LACUSTRINE BIOTIC ASSEMBLAGES IN THE EARLY CRETACEOUS OF CENTRAL-WESTERN ARGENTINA: LA CANTERA AND LAGARCITO FORMATIONS

ANDREA BEATRIZ ARCUCCI; MERCEDES B. PRÁMPARO; LAURA CODORNIU; GUILLERMINA GUIORDANO; GABRIELA CASTILLO ELÍAS; G. G. PUEBLA; N. MEGO; M. GOMEZ; EVELYN BUSTOS ESCALONA

Mendoza

Congreso; International Paleontology Congress IV; 2015

International Paleontological Association

ENVIADO Y ACEPTADO. During  the  last  decade  abundant  and  significant  paleobiological  data  came  out  from  the  San Luis  Basin  (Early  Cretaceous,  Aptian-Albian, central-western  Argentina).  Two  units  in  this basin,  La  Cantera  and  Lagarcito  Formations  include  lacustrine  facies  with  important  fossil content in a mode of preservation that could be considered as Konservatt Lagerstatte deposits by some authors. The fossil record of La Cantera Formation include a variety of palynomorphs (pollen grains and spores) and plant remains (leaves, stems, reproductive structures like cones, seeds  and  flowers)  from Bryphyta,Ferns, Gnetales,  Gymnospermae  and  Angiospermae The palynoflora is dominated by aquatic  forms  (fresh  water algae),  in some  levels  of the sections they constitute more than 80% of the total population. Classopollis and plicate grains (Ephedra type)  are  also  abundant.  Among  angiosperms Afropollis,  Retimonocolpites,  Stellatopollis, Clavatipollenites,  Tucanopollis,  Pennipollis and Asteropollis complex  are  recorded.  The bryophyte  association  constitutes  one  the  most  complete  record  of  its  type  in  Argentina. The association  of  fossil leaves  and  pollen  grains  from  La  Cantera  Formation is one  of  the  most ancient and complete record of first angiosperms in South America, which allowed considering the  unit  as  Late  Aptian  in  age.  The  Lagarcito  Formation yielded  a  palynoflora  dominated  by gymnospermous elements (mainly polyplicate and rimulate grains). The aquatic forms are also abundant. Reyrea polymorphus Herngreen, identified in the association is an excellent marker for  the  Aptian-Albian  of  northern Gondwan. The  arthropod  remains  in  both  units  include Ostracoda  and  Conchostraca  with  several  endemic  species.  The  insects  from  La  Cantera Formation even fragmentary allow the identification of five different orders, and three endemic species of aquatic insects were described belonging to the Families Notonectidae and Corixidae, including  the  oldest  member  of  the  Anisopinae  subfamily.  The  actinopterigian  fishes  were abundant  in  both  paleolakes  but  the  associations  show  different taxonomic  composition. The Pleuropholid  fishes  from  Lagarcito  Formation,  are  the  only  record  of  this  rare  group  in Argentina  and  the  second  from  South  America. Pterodaustro  guinazui, the  only  and  unique species  of  Pterosauria  from  Lagarcito  Formation  is  present  with  a  collection  of hundreds  of bones, being one of the few fossil accumulations of pterosaur remains available worldwide from which  is  possible  to  make  studies  on  the  life  history,  parameters  like  growth  patterns  and ontogenetic  development. The  reunion  of  all  the  biotic  information  available  reveals  a  wide paleobiodiversity  although  much  work needs to  be  done  on  the  interpretation  of  these associations, the correlation between them and its depositional environment.