The problem of the origin of terrestrial tetrapods is one of the controversial questions of 

 biologyt Many investigations havebeen devoted to it in the field of paleor t ology, comparative 

 anatomy and embryology. In the past decade, interest in this problem has increased especially 

 in connection with new discoveries of fossil forms which are more or less close to the ancestors 

 of the tetrapods. 



As long as the links which connect fishes with tetrapods are not conclusively established, 

 there is room for hypotheses and propositions about the peculiarities of the structure, taxonomic 

 position, singleness and multiplicity of initial forms, the time and places of the appearance of 

 the first tetrapods and the causes for their appearance. 



At the end of the 19th century, terrestrial amphibians were linked with dipnoan fishes. 

 Paleontology rejected this proposition, based on the great specialization in the Dipnoi and the 

 impossibility of the homology of their bones with the bones of tetrapods. In the 20th century, 

 only a few investigators consider that the origin of some tetrapods, namely tailed amphibians 

 (Urodela), is possible from the Dipnoi (Wintrebert, 1910; Holmgren, 1933; Save-Soderberqh, 193*; 

 Lehman, 1956). At the present time, one can consider it generally accepted that tetrapods derived 

 from lung fishes of the order^ Rhipidistia whichunites two suborders, i.e., Holoptych i ide i ard 

 0s teolep i do i de i , which correspond to the groups Porolep i formes and Osteolep i formes of Jarvik (E. 

 Jarvik, 1942). 



The opirion of investigators is divided as to the actual representatives of the Rhipidistia 

 which served as starting points for the tetrapods. The most widespread hypothesis is that of 

 polyphyletic derivation. Its basic source was the detailed survey of the anatomy of the ethmoid 

 region of the skull of lower Gna thos toma ta by Jarvik (1942). As a result of the comparison of the 

 structure of the snout of Eus thenopteron ( Osteolep i formes) and Porolep i s ( Porolep if ormes) and 

 their comparison with the skull structure of amphibians, primarily R ana (Anura) and Salamandra 

 (Urodela), Jarvik came to the following conclusions: l) The Rhipidistia represent two separate 

 groupings, i.e., Porolepi formes and Osteolep i formes; 2) modern tailless and tailed amphibians are 

 sharply distinguished from one another by the structure of the ethmoid, which indicates their deri- 

 vation from various fishlike ancestors; 3) the distinctions between Anura and Urodela correspond 



—p. 1356- 



to the differences in the structure of the snout of Rhipidistia and in connection with this the 

 former shou.d be considered to ; ssue from Osteolep i formes and the latter from Porolep if ormes. 

 Osteolep i formes served as the beginning for all remaining tetrapods ( Eu tet rapoda ) . L epospondylous 

 amphibians ( Lepospondyl i ) which are brought into question with Urodela just as are Apoda are not 

 examined by Jarvik (fig. l). 



In recent years, Jarvik has published a series of works devoted to the questions of the origin 

 of the tet rapods, wi th an analysis of the structure of separate components of the skeleton and espec- 



— fig. 1 — 

 tally of the skull. The hypotheses of diphyly in his later works has developed into full pol/ph,l. 

 ( Jarvik, 195;). Thus, one of his graphs ( Jarvik, I960, figs. 1 8n and 30) shows that not only 

 Anura and Urodela but also Labyri nthodont ia, Sauromorpha and Theromorpha arise i ndependenf 1 , from 

 Osteolep i formes. The time of th? appearance of tetrapods moves to the lower Siiurian or even 

 Ordovician (jarvik, 1964). 



The investigations of .Jarvik created lively 

 pattern of detailed study of the skeleton of fos 

 are not in agreement with the conclusions of the 

 1964; Eaton, 1959; Szarski, 1962; Parsons and wi 

 Anura and Urodela untenable and reject the hypot 

 of I. I. Shmal'gauzen in thisregard deserve spec 

 questions of the origin of terrestrial vertebrat 

 conducted under his direction on the development 

 succession in evolution of the structure of fish 

 difference in their beginnings in Anura and Urod 

 development of many elements o r the skeleton and 

 their polyphyle'ic origin. On the other hand, d 

 organs of Anura and Urodela along with their pos 

 which hardly could have appeared in a parallel w 



discussion among biologists. They present a 

 sil vertebrates. However, a whole group of scholars 

 se studies. Many zoologists (Shmal'gauzen, 1959> 

 lliams, 1962, I963) consider this contrasting of 

 heses of their diphyletic derivation. Ihe studies 

 ial attention. He has dealt for many years with 

 es. A series of experimental investigations was 

 of amphibians with the aim of clarifying the 

 es and tetrapods and the degree of similarity and 

 ela. The investigations, which dealt with the 



sensory organs in amphibians, in no way support 

 ata from embryology indicating the homology of many 

 session of a complex of tetrapod characteristics 

 ay in various evolutionary lines and along with the 



1 The ta> 



of lungfishes (superorder Crossopteryg i i ) is according to "isnovy paleontolog i i " (1964). 



