Condonts.

[TheFury 0]

What are the Conodonts, an overview of Class Conodonta.

The Conondonta are an extinct class of worm like Chordates that exhibit bilateral symmetry. First described in 1856 by Christian Heinrich Pander, the conodonts were thought to have been the fossilized teeth and jaws of an extinct group of fishes. Pander used the term Conodonten to refer to both the animal and the fossilized jaw parts. Today, we use the term conodont to refer to the whole animal and conodont element to refer to the mineralized skeletal structures. In 1934 Hermann Schmitt and Harold Scott discovered groups of conodont elements preserved in the same bedding plane of black shale. This led to the theory that the individual elements in life, were in pairs. They were termed an apparatus, similar to mouth parts. (Donahue 1998, Sweet et al, 2001, Prothero 2004)

The fossilized conodont elements are constructed of calcium fluroapartite and represent the teeth and jaw like structures found in the head of the conodont animal. In the fossil record the conodonts appear in rocks from the Precambrian. However they are more abundant in rock from the Cambrian onwards. Conodonts like many other creatures of the Paleozoic and mesozoic eras went through a number of radiation and extinction events. During the Ordovician, Devonian conodonts diversified and remained widespread throughout the Carboniferous. During the Permian they suffered a major extinction and finally disappeared from the fossil record during the late Triassic. (Bergstrom 1977, Orchard 2007, Habibi et al, 2008)

The conodont elements range in size from 200 microns to 6mm. Found in marine rocks, they can be easily extracted using a simple three steep process. Firstly the entombing rock is disaggregated into smaller pieces 1 to 2 cm, then the carbonate matrix is decomposed with a week acidic solution like acetic acid. Next the wet residue is sieved through a 100 to 140 mesh screen using a gentle stream of water. Finally the conodonts can be concentrated by differential density using heavy liquids and magnetic separation from the insoluble rock residues. (Austin et al, 1987, Sweet et al, 2001)

Conodonts have a high significance in paleobiology. Generally recognized and vertebrates. Conodonts form one of the earlies and longest lived clades of jawless fish. They show the first direct evidence of macrophagey in vertebrates and their feeding mechanism hold a significant importance in understanding the evolution and diversification of aquatic vertebrates. (Donahue et al, 1999) Within the field of biostratigraphy, conodonts play an important roll as paleothermomitors, a proxy method to show that rocks have been altered by heat. Conodont elements contain traces of organic compounds with their apatitic structure and when subject to heat undergo a chemical transformation. Elements unaltered by heat present a pale yellow with a smooth surface. Gradual increases in temperature change the colour from light to dark brown, to black then grey, white and finally translucent. The Conodont Alteration Index (CAI) is a scale of 1-8 where each colour change is represents a specific temperature band. This makes conodonts useful in petroleum exploration, for dating source rocks and the temperature and pressures that these rocks have been exposed to. (Rasmussen, 2001, Voldman et al, 2008)

The morphology of the conodont elements can be broken into 3 main types, Coniform, Ramiform, Pentiform. Each type can perform a number of basic functions, grasping, filtering, cutting, crushing and grinding. The coniform element is the most simple in structure, consisting of a single curved denticle with a sharp pointed cusp on a rounded basal structure. The convex edge was on the anterior side and the concave edge was to the posterior side. The primary functions of the coniform element were grasping and filtering. (Black 1988, Zhuravlev 2007)

The ramiform elements consists of elongate base with to form a bar like structure with smaller conical denticles in front of and behind the main cusp. The basal cavity is deepest under the main cusp. The first order denticles are stout and stand above the more numerous second order denticles. The primary function of the ramiform element was filtering, grasping and cutting. The roll of cutting has been evidenced by wear marks along the flattened lateral surfaces of the denticles and scissor like arrangement of the elements.(Black 1988, Zhuravlev 2007)

It is believed that the pectiniform elements evolved from the ramiform elements with the development of broad flanges into plates. Pectiniform elements probably performed the widest range of functions. The free blade could have been used for cutting while the platform was used for grinding and crushing. Pectiniform elements without a pronounced blade would have primarily functioned as grinding and crushing apparatus. (Black 1988, Zhuravlev 2007)

Consisting mostly of soft body tissues, the conodont animal does not preserve well as a fossil. There have been very few full bodied conodont fossils. The best examples come from the Granston Shrimp Bed, lower carboniferous period rocks in Scotland. (Sweet 1985, Aldridge et al, 1993) The Granston specimen appears to have an eel like body, with a complete conodont apparatus in its mouth and throat region. The anterior end features large sclerotic ring (Prothero 2004) that some describe as functional eyes. (Bergström 1998) Also present are ears and a pharynx, mouth and apparatus.

The conodont also have fins supported by rays and segmented mussels that run the length of the body with a dorsal fin completing the posterior end. The conodont once reconstructed is much like a modern day Hagfish or Lampray, with an array of conodont elements in its pharyngeal region. (Aldridge et al, 1993 Prothero 2004, Donahue et al, 1998)


References
Aldridge, R.J., Briggs, D.E.G., Smith, M.P., Clarkson, E.N.K., Clark, N.D.K., (1993), The anatomy of conodonts. Philos. Trans. R. Soc. London Ser B 340. p. 405–421

Austin, R.L. (editor). (1987). Conodonts: investigative techniques and applications. Chichester, England: Ellis Horwood, 422 pp.

Bergstrom, S.M., (1977). Early Paleozoic Conodont Biostratigraphy in the Atlantic Borderlands. Developments in Palaeontology and StratigraphyElsevier. Stratigraphic Micropaleontology of Atlantic Basin and Borderlands, p.85-110.

Bergström. J., Naumann. W.W., Viehweg. J., Martí-Mus. M., (1998), Conodonts, Calcichordates and the Origin of Vertebrates. Mitteilungen aus dem Museum für Naturkunde in Berlin. Geowissenschaftliche Reihe 1 (1) p. 81-91.

Black, R.M., (1988), The Elements of Palaeontology, Cambridge University Press. p. 271-274.

Donoghue, P.C.J., (1998), Growth and patterning in the conodont skeleton. Philosophical transactions-Royal Society of London. Biological sciences. 353, P.633-666.

Donoghue, P.C.J., Purnell, M.A., (1999), Mammal-like occlusion in conodonts. Paleobiology, 25(1), p. 58–74

Donoghue, P.C.J., Purnell, M.A., Aldridge, R. J., (1998), Conodont anatomy, chordate phylogeny and vertebrate classifcation. Lethaia 31, p.211-219.

Habibi, T., Corradini, C.,Yazdi, M.., (2008). Conodont biostratigraphy of the Upper Devonian-Lower Carboniferous Shahmirzad section, central Alborz, Iran, Geobios, doi:10.1016/j.geobios.2008.04.002

Orchard, M.J., ( 2007). Conodont diversity and evolution through the latest Permian and Early Triassic upheavals, Palaeogeography, Palaeoclimatology, PalaeoecologyVolume 252, Issues 1-2, , The Permian-Triassic Boundary Crisis and Early Triassic Biotic Recovery, p.93-117.

Prothero, D.R., (2004). Bringing fossils to life: an introduction to paleobiology. McGraw-Hill 2nd ed, p.353-356.

Rasmussen, J.A., Paul Smith. M., (2001), Conodont geothermometry and tectonic overburden in the northernmost East Greenland Caledonides. Geological. Magazine. 138 (6), p. 687–698..

Sweet, W.C., (1985), Conodonts: Those Fascinating Little Whatzits. Journal of Paleontology 59 (3), p.485-494.

Sweet, W.C., Donohue, P.C.J.,.(2001). Conodonts: Past, Present, Future. Journal of Paleontology, p.1174–1184

Voldman, G,G., Albanesi, G.I., Do Campo, M., (2008), Conodont palaeothermometry of contact metamorphism in Middle Ordovician rocks from the Precordillera of western Argentina. Geological. Magazine. 145 (4), p.449–462.

Zhuravlev. A. V., (2007), Morphofunctional Analysis of Late Paleozoic Conodont Elements and Apparatuses, Paleoontological Journal. 41 (5), p.549-557. Edited December 15, 2008 by The_Fury (see edit history)

[ernesto 0]

Great! Whats that image on your profile. IS it a worm too?Never heard of condonts, ut I just figured that they had bilateral symmetry!Whata a complex morphology!, remids me of silkworms.I think science is ever-growing.You included so many references, whata good idea!I enjoy your posts very much.