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Inia sp nov
From Pleistocene deposits of the Rondônia State, Brazil, a partial skull of Inia was found
and is currently under study by me and Vera da Silva (INPA, Manaus, Brazil) (see Cozzuol &
da Silva, 1996; Cozzuol, 1999). The specimen comes from the Rio Madeira Formation
(Quadros et al., 2006) with a radiocarbon date of about 45,000 years. Today the section of the
Madeira River from where this and many other fossil vertebrates comes from is characterized
by a series of more than twenty rapids, some of them very strong, acting as effective barriers
for Inia and Sotalia (also present down-river from the last rapid). The documented presence
of Inia (as well as Trichechus, Cozzuol, 1999) in the area where today it is almost absent
(personal observation), indicate a significant degree of environmental change (Rizzotto et al.,
2006).
In the ongoing study of this specimen, a multivariate analysis of several cranial measures
compared it with Inia geoffrensis geoffrensis , I. geoffrensis humboldtiana and I. boliviensis
and it widely differentiated it from all the living species and subspecies, suggesting that it
may represent the ancestral stock from which the living arose. As the hydrological regime and
the climate in the areas changed, and the rapids became established, Inia populations above
and below the rapids were isolated which triggered the allopatric speciation leading to the
modern species.
I NIIDAE : S UMMARY AND C ONCUSSIONS
Cozzuol (1996) proposed a phylogenetic scheme for fossil and extant Iniids, including
both species of Saurocetes , Ischyrhorhynchus vanbenedeni, and Inia geoffrensis, utilizing
Pontoporia blainvillei as an outgroup. He suggested that Saurocetes and Ischyrhorhynchus
were more closely related to each another than to Inia . He erected a new subfamily of the
Iniidae, Ischyrhorhynchinae, to reflect this view of iniid phylogeny. The co-occurrence of
Saurocetes spp. and Ischyrhorhynchus in the late Miocene freshwater Ituzaingó deposits
suggests that these species somehow ecologically divided their fluviodeltaic environment.
Cozzuol (1989, 1996) suggested that differences in size and tooth morphology may reflect
alternate dietary habits that allowed the coexistence of these species of freshwater
odontocetes.
The presence of two of the species found in the Argentinean deposits in sediments of the
Solimões Formation in Acre, northern Brazil and, probably, in Venezuela, indicate a
continuous aquatic connection between those regions at this time.
Up to now no Iniinae were recorded as being in existence prior to the Pleistocene.
Cozzuol (1996) suggested that this subfamily should always be restricted to northern South
America, where the records are limited. However, as more specimens are being recovered in
those regions, if the absence of Iniinae persists, the hypothesis should be revised.
Up to now, with the sole, probable exception of Goniodelphis hudsonni , all the iniids
have been found in freshwater environments. G . hudsonni represents a challenge of previous
ideas of iniid biogeography (Cozzuol, 1996). However, this is not the only record in the Gulf
region of a South American fresh water species, since remains of Ribodon, a Late Miocene
Trichechidae were located in Argentina and the Peruvian and Brazilian Amazon as well as in
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