Sensory canals and related bones of Tertiary siluriform crania from Bolivia and North America and comparison with Recent forms

ABSTRACT

Narrow, simple cephalic sensory canals enclosed by bone represent the primitive condition found in catfishes (siluroids) such as Diplomystidae, †Hypsidoridae, and Ictaluridae. Derived conditions among siluroids include highly branched (e.g., †Andinichthys, Galeichthys, and Parapimelodus) and reduced (e.g., trichomycterids) canals. The large bone usually termed as the supraoccipital in siluroids is thought to be homologous with the parietals + supraoccipital of other ostariophysans based on position, sutures with surrounding bones, and presence of anterior and middle pitlines. The suture between sphenotic and parieto-supraoccipital is a synapomorphy for catfishes.

In primitive catfishes, the posterolateral corner of the cranial roof is formed by pterotic, extrascapula, and a third bone which attaches the pectoral girdle to the neurocranium; the third element may be homologous with the supracleithrum or a posttemporo-supracleithrum. The presence of a small extrascapula sutured with pterotic, parieto-supraoccipital, and epioccipital (and, occasionally, the posttemporo-supracleithrum) is characteristic of primitive siluroids. The absence of the supratemporal commissure is a synapomorphy of catfishes, as well as the presence of the pterotic branch. The latter is a lateroposterior branch of the temporal canal (on the pterotic) that opens on the skin (e.g., Diplomystidae, Ictaluridae, and † Hypsidoridae), or continues in the posttemporo-supracleithrum joining the main lateral line (e.g., Parapimelodus).

The pitlines are not incised in bone in most extant siluroids or in other extant ostariophysans; however, pitlines and neuromasts incised in grooves and/or pit are characteristic of some catfishes such as †Andinichthys, †Hoffstetterichthys, †Incaichthys, Galeichthys, and Parapimelodus.