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Pteraspidomorphigroup is extinct

Philippe Janvier
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taxon links [up-->]Eriptychiida [up-->]Heterostraci [up-->]Arandaspida [up-->]Astraspida extinct icon extinct icon extinct icon extinct icon Phylogenetic position of group is uncertain[down<--]Vertebrata Interpreting the tree
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Interrelationships of the Pteraspidomorphi.

The main characteristics supporting the nodes of this phylogeny are:

Containing group: Vertebrata


The Pteraspidomorphi, or pteraspidomorphs, is a group of fossil jawless vertebrates which lived from the Early Ordovician to the Late Devonian (i.e. from 470 to 370 million years ago). They possess and extensive dermal armor covering the head, and a scaly tail. They have no other fin than the caudal fin. Their head armor, which always comprises large, median dorsal and ventral plates (or shields), is generally oblong, and this gives them the aspect of a tadpole. Pteraspidormorphs have long been regarded as closely related -or even ancestral- to jawed vertebrates, but the few characteristics they share with the latter are now considered as primitive for all vertebrates.

Most pteraspidomorphs were marine, but lived very near to the shore, in lagoons and deltas. Some groups are thought to have been fresh water. They were certainly bottom-dewellers, as shown by traces of abrasion of the ventral surface of their headshield.


Pteraspidomorphs are characterized by:

The Pteraspidomorphi include four clades, the Arandaspida, Astraspida, Eriptychiida and Heterostraci. Their dermal plates and scales are made up of acellular bone, or aspidine, but this is thought to be a primitive condition for the dermal bone of all bony vertebrates. Pteraspidomorphs have no calcified endoskeleton, except for eriptychiids and possibly arandaspids, which show traces of calcified cartilage. Pteraspidomorphs generally have a fusiform shape, with a head armor almost as long as the body, and have no other fin than the caudal fin, which is generally pad- or fan-shaped. The mouth is armed with elongate dermal plates which could expand as the mouth opened, and served as a scoop. The internal surface of the dermal plates -at any rate in heterostracans- shows impressions of the gills, brain, two vertical semicircular canal and distinctly paired nasal capsules. The nasal capsules of heterostracans seem to have opened ventrally into a separate median duct comparable to the nasopharyngeal duct of hagfishes. They are put among the Vertebrata because some heterostracans show impressions of arcualia (dorsal components of the vertebrae), and because they have a well-developed sensory-line system.

Discussion of Phylogenetic Relationships

Pteraspidomorphs have been first regarded as related to bony fishes, then to sharks, then ancestral to hagfishes, and finally as the closest jawless relatives of the gnathostomes. This last theory was based on the fact that they seem to have a paired olfactory organ and a sensory-line pattern which is quite similar to that of the gnathostomes. These characteristics are, however, likely to be general for either the vertebrates or, at any rate, for the ensemble of all "ostracoderms"+ the gnathostomes. Other "ostracoderms", such as the Galeaspida are now known to have a paired olfactory organ. Current phylogenetic analysis using a large number of characteristics (see Vertebrata page) now place pteraspidomorphs as the sister-group of all other "ostracoderms" and the gnathostomes.

The interrelationships of the Pteraspidomorphi are still poorly corroborated. The Astraspida share with the Heterostraci the dorsolateral position of the gill openings (single in heterostracans). The poorly known Eriptychiida seem to share with the Heterostraci the same type of dentine in the tubercles.


Blieck, A., Elliott, D. and Gagnier, P. Y. (1991). Some questions concerning the phylogenetic relationships of heterostracans, Ordovician to Devonian jawless vertebrates. In M.-M. Chang et al. (Eds.), Early vertebrates and related problems of evolutionary biology. Science Press, Beijing.

Halstead, L. B. (1982). Evolutionary trends and the phylogeny of the Agnatha. In Problems of phylogenetic reconstruction, The Systematics Association Special Volume, No. 21, (ed. K. A. Joysey and A. E. Friday), pp. 159-196. Academic Press, London.

Janvier, P. (1996a). Early vertebrates. Oxford Monographs in Geology and Geophysics, 33, Oxford University Press, Oxford.

Janvier, P. (1996b). The dawn of the vertebrates: characters versus common ascent in current vertebrate phylogenies. Palaeontology, 39, 259-287.

Stensiö, E.A. (1964). Les Cyclostomes fossiles ou Ostracodermes. In: Traité de paléontologie (ed. J. Piveteau), Vol. 4(1), pp. 96-383, Masson, Paris

Title Illustrations
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Scientific Name Pteraspida
Comments Pteraspidomorphs are among the earliest known vertebrates. They were jawless and possessed a massive dermal skeleton. They are characterized by their dermal head armor having large, median, ventral and dorsal plates or "shields" (red).
Reference after Janvier 1996
Specimen Condition Fossil
Image Use creative commons This media file is licensed under the Creative Commons Attribution License - Version 3.0.
Copyright © 1997
About This Page

Muséum National d'Histoire Naturelle Paris, France

Page: Tree of Life Pteraspidomorphi. Authored by Philippe Janvier. The TEXT of this page is licensed under the Creative Commons Attribution License - Version 3.0. Note that images and other media featured on this page are each governed by their own license, and they may or may not be available for reuse. Click on an image or a media link to access the media data window, which provides the relevant licensing information. For the general terms and conditions of ToL material reuse and redistribution, please see the Tree of Life Copyright Policies.

Citing this page:

Janvier, Philippe. 1997. Pteraspidomorphi. Version 01 January 1997 (under construction). http://tolweb.org/Pteraspidomorphi/14834/1997.01.01 in The Tree of Life Web Project, http://tolweb.org/

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