Conodont - AbsoluteAstronomy.com

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

Eel

Eels are an order of fish, which consists of four suborders, 20 families, 111 genera and approximately 800 species. Most eels are predators...

-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 to the giant Promissum
Promissum
Promissum is an extinct genus of primitive chordate that lived in the Ordovician period, about 500 million years ago.A conodont, Promissum had a primitive mouth under its eyes with mineralized teeth, which are both typical for conodonts, and also a primitive backbone...

, 40 cm in length. It is now widely agreed that conodonts had large eyes, fins with fin rays, chevron-shaped muscles and a notochord

Notochord

The notochord is a flexible, rod-shaped body found in embryos of all chordates. It is composed of cells derived from the mesoderm and defines the primitive axis of the embryo. In some chordates, it persists throughout life as the main axial support of the body, while in most vertebrates it becomes...

.

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.

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. Others have been interpreted as a "grasping and crushing array".

The lateral position of the eyes makes a predatory role unlikely.

The preserved musculature hints that some conodonts (Promissum at least) were efficient cruisers but incapable of bursts of speed.

Classification and Phylogeny

The conodonts are currently classified in the phylum Chordata because their fins with fin rays, chevron-shaped muscles and notochord

Notochord

are characteristic of Chordata.

They are considered by Milsom and Rigby to be vertebrates similar in appearance to modern hagfish and lampreys,
and phylogenetic analysis suggests that they are more derived

Derived

In phylogenetics, a derived trait is a trait that is present in an organism, but was absent in the last common ancestor of the group being considered. This may also refer to structures that are not present in an organism, but were present in its ancestors, i.e. traits that have undergone secondary...

than either of these groups. name="Donoghue2000"> 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

Chaetognatha

Chaetognatha, meaning hair-jaws, and commonly known as arrow worms, are a phylum of predatory marine worms that are a major component of plankton worldwide. About 20% of the known species are benthic, that is belonging to the lowest zone of the ocean, or benthic zone, and can attach to algae and...

worms, indicating that they are not close relatives of true conodonts. name="Szaniawski2002">
Moreover, some analyses suggest that Conodonts were not Vertebrates nor Craniates, because they lack the main characteristics of these groups. name="Turner&al2010">

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

Hydroxylapatite

Hydroxylapatite, also called hydroxyapatite , is a naturally occurring mineral form of calcium apatite with the formula Ca53, but is usually written Ca1062 to denote that the crystal unit cell comprises two entities. Hydroxylapatite is the hydroxyl endmember of the complex apatite group...

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

Neil Shubin

Neil Shubin is an American paleontologist, evolutionary biologist and popular science writer. He is the Robert R. Bensley Professor of Organismal Biology and Anatomy, Associate Dean of Organismal Biology and Anatomy and Professor on the Committee of Evolutionary Biology at the University of...

, 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

Biostratigraphy

Biostratigraphy is the branch of stratigraphy which focuses on correlating and assigning relative ages of rock strata by using the fossil assemblages contained within them. Usually the aim is correlation, demonstrating that a particular horizon in one geological section represents the same period...

.

Conodont elements are also used as paleothermometer

Paleothermometer

A paleothermometer is a methodology for determining past temperatures using a proxy found in a natural record such as a sediment, ice core, tree rings or TEX86.=...

s, 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

Conodont Alteration Index

The Conodont Alteration Index is used to estimate the maximum temperature reached by a sedimentary rock using thermal alteration of conodont fossils. Conodonts in fossiliferous carbonates are prepared by dissolving the matrix with acid, since the conodonts are composed of apatite and thus do not...

. This has made them useful for petroleum exploration where they are known, in rocks dating from the Cambrian

Cambrian

The Cambrian is the first geological period of the Paleozoic Era, lasting from Mya ; it is succeeded by the Ordovician. Its subdivisions, and indeed its base, are somewhat in flux. The period was established by Adam Sedgwick, who named it after Cambria, the Latin name for Wales, where Britain's...

to the Late Triassic

Triassic

The Triassic is a geologic period and system that extends from about 250 to 200 Mya . As the first period of the Mesozoic Era, the Triassic follows the Permian and is followed by the Jurassic. Both the start and end of the Triassic are marked by major extinction events...

.

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

Lagerstätte

A Lagerstätte is a sedimentary deposit that exhibits extraordinary fossil richness or completeness.Palaeontologists distinguish two kinds....

. 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.

Description

Ecology

Classification and Phylogeny

Elements

Further reading