THE BRAINCASE ANATOMY OF LAWRENCIELLA SCHAEFFERl, ACTINOPTERYGIAN FROM THE UPPER CARBONIFEROUS OF KANSAS (USA)

摘要

A full description and diagnosis are given of Lawrenciella schaefferi Poplin 1984, from the Pennsylvanian (Late Carboniferous) of Kansas, USA This taxon is only known by braincases and associated pai asphenoids, which are exceptionally well preserved as phosphatic nodules. The external and internal morphology of the endocrania were studied from serial sectionings which allowed detailed three-dimensional reconstructions. The study shows that, besides synapo-morphies inherent to basal actinopterans, L schaefferi displays a set of very peculiar features such as prespiracular fossae, intracranial ossicles, and paired anterior nryodomes for nonocular eye muscles. Another conspicuous feature, the notochordal canal ending blindly anteriorly, has been observed until now only in more advanced Triassic actinopterans The anatomical characters of L, schaefferi indicate, in the light of recent cladistrc analyses, that this Carboniferous taxon is a relatively advanced actinopteran compared to basal forms such as Kentuckia, Mimia, or Moythomasia.