FOSSIL RECORD AND THE EVOLUTIONARY HISTORY OF INIODEA - Biology, Evolution and Conservation of River Dolphins Within South America and Asia - page 207

Some authors expressed reasonable doubts about the iniid relationship of this species
because the absence of more complete cranial material (Muizon, 1988a). However, despite
that, the evidence from the palatal region of a preserved specimen support that S. argentinus
has an important iniid synapomorphy because its vomer is exposed all along the palate,
preventing the palatines to meet in the midline of the palate as in other odontocetes (Zhou,
1981), which support the hypothesis that it belongs to the family Iniidae (Cozzuol, 1985).
As with I. vanbenedeni , this species was originally found in the Late Miocene outcrops of
the Paraná River in the Entre Rios Province, but subsequently remains of this species were
found in the Late Miocene Solimões Formation in the Acre State, northwestern Brazil (Rancy
et al., 1989; Cozzuol, 2006)
S. gigas Cozzuol, 1989
Based on a detailed review of all material identified as Saurocetes in the Entre Rios
Museum and the La Plata Museum, a second species, S. gigas, was erected by Cozzuol
(1989). The type specimen is a proximal fragment of the mandibular symphysis without teeth,
originating from the Ituzaingó Formation. He also attributed to S. gigas five isolated teeth that
originated from these same deposits. His justification for establishing a second species is
based primarily on the large relative size of the attributed material, after rejecting the
possibility of size variation in Saurocetes argentinus. Other minor morphological differences
between the teeth of S. argentinus and S. gigas are considered as support for erecting a second
species. Although Cozzuol (1989) noted that other paleocetologists discourage the
establishment of new species based on isolated mandibular fragments, he considered that the
results of comparing available material justified the establishment of S. gigas. Contrarily, the
other species has yet to be found outside the Paraná outcrops nor has further material for this
species been found.
The significance of this species relies is its large body size, estimated from the length of a
skull (1 meter) and according the proportions for Inia spp, to be about 4.5 meters in total
length. This is an uncommon size for a top, warm blooded predator in continental waters,
reinforcing the perception that the inland aquatic environment during the Late Miocene in
those areas was uncommon, extremely diverse and rich.
Subfamily INIINAE Cozzuol, 1996
Plicodontinia mourai Miranda Ribeiro, 1938
Plicodontinia mourai was described by Miranda Ribeiro (1938) based on a single tooth
found in the Acre region of Brazil, probably from Pleistocene deposits. Muizon (1988c)
described this specimen as "totally inadequate to define an Odontocete and should be
regarded as ― incertae sedis " (Muizon 1988c).
Although I agree with Muizon's statement, the holotype tooth has some features that
deserves to be considered. It is a posterior tooth, probably an upper one, showing the postero-
lingual platform characteristic of the genus Inia , the only known representative of the
subfamily Iniinae. Consequently, it belongs to a species of the subfamily Iniinae, maybe even
to the genus Inia.