﻿EXTINCTION 
  AND 
  EXTERMINATION 
  

  

  By 
  I. 
  P. 
  TOLMACHOFF 
  

  

  EXAMPLES 
  OF 
  EXTINCTION 
  AND 
  THEIR 
  USUAL 
  EXPLANATIONS 
  

  

  GENERAL 
  STATEMENT 
  

  

  The 
  extinction 
  of 
  species, 
  genera, 
  families, 
  orders, 
  classes, 
  and 
  even 
  

   phyla 
  and 
  complete 
  faunas, 
  is 
  a 
  phenomenon 
  well 
  known 
  to 
  paleontol- 
  

   ogists 
  and 
  biologists, 
  and 
  it 
  is 
  "so 
  common 
  that 
  this 
  has 
  come 
  to 
  be 
  

   looked 
  upon 
  as 
  the 
  normal 
  course 
  of 
  evolution." 
  ^ 
  Some 
  well- 
  

   known 
  typical 
  examples 
  of 
  this 
  phenomenon 
  are 
  the 
  extinction 
  of 
  the 
  

   trilobites 
  at 
  the 
  end 
  of 
  the 
  Paleozoic 
  era, 
  of 
  the 
  ammonites 
  and 
  the 
  

   gigantic 
  reptiles 
  in 
  the 
  Mesozoic 
  era, 
  of 
  the 
  mammoth 
  at 
  the 
  dawn 
  of 
  

   human 
  history, 
  and 
  of 
  the 
  sea 
  cow 
  of 
  Bering 
  Strait 
  in 
  the 
  eighteenth 
  

   century. 
  Although 
  it 
  is 
  so 
  common, 
  extinction 
  is, 
  in 
  its 
  essentials 
  or 
  

   causes, 
  very 
  little 
  known, 
  or 
  even 
  quite 
  unknown. 
  The 
  examples 
  of 
  

   extinction 
  just 
  cited 
  have 
  been 
  explained 
  in 
  different 
  ways, 
  but 
  all 
  the 
  

   explanations, 
  some 
  of 
  which 
  are 
  very 
  detailed, 
  can 
  not 
  withstand 
  

   criticism. 
  

  

  THE 
  TRILOBITES 
  

  

  The 
  extinction 
  of 
  the 
  trilobites 
  has 
  been 
  attributed 
  to 
  the 
  rise 
  of 
  the 
  

   cephalopods 
  and 
  the 
  fishlike 
  animals 
  in 
  early 
  Paleozoic 
  time, 
  and 
  of 
  the 
  

   true 
  fishes 
  in 
  Devonian 
  time.^ 
  These 
  animals 
  undoubtedly 
  fed 
  on 
  the 
  

   trilobites 
  and 
  forced 
  them 
  from 
  the 
  dominion 
  of 
  the 
  early 
  seas, 
  ulti- 
  

   mately 
  contributing 
  to 
  their 
  complete 
  extinction, 
  but 
  we 
  know 
  that 
  

   extermination 
  which 
  is 
  brought 
  about 
  solely 
  by 
  the 
  development 
  of 
  a 
  

   higher 
  or 
  stronger 
  type 
  of 
  life 
  can 
  happen 
  only 
  under 
  exceptional 
  con- 
  

   ditions. 
  Usually 
  the 
  smaller 
  and 
  weaker 
  animals 
  have 
  time 
  to 
  make 
  

   compensating 
  adjustments 
  to 
  avoid 
  extermination. 
  We 
  know, 
  for 
  

   instance, 
  that 
  the 
  eggs 
  and 
  the 
  young 
  of 
  fish 
  are 
  an 
  easy 
  prey 
  of 
  their 
  

   many 
  enemies 
  and 
  are 
  destroyed 
  in 
  immense 
  numbers. 
  The 
  chance 
  

   of 
  survival 
  of 
  an 
  egg 
  of 
  the 
  ling, 
  for 
  example, 
  is 
  1 
  in 
  14,000,000.'' 
  Yet 
  

   the 
  Ung 
  is 
  not 
  dying 
  out, 
  at 
  least 
  not 
  under 
  natural 
  conditions, 
  but, 
  

  

  1 
  Reprinted 
  by 
  permission 
  from 
  the 
  Bulletin 
  of 
  the 
  Geological 
  Society 
  of 
  America, 
  Dec. 
  ?.0, 
  1928. 
  

  

  2 
  W. 
  R. 
  Gregory, 
  Two 
  views 
  on 
  the 
  origin 
  of 
  man. 
  Science, 
  vol. 
  Ixv. 
  No. 
  1695, 
  p. 
  C02, 
  1927. 
  

   ' 
  Charles 
  Schuchert, 
  Historical 
  geology, 
  pp. 
  210 
  and 
  324. 
  

  

  * 
  R. 
  S. 
  Lull, 
  Organic 
  evolution, 
  p. 
  103. 
  

  

  269 
  

  

  