II.Microbrachis, the type microsaur

Abstract

Microbrachis (Limnerpeton) obtusatum(Fritsch) is redescribed, and additions to our knowledge of the vertebrae and skull structure ofMicrobrachishave been made. The vertebrae ofMicrobrachisare apsidospondylous, the centrum is a pleurocentrum, the intercentra are small, caudal intercentra always being present with a varying number of pre-sacral intercentra. In theMicrobrachisskull there is a free attachment of the cheek and skull table the supratemporal resting on a shelf which projects inwards from the dorsal edge of the squamosal. In thisMicrobrachisresembles the pre-captorhinomorphsProtorothyrisand M.C.Z. 1963 in which the relation of these two bones is similar. The occiput ofMicrobrachishas been described. A statement of microsaur characters is given and the list of characters separating microsaurs from captorhinids given by Gregory is critically examined. The conclusion is reached that microsaurs and captorhinomorphs are basically of similar structure and form part of a related group which separated from labyrinthodonts in pre-Carboniferous times, or had a separate origin from the rhipidistian fishes. The differences between microsaurs and captorhinomorphs lie not in basic structure but in evolutionary timing, the microsaurs, for example, being precocious in the structure of their vertebrae.