﻿428 
  PROCEEDINGS 
  OF 
  THE 
  NATIONAL 
  MUSEUM 
  vol. 
  103 
  

  

  mandibular 
  fragments 
  in 
  Carnegie 
  Museum; 
  all 
  from 
  locality 
  No. 
  

   24LC15; 
  and 
  CM 
  8995, 
  two 
  mandibular 
  fragments, 
  from 
  the 
  upper 
  

   levels 
  of 
  locality 
  No. 
  24BW18. 
  

  

  A 
  comparison 
  of 
  this 
  material 
  with 
  the 
  type 
  of 
  L. 
  evansi 
  Leidy 
  

   (USNM 
  157) 
  and 
  the 
  abundant 
  material 
  from 
  the 
  Middle 
  Oligocene 
  

   of 
  Wyoming 
  fails 
  to 
  reveal 
  any 
  constant 
  differences 
  in 
  the 
  details 
  of 
  

   the 
  upper 
  and 
  lower 
  cheek 
  teeth. 
  This 
  material 
  averages 
  about 
  

   3 
  percent 
  smaller 
  than 
  the 
  type, 
  but 
  the 
  sample 
  is 
  too 
  limited 
  for 
  this 
  

   to 
  be 
  of 
  any 
  significance. 
  

  

  Climatic 
  zoning 
  of 
  Lower 
  Oligocene 
  faunas 
  

  

  The 
  possibility 
  of 
  climatic 
  zoning 
  of 
  fossil 
  faunas 
  has 
  received 
  very 
  

   little 
  consideration 
  in 
  the 
  literature. 
  This 
  is 
  partially 
  due 
  to 
  the 
  lack 
  

   of 
  data 
  (widely 
  separated 
  fossiliferous 
  deposits 
  of 
  equivalent 
  ages 
  

   have 
  become 
  laiown 
  only 
  recently) 
  and 
  partially 
  to 
  the 
  rather 
  general 
  

   belief 
  that 
  the 
  Early 
  Tertiary 
  climates 
  were 
  uniformly 
  mild. 
  In 
  

   regard 
  to 
  the 
  latter. 
  Berry 
  (1922) 
  pointed 
  out 
  that 
  while 
  the 
  over-all 
  

   climate 
  of 
  the 
  Eocene 
  may 
  have 
  been 
  much 
  milder 
  than 
  today 
  the 
  

   "arctic 
  flora" 
  of 
  that 
  time 
  was 
  not 
  only 
  distinct 
  from 
  that 
  of 
  temperate 
  

   latitudes 
  but 
  was 
  of 
  circumpolar 
  distribution. 
  He 
  also 
  points 
  out 
  

   (1922, 
  p. 
  13) 
  that 
  the 
  southern 
  limit 
  of 
  the 
  Eocene 
  "arctic 
  flora" 
  is 
  

   about 
  15° 
  north 
  of 
  the 
  southern 
  limit 
  of 
  the 
  existing 
  species 
  of 
  the 
  

   same 
  genera 
  and 
  that 
  the 
  present 
  isotherm 
  (p. 
  9) 
  would 
  have 
  to 
  swing 
  

   15° 
  to 
  20° 
  northward 
  to 
  permit 
  the 
  present 
  existence 
  of 
  the 
  same 
  

   floras 
  in 
  the 
  same 
  areas 
  from 
  which 
  we 
  know 
  the 
  Eocene 
  floras. 
  Such 
  

   a 
  change 
  would 
  only 
  eliminate 
  the 
  Arctic 
  Zone 
  of 
  C. 
  Hart 
  Merriam 
  

   as 
  it 
  is 
  defined 
  today 
  and 
  would 
  by 
  no 
  means 
  be 
  sufficient 
  change 
  to 
  

   produce 
  a 
  uniformly 
  mild 
  warm-temperate 
  to 
  subtropical 
  climate. 
  

   Simpson 
  (1947, 
  pp. 
  645-654) 
  briefly 
  cites 
  evidence 
  for 
  climatic 
  zoning 
  

   in 
  the 
  Miocene 
  in 
  Asia 
  and 
  considers 
  that 
  climate 
  was 
  probably 
  a 
  

   relatively 
  important 
  selective 
  factor 
  in 
  intercontinental 
  migration. 
  

   He 
  also 
  points 
  out 
  (p. 
  652) 
  that 
  while 
  the 
  evidence 
  for 
  climatic 
  zoning 
  

   is 
  meager 
  there 
  is 
  none 
  against 
  it. 
  

  

  The 
  possibility 
  of 
  climatic 
  zoning 
  in 
  the 
  Tertiary 
  was 
  first 
  brought 
  to 
  

   my 
  attention 
  by 
  the 
  relative 
  abundance 
  of 
  the 
  protoceratids 
  in 
  the 
  

   Miocene 
  of 
  Texas 
  and 
  their 
  extreme 
  scarcity 
  in 
  equivalent 
  deposits 
  

   of 
  Nebraska 
  and 
  Wyoming, 
  These 
  animals 
  are 
  large 
  enough 
  that 
  

   they 
  would 
  not 
  be 
  easily 
  overlooked. 
  There 
  are 
  few 
  areas 
  in 
  North 
  

   America 
  which 
  have 
  remained 
  as 
  consistently 
  productive 
  over 
  a 
  

   period 
  of 
  years 
  as 
  has 
  the 
  Miocene 
  of 
  Nebraska 
  and 
  Wyoming. 
  Yet, 
  

   from 
  this 
  area, 
  Syndyoceros 
  is 
  known 
  from 
  only 
  two 
  specimens 
  and 
  

   Prosynthetoceros 
  is 
  entirely 
  unknown. 
  Even 
  on 
  such 
  meager 
  evidence 
  

   it 
  seemed 
  highly 
  probable 
  that 
  the 
  factors 
  which 
  controlled 
  the 
  

  

  