Protopanderodontida
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Protopanderodontida is an
order Order, ORDER or Orders may refer to: * A socio-political or established or existing order, e.g. World order, Ancien Regime, Pax Britannica * Categorization, the process in which ideas and objects are recognized, differentiated, and understood ...
of
conodont Conodonts, are an extinct group of marine jawless vertebrates belonging to the class Conodonta (from Ancient Greek κῶνος (''kōnos''), meaning " cone", and ὀδούς (''odoús''), meaning "tooth"). They are primarily known from their hard ...
s which lived from the
Furongian The Furongian is the fourth and final epoch and series of the Cambrian The Cambrian ( ) is the first geological period of the Paleozoic Era, and the Phanerozoic Eon. The Cambrian lasted 51.95 million years from the end of the preceding ...
(Late Cambrian) to the Wenlock (mid-
Silurian The Silurian ( ) is a geologic period and system spanning 23.5 million years from the end of the Ordovician Period, at million years ago ( Mya), to the beginning of the Devonian Period, Mya. The Silurian is the third and shortest period of t ...
). They had a relative simple apparatus with several pairs of coniform elements (single-cusped tooth-like structures) in the mouth, lacking the more elaborate arrangements found in "complex conodonts" ( Prioniodontida). Protopanderodontids were a common component of
Ordovician The Ordovician ( ) is a geologic period and System (geology), system, the second of six periods of the Paleozoic Era (geology), Era, and the second of twelve periods of the Phanerozoic Eon (geology), Eon. The Ordovician spans 41.6 million years f ...
conodont faunas, and were probably a grade ancestral to later conodonts in the orders Panderodontida and Prioniodontida. They may have been the earliest conodonts with an odd number of elements in the jaw. A single median symmetrical element (the S0 element) is found at the midline of the apparatus, potentially originating from a fusion of paired coniform elements in an earlier ancestor. The only putative protopanderodontid to preserve an articulated partial apparatus is '' Besselodus arcticus'', from the Late Ordovician of
Greenland Greenland is an autonomous territory in the Danish Realm, Kingdom of Denmark. It is by far the largest geographically of three constituent parts of the kingdom; the other two are metropolitan Denmark and the Faroe Islands. Citizens of Greenlan ...
.


Taxonomy

Sweet Sweetness is a basic taste most commonly perceived when eating foods rich in sugars. Sweet tastes are generally regarded as pleasurable. In addition to sugars like sucrose, many other chemical compounds are sweet, including aldehydes, ketones, ...
(1988) named both Protopanderodontida and Panderodontida as new conodont orders, identifying the former as ancestral to the latter. The main difference between the two orders is that the elements of panderodontids have deep furrows on their sides, while those of protopanderodontids bear shallow striations. Sweet's decision to classify each group as inherently separate taxonomic orders would render Protopanderodontida a
paraphyletic Paraphyly is a taxonomic term describing a grouping that consists of the grouping's last common ancestor and some but not all of its descendant lineages. The grouping is said to be paraphyletic ''with respect to'' the excluded subgroups. In co ...
grade according to modern
cladistic Cladistics ( ; from Ancient Greek 'branch') is an approach to biological classification in which organisms are categorized in groups ("clades") based on hypotheses of most recent common ancestry. The evidence for hypothesized relationships is ...
standards. Panderodontida could be reconsidered a suborder or superfamily within Protopanderodontida, though others note that this would not solve the issue of paraphyly, since Protopanderodontida is probably also ancestral to Prioniodontida. The "distacodontid" '' Paltodus'' has been proposed as a transitional form between protopanderodontids and "complex conodonts". Exclusively coniform conodonts such as protopanderodontids are noted to be notoriously difficult to classify.


List of families

* Acanthodontidae Lindström, 1970 * Clavohamulidae Lindström, 1970 * Drepanoistodontidae Fåhraeus & Nowlan, 1978 istacodontidae Bassler, 1925* Protopanderodontidae Lindström, 1970 colopodontidae Bergström, 1981; Oneotodontidae Miller, 1980; Teridontidae Miller, 1981* Serratognathidae Zhen et al., 2009 * Strachanognathidae? Bergström, 1981 ornuodontidae Stouge, 1984* ''
Incertae sedis or is a term used for a taxonomy (biology), taxonomic group where its broader relationships are unknown or undefined. Alternatively, such groups are frequently referred to as "enigmatic taxa". In the system of open nomenclature, uncertainty ...
'' ** '' Besselodus''? Aldridge, 1982 ** '' Dapsilodus''? Cooper, 1976


References

Protopanderodontida {{Conodont-stub