Conodont

Conodonts Temporal range: 495–199.6 Ma PreЄ Є O S D C P T J K Pg N Late Cambrian to Late Triassic
Reconstruction of a Conodont
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
clade:	Craniata
Subphylum:	Vertebrata
Class:	†Conodonta Eichenberg 1930
Groups
Protoconodonta Conodonta Paraconodonta Euconodonta Panderodontida Prioniodontida Prioniodinina Ozarkodinina
Synonyms
†Conodontophorida

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

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 to this day. The animals are also called Conodontophora (conodont bearers) to avoid ambiguity.

Description

The eleven 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. There are three forms of teeth, coniform cones, ramiform bars, and pectiniform platforms, which may have performed different roles.

The organisms range from a centimeter or so^{[verification needed]} to the giant Promissum, 40 cm in length.^[1] 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, or at least what was left of them at the time, are postulated to have been wiped out by the Triassic–Jurassic extinction event, which occurred roughly 200 million years ago.^[2]

Ecology

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".^[1]

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.^[1]

Classification and Phylogeny

The conodonts are currently classified in the phylum Chordata because their fins with fin rays, chevron-shaped muscles and notochord are characteristic of Chordata.^[3]

They are considered by Milsom and Rigby to be vertebrates similar in appearance to modern hagfish and lampreys,^[4] and phylogenetic analysis suggests that they are more derived than either of these groups.^[5] 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. It appears likely that the protoconodonts represent a stem group to the phylum containing chaetognath worms, indicating that they are not close relatives of true conodonts.^[6] Moreover, some analyses suggest that Conodonts were not Vertebrates nor Craniates, because they lack the main characteristics of these groups.^[7]

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

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. This confusion is apparent for the non-specialist in the book "Your Inner Fish", by Neil Shubin, who describes the origin of teeth in chapter 4. In this chapter, the author attaches the name "conodont" to both the "conodont bearer" (the animal) and the "conodont elements" (the teeth), and the reader may have a hard time to make sense of the concept of "animals living in the mouths of animals".

They are widely used in biostratigraphy.

Conodont elements are also used as paleothermometers, a proxy for thermal alteration in the host rock. This is 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.

It was not until early 1980s that the conodont teeth were found in association with fossils of the host organism, in a konservat lagerstätte.^[10] 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.^[11]

Further reading

• 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. http://tolweb.org/tree?group=Euconodonta&contgroup=Vertebrate. Retrieved 2007-09-05. 
• 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

• Mark Purnell. "An oblique anterior view of a model of the apparatus of the Pennsylvanian conodont Idiognathodus". http://www.le.ac.uk/geology/map2/map2stuff/model.html. 
• ""The Jaws That Catch": an Introduction to the Conodonta". Palæos. http://www.palaeos.com/Vertebrates/Units/030Conodonta/030.000.html. Retrieved 2007-09-05. 
• Jim Davison (2002-10-15). "Ordovician conodonts". http://www.conodont.info. Retrieved 2009-07-07. 

Notes

1. ^ Here, the Hagfish are treated as a separate clade, as in Sweet and Donoghue's 2001 tree produced without cladistic analysis.^[8] However, it has been recognised by some ^[9] 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,^[8] although this is not widely used^{[original research?]}.

References

Paleontology portal

1. ^ ^{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. 
2. ^ The extinction of conodonts —in terms of discrete elements— at the Triassic-Jurassic boundary
3. ^ 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. 
4. ^ Milsom, Clare; Rigby, Sue (2004). "Vertebrates". Fossils at a Glance. Victoria, Australia: Blackwell Publishing. p. 88. ISBN 0632060476. 
5. ^ 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. http://journals.cambridge.org/abstract_S0006323199005472. Retrieved 2008-04-07. 
6. ^ Szaniawski, H. (2002). "New evidence for the protoconodont origin of chaetognaths". Acta Palaeontologica Polonica 47 (3): 405. http://app.pan.pl/archive/published/app47/app47-405.pdf. 
7. ^ 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. http://www.mnhn.fr/museum/front/medias/publication/31374_g2010n4a1.pdf. 
8. ^ ^{a b} Sweet, W. C; P. C.J Donoghue (2001). "Conodonts: past, present, future". Journal of Paleontology 75 (6): 1174. doi:10.1666/0022-3360(2001)075<1174:CPPF>2.0.CO;2. 
9. ^ 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. 
10. ^ 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
11. ^ "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. JSTOR 1303249.  edit