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stratigraphic nomenclature (Leonian Stage, Late Oligocene-Earliest Miocene). Its age make it
the oldest reputed iniid species.
Assignment of P. patagonica to the family Iniidae by True (1909) was tentatively
accepted by Kellogg (1928:55), although he misquoted Cabrera (1926) in suggesting that the
skull belonged to Notocetus (= Diochoticus ). Cabrera (1926) in fact, had only transferred to
Notocetus, an isolated cervical vertebra which True (1909) had previously referred to Proinia.
Subsequent discussions of this species have been restricted to the quoted references, and no
additional material has been referred to P. patagonica until now.
I examined a cast of the holotype (number YPM-PU15459), now deposited in the
Department of Vertebrate Paleontology at the La Plata Museum as item number PU 15459-
CA. (Figure 1)
The specimen consists of a partial skull with the rostrum broken off just anterior to the
nares. It has been strongly compressed dorsoventrally with a result that the supraoccipital is
almost in contact with the basioccipital. All the basicranial structures beyond the basioccipital
were lost, as well as the bullae, periotics, jugals, right zygomatic process and right
paraoccipital process. Despite the deformation, the preserved parts of the skull permit
identification of the bones and the general morphology.
The specimen is divided in two parts that separated along the unclosed sutures. In fact, all
the sutures of the skull are very evident, indicating a young specimen. The smaller (anterior)
part is composed of the frontals, the proximal end of the ascending processes of the
maxillaries and the mesethmoid bones. Both premaxillary bones are missing, but the scars
they left on the inner margin of the maxillaries permit estimation of their extent.
The cranial vertex is composed of the relatively large, high, square and flat exposure of
the frontals. Both nasal bones are missing, but they were sutured to the vertical anterior
border of the frontals and apparently projected onto the narial passages. The posterior part of
the frontals show scars left by the suture with the supraoccipital bone. Consequently the
parietals are excluded from the dorsal view of the skull as in all the modern Odontoceti.
The larger fragment comprises the parietals, part of the supraoccipital, exoccipitals, left
zygomatic arch, and the basioccipital. The zygomatic process is long, massive and of
triangular shape in lateral view. The parietals are largely exposed laterally, and the squamosal
is very short antero-posteriorly and extended dorsally. The supraoccipital is much narrower
than the exoccipitals. The paraoccipital processes are triangular, broad dorsally and with a
rounded end.
In spite of the fact that the skull has been deformed by compression so that some
proportions are changed, most features are visible. The sutures separating the frontals and the
occipital are clearly evident, as are all other sutures. The skull is symmetrical, with a
relatively small brain case. A chamber for the olfactory nerves is present in the anterior part
of the brain cavity. As in several primitive odontocetes and in young specimens of modern
species there are two large foramina between the mesethmoid and the ectethmoid bones. All
this information indicates that the skull belongs to a young specimen.
The features mentioned by True (1909) as evidence for a close relationship with Inia can
be regarded as plesiomorphic and are present in several odontocetes. According to True
(1909) the most important feature resembling Inia is the strongly elevated cranial vertex.
However, the morphology of this area differs from that found in all known iniids. In all
species of this family the cranial vertex is massive and knob-like and does not exhibit the
square shaped frontals and smooth surface found in Proinia .
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