Palæos:		Unit 40: Pteraspidomorphi
The Vertebrates		100: Pteraspidomorphi

Pteraspidomorphi

Anatolepis, Arandaspids & Astraspids

CRANIATA
|--CONODONTA
`--+--THELODONTI
   `--Pteraspidomorphi
      |--Anatolepis
      `--+--Arandaspida
         `--Heterostracomorphi
            |--Astraspidae
            `--Heterostraci
               |--Cyathaspidiformes
               |  |--Cyathaspidida 
               |  `--Amphiaspidida
               `--Pteraspidiformes
                  |--Pteraspididae
                  `--Psammosteida
                     |--Drepanaspis
                     `--Psammosteidae

Taxa on This Page

1. Anatolepis X
2. Arandaspida X
3. Astraspidae X
4. Heterostracomorphi X
5. Pteraspidomorphi X

Sacabambaspis. Sandbian (Late Ordovician) of south east Gondwanaland. Length 25 cm.

Pteraspidomorphi: Loosely synonymous with "Diplorhina". Probably defined as Anatolepis + Psammolepis.

Range: Early Ordovician (or Furongian) to Late Devonian. 

Phylogeny: Vertebrata ::: "Thelodontia" + * : Anatolepis + (Arandaspida + Heterostracomorphi). 

Characters: 10-200 cm; head very long (40-50% body length); paired nasal capsules, and ?openings; solid anterior plates, with at least a major oblong median dorsal and ventral plates and usually a median rostral plate above mouth; rostra and cornua common; pineal opening (psammosteids?); brain with two semicircular canals; some show internal impressions of arcualia on notochord; body tends to be ventrally flattened (numerous exceptions); mobile tail, generally fan- or pad-like; tail hypocercal; no paired appendages; no unpaired fins except caudal; sensory line system present; no cellular bone (but see [H73]); possible traces of calcified cartilage in in some basal lineages; trilaminate aspidine; grebeshki ornamentation on dermal plates (lost independently several times); largely marine nearshore.  

Links: Pteraspidomorphi; Pteraspidomorphi; Gagnier; Pteraspidomorphi; Faktaside om lungefisk (Norwegian); Class Pterapisdomorphi; Life of the Ordovician; Paleozoic Fossils UK (extraordinary images on this site!).

References: Halstead (1973) [H73]. APW040316.

Anatolepis: 

Range: Furongian to Early Ordovician of North America, Greenland & Spitzbergen. 

Phylogeny: Pteraspidomorphi : (Arandaspida + Heterostracomorphi)  + *. 

Characters: Known from fragments only. Apatite with scale-like ornamentation; dentine odontodes with pulp cavity; dentine covered by another mineralized tissue of unknown homology; "exclusively tropical, circum-Laurentian, distribution, where it is restricted to outer shelf settings". 

Notes: [1] It seems I am not the only one who writes haiku about early chordates: see University of Alberta Palaeontological Society Website.  

Links: Histology of the first fish (abstract of one of the articles referred to by Gee);  A possible Late Cambrian vertebrate from Australia (abstract of the other article referred to by Gee); Molecular Evidence for Precambrian Origin of Amelogenin, the Major .... 

References: Young et al. (1996).  APW040316.

Arandaspida: Arandaspis, Sacabambaspis, possibly Porophoraspis. Medium-sized (12-14 cm) very primitive, teardrop-shaped marine fishes. 

Range: Early to Late Ordovician of Australia & South America. 

Phylogeny: Pteraspidomorphi :: Heterostracomorphi + *. 

Characters: Two large, thin (<1 mm) plates on head (dorsal & ventral); ventral plate convex, dorsal plate flattened; main plates ornamented by drop-shaped or lobate tubercles; eyes in extreme anterior; solid sclerotic ring present; nostrils (?) just medial to orbits on embayment in anterior surface just dorsal to mouth; mouth lined ventrally with numerous small scales; possible lingual or velar apparatus; paired pineal (2?) and parapineal (4?) openings on anterior of dorsal plate (which may be endolymphatic ducts instead); probably at least ten gill slits with smaller plates on sides; posterior body & tail may have been laterally compressed; body scales highly elongated and arranged in large chevrons (pointing anteriorly) on each side; no ridge scales; no paired or unpaired fins except caudal (poorly known); caudal fin probably pad-shaped and diphycercal; well-developed small lateral lines on both plates and medioventral surfaces; little or no endoskeleton; scales and plates trilaminar, with basal laminar layer, cancellous central layer (with double walls) and aspidine or cellular bone tubercles. No growth or fusion of scales. 

Links: Fischmarkt Bremerhaven (German); Class Pterapisdomorphi; New Page 1 (large image of arandaspid fragment); Boletín de Publicación mensual de (Spanish translation of a National Geographic article on Sacabambaspis); life-5-b-Xystridura (exemplary short, encyclopedia-like entry with image of Sacabambaspis); Gli Agnati (Italian).    

References: Janvier (1996).  ATW060209.

Heterostracomorphi:  Eriptychius?

Range: Late Ordovician to Late Devonian

Phylogeny: Pteraspidomorphi:: Arandaspida + *: Astraspidae + Heterostraci.

Characters: dorsolateral gill openings.

References: Janvier (1996).  APW040316

Astraspis. Sandbian (Late Ordovician) of Laurentia.

Range: Middle to Late Ordovician of North America & Siberia.

Phylogeny: Heterostracomorphi : Heterostraci + *. 

Characters: Head armor massive; plates grew from multiple centers (tesserae) which fused at maximum growth; eyes lateral; multiple (8-10) gill openings; dorsal shield ribbed with strong longitudinal crests; tail covered with large, diamond-shaped scales; sensory-line system with grooves in dermal plates; globular calcified cartilage present, probably(?) forming endoskeleton; tesserae with large mushroom-shaped dentine tubercles with pulp cavity; dentine covered with enameloid cap; trilaminar bone. 

Links: Tree of Life.

References: Janvier (1996).  APW040316.

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