The First Non Australian Monotreme: an Early Paleocene South American Ornithorhynchid

PASCUAL, ROSENDO; ARCHER, MICHAEL; ORTIZ JAUREGUIZAR, EDGARDO; PRADO, JOSÉ LUIS; GODTHELP, HENK; HAND, SUZANNE J.

Platypus and Echidnas

Royal Zoological Society of New South Wales

Año: 1992; p. 1 - 14

The first  South  American  monotreme  is described from  early Paleocene  (Tiupampian}  sediments  in Patagonia, Argentina.  Monotrematum  sudamericanum  n.  gen.  &  sp.,  represented  by  a single  upper  second  molar,  is the first  monotreme  known  from  outside  the Australian  region  and  the first early  Tertiary  monotreme. It  represents.  a  temporal  position  midway  between  the  early  Cretaceous  Steropodon  galmani  and  the  Oligo­ Miocene  species  of  Obdurodon.  It corroborates  the  geological  distinction  of the  Patagonian  Terrane  which shares unique  aspects  of its earliest  Cainozoic  biota  with  at least  the Australian  part of eastern  Gondwaua.  It also  demonstrates,  in  its  Obdurodon-like  morphology,  a  remarkable  conservatism  of  mammalian  molar morphology spannlng  at least 110 million  years.  Overall,  M.  sudamericanum  appears  to be more plesiomorphic than  the modern  platypus and the species  of Obdurodon.  Its relationships  to S.  galmani are difficult  to determine because  S.  galmani  is only  known from  a lower jaw fragment  with m1-3. It is regarded  to be  one  of three basic platypus  lineages  within  what  may  be,  because  of  the  uncertain  relationships  of  tachyglossids  to  other monotremes,  a paraphyletice  Omlthorhynchidae.