THE EVOLUTIONARY HISTORY AND PHYLOGENETIC RELATIONSHIPS OF THE SUPERFAMILY PLATANISTOIDEA - Biology, Evolution and Conservation of River Dolphins Within South America and Asia - page 455

Mchedlidze, 1976, of Late Oligocene age from Caucasus, and Sachalinocetus cholmicus
Dubrovo, 1971, of Miocene age from Sakhalin Island, Russia, and he suggested that these
cetaceans might also be waipatiids. We have classified them therefore in the family
Waipatiidae (Figure 5).
Family Squalodelphinidae
The type genus of Squalodelphinidae is Squalodelphis Dal Piaz, 1916, whose type and
only included species is Squalodelphis fabianii Dal Piaz, 1916, from Early Miocene deposits
in Italy. Members of the Squalodelphinidae have relatively stout rostra that are not very
elongated, anterior teeth that are reduced in size so that they are not so procumbent as they are
in species of Squalodontidae or Waipatiidae, and cheek teeth with single roots, their
primitively double roots having become coalesced into one root. Squalodelphinids have
dorsoventrally thickened surpaorbital processes, but unlike the species of Platanistidae, they
do not have supraorbital eminences. They do share with species of Platanistidae very
asymmetrical cranial vertices, on which the posterior ends of the premaxillae and the midline
sutures between the nasal and frontal bones are skewed to the anatomical left side of the skull.
They also share with the Platanistidae, to the exclusion of all other platanistoids, transverse
compression of the zygomatic process of the squamosal, so that its medial side is very
concave.
Lydekker (1894) placed the Early Miocene Notocetus vanbenedeni Moreno, 1892, from
Patagonia, in the family Platanistidae, and various authors have placed it in other families.
Following Muizon (1987) and Fordyce (2006), we classify it in the family Squalodelphinidae,
which in our phylogenetic analysis is indicated as being the sister family of the Platanistidae.
Notocetus vanbenedeni is known by at least two well preserved and relatively complete
specimens, the holotype in the La Plata Museum, Argentina (see Lydekker, 1894), and a
referred specimen, described by True (1910; and see Muizon, 1987; and Fordyce, 1994)
(Figure 6).
Fordyce (2006) indicated that Late Oligocene members of this family from New Zealand
include Notocetus marplesi (Dickson, 1964), which is in neither the family nor the genus to
which it was originally assigned, and ― Microcetus” hectori (Benham, 1935), which is in need
of a new generic assignment.
An apparent western North Atlantic member of this family is Phocageneus venustus
Leidy, 1869, a Middle Miocene odontocete known from the Chesapeake Group in Virginia
and Maryland, which was originally named on the basis of a tooth. It is represented by
additional material from the Middle Miocene Pungo River Formation in North Carolina
(Whitmore & Kaltenbach, 2007), and by unpublished material in the USNM from the Middle
Miocene Calvert Formation, that suggest that it is referable to the Squalodelphinidae.