Arthrodira

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Arthrodira
Temporal range:
Ma
Artist's reconstruction of the arthrodire placoderm
Dunkleosteus terrelli
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Infraphylum: Gnathostomata
Class: †Placodermi
Order: †Arthrodira
Woodward, 1891
Subgroups

Arthrodira (Greek for "jointed neck") is an

Placodermi that flourished in the Devonian period before their sudden extinction, surviving for about 50 million years and penetrating most marine ecological niches. Arthrodires were the largest and most diverse of all groups of placoderms.[1]

Description

Arthrodire placoderms are notable for the movable joint between

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 as much as 6 m in length. In contrast, the long-nosed Rolfosteus measured just 15 cm.[2] Fossils of Incisoscutum have been found containing unborn fetuses, indicating that arthrodires gave birth to live young.[3][4]

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

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.[citation needed
]

placoderms. The diagram is based on Michael Benton, 2005.[5]

Phylogeny

The

Eugnathostomata, the clade grouping that contains sharks, bony fish, and all tetrapods.[6][7]

Arthrodira was traditionally divided into the

Phylogenetic studies have since found two of those groups as paraphyletic, as shown in the cladogram below, from Dupret et al. (2009).[9]

Eurycaraspis incilis

Lunaspis broilii

Arthrodira

Yujiangolepis liujingensis

Antarctaspis mcmurdoensis

Wuttagoonaspidae

Wuttagoonaspis fletcheri

Yiminaspis shenme

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

Austrophyllolepis sp.

Cowralepis mclachlani

Phyllolepis orvini

Placolepis budawangensis

Actinolepidae

Bollandaspis woschmidti

Actinolepis spinosa

Actinolepis magna

Actinolepis tuberculata

Bryantolepis brachycephalus

Phlyctaenioidei
Phlyctaeniidae

Pageauaspis russelli

Phlyctaenius acadicus

Groenlandaspidae

Groenlandaspis antarctica

Tiaraspis subilis

Arctaspidae

Dicksonosteus arcticus

Arctolepidae

Arctolepis decipiens

Heintzosteus brevis

Brachythoraci

Antineosteus lehmani

Buchanosteus confertituberculatus

Coccosteus cuspidatus
Actinolepidoidei
Phlyctaeniina

Classification

The pelagic selenosteid Amazichthys trinajsticae
The pelagic selenosteid Amazichthys trinajsticae
Coccosteus cuspidatus
Eastmanosteus pustulosus from the Middle Devonian of Wisconsin
Heterosteus ingens from the Middle Devonian of Estonia

Order Arthrodira Woodward, 1891

References

  1. ISSN 0024-4082
    .
  2. ^ Dennis, Kim, and R. S. Miles. "Eubrachythoracid arthrodires with tubular rostral plates from Gogo, Western Australia." Zoological Journal of the Linnean Society 67.4 (1979): 297–328.
  3. Science Daily
    . June 6, 2008.
  4. S2CID 205215898
    .
  5. ^ Benton, M. J. (2005) Vertebrate Palaeontology, Blackwell, 3rd edition, Figure 3.25 on page 73.
  6. PMID 25581798
    .
  7. S2CID 45922669
    .
  8. doi:10.1111/zoj12089
    .
  9. doi:10.1111/j.1096-3642.2009.00519.x
    .

Further reading
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