Arthrodira

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 Coccosteina 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 1 to as much as 6 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.

Systematics^[1]

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

ORDER ARTHRODIRA

• Clade Aspinothoracidi
  • Superfamily Dinichthyloidea
    • Family Dinichthyidae
    • Family Trematosteidae
    • Family Rhachiosteidae
    • Family Hadrosteidae
    • Family Titanichthyidae
    • Family Bungartiidae
    • Family Selenosteidae
    • Family Mylostomatidae
• Basal infraorder Actinolepina
  • Family Actinolepidae
• Suborder Phlyctaenioidei
  • Basal family Holonematidae
  • Infraorder Phlyctaeniina
    • Family Groenlandaspididae
    • Family Phlyctaeniidae
• Suborder Brachythoraci
  • Infraorder Coccosteina
    • Superfamily Buchanosteoidea
      • Family Buchanosteidae
    • Superfamily Gemuendenaspoidea
      • Family Gemuendenaspidae
    • Superfamily Homostioidea
      • Family Homostiidae
    • Superfamily Brachydeiroidea
      • Family Brachydeiridae
      • Family Leptosteidae
    • Superfamily Coccosteoidea
      • Family Pholidosteidae
      • Family Coccosteidae
      • Family Incisoscutidae
      • Family Camuropiscidae
    • Superfamily Dunkleosteoidea
      • • (basal genus) Westralichthys
      • Family Panxiosteidae
      • Family Dunkleosteidae

Genera incertae sedis

Arthrodira of unresolved relationships

• Antarctolepis
• Aspidichthys - including Anomalichthys, Aspidophorus
• Callognathus
• Copanognathus
• Carolowilhelmina
• Diplognathus
• Glyptaspis
• Grazosteus
• Hollardosteus
• Laurentaspis
• Machaerognathus
• Maideria
• Murmur - including Euptychaspis, Ptychaspis
• Overtonaspis
• Phylactaenium
• Pinguosteus
• Prescottaspis
• Qataraspis
• Taunaspis
• Timanosteus
• Trachosteus
• Wheathillaspis

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

• Haaramo, Mikko (2005): Mikko's Phylogeny Archive: †Arthrodira. Version of 2005-NOV-15. Retrieved 2007-SEP-13.
• 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. 

External links

Wikimedia Commons has media related to Arthrodira.

• https://web.archive.org/web/20060101004255/http://www.palaeos.com/Vertebrates/Units/Unit060/060.100.html

Placoderms
Kingdom: Animalia Phylum: Chordata Subphylum: Vertebrata Infraphylum: Gnathostomata
Major clades Acanthothoraci Antiarchi Arthrodira Petalichthyida Phlyctaeniida Phyllolepida Ptyctodontida Rhenanida
Basal placoderms Acanthothoraci* ?Hagiangellidae ?Hagiangella Palaeacanthaspidae* Arabosteus Dobrowlania Kimaspis Kolymaspis Kosoraspis Palaeacanthaspis Radotina Romundina ?Weejasperaspididae Weejasperaspis Murrindalaspis Rhenanida Asterosteus Bolivosteus Gemuendina Jagorina Nefudina Ohioaspis Others Brindabellaspis Pseudopetalichthys Stensioella Entelognathus
Antiarchi Basal antiarchs Minicrania Silurolepis Sinolepidae Dayaoshania Grenfellaspis Sinolepis Vanchienolepis Xichonolepis Yunnanolepiformes incertae sedis Heteroyunnanolepis Zhanjilepis Shimenolepis Chuchinolepidae Chuchinolepis Yunnanolepididae Parayunnanolepis Phymolepis Mizia Yunnanolepis Euantiarcha Asterolepidoidei Asperaspis Asterolepis Byssacanthus Gerdalepis Grossaspis Hunanolepis Kirgisolepis Pambulaspis Pterichthyodes Remigolepis Sherbonaspis Stegolepis Bothriolepidoidei Dianolepis Kirgisolepis Luquanolepis Nawagiaspis Tenizolepis Bothriolepididae Bothriolepis Briagalepis Grossilepis Monarolepis Vietnamaspis Jiangxilepididae Jiangxilepis Ningxialepis Microbrachiidae Hohsienolepis Microbrachius Wudinolepis
Petalichthyida Basal and incertae sedis Diandongpetalichthys Neopetalichthys Quasipetalichthyidae Quasipetalichthys Eurycaraspis Macropetalichthyidae Ellopetalichthys Epipetalichthys Lunaspis Macropetalichthys Notopetalichthys Shearsbyaspis Tongdzuylepis Wijdeaspis
Ptyctodontida Ptyctodontidae Austroptyctodus Campbellodus Chelyophorus Ctenurella Denisonodus Destnoporella Eczematolepis Goniosteus Materpiscis Palaeomylus Ptyctodopis Ptyctodus Rhamphodopsis Rhynchodus
Arthrodira Actinolepidoidei* Aethaspis Aleosteus Anarthraspis Baringaspis Bryantolepis Erikaspis Eskimaspis Heightingtonaspis Kujdanowiaspis Lataspis Lehmanosteus Mediaspis Proaethaspis Sigaspis Simblaspis Actinolepidae* Actinolepis Ailuracantha Bollandaspis Szeaspis Antarctaspidae* Antarctaspis Qataraspis Yujiangolepis Phyllolepida Austrophyllolepis Cowralepis Gavinaspis Phyllolepis Placolepis Wuttagoonaspidae Wuttagoonaspis Yiminaspis Phlyctaenioidei / Phlyctaenii* Phlyctaenididae Aggeraspis Cartieraspis Diadsomaspis Elegantaspis Neophlyctaenius Pageauaspis Phlyctaenius Arctaspididae Dicksonosteus Arctolepididae Arctolepis Heintzosteus Huginaspis Kueichowlepis Groenlandaspididae Africanaspis Boomeraspis Groenlandaspis Mithakaspis Mulgaspis Tiaraspis Turrisaspis Williamsaspididae Elvaspis Williamsaspis Brachythoraci Basal brachythoracids Antineosteus Gemuendenaspis Maideria Xiangshuiosteus Heterostiidae Herasmius Heterosteus Tollichthys Holonematidae Artesonema Belemnacanthus Bimbianga Deirosteus Deveonema Gyroplacosteus Holonema Megaloplax Rhenonema Tropidosteus Tropinema Homosteidae Angarichthys Cathlesichthys Dhanguura Euleptaspis Euleptaspis Luetkeichthys Migmatocephala Antineosteus Atlantidosteus Homosteus Taemasosteus Tityosteus Buchanosteidae Arenipiscis Buchanosteus Burrinjucosteus Errolosteus Goodradigbeeon Parabuchanosteus Toombsosteus Uralosteus Eubrachythoraci Coccosteomorphi Camuropiscidae Camuropiscis Fallacosteus Latocamurus Simosteus Rolfosteus Tubonasus Coccosteidae Belgiosteus Clarkeosteus Coccosteus Dickosteus Jiuchengia Livosteus Millerosteus Protitanichthys Watsonosteus Incisoscutidae Incisoscutum Plourdosteidae Compagopiscis Gogopiscis ?Kimberleyichthys Menamaraspis ?Plourdosteus Torosteidae Eldenosteus Harrytoombsia Torosteus Pachyosteomorphi Kiangyousteus Brachydeiridae Brachydeirus Oxyosteus Synauchenia Leptosteidae Leptosteus Rachiosteidae Rachiosteus Aspinothoracidi Bungartiidae Bungartius Dinichthyidae* Bruntonichthys Bullerichthys Dinichthys Kianyousteus Protitanichthys Squamatognathus Hadrosteidae Hadrosteus Leiosteidae Erromenosteus Mylostomatidae Dinomylostoma Kendrickichthys Mylostoma Tafilalichthys Selenosteidae Braunosteus Draconichthys Enseosteus Gymnotrachelus Melanosteus Microsteus Pachyosteus Paramylostoma Phymosteus Rhinosteus Selenosteus Stenosteus Walterosteus Titanichthyidae Titanichthys Trematosteidae Belosteus Brachyosteus Cyrtosteus Parabelosteus Trematosteus Dunkleosteoidea Panxiosteidae Janiosteus ?Kimberleyichthys Panxiosteus ?Plourdosteus Dunkleosteidae Dunkleosteus Eastmanosteus Golshanichthys Hussakofia Westralichthys
Related categories Placoderms Devonian fish