TSubclass Heterostraci

Family AMPHIASPIDIDAE (e.g., with the genera Eglonaspis, Kureykaspis, and Prosarctaspis).

Family CYATHASPIDIDAE (e.g., with the genera Anglaspis, Dinaspidella, Irregulareaspis, Poraspis, and Torpedaspis).

Other genera include Nahanniaspis, regarded as the sister group of the Cyathaspididae by Janvier (1996).

fOrder PTERASPIDIFORMES. Dorsal shield composed of several plates, ornamented, except in psammosteids, with concentric dentine ridges. Five major taxa are given in Janvier (1996), given family rank here, as follows.

Family ANCHIPTERASPIDIDAE (e.g., Rhachiaspis and Ulutitaspis). Family PROTASPIDIDAE (e.g., Cyrtaspidichthys). Family PROTOPTERASPIDIDAE (e.g., Protopteraspis).

Family PSAMMOSTEIDAE (e.g., Drepanaspis, Psammolepis, and Pycnosteus).

Family PTERASPIDIDAE (e.g., Errivaspis, Pteraspis, Rhinopteraspis, and Unarkaspis).

myopterygians. Janvier (1996) uses the term Myopterygii for those vertebrates with radial muscles in fins, innervated heart, muscularized unpaired fins, extrinsic eye muscles, and true paired fins (assumed to be secondarily lost in some taxa). He included in this clade the lampreys, which are excluded here, but, for a monophyletic Myopterygii, excluded the Galeaspida, which here are included and assumed to be part of a monophyletic Osteostracomorphi, and added as synapomorphies cellular bone and an open endolymphatic duct (both being subsequently lost several times). If our phylogenetic hypothesis as presented is correct, pectoral fins originated before pelvic fins. Coates (2003) discussed the possible origin of paired fins, and re-evaluated classical theories of limb evolution (i.e., Gegenbaur's transformational hypothesis of gill arches to limb girdles and the more widely accepted lateral fin-fold).

The term Myopterygii is used to include the following taxa, all forming an hypothesized monophyletic taxon.

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