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HIERARCHICAL CLASSIFICATION OF THE SUPERCLASS PTERASPIDOMORPHI+

HIERARCHICAL CLASSIFICATION OF THE SUPERCLASS PTERASPIDOMORPHI+

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SUPERCLASS PTERASPIDOMORPHI

Description of Superclass

The following descriptions come from Benton (2005) and Nelson (2006). The structure of the following system is also based, in part, on the phylogenetic treatment by Mikko’s Phylogeny Web (from the Finnish Museum of Natural History).
  • SUPERCLASS PTERASPIDOMORPHI+
  • This group has a single class with 3 subclasses as given by Nelson (2006).
    • CLASS PTERAPSIDA (=DIPLORHINA)
      • The Pteraspids had dermal bone, particularly in their head shields, which were made of dorsal and ventral plates. The bone appears to have been acellular, which Nelson (2006) interprets as a primitive condition. Their organs of balance had two semicircular canals. The mobile tail was covered by scale-like bony plates. Pteraspids had no paired appendages.
      • Ordovician to the early Devonian.
        • SUBCLASS ASTRASPIDA (1 ORDER)
          • Head covered by separate bony plates. Eyes small and placed laterally. Eight gill slits, all large and without covers. They may have been the sisters to the gnathostomes (Donoghue et al. 2000).
          • Upper Ordovician.to lower Silurian
            • ORDER ASTRASPIDIFORMES
              • FAMILY ASTRASPIDAE
                • Astrapsis, Pycnaspis.
        • SUBCLASS ARANDASPIDA (1 ORDER)
          • Head covered by bony plates. Eyes at the extreme anterior end of the head. They also had paired pineal and parapineal openings. At least 10 gill openings, each with a bony cover.
          • Ordovician.
            • ORDER ARANDASPIDIFORMES
              • FAMILY ARANDASPIDAE
                • Sacabambaspis, Anindaspis(?), Arandaspis, Porophoraspis(?).
        • SUBCLASS HETEROSTRACI (2 ORDERS AND 6 PROBLEMATIC GROUPS)
          • Head shield was heavy and fused in some; the rest of the body was covered by large bony scales. The eyes were lateral and reduced; gills exit through a single opening on each side. They had no anal fin and the tail was hypocercal though the lobes appeared to be symmetrical.
          • Lower Silurian through upper Devonian.
            • ORDER CYATHASPIDIFORMES
            • The head shield was ornamented by ridges of dentine-covered bone. The dorsal head shield was made of a single plate. Paired appendages, if present, were little more than immovable spines.
              • FAMILY CYATHASPIDAE
              • Fish completely encased in bony plates: dorsal and ventral head shields and body scales that are imbricate to the back. They had no apparent paired appendages.
                • Anglaspis, Dinaspidella, Irregulareaspis, Poraspis, Torpedaspis.
              • FAMILY AMPHIASPIDIDAE
              • The armored shields that surround the head were completely fused to form a carapace; and reduced eyes. They may have been burrowers. Some had a long narrow snorkel-like mouth, likely an adaptation to respiring while buried in a burrow.
                • Eglonaspis, Kureykaspis, Prosarctaspis.
            • ORDER PTERASPIDIFORMES
            • The dorsal head shield was made of multiple plates that had rings of dentine.
              • FAMILY PTERASPIDAE
              • These had head shields made of separate plates above, below, on the rostrum and around the eyes. Their body scales were small and modern looking. Their tails were fan-shaped.
              • Lower to middle Devonian
                • Errivaspis, Pteraspis, Rhinopteraspis, Unarkaspis.
              • FAMILY PSAMMOSTEIDAE
              • These animals were dorso-ventrally flattened, some were quite large with heads up to 1.5m wide. The head shield plates of the psammosteids were the same as those of the pteraspids except that they had smaller plates (called tesserae) in between them. They had widely-separated eyes and an upturned mouth. These animals seemed to have been adapted to lying on the bottom in wait for prey.
                • Drepanaspis, Psammolepis, Pycnosteus.
              • FAMILY ANCHIPTERASPIDAE
                • Rhachiaspis, Ulutitaspis.
              • FAMILY PROTASPIDAE
                • Cyrtaspidichthys
              • FAMILY PROTOPTERASPIDIDAE
                • Protopteraspis
            • ORDER CARDIPELTIDIFORMES (INCERTAE SEDIS)
              • Cardipeltis.
            • ORDER CORVASPIDIFORMES (INCERTAE SEDIS)
              • Corvaspis.
            • ORDER LEPIDASPIDIFORMES (INCERTAE SEDIS)
              • Lepidaspis.
            • ORDER TESSERASPIDIFORMES (INCERTAE SEDIS)
              • Tesseraspis.
            • ORDER TRAQUAIRASPIDIFORMES (INCERTAE SEDIS)
              • Phialaspis, Toombsaspis, Traquairaspis.
            • ORDER TOLYPELEPIDIFORMES (INCERTAE SEDIS)
              • Athenaegis, Tolypelepis.
LITERATURE CITED

Benton, M. J. 2005. Vertebrate Paleontology. Third Edition. Blackwell Publishing, Malden, MA.

Janvier, P. 2008a. Early jawless vertebrates and cyclostome origins. Zoological Science. 25: 1045-1056.

Nelson, J. S. 2006. Fishes of the World. 4th edition. John Wiley and Sons, Inc. New York.

Sweet, W. C. and P. C. J. Donoghue. 2001. Conodonts: past, present, future. Journal of Paleontology. 75:1174-1184.
By Jack R. Holt. Last revised: 01/17/2013
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