CEPHALOPOD ADAPTATIONS 



97 



an epitome of the general and normal 

 trend of evolution in the shelled ceph- 

 alopods. The end product would be a 

 nectonic animal with greater or less loco- 

 motive powers — as were the majority of 

 shelled forms. But there are a host of 

 exceptions to this general trend, as there 

 necessarily must have been if these 

 animals were to adapt themselves fully 

 to the varying environments of the seas — 

 as they undoubtedly did. 



LIKE HABITS OF THE ORTHOCONES 



In considering these modifications we 

 may first consider the variations shown 

 in the early orthocones. Fully half of 

 the known Ordovician cephalopods had 

 shells which were orthocones. Specula- 

 tions as to their habits of life have been 

 more fantastic and mutually exclusive 

 than is the case in any of the later cephalo- 

 pods. They have been pictured as swim- 

 ming in both vertical and horizontal 

 attitudes, as having dragged their hori- 

 zontal shells over the bottom, as having 

 lived obliquely buried in the bottom, or 

 as having been attached vertically by the 

 apical end. 



Ruedemann (19Z1) has shown conclu- 

 sively that some of them were horizontal 

 in their normal attitude. This is proved 

 in the case of Geisonoceras temiitextum of 

 the Ordovician of New York by the 

 preservation of a well marked longitudinal 

 color pattern (Plate 4, fig. 5) on one side 

 of the shell, which must have been the 

 dorsal, since all marine organisms with 

 a color pattern have the side toward the 

 light contrasted with the opposite side. 

 Not only so, but this author cites shells of 

 this species with incrusting bryozoa in 

 which the zoarium begins near the apex 

 and extends forward on one side of the 

 shell only, -pari passu with its growth, 

 which would be a most unlikely occur- 



rence if the bryozoan had started on a 

 dead shell. 



If this dorso-ventral color pattern were 

 an isolated case it might possibly be open 

 to doubt, but it has been observed in 

 specimens of orthocones of very different 

 ages and widely separated geographically. 

 Naturally the preservation of the color 

 pattern of life in fossils of great antiquity 

 is unusual, so that many such instances are 

 not to be expected. Nevertheless I may 

 cite such features in Orthoceras trusitum of 

 the Silurian of New York, Orthoceras 

 anguliferum of the Devonian of Germany 

 (Plate 4, fig. 4), Orthoceras sp., of the 

 Upper Carboniferous of Oklahoma, and I 

 have no doubt that a protracted search 

 through the systematic literature would 

 disclose other instances. Those cited 

 extend pretty well through the Paleozoic 

 and over two continents, and I think that 

 we may legitimately conclude that the 

 horizontal attitude was the normal one 

 for the majority of the orthocones . 



Ruedemann considers such forms to have 

 been benthonic and to have dragged their 

 shells over the Paleozoic sea-bottoms. 

 The objections to this interpretation are 

 that their apertures are not oblique, the 

 shells do not show wear incident to such 

 a mode of life, and many show a hypo- 

 nomic sinus which is usually correlated 

 with a functional hyponomic funnel. 



This last is not an especially weighty objection, 

 since all cephalopods must have preserved the funnel 

 for respiratory purposes even when it ceased to be 

 functional as a locomotive organ; at lease in the 

 modern Nautilus its regular pulsation causes incurrent 

 and excurrent streams, and the mantle does not take 

 part in causing these movements, as it does in the 

 dibranchiates. 



I believe such forms to have been swim- 

 mers. Some doubtless hovered near the 

 bottom or spent most of their time resting 

 upon it, but others surely must have been 

 more active. The idea that locomotion 



