•ON THE HABITAT OF THE EARLY VERTEBRATES 



If we take the record as it stands, the appearance of the 

 iishes, the first known vertebrates, is one of the most abrupt and 

 dramatic in the life-history of the earth. They seem to come 

 trooping on the stage of action from some concealed source in 

 full company and clothed in varied and curious armor, and at 

 once a battle scene of prodigious range and duration begins. 

 There had been some feeble premonitions, but these had revealed 

 little of the coming drama. That there had been a long series 

 •of preliminary trainings, with trials and changes of armor, and 

 rehearsals, and shiftings of parts, we cannot doubt, but where 

 and how this transpired has been an unsolved mystery, though 

 we have tried industriously to get behind the scenes. 



The trivial premonitory signs of the apparition, even when 

 interpreted by retrospective light, only serve to render their 

 meagerness the more singular. If the fishes were armored in 

 the Ordovician period, as the Colorado relics found by Walcott 

 seem to show, and if these mail-clad fishes continued to live in 

 the seas and to develop into the panoplied host 'that made its 

 apparition during the transition stage from the Silurian to the 

 Devonian, why did they not leave a more fitting registration of 

 their presence? The "imperfection of the geological record" 

 is indeed great, but in seas that preserved soft medusae and 

 delicate graptolites, it would seem that armored fish should have 

 left abundant and substantial signs of themselves, if they were 

 there. The Trenton relics of Colorado, if taken at their fullest 

 assigned value, help to make such a record, it is true, but at the 

 same time they emphasize its scantiness and nullify the familiar 

 appeal to an unfossilizable softness of structure and perishable- 

 ness of parts. While they contribute a little to the record, the 

 chief effect of their discovery is to greatly strengthen the opinion 

 long entertained that the fishes must have had a very protracted 



