﻿EXTINCTION 
  AND 
  EXTERMINATION 
  TOLMACHOFF 
  273 
  

  

  also 
  a 
  number 
  of 
  objections 
  to 
  the 
  theory 
  that 
  the 
  ammonites 
  were 
  

   completely 
  destroyed 
  by 
  reptiles. 
  Many 
  Cretaceous 
  ammonites 
  were 
  

   deep-sea 
  forms, 
  which 
  were 
  inaccessible 
  to 
  reptiles. 
  It 
  is 
  also 
  worthy 
  

   of 
  note 
  that 
  the 
  squids, 
  upon 
  which 
  Jurassic 
  reptiles 
  fed,^*' 
  survived 
  

   the 
  ammonites, 
  although 
  they 
  could 
  have 
  been 
  more 
  easily 
  extermi- 
  

   nated 
  than 
  the 
  ammonites. 
  

  

  In 
  the 
  history 
  of 
  the 
  ammonites 
  we 
  see 
  a 
  remarkable 
  phenomenon. 
  

   The 
  stock 
  declined 
  twice. 
  The 
  first 
  time 
  it 
  was 
  vigorous 
  enough 
  to 
  

   escape 
  extinction 
  and 
  to 
  develop 
  to 
  a 
  degree 
  unsurpassed 
  in 
  the 
  history 
  

   of 
  animal 
  life; 
  but 
  the 
  second 
  time, 
  in 
  the 
  Cretaceous 
  period, 
  it 
  reached 
  

   senility 
  and 
  died 
  out. 
  Overspecialization, 
  such 
  as 
  exaggeration 
  of 
  

   parts, 
  was 
  expressed 
  in 
  the 
  Cretaceous 
  ammonites 
  no 
  less 
  clearly 
  than 
  

   in 
  the 
  trilobites 
  and 
  in 
  the 
  Mesozoic 
  reptiles. 
  " 
  Their 
  doom 
  was 
  fore- 
  

   shadowed 
  in 
  the 
  uncoiling, 
  the 
  unnatural 
  twisting 
  of 
  the 
  shells, 
  and 
  

   the 
  straight 
  baculites."^^ 
  Nothing 
  similar 
  is 
  known 
  of 
  the 
  Triassic 
  

   ammonites, 
  all 
  of 
  which 
  had 
  the 
  typical 
  ammonite 
  shape, 
  worked 
  out 
  

   through 
  millions 
  of 
  generations. 
  This 
  race 
  also 
  died 
  out 
  only 
  because 
  

   of 
  some 
  inner 
  cause 
  or 
  causes. 
  It 
  was 
  unable 
  to 
  establish 
  and 
  keep 
  

   the 
  natural 
  balance 
  and 
  was 
  doomed 
  to 
  extinction. 
  

  

  Though 
  these 
  examples 
  of 
  the 
  extinction 
  of 
  large 
  ancient 
  groups 
  of 
  

   animals 
  are, 
  perhaps, 
  the 
  most 
  typical 
  and 
  most 
  widely 
  known, 
  the 
  

   number 
  of 
  examples 
  of 
  extinction 
  could 
  be 
  increased 
  a 
  hundredfold. 
  

   In 
  addition 
  to 
  those 
  already 
  cited, 
  there 
  are 
  a 
  few 
  isolated 
  extinct 
  

   forms 
  having 
  some 
  aberrant 
  structure, 
  which 
  appeared 
  only 
  for 
  a 
  short 
  

   geological 
  time, 
  and 
  which, 
  being 
  doomed 
  to 
  extinction 
  from 
  the 
  begin- 
  

   ning, 
  vanished 
  \vithout 
  descendants. 
  Such 
  were 
  Lyttonia 
  of 
  the 
  

   brachiopods 
  and 
  Helicoprion 
  of 
  the 
  fishes. 
  These 
  forms, 
  being 
  highly 
  

   specialized, 
  showed 
  sharp 
  deviation 
  from 
  the 
  standard 
  of 
  their 
  group, 
  

   which 
  foretold 
  for 
  them 
  ''a 
  relatively 
  brief 
  career." 
  ^^ 
  At 
  the 
  same 
  

   time 
  the 
  special 
  features 
  of 
  these 
  aberrant 
  creatures 
  were 
  probably 
  of 
  

   great 
  biological 
  importance, 
  because, 
  in 
  spite 
  of 
  their 
  short 
  life, 
  some 
  

   of 
  them 
  were 
  of 
  widespread 
  geographical 
  distribution. 
  However, 
  they 
  

   left 
  no 
  issie, 
  because 
  a 
  "highly 
  adapted 
  or 
  specialized 
  form 
  becomes 
  

   stereotyped 
  and 
  incapable 
  of 
  racial 
  change." 
  ^^ 
  Their 
  extinction 
  may 
  

   therefore 
  be 
  parallel 
  to 
  that 
  of 
  the 
  large 
  groups 
  already 
  considered. 
  

  

  The 
  examples 
  here 
  cited 
  include 
  two 
  species 
  that 
  became 
  extinct 
  

   during 
  the 
  period 
  of 
  human 
  history 
  under 
  fairly 
  well-known 
  conditions, 
  

   and 
  their 
  extinction 
  therefore 
  has 
  none 
  of 
  the 
  mystery 
  that 
  is 
  con- 
  

   nected 
  with 
  the 
  extinction 
  of 
  Paleozoic 
  and 
  Mesozoic 
  forms. 
  

  

  2» 
  Charles 
  Schuchert, 
  Historical 
  geology, 
  p 
  .476, 
  

  

  21 
  Idem, 
  p. 
  576. 
  

  

  " 
  R. 
  S. 
  Lull, 
  Organic 
  evolution, 
  p. 
  220. 
  

  

  " 
  Idem, 
  p. 
  293. 
  

  

  