Conodont
Conodonts are extinct worm-like forms with distinctive multi-bladed teeth made of apatite (calcium phosphate). The animals are sometimes referred to as conodontophora ("bearers of conodonts"), taking the word "conodont" to refer to the teeth themselves. These tiny teeth are quite common in Paleozoic rocks and sands (250 to 500 million years old), but body fossils were not found until the late 1980s. They show complex, specialized structures, and survived through the ages and the fossilization process due to their resilient chemical composition (they are normally chitinous or phosphatic).
Conodonts and their presumed relatives are known from the Precambrian to the Late Triassic. The earliest forms are identified as Protoconodonts, followed by Paraconodonts, followed by Euconodonts, followed finally by the true Conodonts. Some authors regard the Euconodonts and Conodonts as being a continuous lineage.
Following the discovery of several body fossils in Scotland and South Africa, most paleontologists think conodonts — which turn out to have fins, cheveron shaped muscles, and eyes — are in the phylum chordata. There are a lot of opinions about where the conodonts belong amongst the chordates/vertebrates. Some paleontologists (Cochrane) place the Protoconodonts (therefore possibly also the conodonts) in a phylum along with the chaetognath worms. Complete fossils are rare, but the few, poorly preserved, imprints that have been found would seem to suggest an eel-like creature with up to 7 different kinds of tooth elements clustered together in the head, defining a feeding apparatus radically different from the jaws of modern animals.
A cladistic analysis by Donoghue et. al (1998). suggests that conodonts and Euconodonts are vertebrates. The paraconodonts (known only from teeth) are thought to be related, but the relationship is unclear. According to Donoghue, Paraconodonts are not related to the rest.
External links and references
- http://animaldiversity.ummz.umich.edu/site/accounts/information/Vertebrata.html
- http://tolweb.org/tree?group=Euconodonta&contgroup=Vertebrata
- Donoghue, P. C. J., Purnell, M. A., & Aldridge, R. J. (1998), Conodont anatomy, chordate phylogeny and vertebrate classification. Lethaia, 31, 211-219.
