| SYSTEMATIC BIOLOGY |
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| SUPERCLASS ANASPIDOMORPHI+ |
Anaspidomorphi (an-as-pid-o-MORF-e) is formed of three Greek roots which mean "forms without a shield" [without- an (áv), a shield- aspis (áσπὶς), form [morphi (μορφή)]. The reference is to a jawless fish without a shield of bony armor that is common to many of the other agnathans.
Anaspids were small (up to 15cm long) freshwater fishes that persisted from the Silurian through the Devonian. As the name implies, these fishes did not have bony armor, particularly bony head shields. However, they did have bony scales, scutes, and plates. Like the thelodonts with which they are usually grouped, the tails of the anaspids were hypocercal, and they had a terminal mouth. However, the anaspids had a pair of pectoral spines (rather than pectoral fins) and their bodies were laterally compressed.
Janvier (2007) considers the theory that the Petromyzontomorphi are sisters to the anaspidomorphs. Indeed, the naked, or nearly scaleless, Euphanerops has many of the same general characters common to lampreys: the same kind of tail and in-line fins, branchial basket, and gill openings. That they share these characters may mean that Euphanerops and other naked agnathans may be in the lamprey lineage, but most of the anaspidomorphs are not, or the shared characters may indicate that the modern lampreys are descendants of the anaspidomorphs. However, the characters may be primitive, in which case the relationships remain unclear.
| HIERARCHICAL TAXONOMY OF THE SUPERCLASS ANASPIDOMORPHI+. 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 Pharyngolepis from: www.tolweb.org/tree/ToLimages/anaspida.gif SUPERCLASS ANASPIDOMORPHI+ The superclass has a single class with two orders. CLASS ANASPIDA Anaspids were fishes of freshwater and up to 15cm long. They were covered by characteristic bony scales, no large head shields, but some did have bony scutes and plates. Their bodies were laterally compressed and the mouth was terminal. The in-line fins were reduced to an anal fin and two lobes of the caudal fin, which was hypocercal (i.e. the vertebral column bent down into the lower lobe). The fin of the upper lobe of the caudal might have been the posterior dorsal fin. They had paired pectoral spines in addition to in-line fins. They had separate gill openings (up to 15 pairs), well back of the eyes. Benton (2005) groups the the anaspids and thelodonts together into a single class. I have followed the system of Nelson (2006) in which the anaspids and thelodonts are given superclass status each. Silurian through Devonian UNASSIGNED GENERA: Schidiosteus, Rytidolepis, Vesikulepis, Maurylepis, Silmalepis, Septendrionalis, Livilepis, Hoburgilepis, Tahulalepis, Spokoinolepis, Manbrookia, Ruhnulepis. ORDER JAYMOTIIFORMES FAMILY ENDEIOLEPIDAE Endeiolepis. FAMILY ACHANARELLIDAE Achanarella FAMILY JAYMOYTIIDAE Jaymoytius FAMILY EUPHAEROPIDAE Cornovichthys, Euphanerops. FAMILY RHYNCHOLEPIDIDAE Rhyncholepis. ORDER ANASPIDIFORMES (BIRKENIAE) UNASSIGNED GENERA Pharyngolepis, Pterygolepis. FAMILY LASANIIDAE Lasanius. FAMILY RAMSAASALEPIDIDAE Ramsaasalepis. FAMILY BIRKENIIDAE Vilkitskilepis, Birkenia, Ctenopleuron, Saarolepis. |
