Cephalaspidomorphi

Information about Cephalaspidomorphi

Cephalaspidomorphs

Reconstruction of Cephalaspis sp.

Kingdom:	Animalia
Phylum:	Chordata
(unranked)	Craniata
(unranked)	Cephalaspidomorphi

Subgroups

Osteostraci
Galeaspida
Pituriaspida
Anaspida
Hyperoartia - lampreys (disputed)

Cephalaspidomorphs are a taxon of jawless fishes named for the cephalaspids, a group of osteostracans. Most of the members of this group are extinct; however, it interests modern biologists because it may include the lampreys. If so, the lampreys extend the known range of the group from the Silurian and Devonian periods to the present day.

Classification

In the 1920s, the biologists Kiaer and StensiÃ¶ first recognized the Cephalaspidomorphi as including the osteostracans, anaspids, and lampreys, because all three groups share a single dorsal "nostril", now known as a nasohypophysial opening.

Since then, opinions on the relations among jawless vertebrates have varied. Most workers have come to regard the agnatha as paraphyletic, having given rise to the jawed fishes. Because of shared features such as paired fins, the origins of the jawed vertebrates may lie within the Cephalaspidomorphi. Some biologists no longer use the name Cephalaspidomorphi because relations among osteostraci and anaspida are unclear, and the affinities of the lampreys are also contested. Others have restricted the cephalaspidomorphs to include only groups more clearly related to the Osteostraci, such as Galeaspida and Pituriaspida, that were largely unknown in the 1920s.

Lampreys

Many reference works still regard Cephalaspidomorphi as a Linnean class whose sole living representaties are the lampreys.

External links

References

Janvier, Philippe. Early Vertebrates Oxford, New York: Oxford University Press, 1998. ISBN 0-19-854047-7

StensiÃ¶, E. A. (1927). The Devonian and Downtonian vertebrates of Spitsbergen. 1. Family Cephalaspidae. Skrifter om Svalbard og Ishavet, 12, 1-391.

Cephalaspis

Species

C. lyelli
C. magnificans

Cephalaspis ("Head Shield") was a genus of armored goldfish-sized to trout-sized detritivorous fish that lived in freshwater streams and estuaries of
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Scientific classification or biological classification is a method by which biologists group and categorize species of organisms. Scientific classification also can be called scientific taxonomy, but should be distinguished from folk taxonomy, which lacks scientific basis.
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Chordata
Bateson, 1885

Typical Classes

See below

Chordates (phylum Chordata) are a group of animals that includes the vertebrates, together with several closely related invertebrates.
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Craniata
Janvier 1981

Subphyla

Cephalaspidomorphi (disputed)
Myxini
Vertebrata

Craniata (sometimes Craniota) is a proposed clade of chordate animals that contains the vertebrates (subphylum Vertebrata) and Myxini (hagfish) as living
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Osteostraci ("Bony Shields") was a group of bony-armored jawless fish, termed "ostracoderms", that lived in what is now North America, Europe and Russia from the Middle Silurian to Late Devonian.
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Galeaspida

Galeaspida ("Helmet shields") is an extinct taxon of jawless marine and freshwater fish. Their name is derived from a latin word for helmet, galea, and refers to their massive bone shield on the head.
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Pituriaspida

Species

Pituriaspis doylei
Neeyambaspis enigmatica

The Pituriaspida ("Pituri Shield") are a small group of armored jawless fishes with tremendous nose-like rostrums, which lived in the marine, deltaic environments
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Anaspida ("Without Shields") are stem gnathostomes, and are classically regarded as the ancestors of lampreys. Anaspids were small marine agnathans that lacked scales and paired fins.
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Hyperoartia

subgroups

Jamoytius
Endeiolepis
Euphanerops
Petromyzontiformes (lampreys)

Hyperoartia is a group of jawless fishes that includes the modern lampreys and their fossil relatives.
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For the journal, see .

A taxon (plural taxa), or taxonomic unit, is a name designating an organism or group of organisms. A taxon is assigned a rank and can be placed at a particular level in a systematic hierarchy reflecting evolutionary
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Agnatha (Greek, "no jaws") is a paraphyletic superclass of jawless fish in the phylum Chordata, subphylum Vertebrata. Agnatha have existed since the Cambrian, and continue to live in modern times.
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Petromyzontiformes

Family: Petromyzontidae

Subfamilies

Geotriinae
Mordaciinae
Petromyzontinae

A lamprey (sometimes also called lamprey eel
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The Silurian is a major division of the geologic timescale that extends from the end of the Ordovician period, about 443.7 Â± 1.5 Ma (million years ago), to the beginning of the Devonian period, about 416.0 Â± 2.8 Ma (ICS 2004).
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Devonian is a geologic period of the Paleozoic era spanning from roughly 416 to 359 million years ago. It is named after Devon, England, where rocks from this period were first studied.
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In phylogenetics, a group of organisms is said to be paraphyletic (Greek para = near and phyle = race) if the group contains its most recent common ancestor, but does not contain all the descendants of that ancestor.
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Gnathostomata

Subgroups

Class Placodermi
Superclass Chondrichthyes
Microphylum Teleostomi
Class Acanthodii
Class Actinopterygii

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Linnaean taxonomy is a method of classifying living things originally devised by, and named for, Carl Linnaeus although it has changed considerably since his time. The greatest innovation of Linnaeus, and still the most important aspect of this system, is the general use of
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class is the rank in the scientific classification of organisms in biology below Phylum and above Order.

For example, Mammalia is the class used in the classification of dogs, whose phylum is Chordata (animals with notochords) and order is Carnivora (mammals that eat meat).
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