D.; Bloomquist, R. F.; Uyesugi, K.; Manley, N. R.; Streelman, J. T. An ancient gene network is co-opted for teeth on old and new jaws. PLOS Biology. 2009, 7 (2): e1000031. PMC 2637924 . PMID 19215146. doi:10.1371/journal.pbio.1000031. 
  2. ^ Mabuchi, K.; Miya, M.; Azuma, Y.; Nishida, M. Independent evolution of the specialized pharyngeal jaw apparatus in cichlid and labrid fishes. BMC Evolutionary Biology. 2007, 7 (1): 10. PMC 1797158 . PMID 17263894. doi:10.1186/1471-2148-7-10. 
  3. ^ Alfaro, M. E.; Brock, C. D.; Banbury, B. L.; Wainwright, P. C. Does evolutionary innovation in pharyngeal jaws lead to rapid lineage diversification in labrid fishes?. BMC Evolutionary Biology. 2009, 9 (1): 255. PMC 2779191 . PMID 19849854. doi:10.1186/1471-2148-9-255. 
  4. ^ 4.0 4.1 Westneat, Mark W. Feeding mechanics of teleost fishes (Labridae; Perciformes): A test of four-bar linkage models. Journal of Morphology. September 1990, 205 (3): 269–295. PMID 29865760. S2CID 46933606. doi:10.1002/jmor.1052050304. 
  5. ^ Olsen, Aaron M.; Camp, Ariel L.; Brainerd, Elizabeth L. The opercular mouth-opening mechanism of largemouth bass functions as a 3D four-bar linkage with three degrees of freedom. Journal of Experimental Biology. 15 December 2017, 220 (24): 4612–4623. PMID 29237766. doi:10.1242/jeb.159079 . 
  6. ^ Muller, M. A novel classification of planar four-bar linkages and its application to the mechanical analysis of animal systems. Philosophical Transactions of the Royal Society of London. Series B: Biological Sciences. 29 May 1996, 351 (1340): 689–720. Bibcode:1996RSPTB.351..689M. PMID 8927640. doi:10.1098/rstb.1996.0065. 
  7. ^ Benton 2005.
  8. ^ Placodermi: Overview. Palaeos. [10 December 2014]. (原始內容存檔於2022-06-28). 
  9. ^ Acanthodii. Palaeos. [10 December 2014]. (原始內容存檔於2022-06-28). 
  10. ^ Gai, Z.; Zhu, M. The origin of the vertebrate jaw: Intersection between developmental biology-based model and fossil evidence. Chinese Science Bulletin. 2012, 57 (30): 3819–3828. Bibcode:2012ChSBu..57.3819G. doi:10.1007/s11434-012-5372-z . 
  11. ^ Maisey, J. G. Discovering Fossil Fishes. Westview Press. 2000: 1–223 [2023-01-06]. ISBN 978-0-8133-3807-1. (原始內容存檔於2022-06-30). 
  12. ^ Kimmel, C. B.; Miller, C. T.; Keynes, R. J. Neural crest patterning and the evolution of the jaw. Journal of Anatomy. 2001, 199 (1&2): 105–119. PMC 1594948 . PMID 11523812. doi:10.1017/S0021878201008068. 
  13. ^ Janvier, P. Homologies and Evolutionary Transitions in Early Vertebrate History. Anderson, J. S.; Sues, H.-D. (編). Major Transitions in Vertebrate Evolution. Indiana University Press. 2007: 57–121 [2023-01-06]. ISBN 978-0-253-34926-2. (原始內容存檔於2022-06-29). 
  14. ^ Khonsari, R. H.; Li, B.; Vernier, P.; Northcutt, R. G.; Janvier, P. Agnathan brain anatomy and craniate phylogeny. Acta Zoologica. 2009, 90 (s1): 52–68. S2CID 56425436. doi:10.1111/j.1463-6395.2008.00388.x. 
  15. ^ For example: (1) both sets of bones are made from neural crest cells (rather than mesodermal tissue like most other bones); (2) both structures form the upper and lower bars that bend forward and are hinged in the middle; and (3) the musculature of the jaw seem homologous to the gill arches of jawless fishes. (Gilbert 2000)
  16. ^ Gilbert. Evolutionary Embryology. 2000 [2022-06-27]. (原始內容存檔於2021-09-07). 
  17. ^ Clack, J. A. Earliest known tetrapod braincase and the evolution of the stapes and fenestra ovalis. Nature. 1994, 369 (6479): 392–394. Bibcode:1994Natur.369..392C. S2CID 33913758. doi:10.1038/369392a0. 
  18. ^ Donoghue, P. C.; Purnell, M. A. Genome duplication, extinction and vertebrate evolution. Trends in Ecology & Evolution. 2005, 20 (6): 312–319. PMID 16701387. doi:10.1016/j.tree.2005.04.008. 
  19. ^ Forey, P. L.; Janvier, P. Agnathans and the origin of jawed vertebrates. Nature. 1993, 361 (6408): 129–134. Bibcode:1993Natur.361..129F. S2CID 43389789. doi:10.1038/361129a0. 

額外閱讀 編輯

外部連結 編輯

外部影片連結
  Video of a slingjaw wrasse catching prey by protruding its jaw
  Video of a red bay snook catching prey by suction feeding