DESCRIPTION OF THE SUPERCLASS CONODONTOMORPHI+ (NELSON 2006)
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SUPERCLASS CONODONTOMORPHI LINKS
| Conodontomorphi (KON-o-don-to-MOPF-e) is formed from three Greek roots meaning “cone-toothed forms” [cone- konos (κώνος); tooth- donti (δόντι); form- morfi (μορφή)]. The name is derived from denticles that are very abundant in Paleozoic strata. This name for the group was created by Nelson (2006) in recognition of its elevation to a taxon higher than class and a modification of its former class name, Conodota (Eichenberg 1930). |
| INTRODUCTION TO THE CONODONTOMORPHI The biology of the conodonts is a little difficult to infer from the scant evidence that we have today. Though conodont teeth are common, indeed so common that they are used as stratographic standards, the nature of the conodont organism was in doubt until 1983 (Briggs et al. 1983; and Briggs 1992) when lamprey-like animals with conodont teeth were found as nearly complete and highly detailed carbonized films in Scotland. The animals had in-line fins only and appeared to be similar to lampreys with two large paired eyes. Likely they were free-swimming and predators (or at least scavengers) much like the hagfishes (Figure 1). The jawless mouths of conodont animals had batteries of teeth that seemed to serve the functions of grasping and then chopping prey (Figure 2). Only in a few sites have the carbonized bodies of conodonts been found; so, the taxonomic system of the animals rests entirely on the structure of the teeth, which are remarkably abundant from the Cambrian to the Triassic. Their dental elements came in 3 forms called S, M, and P. S and M elements were associated with the front end of the mouth and served to grasp prey. P elements were at the back of the pharynx and served to chop the prey to pieces. Szaniawski (2006 and 2009) interpreted grooves in the grasping elements of certain conodonts as venom-delivery structures. If so, the conodonts of the Ordovician and Devonian periods are the oldest known venomous animals. |
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| FIGURE 1. Reconstruction of the conodont animal. Note the large eyes and eel-like appearance. Image From: http://palaeo.gly.bris.ac.uk/palaeofiles/triassic/whaext.htm | FIGURE 2. Conodont teeth of three major types: BA (bar), BL (blade), P (platform), and S (single cone). Image from: http://energy.usgs.gov/images/oilgas/ha000001_sm.jpg |
FIGURE 3. A cladogram that shows the relationship between the conodonts, lampreys (Petromyzontomorphi), and the rest of the agnathan taxa. It is based primarily on Janvier (2008a, 2013) and Donoghue and Purnell (2005).
| Their particular position in the Vertebrata is still in doubt. Donoghue et al. (2000) placed them in a separate Subphylum Conodontophorida as distinct from the Vertebrata (craniata) and sisters to the Myxiniodea. Turner et al. (2010) suggest that the conodonts are not vertebrates at all, but are morphologically too simple and should be considered sisters to the vertebrates. The consensus view is that they are vertebrates and related to the lampreys, a group that they resemble very much (e.g. Benton 2005). However, that particular relationship between the lampreys and conodonts is not universally accepted. Benton (2005) proposes a sister relationship between the two groups while Janvier (2008a) suggests that the conodonts are more derived by the acquisition of a dermoskeleton in the mouth and pharynx. The acquisition of the dermoskeleton is the marker that Donoghue and Purnell (2005) and Janvier (2013) use to theorize that the conodonts emerged after the second round of whole genome duplication (2R). Our system is based on the emergence of the conodonts at the base of the 2R whole genome duplication. |
| LITERATURE CITED Benton, M. J. 2005. Vertebrate Paleontology. Third Edition. Blackwell Publishing, Malden, MA. Briggs, D. E. G. 1992. Conodonts: a major extinct group added to the vertebrates. Science. 256: 1285-1286. Briggs, D. E. G., E. N. K. Clarkson, and R. J. Aldridge. 1983. The conodont animal. Lethaia. 20: 1–14. Donoghue, P. C. J., P. L. Forey, and R. J. Aldridge. 2000. Conodont affinity and chordate phylogeny. Biological Reviews. 75: 191–251. Donoghue, P. C. J. and M. A. Purnell. 2005. Genome duplication, extinction, and vertebrate evolution. Trend in Ecology and Evolution. 20(6):312-319. Eichenberg, W. 1930. Conodonten aus dem Culm des Harzes. Paläontologische Zeitschrift. 12: 177-182. Janvier, P. 2008a. Early jawless vertebrates and cyclostome origins. Zoological Science. 25: 1045-1056. Nelson, J. S. 2006. Fishes of the World. 4th edition. John Wiley and Sons, Inc. New York. Sweet, W. C. and P. C. J. Donoghue. 2001. Conodonts: past, present, future. Journal of Paleontology. 75:1174-1184. Szaniawski, H. 2006. Biological interpretation of the structure of Panderodontidae. In: Purnell, M., P. Donoghue, R. Aldridge, and J. Repetski, eds. International Conodont Symposium 2006, Programme and Abstracts. 78. Leicester, UK. Szaniawski, H. 2009. The earliest known venomous animals recognized among conodonts. Acta Palaeontologica Polonica. 54(4): 669-676. Turner, S., C. J. Burrow, H-P. Schultze, A. Blieck, W-E. Reif, C. B. Rexroad, P. Bultynck, and G. S. Nowlan. 2010. False teeth: conodont-vertebrate phylogenetic relationships revisited. Geodiversitas. 32(4): 545-594. |
| By Jack R. Holt and Carlos A. Iudica. Last revised: 02/03/2018 |
