Conodont

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Conodonts
Temporal range: 495–199.6Ma
Late Cambrian to Late Triassic
ConodontZICA.png
Reconstruction of a conodont
Euconodonta.gif
Two conodont "teeth" and a reconstruction of a conodont
Scientific classification e
Kingdom: Animalia
Phylum: Chordata
Clade: Craniata
Subphylum: Vertebrata
Class: Conodonta
Eichenberg 1930
Groups
Synonyms
  • Conodontophorida

Conodonts are extinct chordates resembling eels, classified in the class Conodonta. For many years, they were known only from tooth-like microfossils now called conodont elements, found in isolation. Knowledge about soft tissues remains relatively sparse. The animals are also called Conodontophora (conodont bearers) to avoid ambiguity.

The conodont's teeth are the earliest teeth that we find in the fossil record. Neil Shubin writes: "For a long time conodonts were enigmas: scientists disagreed over whether they were animalian, plant or mineral. Conodonts were claimed to be pieces of clams, sponges, vertebrates, even worms. The speculation ended when whole animals started to show up in the fossil record. For years, paleontologists have argued about why hard skeletons, those containing hydroxyapatite, arose in the first place. For those who believed that skeletons began with the backbones, or body armor, conodonts provide an 'inconvenient tooth' if you will. The first hydroxyapatite-containing body parts were teeth. Hard bones arose not to protect animals but to eat them."[1]

Description[edit]

Conodont elements from the Deer Valley Member of the Mauch Chunk Formation

The 11 known fossil imprints of conodont animals depict an eel-like creature with 15, or more rarely, 19 elements forming a bilaterally symmetrical array in the head. This array constituted a feeding apparatus radically different from the jaws of modern animals. The three forms of teeth, coniform cones, ramiform bars, and pectiniform platforms, may have performed different functions.

The organisms range from a centimeter or so[verification needed] to the giant Promissum, 40 cm in length.[2] It is now widely agreed that conodonts had large eyes, fins with fin rays, chevron-shaped muscles and a notochord.

The entire class of conodonts is postulated to have been wiped out in the Triassic–Jurassic extinction event, which occurred roughly 200 million years ago.[3]

Ecology[edit]

The "teeth" of some conodonts have been interpreted as filter-feeding apparatuses, filtering out plankton from the water and passing it down the throat.[citation needed] Others have been interpreted as a "grasping and crushing array".[2] The lateral position of the eyes makes a predatory role unlikely.[citation needed] The preserved musculature hints that some conodonts (Promissum at least) were efficient cruisers, but incapable of bursts of speed.[2]

Classification and phylogeny[edit]

As of 2012 scientists classify the conodonts in the phylum Chordata on the basis of their fins with fin rays, chevron-shaped muscles and notochord.[4]

Milsom and Rigby envision them as vertebrates similar in appearance to modern hagfish and lampreys,[5] and phylogenetic analysis suggests they are more derived than either of these groups.[6] This analysis, however, comes with one caveat: early forms of conodonts, the protoconodonts, appear to form a distinct clade from the later paraconodonts and euconodonts. The protoconodonts likely represent a stem group to the phylum containing chaetognath worms, indicating they are not close relatives of true conodonts.[7] Moreover, some analyses do not regard conodonts as either vertebrates or craniates, because they lack the main characteristics of these groups.[8]

 Craniata 

Hagfish[Note 1]


 Vertebrata 
 Hyperoartia 

Lampreys



 Conodonta 

Paraconodontida




Proconodontida[Note 2]


 Euconodonta[Note 3] 


Protopanderodontida



Panderontida



 Prioniodontida 

Paracordylodus




Balognathidae




Prioniodinida



Ozarkodinida









Heterostracans, osteostracans and gnathostomes





Elements[edit]

For many years, conodonts were known only from enigmatic tooth-like microfossils, which occur commonly, but not always in isolation, and were not associated with any other fossil. These phosphatic microfossils are now termed "conodont elements" to avoid confusion. They are widely used in biostratigraphy.

Conodont elements are also used as paleothermometers, a proxy for thermal alteration in the host rock, because under higher temperatures, the phosphate undergoes predictable and permanent color changes, measured with the conodont alteration index. This has made them useful for petroleum exploration where they are known, in rocks dating from the Cambrian to the Late Triassic.

Until the early 1980s, conodont teeth had not been found in association with fossils of the host organism, in a konservat lagerstätte.[11] This is because most of the conodont animal was soft-bodied, thus everything but the teeth were not suited for preservation under normal circumstances.

The conodont apparatus may comprise a number of discrete elements, including the spathognathiform, ozarkodiniform, trichonodelliform, neoprioniodiform, and other forms.[12]

See also[edit]

  • Lau event - mass extinction event with major impact on conodonts

Notes[edit]

  1. ^ Here, the hagfish are treated as a separate clade, as in Sweet and Donoghue's 2001 tree produced without cladistic analysis.[9] However, it has been recognised by some [10] that the hagfish and lampreys may be closer to one another in their own clade, the Cyclostomata.
  2. ^ The clade Proconodontida is also known as Cavidonti.
  3. ^ Euconodonta is referred to as "Conodonti" by Sweet and Donoghue,[9] although this is not widely used[original research?].

References[edit]

  1. ^ Shubin, Neil (2009). Your Inner Fish: A Journay into the 3.5 Billion Year History of the Human Body (reprint ed.). New York: Pantheon Books. pp. 85–86. ISBN 9780307277459. 
  2. ^ a b c Gabbott, S.E.; R. J. Aldridge; J. N. Theron (1995). "A giant conodont with preserved muscle tissue from the Upper Ordovician of South Africa". Nature 374 (6525): 800–803. doi:10.1038/374800a0. 
  3. ^ The extinction of conodonts —in terms of discrete elements— at the Triassic-Jurassic boundary
  4. ^ Briggs, D. (May 1992). "Conodonts: a major extinct group added to the vertebrates". Science 256 (5061): 1285–1286. doi:10.1126/science.1598571. PMID 1598571. 
  5. ^ Milsom, Clare; Rigby, Sue (2004). "Vertebrates". Fossils at a Glance. Victoria, Australia: Blackwell Publishing. p. 88. ISBN 0-632-06047-6. 
  6. ^ Donoghue, P.C.J.; Forey, P.L.; Aldridge, R.J. (2000). "Conodont affinity and chordate phylogeny". Biological Reviews 75 (2): 191–251. doi:10.1017/S0006323199005472. PMID 10881388. Retrieved 2008-04-07. 
  7. ^ Szaniawski, H. (2002). "New evidence for the protoconodont origin of chaetognaths". Acta Palaeontologica Polonica 47 (3): 405. 
  8. ^ Turner, S., Burrow, C.J., Schultze, H.P., Blieck, A., Reif, W.E., Rexroad, C.B., Bultynck, P., Nowlan, G.S. (2010). "False teeth: conodont-vertebrate phylogenetic relationships revisited". Geodiversitas 32 (4): 545–594. doi:10.5252/g2010n4a1. 
  9. ^ a b Sweet, W. C.; P. C. J Donoghue (2001). "Conodonts: past, present, future". Journal of Paleontology 75 (6): 1174–1184. doi:10.1666/0022-3360(2001)075<1174:CPPF>2.0.CO;2. 
  10. ^ Bourlat, S. J; T. Juliusdottir, C. J Lowe, R. Freeman, J. Aronowicz, M. Kirschner, E. S Lander, M. Thorndyke, H. Nakano, A. B Kohn, others (2006). "Deuterostome phylogeny reveals monophyletic chordates and the new phylum Xenoturbellida". Nature 444 (7115): 85–88. doi:10.1038/nature05241. ISSN 0028-0836. PMID 17051155. 
  11. ^ Briggs, D. E. G.; Clarkson, E. N. K.; Aldridge, R. J. (1983). "The conodont animal". Lethaia 16 (1): 1–14. doi:10.1111/j.1502-3931.1983.tb01993.x.  edit
  12. ^ "Appalachignathus, a New Multielement Conodont Genus from the Middle Ordovician of North America". Journal of Paleontology (Paleontological Society) 48 (2): 227–235. 1974. doi:10.2307/1303249 (inactive 2014-04-16). JSTOR 1303249.  edit

Further reading[edit]

  • Aldridge, R. J.; Briggs, D. E. G.; Smith, M. P.; Clarkson, E. N. K.; Clark, N. D. L. (1993). "The anatomy of conodonts". Philosophical Transactions of the Royal Society of London, Series B 340 (1294): 405–421. doi:10.1098/rstb.1993.0082. 
  • Aldridge, R. J.; Purnell, M. A. (1996). "The conodont controversies". Trends in Ecology and Evolution 11 (11): 463–468. doi:10.1016/0169-5347(96)10048-3. PMID 21237922. 
  • Donoghue, P. C. J.; Forey, P. L.; Aldridge, R. J. (2000). "Conodont affinity and chordate phylogeny". Biological Reviews 75 (2): 191–251. doi:10.1017/S0006323199005472. PMID 10881388. 
  • Gould, Stephen Jay (1985). "Reducing Riddles". In The Flamingo's Smile, 245-260. New York, W.W. Norton and Company. ISBN 0-393-30375-6.
  • Janvier, P (1997). "Euconodonta". The tree of life web project, http://tolweb.org. Retrieved 2007-09-05. 
  • Knell, Simon J. The Great Fossil Enigma: The Search for the Conodont Animal (Indiana University Press; 2012) 440 pages
  • Sweet, Walter. The Conodonta.
  • Sweet, W. C.; Donoghue, P. C. J. (2001). "Conodonts: past, present and future". Journal of Paleontology 75 (6): 1174–1184. doi:10.1666/0022-3360(2001)075<1174:CPPF>2.0.CO;2. ISSN 0022-3360. 

External links[edit]