﻿336 
  PROCEEDINGS 
  OF 
  THE 
  NATIONAL 
  MUSEUM 
  VOL.96 
  

  

  National 
  Museum 
  specimen, 
  however, 
  leaves 
  no 
  doubt 
  of 
  the 
  

   direction 
  and 
  extent 
  of 
  specialization, 
  which 
  quite 
  parallels 
  that 
  

   seen 
  in 
  the 
  machairodonts 
  but 
  not 
  to 
  the 
  extent 
  exhibited 
  in 
  the 
  

   Uinta 
  Apataelurus 
  kayi 
  described 
  by 
  Scott. 
  ^ 
  Structurally 
  no 
  

   characters 
  are 
  observed 
  in 
  the 
  illustrations 
  of 
  the 
  lower 
  jaws 
  of 
  

   A. 
  kayi 
  that 
  would 
  preclude 
  derivation 
  of 
  this 
  form 
  from 
  M, 
  

   eothen, 
  with 
  the 
  characteristics 
  attendant 
  upon 
  sabertooth 
  de- 
  

   velopment 
  reaching 
  a 
  high 
  degree 
  of 
  specialization 
  within 
  an 
  

   interval 
  of 
  time 
  suggesting 
  a 
  comparatively 
  rapid 
  evolutionary 
  

   tempo. 
  

  

  Matthew 
  regarded 
  Machaeroides 
  eothen 
  as 
  an 
  oxyaenid 
  type 
  

   of 
  creodont, 
  closely 
  related 
  to 
  forms 
  included 
  in 
  the 
  subfamily 
  

   Limnocyoninae, 
  to 
  which 
  he 
  allocated 
  it 
  (p. 
  410) 
  , 
  * 
  having 
  created, 
  

   however, 
  the 
  subfamily 
  name 
  "Machairoidinae" 
  on 
  an 
  earlier 
  

   page 
  (330). 
  Denison 
  ^ 
  retained 
  the 
  supergeneric 
  separation, 
  

   which 
  was 
  entirely 
  justified 
  by 
  the 
  discovery 
  of 
  Apataelurus, 
  

   recognizing 
  a 
  natural 
  phyletic 
  subfamily. 
  However, 
  Denison 
  

   removed 
  the 
  Limnocyoninae 
  and 
  Machaeroidinae 
  from 
  the 
  Oxyae- 
  

   nidae 
  and 
  placed 
  them 
  in 
  the 
  Hyaenodontidae. 
  Justification 
  for 
  

   this 
  was 
  claimed 
  on 
  the 
  basis 
  of 
  morphological 
  differences 
  between 
  

   the 
  Oxyaeninae 
  and 
  Limnocyoninae 
  and 
  similarities 
  between 
  the 
  

   Limnocyoninae 
  and 
  Proviverrinae, 
  particularly 
  between 
  Prolim- 
  

   nocyon 
  and 
  Sinopa. 
  Separation 
  from 
  the 
  Oxyaenidae 
  seems 
  sup- 
  

   ported, 
  and, 
  moreover, 
  carnassial 
  specialization, 
  which 
  has 
  been 
  

   the 
  key 
  to 
  their 
  supposed 
  affinity, 
  may 
  well 
  have 
  developed 
  inde- 
  

   pendently 
  in 
  the 
  two 
  groups. 
  I 
  cannot, 
  however, 
  but 
  regard 
  the 
  

   carnassial 
  differentiation 
  that 
  so 
  readily 
  distinguishes 
  the 
  Lim- 
  

   nocyoninae 
  from 
  members 
  of 
  the 
  Hyaenodontidae 
  as 
  being 
  of 
  

   fundamental 
  importance, 
  and 
  hold 
  that 
  the 
  morphological 
  simi- 
  

   larities 
  may 
  be 
  as 
  easily 
  attributed 
  to 
  similar 
  adaptation 
  or 
  

   parallelism. 
  It 
  is 
  in 
  a 
  similar 
  manner 
  that 
  the 
  Machaeroidinae 
  

   so 
  markedly 
  resem.ble 
  the 
  machairodonts, 
  although 
  obviously 
  not 
  

   derived 
  one 
  from 
  the 
  other. 
  Derivation 
  of 
  the 
  Limnocyoninae 
  

   from 
  an 
  early 
  proviverrine 
  stock 
  is 
  not 
  disproved 
  and 
  may 
  be 
  

   reasonable 
  as 
  suggested 
  by 
  the 
  similarity 
  of 
  lower 
  jaws 
  belonging 
  

   to 
  forms 
  of 
  Prolimnocyon 
  and 
  Sinopa 
  morclax, 
  but 
  their 
  di- 
  

   vergence 
  must 
  originate 
  in 
  a 
  primitive 
  form 
  with 
  molars 
  as 
  yet 
  

   undifferentiated 
  as 
  to 
  carnassials, 
  and 
  where 
  M-, 
  for 
  example, 
  has 
  

   not 
  taken 
  on 
  characteristics 
  so 
  markedly 
  different 
  in 
  the 
  two 
  

   groups. 
  

  

  3 
  Scott. 
  W. 
  B., 
  Ann. 
  Carnegie 
  Mus., 
  vol. 
  27, 
  art. 
  6, 
  pp. 
  113-120, 
  1938. 
  

  

  * 
  Matthew, 
  W. 
  D., 
  ibid. 
  

  

  » 
  Denison, 
  R. 
  H., 
  ibid., 
  p. 
  181. 
  

  

  