THE EVOLUTIONARY HISTORY AND PHYLOGENETIC RELATIONSHIPS OF THE SUPERFAMILY PLATANISTOIDEA - Biology, Evolution and Conservation of River Dolphins Within South America and Asia - page 461

The platanistid subfamily Platanistinae, in the context used by Barnes (2002b, 2006),
includes Platanistidae that have an anteroposteriorly lengthened zygomatic process of the
squamosal, transversely flattened rostrum and symphyseal portion of the mandible (Figure 8),
and a large pneumaticized supraorbital crest (Figure 11).
Figure 10. Part of the symphyseal region of a mandible, LACM 131112, of an unidentified genus and
species, an Early Miocene marine member of the subfamily Platanistinae of the family Platanistidae,
from the Nye Formation in Lincoln County, coastal Oregon, U. S. A; A, left lateral view; B, occlusal
view; C; anterior view of broken cross section; D, lateral view of a mandible of Recent Platanista
gangetica (Roxburgh, 1801), with lines bracketing the part of the specimen that is represented by the
fossil; A-C modified from Barnes (2006: Figure 7); D modified and reversed from Van Beneden and
Gervais (1868-1880: pl. XXXI, Figure 2); arrow indicates the anterior direction of the specimen as
shown in A and B; scale bar for A-C equals 5 cm; D is not to scale.
Around the eastern margin of the North Pacific, fossils have been found that appear to
belong to the subfamily Platanistinae (Crowley et al., 1999), but none of these have been
named. One of these apparent platanistine fossils, from the marine, Early Miocene age, Nye
Formation on the coast of Oregon, U. S. A., is part of the symphysis of a mandible (Figure
10, and see Barnes, 2006: Figure 7) that is approximately three times the size of the
corresponding part of the mandible of Platanista gangetica. It includes the posterior parts of
both fused dentaries, extending posteriorly as far as the anterior-most part of the divergence
of the two horizontal rami. It shares with P. gangetica transverse compression of the
symphysis of the mandible, close approximation of the right and left tooth rows, a
longitudinal groove at approximately one-third of the height on the lateral side of the dentary,
nutrient foramina positioned dorsal to this groove, and a very slight posterior divergence of
the horizontal rami. It differs from P. gangetica by being larger, by having a greater
separation between the alveolar rows, and by having dental alveoli which at their alveolar