﻿318 
  ANNUAL 
  REPOKT 
  SMITHSONIAN 
  INSTITUTION, 
  1927 
  

  

  presence 
  of 
  comparatively 
  small 
  tubercles 
  and 
  perhaps 
  by 
  a 
  few 
  

   short 
  and 
  slender 
  spines. 
  In 
  the 
  Silurian 
  faunas 
  they 
  attain 
  larger 
  

   proportions 
  and 
  become 
  more 
  ornate, 
  with 
  numerous 
  spines 
  and 
  

   tubercles 
  of 
  an 
  extravagant 
  sort. 
  In 
  our 
  American 
  faunas 
  these 
  

   Lichads 
  culminate 
  in 
  the 
  gigantic 
  Terataspis 
  grandis 
  of 
  the 
  early 
  

   Middle 
  Devonian, 
  a 
  creature 
  which 
  attained 
  a 
  length 
  of 
  eighteen 
  or 
  

   more 
  inches 
  and 
  which 
  developed 
  most 
  elaborate 
  spines, 
  many 
  of 
  

   which 
  bore 
  secondary 
  spines 
  and 
  tubercles. 
  Altogether 
  this 
  creature 
  

   must 
  have 
  been 
  one 
  of 
  the 
  most 
  bizarre 
  trilobites 
  of 
  all 
  time. 
  The 
  

   Dalmanites 
  also, 
  another 
  group 
  of 
  trilobites, 
  originated 
  in 
  the 
  Ordo- 
  

   vician 
  as 
  small, 
  unornamented 
  individuals. 
  In 
  the 
  Silurian 
  they 
  

   developed 
  some 
  degree 
  of 
  ornamentation, 
  but 
  in 
  the 
  Lower 
  and 
  lower 
  

   Middle 
  Devonian 
  these 
  ornamental 
  characters 
  attained 
  the 
  highest 
  

   development 
  and 
  the 
  creatures 
  increased 
  greatly 
  in 
  size. 
  With 
  the 
  

   close 
  of 
  Onondagan 
  time 
  in 
  America 
  all 
  of 
  these 
  gigantic 
  and 
  ornate 
  

   trilobites 
  became 
  extinct, 
  and 
  from 
  that 
  time 
  to 
  the 
  final 
  disappear- 
  

   ance 
  of 
  the 
  whole 
  class 
  they 
  were 
  represented 
  by 
  small, 
  unornamented 
  

   forms 
  which 
  had 
  persisted 
  from 
  early 
  Paleozoic 
  time 
  without 
  the 
  

   development 
  of 
  such 
  ornate 
  features 
  as 
  were 
  shown 
  by 
  their 
  gigantic 
  

   relatives. 
  

  

  Another 
  group 
  of 
  organisms 
  with 
  a 
  similar 
  history 
  are 
  the 
  cham- 
  

   bered 
  cephalopods. 
  These 
  started 
  in 
  early 
  Paleozoic 
  time 
  with 
  

   smooth 
  shells 
  and 
  simple 
  sutures. 
  By 
  the 
  end 
  of 
  Paleozoic 
  time 
  

   some 
  of 
  them 
  had 
  developed 
  fairly 
  complex 
  sutures, 
  and 
  some 
  shells 
  

   with 
  nodes 
  and 
  ribs 
  were 
  in 
  evidence. 
  Associated 
  with 
  these 
  were 
  

   others 
  with 
  sutures 
  as 
  simple 
  and 
  shells 
  as 
  smooth 
  as 
  the 
  oldest 
  

   forms. 
  The 
  development 
  of 
  increasing 
  sutural 
  complexity 
  and 
  in- 
  

   creasing 
  ornateness 
  of 
  the 
  shells 
  continued 
  through 
  Mesozoic 
  time, 
  

   when 
  nearly 
  the 
  whole 
  group 
  became 
  extinct. 
  The 
  simple 
  sutured, 
  

   smooth-shelled 
  nautilus 
  alone 
  survived, 
  and 
  it 
  continues 
  to 
  live 
  in 
  

   the 
  seas 
  to-day 
  as 
  the 
  only 
  survivor 
  of 
  its 
  race. 
  

  

  Additional 
  examples, 
  similar 
  to 
  those 
  cited, 
  could 
  be 
  suggested 
  in 
  

   other 
  organic 
  groups 
  among 
  both 
  the 
  invertebrate 
  and 
  vertebrate 
  

   phyla 
  of 
  the 
  animal 
  kingdom. 
  Indeed, 
  it 
  may 
  be 
  asserted 
  with 
  much 
  

   certainty 
  that 
  the 
  extravagant 
  development 
  of 
  ornate 
  characteristics 
  

   is 
  a 
  condition 
  preceding 
  by 
  no 
  long 
  period 
  the 
  extinction 
  of 
  the 
  race 
  

   so 
  developing. 
  Among 
  living 
  gastropod 
  mollusks 
  su<;h 
  races 
  as 
  

   Murex 
  and 
  its 
  allies, 
  which 
  are 
  highly 
  ornate 
  with 
  spines 
  and 
  proc- 
  

   esses, 
  are 
  doubtless 
  rapidly 
  approaching 
  their 
  time 
  of 
  extinction. 
  

  

  May 
  not 
  these 
  events 
  in 
  the 
  paleontologic 
  history 
  of 
  creatures 
  of 
  

   the 
  past 
  convey 
  a 
  lesson 
  to 
  the 
  student 
  of 
  human 
  relations 
  ? 
  Human 
  

   civilizations 
  and 
  social 
  organizations 
  have 
  arisen 
  in 
  the 
  past 
  and 
  have 
  

   dwindled 
  and 
  become 
  extinct, 
  just 
  as 
  have 
  the 
  societies 
  of 
  prehuman 
  

   inhabitants 
  of 
  our 
  earth. 
  Their 
  places 
  have 
  been 
  taken 
  by 
  other 
  

  

  