Left (Fig. 1): The peculiar armored fish, 

 Bothriolepis, was adapted for life on Devon- 

 ian stream bottoms. 



Cover: Dunkleosteus, giant placoderm of 

 Devonian seas, as he may have appeared in 

 life. The restoration is based on specimens 

 from the Cleveland region. Superimposed on 

 the background painting is a photograph of 

 a cast of the shield displayed in this month's 

 featured exhibit. 



Paintings by Maidi W. Leibhardt 



ARMORED FISHES OF DEVONIAN SEAS 



O 



"ne of the most striking, and at the 

 same time least known, groups of fishes 

 is the placoderms. They are remark- 

 able for their evolutionary radiation into 

 a wide variety of adaptive types, culmi- 

 nating in huge predators of late Devo- 

 nian seas. Yet they are not widely known 

 because their remains have been identi- 

 fied with certainty only in rocks of the 

 Devonian period, which ended nearly 

 350 million years ago. 



A variety of placoderms is illustrated 

 in the Museum's featured exhibit for 

 March — "Armored Fishes of The De- 

 vonian Period" — located at the south 

 end of Hall 38. The exhibit shows ac- 

 tual fossils, as well as models and paint- 

 ings of the major placoderm groups. 



The first known fossil remains of pla- 

 coderms appear in early Devonian rocks 



Page 2 MARCH 



ROBERT H. DENISON 

 CURATOR, FOSSIL FISHES 



about 400 million years old. These 

 fishes were typically small, heavily ar- 

 mored, bottom dwellers. The heavy 

 armor, a characteristic of the group, is 

 what gives them their name : placoderm 

 means plate-skinned. The armor con- 

 sisted of a number of bony plates, some 

 of which formed a shield for the head, 

 while others formed a cover for the shoul- 

 der or trunk region, the two shields be- 

 ing united by a movable joint in the 

 neck. Rarely are the body and tail pre- 

 served, presumably because they lacked 

 any hard parts capable of fossilization. 

 A much enlarged restoration of the ar- 

 mor of one of these early placoderms, 

 Bryantolepis, appears in the featured ex- 

 hibit. 



We can say little about the habits of 

 these early placoderms, except that most 



of them lived and fed on the bottoms of 

 streams and seas. This is shown by the 

 flatness of their lower side, the project- 

 ing spines behind the head, the absence 

 of well-developed paired fins, and by the 

 presence of the heavy shield . This shield 

 may have served as an armor, protecting 

 the placoderms from contemporary pre- 

 daceous fishes and eurypterids. 



Some of the descendants of these early 

 forms became more powerful swimmers, 

 as is shown by their streamlined bodies 

 and well-developed paired fins. Flat 

 crushing surfaces on the jaws of some 

 forms show that they fed on hard-shelled 

 food such as molluscs and arthropods. 

 The huge Dunkleosteus (shown on this 

 month's cover) developed scissors-like 

 shearing blades on its jaws, which would 

 {Continued on page 8) 



