| Pachyosteomorphi Temporal range: Devonian
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| Artist's reconstruction of various Cleveland Shale Pachyosteomorphi arthrodires, including Titanichthys (top), Selenosteus (eating a shark), adult and juvenile Dunkleosteus terrelli (center), and Gorgonichthys (bottom). From the Famennian stage of the Late Devonian. | |
Scientific classification 
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| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | †Placodermi |
| Order: | †Arthrodira |
| Suborder: | †Brachythoraci |
| Clade: | †Eubrachythoraci |
| Clade: | †Pachyosteomorphi Stensiö, 1963 |
| Sub-clades | |
Pachyosteomorphi is an extinct clade of arthrodire placoderms within the Eubrachythoraci (of the suborder Brachythoraci), armored fish most diverse during the Devonian. Most are considered to be pelagic (open ocean) long-distance swimmers, leading to their widespread distribution beginning from at least the Middle Devonian period.[1]