Semionotids (Neopterygii, Semionotiformes) from the Lower Cretaceous Lagarcito Formation, San Luis Province, Argentina

LÓPEZ-ARBARELLO, A. AND CODORNIÚ, L.

JOURNAL OF VERTEBRATE PALEONTOLOGY

Society of Vertebrate Paleontology

Lugar: Ilinois, USA; Año: 2007 vol. 27 p. 811 - 826

0272-4634

A revision of the semionotids from the Lower Cretaceous Lagarcito Formation of Argentina leads to the conclusion that only one taxon, Neosemionotus puntanus Bocchino, 1973, is represented, instead of two monospecific genera and one species of Lepidotes as originally thought. Neosemionotus shares with Lepidotes the presence of more than one suborbital arranged in one row and a long posteroventral process of the dentary, features that have previously been thought to be diagnostic of Lepidotes. On the other hand, it shares with Semionotus the presence of conspicuous dorsal ridge scales. However, Neosemionotus is unique in the characteristics of its dorsal and anal fins, which are both flanked only by high and strong paired basal fulcra. These fulcra become gradually higher/deeper posteriorly, reaching approximately the heigh/depth of the first fin ray. Other probable synapomorphies of Neosemionotus are the presence of a long parietal pit line, a small, approximately triangular interoperculum, the complete absence of fringing fulcra on the dorsal, and anal fins, and the presence of only very few long and slender fringing fulcra on the pelvic and caudal fins. The systematic position of Neosemionotus is still unknown, but the presence of probably primitive features like the high number of extrascapulars, short parietals, the arrangement of suborbitals, and short snout indicate a relatively basal position among semionotids.