| SYSTEMATIC BIOLOGY |
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| SUPERCLASS THELODONTOMORPHI+ |
Thelodontomorphi (THE-lo-don-ta-MOR-fe) is derived from three Greek roots that mean "nipple-toothed forms" [nipple- theli (θηλή), tooth- donti (δόντι), form- morphi (μορφή)]. The reference is to jawless fishes whose pharynx was covered with small tooth-like structures.
The thelodonts were similar to the Anaspidomorphi in that they had hypocercal tails and had terminal mouths. They were different in that they were marine animals that were generally dorso-ventrally compressed (though the fork-tailed taxa tended to be laterally-compressed). Their bodies were covered with placoid scales, and they had pectoral fins. Most seem to have been adapted as bottom-dwellers; however, the fork-tailed thelodonts (the Furcacaudiformes) seemed to be adapted to life in the open water with laterally-compressed bodies, large tails, and large eyes.
| HIERARCHICAL TAXONOMY OF THE SUPERCLASS THELODONTOMORPHI+. 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). Taxa in red are extinct. |
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Drawing of a furciform thelodont from: http://www2.biology.ualberta.ca/wilson.hp/mvhw/thelodont.html SUPERCLASS THELODONTOMORPHI+ CLASS THELODONTI Thelodonts
occupied marine environments of shallow continental shelves.
They were dorso-ventrally compressed and were covered by tiny scales that
had an internal pulp cavity (making them similar to the placoid scales of
sharks). These had lateral pectoral
fins and and a single dorsal fin, and anal fin.
The caudal fin was hypocercal (see Anaspidomorphi) though some had an almost
fork-like tail (they were laterally compressed).
They had 8 small gill openings below the pectoral fins.
The pharynx was lined with small denticles. Upper
Silurian to lower Devonian (possible thelodont scales have been identified from
Ordovician strata). Unassigned
Genera: Apalolepis, Stroinolepis, Turinia. ORDER
THELODONTIFORMES (=COELOLEPIDIFORMES) FAMILY
COELOLEPIDAE Thelodus FAMILY
LANARKIIDAE Lanarkia,
Phillipsilepis FAMILY
ARCHIPEKEPIDIDAE Archipelepis FAMILY
NIKOLIVIIDAE Chatterdonotus,
Nikolivia FAMILY
TALIVALIIDAE Glacialepis,
Talivalia FAMILY
EESTILEPIDIDAE Eestilepis ORDER
LOGANELLIFORMES FAMILY
LOGANIIDAE Illoganellia,
Loganellia, Angaralepis, Paralogania, Sandivia, Logania FAMILY
NUNAVUTIIDAE Nunavutia ORDER
SHIELLIFORMES FAMILY
SHELIIDAE Paralogania, Praetrilogania, Shielia ORDER
PHLEBOLEPIDOFORMES FAMILY
PHLEBOLEPIDIDAE Erepsilepis,
Helenolepis, Phlebolepis FAMILY
KATOPORODIDAE Goniporus,
Katoporodus, Overia, Zueglepis ORDER
FURCACAUDIFORMES These
were the forktail thelodonts. Body
compressed, eyes large; and gill openings oblique.
Tail fin had large dorsal and ventral lobes; dorsal and ventro-lateral fin
flaps. Lateral line extended into
both lobes of the tail. FAMILY
FURCACAUDIDAE Canonia,
Cometicercus, Drepanolepis, Furcacauda, Furcacaudata, Sphenonectris FAMILY
PEZOPALLICHTHYIDAE Pezopallichthys FAMILY
BARLOWODIDAE Barlowodus,
Sophialepis |
