VI. Croonian lecture.— The evolution and origin of the amphibia

Abstract

In this Croonian lecture a detailed account of the structure of the skull, lower jaw, vertebral column, shoulder girdle, and pelvis of the embolomerous Labyrinthodontia from the Coal Measures of Britain, and of the skeleton of Di-plovertebron from the Stephanian of Nyran, is used as the basis of the discussion of the relationship of the Amphibia to bony fish. The structure of the head of certain osteolepid fish is described in order to afford adequate materials for comparison. It is shown that the Embolomeri include the ancestors of all later labyrintho-donts, and that they are directly comparable in detail with osteolepid fish. It is concluded that air-breathing had become fully established in the fish ancestors of Amphibia, and that the body movements involved in walking are essentially similar to those by which primitive fish swam. Respiratory movements follow the same rhythm in the 2 groups. The ear of the Embolomeri is remarkable for the absence of a fenestra ovalis; a discussion of the origin of the columella is included. The problem presented by the occurrence of external gills in the larvae of Polypterus, the Dipnoi, and the Amphibia is discussed. The following new forms and synonymy are reported PALAEOGYRINUS (p. 215), (Labyrinthodontia, Embolomeri), type P. decorus* (p. 215), and EOGYRINUS (p. 222), type E. attheyi* (p. 222), Carboniferous, England; types in Newcastle Mus. The author considers E. attheyi, of which a reconstruction of the skeleton is given, the most primitive of all known Amphibia. Diplovertebron punctatum* Fritsch (=Gephyro$tegus bohemicus Jaekel) is rede-scribed. Full descriptions are also given of the osteolepid fish, Osteolepis macrolepidotus*, from the Middle Red Sandstone, Megalichthys*, and Eusthenopteron.*[long dash]D. M. S. Watson.