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




and see text

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.

Greek for "jointed neck", the arthrodires had movable joint between armor surrounding the head and body. The mouth is interesting because as the lower jaw moved down, the head shield moved, allowing for a large opening. 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 3 to as much as 9 m in length. In contrast, the long-nosed Rolfosteus measured just 15 cm.

Heterosteus ingens from the Middle Devonian of Estonia

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.


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

 Lunaspis broilii

 Eurycaraspis incilis


 Yujiangolepis liujingensis 

 Antarctaspis mcmurdoensis 


 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 


 Gavinaspis convergens 

 Phyllolepis orvini 

 Austrophyllolepis sp. 

 Cowralepis mclachlani 

 Placolepis budawangensis 


 Bollandaspis woschmidti 

 Actinolepis spinosa 

 Actinolepis magna 

 Actinolepis tuberculata 

 Bryantolepis brachycephalus 


 Phlyctaenius acadicus 

 Pageauaspis russelli 


 Groenlandaspis antarctica 

 Tiaraspis subilis 


 Dicksonosteus arcticus 


 Arctolepis decipiens 

 Heintzosteus brevis 


 Antineosteus lehmani

 Buchanosteus confertituberculatus

 Coccosteus cuspidatus



Genera incertae sedis[edit]

Arthrodira of unresolved relationships

Timeline of genera[edit]

Devonian Famennian Frasnian Givetian Eifelian Emsian Pragian Lochkovian Trachosteus Stenosteus Paramylostoma Mylostoma Hussakofia Holdenius Gymnotrachelus Gorgonichthys Glyptaspis Bungartius Titanichthys Selenosteus Diplognathus Africanaspis Tafilalichthys Aspidichthys Trematosteus Tapinosteus Synauchenia Rhinosteus Pholidosteus Parabelosteus Pachyosteus Microsteus Leptosteus Erromenosteus Enseosteus Cyrtosteus Braunosteus Brachyosteus Belosteus Oxyosteus Brachydeirus Operchaliosteus Hadrosteus Dinichthys Deveonema Heintzichthys Groenlandaspis Cosmacanthus Callognathus Timanosteus Rolfosteus Platyaspis Megaloplax Malerosteus Latocamurus Dinomylostoma Tubonasus Torosteus Plourdosteus Panxiosteus Melanosteus Mcnamaraspis Machaerognathus Kimberleyichthyes Kimberia Kendrichthys Incisoscutum Harrytoombsia Gyroplacosteus Fallacosteus Eldenosteus Copanognathus Camuropiscis Bullerichthys Bruntonichthys Dunkleosteus Rachiosteus Yinosteus Tropidosteus Rhenonema Kiangyousteus Hollardosteus Heterosteus Eastmanosteus Squamatognathus Deirosteus Holonema Grazosteus Belemnacanthus Arctonema Atlantidosteus Taemasosteus Laurentaspis Williamsaspis Toombsosteus Parabuchanosteus Goodradigbeeon Errolosteus Burrinijucosteus Buchanosteus Arenipiscis Stuertzaspis Gemuendenaspis Tiaraspis Taunaspis Murmur Kweichowlepis Wheathillaspis Prescottaspis Overtonaspis Eskimaspis Qataraspis Devonian Famennian Frasnian Givetian Eifelian Emsian Pragian Lochkovian


  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[edit]

List of placoderms


External links[edit]