Conodont

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Not to be confused with Conodon or Cynodont.

Conodonts
Conodonts from the Glen Dean formation (Chester) of the Illinois basin (1958) (20654535006).jpg
Conodont elements
Scientific classification e
Kingdom: Animalia
Phylum: Chordata
Subphylum: Vertebrata
Class: †Conodonta
Eichenberg, 1930[1]
Groups
Synonyms
  • †Conodontophorida (otherwise an order according to Sepkoski, 2002[2])

Conodonts (Greek kōnos, "cone", + odont, "tooth") are an extinct group of agnathan (jawless) vertebrates resembling eels, classified in the class Conodonta. For many years, they were known only from their tooth-like oral elements, which are usually found in isolation and are now called conodont elements. Knowledge about soft tissues remains limited. They existed in the world's oceans for over 300 million years, from the Cambrian to the beginning of the Jurassic. Conodont elements are widely used as index fossils, fossils used to define and identify geological periods. The animals are also called Conodontophora (conodont bearers) to avoid ambiguity.

Discovery and understanding of conodonts

The teeth-like fossils of the conodont were first discovered by Heinz Christian Pander and the results published in Saint Petersburg, Russia, in 1856.[3] The name pander is commonly used in scientific names of conodonts.

It was only in the early 1980s that the first fossil evidence of the rest of the animal was found (see below). In the 1990s exquisite fossils were found in South Africa in which the soft tissue had been converted to clay, preserving even muscle fibres. The presence of muscles for rotating the eyes showed definitively that the animals were primitive vertebrates.[4]

Description

Life restoration of Promissum pulchrum

The 11 known fossil imprints of conodont animals record an eel-like creature with 15 or, more rarely, 19 elements that form a bilaterally symmetrical array in the head.[citation needed]

The organisms ranged from 1–40 cm (Promissum) in length.[5] Conodonts had large eyes, fins with fin rays, chevron-shaped muscles and a notochord.[6]

Elements

Conodont elements consist of mineralised teeth-like structures of varying morphology and complexity. The evolution of mineralized tissues has been puzzling for more than a century. It has been hypothesized that the first mechanism of chordate tissue mineralization began either in the oral skeleton of conodonts or the dermal skeleton of early agnathans.

The element array constituted a feeding apparatus that is radically different from the jaws of modern animals. They are now termed "conodont elements" to avoid confusion. The three forms of teeth, i.e., coniform cones, ramiform bars, and pectiniform platforms, probably performed different functions.

For many years, conodonts were known only from enigmatic tooth-like microfossils (200 micrometers to 5 millimeters in length[7]), which occur commonly, but not always, in isolation and were not associated with any other fossil. Until the early 1980s, conodont teeth had not been found in association with fossils of the host organism, in a konservat lagerstätte.[8] This is because the conodont animal was soft-bodied, thus everything but the teeth was unsuited for preservation under normal circumstances.

These microfossils are made of hydroxylapatite (a phosphatic mineral).[9] The conodont elements can be extracted from rock using adequate solvents.[10][11][12]

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.

Multielement conodonts

Preserved articulated association of conodont elements belonging to the species Archeognathus primus (Ordovician, North America)
Complete element set of the conodont Hindeodus parvus

The conodont apparatus may comprise a number of discrete elements, including the spathognathiform, ozarkodiniform, trichonodelliform, neoprioniodiform, and other forms.[13]

In the 1930s, the concept of conodont assemblages was described by Hermann Schmidt[14] and by Harold W. Scott in 1934.[15][16][17][18]

Elements of ozarkodinids

The feeding apparatus of ozarkodinids is composed of an axial Sa element at the front, flanked by two groups of four close-set elongate Sb and Sc elements which were inclined obliquely inwards and forwards. Above these elements lay a pair of arched and inward pointing (makellate) M elements. Behind the S-M array lay transversely oriented and bilaterally opposed (pectiniform, i.e. comb-shaped) Pb and Pa elements.[19]

Ecology

Model of elements of Manticolepis subrecta – a conodont from the Upper Frasnian of Poland – photography taken in the Geological Museum of the Polish Geological Institute in Warsaw

The "teeth" of some conodonts have been interpreted as filter-feeding apparatuses, filtering plankton from the water and passing it down the throat.[20] Others have been interpreted as a "grasping and crushing array".[5] Wear on some condont elements suggests that they functioned like teeth, with both wear marks likely created by food as well as by occlusion with other elements.[21] Studies have concluded that conodonts taxa occupied both pelagic (open ocean) and nektobenthic (swimming above the sediment surface) niches.[21] The preserved musculature suggests that some conodonts (Promissum at least) were efficient cruisers, but incapable of bursts of speed.[5] Based on isotopic evidence, some Devonian conodonts have been proposed to have been low-level consumers that fed on zooplankton.[21]

A study on the population dynamics of Alternognathus has been published. Among other things, it demonstrates that at least this taxon had short lifespans lasting around a month.[22] A study Sr/Ca and Ba/Ca ratios of a population of conodonts from a carbonate platform from the Silurian of Sweden found that the different conodont species and genera likely occupied different trophic niches.[21]

The some species of the genus Panderodus have been speculated to be venomous, based on grooves found on some elements..[23]

A rare body fossil of a Panderodus unicostatus from the Silurian aged Waukesha biota in southeastern Wisconsin.

Classification and phylogeny

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.[24]

Milsom and Rigby envision them as vertebrates similar in appearance to modern hagfish and lampreys,[25] and phylogenetic analysis suggests they are more derived than either of these groups.[26] However, this analysis comes with one caveat: early forms of conodonts, the protoconodonts, appear to form a distinct clade from the later paraconodonts and euconodonts. Protoconodonts likely represent a stem group to the phylum that includes chaetognath worms; this conclusion suggests that chaetognaths are not close relatives of true conodonts.[27] Moreover, some analyses do not regard conodonts as either vertebrates or craniates, because they lack the main characteristics of these groups.[28] More recently it has been proposed that conodonts may be stem-cyclostomes, more closely related to hagfish and lampreys than other living vertebrates.[29]

 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

 
 
 
 


  1. ^ Here, the hagfish are treated as a separate clade, as in Sweet and Donoghue's 2001 tree produced without cladistic analysis.[30] However, many recent analyses are finding out[31] that the hagfish and lampreys are closer to one another in their own clade, the Cyclostomata.
  2. ^ The clade Proconodontida is also known as Cavidonti.[30]
  3. ^ Euconodonta is referred to as "Conodonti" by Sweet and Donoghue.[30]

Evolutionary history

Conodont elements from the Deer Valley Member of the Mauch Chunk Formation in Pennsylvania, Maryland, and West Virginia, USA
detail
Figures 1, 2. Conodonts from the Deer Valley Member of the Mauch Chunk Formation, Keystone quarry, Pa. This collection (93RS–79c) is from the lower 10 cm of the Deer Valley Member. Note the nonabraded, although slightly broken, conodont elements of the high-energy oolitic marine facies of the Deer Valley Member.
1. Kladognathus sp., Sa element, posterior view, X140 2. Cavusgnathus unicornis, gamma morphotype, Pa element, lateral view, X140
3–9. Conodonts from the uppermost Loyalhanna Limestone Member of the Mauch Chunk Formation, Keystone quarry, Pa. This collection (93RS–79b) is from the upper 10 cm of the Loyalhanna Member. Note the highly abraded and reworked aeolian forms.
3, 4. Kladognathus sp., Sa element, lateral views, X140
5. Cavusgnathus unicornis, alpha morphotype, Pa element, lateral view, X140
6, 7. Cavusgnathus sp., Pa element, lateral view, X140
8. Polygnathus sp., Pa element, upper view, reworked Late Devonian to Early Mississippian morphotype, X140
9. Gnathodus texanus?, Pa element, upper view, X140
10–14. Conodonts from the basal 20 cm of the Loyalhanna Limestone Member of the Mauch Chunk Formation, Keystone quarry, Pa. (93RS–79a), and Westernport, Md. (93RS–67), note the highly abraded and reworked aeolian forms
10. Polygnathus sp., Pa element, upper view, reworked Late Devonian to Early Mississippian morphotype, 93RS–79a, X140
11. Polygnathus sp., Pa element, upper view, reworked Late Devonian to Early Mississippian morphotype, 93RS–67, X140
12. Gnathodus sp., Pa element, upper view, reworked Late Devonian(?) through Mississippian morphotype, 93RS–67, X140
13. Kladognathus sp., M element, lateral views, 93RS–67, X140
14. Cavusgnathus sp., Pa element, lateral view, 93RS–67, X140

The earliest fossils of conodonts are known from the Cambrian period. Conodonts extensively diversified during the early Ordovician, reaching their apex of diversity during the middle part of the period, and experienced a sharp decline during the late Ordovician and Silurian, before reaching another peak of diversity during the mid-late Devonian. Conodont diversity declined during the Carboniferous, with an extinction event at the end of the middle Tournaisian[32] and a prolonged period of significant loss of diversity during the Pennsylvanian.[33] Only a handful of conodont genera were present during the Permian, though diversity increased after the P-T extinction during the Early Triassic. Diversity continued to decline during the Middle and Late Triassic, culminating in their extinction at the Triassic-Jurassic boundary. Much of their diversity during the Paleozoic was likely controlled by sea levels and temperature, with the major declines during the Late Ordovician and Late Carboniferous due to cooler temperatures, especially glacial events and associated marine regressions which reduced continental shelf area. However, their final demise is more likely related to biotic interactions, perhaps competition with new Mesozoic taxa.[34]

Taxonomy

Conodonta taxonomy based on Sweet & Donoghue,[30][35] Mikko's Phylogeny Archive[36] and Fish classification 2017.[37][clarification needed]

Conodonta Pander, 1856 non Eichenberg, 1930 sensu Sweet & Donoghue, 2001 [Conodontia; Conodontophorida Eichenberg, 1930; Conodontochordata]

See also

References

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  2. ^ Sepkoski, J. J. (2002). "A compendium of fossil marine animal genera". Bulletins of American Paleontology. 363: 1–560.
  3. ^ Sweet, Walter C.; Cooper, Barry J. (December 2008). "C.H. Pander's introduction to conodonts, 1856". Retrieved 3 January 2019.
  4. ^ Jan Zalasiewicz and Sarah Gabbott (Jun 5, 1999). "The quick and the dead". New Scientist.
  5. ^ 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. Bibcode:1995Natur.374..800G. doi:10.1038/374800a0. S2CID 4342260.
  6. ^ Foster, John (2014-06-06). Cambrian Ocean World: Ancient Sea Life of North America. Indiana University Press. pp. 300–301. ISBN 978-0-253-01188-6.
  7. ^ MIRACLE. "Conodonts". Retrieved 26 August 2014.
  8. ^ 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.
  9. ^ Trotter, Julie A. (2006). "Chemical systematics of conodont apatite determined by laser ablation ICPMS". Chemical Geology. 233 (3–4): 196–216. Bibcode:2006ChGeo.233..196T. doi:10.1016/j.chemgeo.2006.03.004.
  10. ^ Jeppsson, Lennart; Anehus, Rikard (1995). "A Buffered Formic Acid Technique for Conodont Extraction". Journal of Paleontology. 69 (4): 790–794. doi:10.1017/s0022336000035319. JSTOR 1306313.
  11. ^ Green, Owen R. (2001). "Extraction Techniques for Phosphatic Fossils". A Manual of Practical Laboratory and Field Techniques in Palaeobiology: 318–330. doi:10.1007/978-94-017-0581-3_27. ISBN 978-90-481-4013-8.
  12. ^ Quinton, Page C. (2016). "Effects of extraction protocols on the oxygen isotope composition of conodont elements". Chemical Geology. 431: 36–43. Bibcode:2016ChGeo.431...36Q. doi:10.1016/j.chemgeo.2016.03.023.
  13. ^ Bergström, S. M.; Carnes, J. B.; Ethington, R. L.; Votaw, R. B.; Wigley, P. B. (1974). "Appalachignathus, a New Multielement Conodont Genus from the Middle Ordovician of North America". Journal of Paleontology. 48 (2): 227–235. doi:10.1666/0022-3360(2001)075<1174:CPPF>2.0.CO;2. JSTOR 1303249.
  14. ^ Schmidt, Hermann (1934). "Conodonten-Funde in ursprünglichem Zusammenhang". Paläontologische Zeitschrift. 16 (1–2): 76–85. doi:10.1007/BF03041668. S2CID 128496416.
  15. ^ Harold W. Scott, "The Zoological Relationships of the Conodonts. Journal of Paleontology, Vol. 8, No. 4 (Dec., 1934), pages 448-455 (Stable URL)
  16. ^ Scott, Harold W. (1942). "Conodont Assemblages from the Heath Formation, Montana". Journal of Paleontology. 16 (3): 293–300. JSTOR 1298905.
  17. ^ Dunn, David L. (1965). "Late Mississippian conodonts from the Bird Spring Formation in Nevada". Journal of Paleontology. 39: 6. Archived from the original on 2016-08-18. Retrieved 2016-07-15.
  18. ^ Barnes, Christopher R. (1967). "A Questionable Natural Conodont Assemblage from Middle Ordovician Limestone, Ottawa, Canada". Journal of Paleontology. 41 (6): 1557–1560. JSTOR 1302203.
  19. ^ Purnell, M. A.; Donoghue, P. C. (1997). "Architecture and functional morphology of the skeletal apparatus of ozarkodinid conodonts". Philosophical Transactions of the Royal Society B: Biological Sciences. 352 (1361): 1545–1564. Bibcode:1997RSPTB.352.1545P. doi:10.1098/rstb.1997.0141. PMC 1692076.
  20. ^ Purnell, Mark A. (1 April 1993). "Feeding mechanisms in conodonts and the function of the earliest vertebrate hard tissues". Geology. 21 (4): 375–377. Bibcode:1993Geo....21..375P. doi:10.1130/0091-7613(1993)021<0375:FMICAT>2.3.CO;2. Retrieved 15 July 2021.
  21. ^ a b c d Terrill, David F.; Jarochowska, Emilia; Henderson, Charles M.; Shirley, Bryan; Bremer, Oskar (2022-04-08). "Sr/Ca and Ba/Ca ratios support trophic partitioning within a Silurian conodont community from Gotland, Sweden". Paleobiology: 1–21. doi:10.1017/pab.2022.9. ISSN 0094-8373.
  22. ^ Świś, Przemysław (2019). "Population dynamics of the Late Devonian conodont Alternognathus calibrated in days". Historical Biology: An International Journal of Paleobiology: 1–9. doi:10.1080/08912963.2018.1427088. S2CID 89835464.
  23. ^ Szaniawski, Hubert (December 2009). "The Earliest Known Venomous Animals Recognized Among Conodonts". Acta Palaeontologica Polonica. 54 (4): 669–676. doi:10.4202/app.2009.0045.
  24. ^ Briggs, D. (May 1992). "Conodonts: a major extinct group added to the vertebrates". Science. 256 (5061): 1285–1286. Bibcode:1992Sci...256.1285B. doi:10.1126/science.1598571. PMID 1598571.
  25. ^ Milsom, Clare; Rigby, Sue (2004). "Vertebrates". Fossils at a Glance. Victoria, Australia: Blackwell Publishing. p. 88. ISBN 978-0-632-06047-4.
  26. ^ Donoghue, P.C.J.; Forey, P.L.; Aldridge, R.J. (2000). "Conodont affinity and chordate phylogeny". Biological Reviews. 75 (2): 191–251. doi:10.1111/j.1469-185X.1999.tb00045.x. PMID 10881388. S2CID 22803015. Retrieved 2008-04-07.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  27. ^ Szaniawski, H. (2002). "New evidence for the protoconodont origin of chaetognaths" (PDF). Acta Palaeontologica Polonica. 47 (3): 405.
  28. ^ Turner, S., Burrow, C.J., Schultze, H.P., Blieck, A., Reif, W.E., Rexroad, C.B., Bultynck, P., Nowlan, G.S.; Burrow; Schultze; Blieck; Reif; Rexroad; Bultynck; Nowlan (2010). "False teeth: conodont-vertebrate phylogenetic relationships revisited" (PDF). Geodiversitas. 32 (4): 545–594. doi:10.5252/g2010n4a1. S2CID 86599352. Archived from the original (PDF) on 2012-03-19. Retrieved 2011-02-11.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  29. ^ Miyashita, Tetsuto; Coates, Michael I.; Farrar, Robert; Larson, Peter; Manning, Phillip L.; Wogelius, Roy A.; Edwards, Nicholas P.; Anné, Jennifer; Bergmann, Uwe; Palmer, A. Richard; Currie, Philip J. (2019-02-05). "Hagfish from the Cretaceous Tethys Sea and a reconciliation of the morphological–molecular conflict in early vertebrate phylogeny". Proceedings of the National Academy of Sciences. 116 (6): 2146–2151. Bibcode:2019PNAS..116.2146M. doi:10.1073/pnas.1814794116. ISSN 0027-8424. PMC 6369785. PMID 30670644.
  30. ^ a b c d Sweet, W. C.; Donoghue, P. C. J. (2001). "Conodonts: Past, Present, Future" (PDF). Journal of Paleontology. 75 (6): 1174–1184. doi:10.1666/0022-3360(2001)075<1174:CPPF>2.0.CO;2. Archived (PDF) from the original on 2022-10-30.
  31. ^ Bourlat, Sarah J.; Juliusdottir, Thorhildur; Lowe, Christopher J.; Freeman, Robert; Aronowicz, Jochanan; Kirschner, Mark; Lander, Eric S.; Thorndyke, Michael; Nakano, Hiroaki; Kohn, Andrea B.; Heyland, Andreas; Moroz, Leonid L.; Copley, Richard R.; Telford, Maximilian J. (2006). "Deuterostome phylogeny reveals monophyletic chordates and the new phylum Xenoturbellida". Nature. 444 (7115): 85–88. Bibcode:2006Natur.444...85B. doi:10.1038/nature05241. ISSN 0028-0836. PMID 17051155. S2CID 4366885.
  32. ^ Zhuravlev, Andrey V.; Plotitsyn, Artem N. (18 January 2022). "The middle–late Tournaisian crisis in conodont diversity: a comparison between Northeast Laurussia and Northeast Siberia". Palaeoworld. doi:10.1016/j.palwor.2022.01.001. Retrieved 16 October 2022.
  33. ^ Shi, Yukun; Wang, Xiangdong; Fan, Junxuan; Huang, Hao; Xu, Huiqing; Zhao, Yingying; Shen, Shuzhong (September 2021). "Carboniferous-earliest Permian marine biodiversification event (CPBE) during the Late Paleozoic Ice Age". Earth-Science Reviews. 220. doi:10.1016/j.earscirev.2021.103699. Retrieved 4 September 2022.
  34. ^ Ginot, Samuel; Goudemand, Nicolas (December 2020). "Global climate changes account for the main trends of conodont diversity but not for their final demise". Global and Planetary Change. 195: 103325. Bibcode:2020GPC...19503325G. doi:10.1016/j.gloplacha.2020.103325. S2CID 225005180.
  35. ^ Sweet, W. C. (1988). "The Conodonta: morphology, taxonomy, paleoecology and evolutionary history of a long-extinct animal phylum". Oxford Monographs on Geology and Geophysics (10): 1–211. ISBN 978-0-19-504352-5.
  36. ^ Mikko's Phylogeny Archive [1] Haaramo, Mikko (2007). "Conodonta - conodonts". Retrieved 2015-12-30.
  37. ^ "Fish classification 2017". mayatan.web.fc2.com. Retrieved 2018-12-27.

Further reading

External links

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