Neopterygii: Semionotiformes

Taxa on This Page

1. Pachycormiformes X
2. Pycnodontiformes X
3. Semionotiformes X

Descriptions

Semionotiformes: Acentrophorus, Dapedium, Lepidotes.

Range: Late Permian to Late Cretaceous, cosmopolitan.

Phylogeny: Halecostomi::: Pycnodontiformes + *.

Characters: supramaxilla absent (primitive) [C88]; maxilla does not contact opercular series [C88]; 1+ suborbitals [GB98]; interopercular present [C88]; retain ganoine on scales [C88].

Notes: [1] A strong body of opinion holds that the lepisosteiforms (gars) are members of this taxon. [2] Includes the oldest known neopterygian, the Late Permian Acentrophorus.  

Image: from Cartões Postais/ Postcards série Paleontologia Brasileira. The semionotiform Lepidotes is on the left, below the two actinistians Mawsonia) in this scene from the Cretaceous.

Links: Semionotiformes; temp; The Journal of Vertebrate Paleontology; Class:Osteichthyes; Lepidotes. APW 040806.

References: Carroll (1988) [C88]; Grande & Bemis (1998) [GB98].  .

Pycnodontiformes:

Range: Late Triassic to Eocene Miocene? see UCMP) of Africa, Asia, Europe, North & South America.

Phylogeny: Halecostomi::: Semionotiformes + *.

Characters: $? deep-bodied [PW02]; laterally compressed, with almost circular outline [PW02]; snout large and ventrally expanded [PW02]; premaxilla posterodorsal process thin, elongate & superficial [PW02]; mesethmoid large, robust & forms most of nasal capsule [PW02]; $ mesethmoid T-shaped in cross-section [PW02]; maxilla loose, thin & unornamented [PW02]; maxilla lost in more derived species [PW02]; $ supramaxilla absent [PW02]; $ frontals short, with strong ventral curvature [PW02]; frontals often not reaching ventral level of the orbit [PW02]; $? suborbitals present as mosaic of small bones [PW02]; symplectic articulates with lower jaw as in halecomorphs [C88]; $? preopercular larger than opercular [PW02]; preopercular separated from neurocranium by a lacuna [PW02]; $? opercular process of hyomandibular reduced [PW02];  "dermohyal" present in opercular series probably fusion of a dermal bone to hyomandibular) [PW02]; $? subopercular and interopercular absent [PW02]; $ at least one dermal supraoccipital present, primitively as unpaired median bones [PW02]; $ parasphenoid large, toothless & inflected ventrally [PW02]; $ dentary reduced & usually posteriorly bifurcated [PW02]; $ mandibular symphysis long & stout [PW02]; coronoid process formed by prearticular [PW02]; $ coronoid process primitively tall, with straight dorsal border [PW02]; prearticular probably incorporates coronoid [PW02]; $? gular reduced to series of tesserae or even absent [PW02]; 3, and usually 2 pairs of branchiostegal rays [PW02]; maxilla usually edentulous [PW02]; $ premaxillary teeth columnar to hamate [PW02]; long, flat durophagous teeth [PW02]; $? crushing teeth on vomer and prearticular, both primitively circular [PW02]; number of teeth on vomer & prearticular increases with age [PW02]; vomerine teeth increase size from mesial to distal [PW02]; $ vomerine teeth in rows [PW02]; prearticular teeth arranged in 2-5 rows [PW02]; $ 4 dentary teeth [PW02]; notochord not constrained in most species [PW02]; neural & hemal arches articulate through expanded bases, sometimes also zygapophyses [PW02]; neural & hemal spines with anterior sagittal flanges which may overlap precurrent spine [PW02]; $ ribs wing-like [PW02]; fringing fulcra present, but few [PW02]; cleithrum vertical, with a ventrally-directed ventral portion [PW02]; squamation frequently reduced; $? specialized contour scales scales forming contour in lateral view) large, reinforced, with stout crest, often bearing spines [PW02]; contour scales most often present between occiput & dorsal fin and between cleithrum & anal fin [PW02]; most anterior dorsal ridge scale fuses with supraoccipital [PW02]; also specialized scales around cloaca [PW02].

Notes: lots of ordered characters. long-term trends. Sure look like Guildayichthyiforms.

Links: Pycnodontiformes; A new insight into pycnodontiform fishes; 3°) LES POISSONS OSSEUX French); SyrenCRL; Poissons teleosteens; 207.htm; A Revision of the Pycnodontid genus Macromesodon; First occurrence of Nursallia; Rare Palaeobalistum fish fossil; Cretaceous Lebanese Pycnodontiform Fossil Fish.

Image: (right) from Vertébré Fossiles.

References: Carroll (1988) [C88]; Poyato-Ariza & Wenz (2002) [PW02]. APW 040806.

Pachycormiformes:  Asthenocormus, Eugnathides, Euthynotoides, Euthynotus, Hypsocormus, Leedsichthys, Orthocormus, Pachycormus, Prosauropsis, Protosphyraena, Sauropsis, Saurostomus.

Range: Late Triassic to Late Cretaceous of Asia, Europe, North & South America

Phylogeny: Halecostomi::: Teleostei + *.

Characters: rostrum bony & elongate [C88]; premaxilla present, small, lateral & mobile [C88]; one supramaxilla present [C88]; symplectic does not reach the articular [C88]; vomers paired [C88]; pectoral fins elongated, serrated, scythe-like [C88]; pelvic fins reduced or absent [C88]; uroneurals probably present [C88]; first hypural separate, with 2nd fused to several others to form broad triangular plate [C88].

Note: Leedsichthys (pictured) has two unique distinctions. First, it is probably the only actinopterygian ever mistaken for a stegosaur. See, Lexovisaurus -- The Dinosauricon. Second, at 10-15 m, it is supposed to have been the largest actinopterygian of all time.

Links: Untitled Document; The CDM's Earth Sciences Resource Site- Pachycormidae;  Hypsocormus & Orthocormus); BBC - Walking with Dinosaurs - Fact Files Leedsichthys); The Osteology of Leedsichthys problematicus; Fische; Enchodus Mâchoire inférieure Taille - environ 20 centimètres ... at last, someone who draws worse than I do!); Protosphyraena.

References: Carroll (1988) [C88]. APW 040806.