The structure of certain Jurassic holostean fishes, with special reference to their neurocrania

Abstract

The term Holostei is in the process of being transformed from one expressing (or intending to express) some phylogenetic type of classification into one denoting a structural grade— a transformation commonly suffered by a term of long standing as the essential characters of its component genera are better understood. Unfortunately, understanding of this particular stage in Actinopterygian evolution is far from complete, and at present it is not possible to replace the old classification by one that will not have to be thoroughly revised in a few years’ time. Since, therefore, the present work (which was essentially complete in 1940) deals primarily with the structure of a few Jurassic neurocrania the term Holostei may still serve conveniently to cover the families in which they are found, although the origin of these is largely unknown and their degree of relationship a matter of debate. It will be found that a study of neurocrania occasionally produces some new evidence on these problems, but for a more complete'discussion on classification reference may be made to those works expressly dealing with the subject, especially Brough (1939), Rayner (1941) and Westoll (1944)