A group of low diversity, with several genera (e.g., Eurycaraspis, Lunaspis, and Macropetalichthys, Janvier, 1996) from Lower to Upper Devonian (marine) in North America, Europe, Morocco, Asia, and Australia.
Order PTYCTODONTIFORMES. Large sexually dimorphic pelvic fins with claspers in males (fertilization was probably internal); many resemblances with living holocephalans. One family, Ptyctodontidae (e.g., Ctenurella and Rhamphodopsis), from Lower Devonian to possibly Lower Mississippian (primarily marine) in North America, Europe, Asia, Libya, Algeria, and Australia (e.g., Forey and Gardiner, 1986; Janvier, 1996).
Order ARTHRODIRIFORMES (arthrodires). Most arthrodires were probably nektonic predators. This group, the largest in number of genera and best known of the placoderms, occurs from Lower Devonian to Lower Mississippian and is found on all major land masses. Several major groups are recognized (e.g., see Goujet and Young, 2004; Janvier, 1996).
Suborder Actinolepidoidei. Includes Actinolepidae, the most primitive arthrodires, with e.g., Actinolepis, Aethaspis, Bollandaspis, Eskimaspis, Heightingtonaspis, and Kujdanowiaspis (Johnson et al., 2000).
Suborder Phyllolepida. One Middle and Upper Devonian (freshwater) family, Phyllolepidae, with three genera, Austrophyllolepis, Placolepis, and Phyllolepis, known from Antarctica, Australia, Europe, and Greenland (Long, 1984; Ritchie, 1984). The Antarctaspidae may be related to this group.
Phlyctaeniidae (e.g., Arctolepis-in figure) and Groenlandasididae.
Suborder Brachythoraci. Includes the Eubrachythoraci with, based on information in Carr (2004), two major subgroups, the pachyosteomorphs and the coccosteomorphs. The brachythoracoids of the late Devonian were the first large marine vertebrate predators, with Dunkleosteus with large blade-like jawbones getting to be at least 6 m in length (e.g., Young, 2003).
Other arthrodires, whether belonging in the above groups or not, include: Buchanosteidae (a basal brachythoracid group, Carr, 2003), Camuropiscidae (e.g., Camuropiscis), Coccosteidae (e.g., Coccosteus, in figure), Dinichthyidae (Carr and Hlavin, 1995, moved several genera from this family into other families), Dunkleosteidae (e.g., Dunkleosteus, Eastmanosteus), Hadrosteus, Mylostomatidae, Panxiosteidae, Selenosteidae, Titanichthyidae, and Wuttagoonaspidae.
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