Category:Conodont

Conodonts (Greek kōnos, "cone", + odont, "tooth") are extinct agnathan chordates resembling eels, classified in the class Conodonta. For many years, they were known only from tooth-like microfossils found in isolation and now called conodont elements. Knowledge about soft tissues remains limited. The animals are also called Conodontophora (conodont bearers) to avoid ambiguity.

Conodonts are considered index fossils, fossils used to define and identify geological periods.

Ecology
The "teeth" of some conodonts have been interpreted as filter-feeding apparatuses, filtering plankton from the water and passing it down the throat.[citation needed] Others have been interpreted as a "grasping and crushing array".[8] The lateral position of the eyes makes it unlikely that conodonts were active predators.[citation needed] The preserved musculature suggests that some conodonts (Promissum at least) were efficient cruisers, but incapable of bursts of speed.[8]

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.[23]

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. 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]

Geological history
The conodonts first appeared during the Cambrian Stage 2 (also referred as Tommotian).[3] The still unnamed Cambrian Stage 10 can be defined as the first appearance of Eoconodontus notchpeakensis. The upper boundary is defined as the appearance of Iapetognathus fluctivagus which marks the beginning of the Tremadocian and is radiometrically dated as 485.4 ± 1.9 million years ago.

The Cambrian–Ordovician extinction event occurred approximately 488 million years ago. This early Paleozoic extinction event extirpated many conodonts.

The Lau event, about 420 million years ago, a relatively minor mass extinction during the Silurian period, had a major impact on conodont populations.

The Kačák Event was a period of significant extinctions. The group most affected was the Ammonoidea, although there were also faunal turnovers amongst conodonts and dacryoconarids.[4]

The entire class is postulated to have been wiped out in the Triassic–Jurassic extinction event, which occurred roughly 200 million years ago.[5] Near the end of the Triassic deadly marine biocalcification began to occur, along with oceanic acidification, sea-level fluctuations and the Central Atlantic Magmatic Province (CAMP) releasing carbon dioxide, sulfur dioxide and aerosols. These environmental catastrophes caused the extinction of the conodonts, along with 34% of other marine genera.[6]