|Title||Development and variation of the suspensorium of primitive catfishes (Teleostei: Ostariophysi) and their phylogenetic relationships|
|Publication Type||Journal Article|
|Year of Publication||1992|
|Journal||Bonner Zoologische Monographien|
|Keywords||Anatomy and Histology - Comparative anatomy 18002, Anatomy and Histology - Gross anatomy 11103, Bones, Chordata: general and systematic - Pisces, connective and adipose tissue - Anatomy 62510, Evolution 11102, fasciae, joints, Osteichthyes  Evolution and Adaptation Morphology Systematics and Taxonomy Pisces Vertebrata Chordata Animalia 01500|
The suspensorium of ostariophysans as well as that of other teleosts is characterized by the presence of chondral elements (autopalatine, metapterygoid, and quadrate) and dermal elements (ectopterygoid and entopterygoid). The dermopalatine fused to the autopalatine present in primitive clupeocephalans is absent in ostariophysans. Tendon bone pterygoids and additional elements as toothplates may be found among catfishes. The suspensorium of cypriniforms, gymnotoids, and catfishes is highly specialized and several synapomorphies characterize each of these groups. Among the ostariophysans, gymnotoids and catfishes have very different and highly specialized suspensoria; still they share three synapomorphies - the anterior cartilage of the autopalatine or pars autopalatina does not articulate with the neurocranium, ligamentum primordiale inserts on the dorsal tip of the lower jaw, and the ectopterygoid is rudimentary or absent. The suspensorium of catfishes is highly specialized from early in ontogeny. Differences in the palatoquadrate separate siluriforms from the other teleosts. For example, the palatoquadrate is divided into the pars autopalatina and the pars pterygoquadrata; the pars pterygoquadrata is fused to the dorsal limb of the hyoid arch to form the hyosymplectic-pterygoquadrate plate and this produces a special alignment of the suspensorium in catfishes. The bones commonly identified as the ectopterygoid and the entopterygoid in catfishes are tendon bones that are characterized by unique ligamentous connections with other bones of the suspensorium (e.g., metapterygoid) and/or cranial bones (e.g., vomer, lateral ethmoid, orbitosphenoid), and they are sesamoid elements. The sesamoid 'entopterygoid' (types 2-7) is an evolutionary transformation of the dermal entopterygoid; both bones are homologous. In contrast, the sesamoid 'ectopterygoid' present in some catfishes such as 'pimelodids', 'bagrids', and ariids is nonhomologous with the dermal ectopterygoid present in diplomystids. This is because both - a tendon bone 'ectopterygoid' and an ectopterygoid - are missing in the ancestor of 'pimelodids', 'bagrids', and ariids. The ligamentous and/or connective tissue connections present between the 'entopterygoid' and vomer, 'entopterygoid' and lateral ethmoid, and 'entopterygoid' and metapterygoid are homologous among members of Siluroidea; one or another is lost in some advanced members of this clade. The presence of the autopalatine-metapterygoid ligament is a synapomorphy of catfishes; the division of this ligament into two due to the appearance of the calcification of the 'ectopterygoid' is considered as a derived conditon. Because of their origin and distribution among catfishes, the autopalatine-'ectopterygoid' ligament and the 'ectopterygoid'-metapterygoid ligament are homologous with the autopalatine-metapterygoid ligament. The study of the suspensorium reveals that it is difficult to understand the bony suspensorium of siluroids without ontogenetic investigations. In this way the sesamoid 'entopterygoid' and its ligamentous connections become a tool in systematic and phylogenetic interpretations. The presence of toothplates or other dermal elements should be investigated early in ontogeny to determine their early position and relationships, allowing more useful comparisons to be made. A phylogenetic analysis based on 130 morphological characters confirms the scheme of phylogenetic relationships of ostariophysans proposed by Fink and Fink (1981). Phylogenetic analyses based on 75 morphological characters of certain primitive catfishes confirms Diplomystidae as the sistergroup of ( dbldag Hypsidoridae + Siluroidea); among Siluroidea, nematogenyids are more primitive than ictalurids, 'pimelodids', and ariids. The characterization of the higher categories of Siluriformes sensu Grande (1987) such as the Diplomystoidei, Siluroidei, dag Hypsidoroidea, and Siluroidea are analyzed and discussed. Additional diagnostic characters are provided for these clades.