Arthrodira

Arthrodira is an order of extinct armoured, jawed fishes of the class Placodermi that flourished in the Devonian period before their sudden extinction, surviving for about 50 million years and penetrating most marine ecological niches.

Arthrodira
Temporal range: Devonian
Dunkleosteus terrelli
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Placodermi
Order: Arthrodira
Woodward, 1891
Suborders and infraorders

basal

  • Actinolepina

Phlyctaenioidei

  • Phlyctaeniina

Brachythoraci

and see text

Greek for "jointed neck", the arthrodires had movable joint between armor surrounding the head and body. Lacking distinct teeth, like all placoderms, they used the sharpened edges of a bony plate as a biting surface. The eye sockets are protected by a bony ring, a feature shared by birds and some ichthyosaurs. Early arthrodires, such as the genus Arctolepis, were well-armoured fishes with flattened bodies. The largest member of this group, Dunkleosteus, was a true superpredator of the latest Devonian period, reaching 1 to as much as 6 m in length. In contrast, the long-nosed Rolfosteus measured just 15 cm.

A common misconception is the arthrodires (along with all other placoderms) were sluggish bottom-dwellers that were outcompeted by more advanced fish. Leading to this misconception is that the arthrodire body plan remained relatively conserved (that is, the majority of arthrodires were bullet- or torpedo-shaped) during the Devonian period, save for increasing in size. However, during their reign, the arthrodires were one of the most diverse and numerically successful, if not the most successful, vertebrate orders of the Devonian, occupying a vast spectrum of roles from apex predator to detritus-nibbling bottom dweller. Despite their success, the arthrodires were one of many groups eliminated by the environmental catastrophes of the Late Devonian extinction, allowing other fish such as sharks to diversify into the vacated ecological niches during the Carboniferous period.

Systematics[1]

Below is a cladogram from Dupret et al. (2009).[2]

Lunaspis broilii

Eurycaraspis incilis

Arthrodira

Yujiangolepis liujingensis

Antarctaspis mcmurdoensis

Wuttagoonaspidae

Yiminaspis shenme

Wuttagoonaspis fletcheri

Aethaspis major

Aethaspis utahensis

Lehmanosteus hyperboreus

Aleosteus eganensis

Simblaspis cachensis

Kujdanowiaspis buczacziensis

Kujdanowiaspis podolica

Erikaspis zychi

Sigaspis lepidophora

Eskimaspis heintzi

Baringaspis dineleyi

Proaethaspis ohioensis

Anarthraspis chamberlini

Heightingtonaspis anglica

Phyllolepida

Gavinaspis convergens

Phyllolepis orvini

Austrophyllolepis sp.

Cowralepis mclachlani

Placolepis budawangensis

Actinolepidae

Bollandaspis woschmidti

Actinolepis spinosa

Actinolepis magna

Actinolepis tuberculata

Bryantolepis brachycephalus

Phlyctaenioidei
Phlyctaeniidae

Phlyctaenius acadicus

Pageauaspis russelli

Groenlandaspidae

Groenlandaspis antarctica

Tiaraspis subilis

Arctaspidae

Dicksonosteus arcticus

Arctolepidae

Arctolepis decipiens

Heintzosteus brevis

Brachythoraci

Antineosteus lehmani

Buchanosteus confertituberculatus

Coccosteus cuspidatus

Actinolepidoidei
Phlyctaeniina

ORDER ARTHRODIRA

Genera incertae sedis

Arthrodira of unresolved relationships

Timeline of genera

Footnotes

  1. For sources, see Haaramo (2005)
  2. Dupret, V.; Zhu, M. I. N.; Wang, J. N. Q. (2009). "The morphology of Yujiangolepis liujingensis (Placodermi, Arthrodira) from the Pragian of Guangxi (south China) and its phylogenetic significance". Zoological Journal of the Linnean Society. 157: 70. doi:10.1111/j.1096-3642.2009.00519.x.

See also

List of placoderms

References

  • Long, John A. (1996): The Rise of Fishes: 500 Million Years of Evolution. Johns Hopkins University Press, Baltimore. ISBN 0-8018-5438-5
  • Sepkoski, Jack (2002). "A compendium of fossil marine animal genera (Placodermi entry)". Bulletins of American Paleontology. 364: 560. Archived from the original on 2004-10-14. Retrieved 2011-05-20.
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