244 UPPER CRETACEOUS TELEOSTS 
from the basal salmoniform stock before forms such as the myctophiforms and 
ctenothrissiforms had arisen. Weitzman (1967 : 526) doubts that the proethmoids 
of esocoids have any relation to the evolution of the ascending premaxillary processes 
in other teleosts. He suggests that the esocoids exhibit an experiment in jaw 
design which did not impart any significant evolutionary advantages. Due to 
the fresh-water habitat of the Esocoidei this group may represent an early offshoot 
from the salmoniform ancestral stock in the Jurassic fresh waters. 
The fossil salmoniform suborders Enchodontoidei, Ichthyotringoidei, Cimolich- 
thyoidei and Halecoidei extend throughout the greater part of the Upper Cretaceous, 
but all seem to have disappeared by the Maastrichtian. The myctophiforms are 
represented throughout the Upper Cretaceous but the ctenothrissiforms had 
disappeared by the Middle Turonian, this latter group having been replaced by its 
more advanced descendants, the Beryciformes. The Beryciformes were evolving 
and diversifying throughout the Cretaceous, and towards the close of this period 
several of the lines represented in the present day Beryciformes and Perciformes 
were established (Patterson, 1964, 1967a, 1967b). 
In the Cretaceous period the Elopiformes, Anguilliformes, Notacanthiformes, 
Clupeiformes, Osteoglossiformes, Salmoniformes, Myctophiformes, Ctenothrissi- 
formes and Beryciformes would have inhabited similar environments and would have 
been in direct competition with each other for food and living space. The Cretaceous 
fauna would have lived in the most productive parts of the ocean, these favourable 
parts being inshore waters (above the upper reaches of the continental shelves) or 
the surface waters of equatorial oceanic regions (Marshall, 1963 : 189). Throughout 
the Upper Cretaceous the Beryciformes were increasing and perfecting the protrusile 
mouth which opened up new and hitherto unused food sources. At the same time 
the Beryciformes were becoming more effective swimmers and were developing 
protective spines on fins and scales. A true protrusile mouth is not developed in any 
other group, although all the basic requirements are present in the Myctophiformes. 
Towards the close of the Cretaceous the Beryciformes gave rise to lines leading on to 
the Perciformes and other advanced Acanthopterygii (Patterson, 1964, 19674). 
Thus the beryciforms and their derivatives would have provided stern competition 
for the less labile, more primitive grades of organization represented by the Elopi- 
formes and the early salmoniform derivatives. Many of these lower teleostean 
groups succumbed to this pressure of competition and died out, e.g. Enchodontoidei, 
Cimolichthyoidei, etc. Others, better adapted to their particular habits, e.g. 
Clupeomorpha, or modified along very specialized lines, e.g. eels, were able to survive 
and compete. Still others at the end of the Cretaceous were forced to seek living 
space elsewhere. This involved the colonization of the less productive parts of the 
ocean, which include the central water masses at increasing depths. Thus groups 
like the myctophiforms and stomiatoids were forced into deeper waters. It is 
interesting to note that the vast majority of the recent bathypelagic fish are all lower 
teleostean in origin. Once in the bathypelagic environment a certain amount of 
adaptive radiation has occurred in both of the above mentioned groups, this radiation 
commencing at the close of the Cretaceous and the beginning of the Tertiary. Thus 
