SENSORY CANALS AND RELATED BONES OF TERTIARY SILURIFORM CRANIA FROM BOLIVIA AND NORTH-AMERICA AND COMPARISON WITH RECENT FORMS

Narrow, simple cephalic sensory canals enclosed by bone represent the primitive condition found in catfishes (siluroids) such as Diplomystid ae, dagger Hypsidoridae, and Ictaluridae. Derived conditions among sil uroids include highly branched (e.g., dagger Andinichthys, Galeichthys , and Parapimelodus) and reduced (e.g., trichomycterids) canals. The l arge bone usually termed as the supraoccipital in siluroids is thought to be homologous with the parietals + supraoccipital of other ostario physans based on position, sutures with surrounding bones, and presenc e of anterior and middle pitlines. The suture between sphenotic and pa rieto-supraoccipital is a synapomorphy for catfishes. In primitive cat fishes, the posterolateral corner of the cranial roof is formed by pte rotic, extrascapula, and a third bone which attaches the pectoral gird le to the neurocranium; the third element may be homologous with the s upracleithrum or a posttemporo-supracleithrum. The presence of a small extrascapula sutured with pterotic, parieto-supraoccipital, and epioc cipital (and, occasionally, the posttemporo-supracleithrum) is charact eristic of primitive siluroids. The absence of the supratemporal commi ssure is a synapomorphy of catfishes, as well as the presence of the p terotic branch. The latter is a lateroposterior branch of the temporal canal (on the pterotic) that opens on the skin (e.g., Diplomystidae, Ictaluridae, and dagger Hypsidoridae), or continues in the posttemporo -supracleithrum joining the main lateral line (e.g., Parapimelodus). T he pitlines are not incised in bone in most extant siluroids or in oth er extant ostariophysans; however, pitlines and neuromasts incised in grooves and/or pit are characteristic of some catfishes such as dagger Andinichthys, dagger Hoffstetterichthys dagger Incaichthys, Galeichth ys, and Parapimelodus.