Miocene balaenids (Cetacea: Mysticeti: Balaenidae) from Patagonia (Argentina) and their implication for early evolution of right whales.

M. R. BUONO; M. S. FERNÁNDEZ; M. A. COZZUOL

Congreso; 4th International Palaeontological Congress,; 2014

Balaenids or right whales are large and skim feeding baleen whales represented by four living species. They have been considered a key group in the understanding of Mysticeti evolution because some phylogenetic studies considered it as the most basal surviving family of Mysticeti. Balaenid fossil record is temporally large (Early Miocene-Present) but it is characterized by large stratigraphic gaps. In particular, the Miocene record is extremely rare and it is restricted to Argentinean Patagonia, with Morenocetus parvus, the oldest known balaenid (Gaiman Formation, Early Miocene, Chubut). Morenocetus was named on the basis of two incomplete skulls and was not re-examined after its original description. It is a critical taxon not only to assist in resolving the balaenid phylogenetic relationships but also for its potential to help resolve higher mysticete relationships. In addition new balaenid specimens, belonging to a new genus and species, were collected from Puerto Madryn Formation (early Late Miocene, Chubut). The importance of Morenocetus and the other taxon from Puerto Madryn Formation makes necessary a detailed study of the Miocene balaenids from Patagonia. The results of anatomic studies showed that Morenocetus is a valid taxon and it is represented by two subadult specimens. Besides the three balaenid specimens from Puerto Madryn Formation included an adult, a subadult and a young which corresponds to a new genus and species (=Taxon A). A heuristic parsimony analysis of 30 species and 168 morphological characters was conducted using traditional search under equal and implied weight. Both analyses resulted in five most parsimonious trees. The strict consensus tree, both under equal and implied weight, shows balaenids forming a well supported group and sister to the clade of Balaenopteroidea and Cetotheriidae. Miocene balaenids (Morenocetus and Taxon A) form a basal clade within Balaenidae, with a well branch support and without unstable taxa. Stratigraphic calibration of cladogram showed an extensive ghost lineage among Miocene balaenids and more derived taxa (Balaenella, Balaenula, Balaena and Eubalaena). The extension of this ghost lineage (~15 Ma) is from Late-early Miocene (Burdigaliense) to Early Pliocene (Zancliense). In addition, there is a large temporal gap in the fossil record of balaenids which covers more than half of their evolutionary history. The recovery of Taxon A from Puerto Madryn Formation interrupts the temporal gap between Morenocetus and more derivated balaenids, but it does not reduce the ghost lineage mentioned above.