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reported by Mitchell and Tedford (1973) from a lower stratigraphic unit in the area where
“Squalodon” errabundus
occurs, and they are from the earliest Miocene Pyramid Hill Sand
in Kern County, California.
Subsequent to Kellogg's (1931) publication, a complete cranium and mandible (LACM
149588) were collected from the Sharktooth Hill Bonebed, and these are directly associated
with it a petrosal and tympanic bulla. The petrosal of this referred specimen is identifiable as
Squalodon errabundus,
but the skull is unquestionably that of an allodelphinid platanistoid
.
Therefore,
Squalodon errabundus
Kellogg, 1931, clearly does not belong in the genus
Squalodon
(see specimens of Squalodontidae in Kellogg, 1923; Whitmore & Sanders, 1977;
Dooley, 2005; and Figure 4 herein), and this is why the generic name
Squalodon
has been
used in quotation marks when the species
Squalodon errabundus
has been referred to in some
previous publications (e.g. Barnes, 1977, 2002b, 2006). No generic name has been proposed
that is appropriate for this species, and for this reason the new genus
Zarhinocetus
is
proposed for it here, yielding the new combination
Zarhinocetus errabundus
(Kellogg, 1931)
.
A
NALYSIS OF
P
HYLOGENETIC
R
ELATIONSHIPS
Our phylogenetic analysis presented here is nearly the same as was presented by Barnes
(2006). The analysis includes 64 characters that were scored for nine taxa (Table 1). Fordyce
(1994) prepared a character list and phylogenetic analysis for the superfamily Platanistoidea
when he described the primitive platanistoid
Waipatia
maerewhenua.
Barnes (2006) and we
here have used many of the characters from that study, some of which are modified, and in
the following list of characters, these are identified by Fordyce's (1994) page and character
numbers. Geisler and Sanders (2003) presented a phylogenetic analysis of all Cetacea, and
several of their characters are used here, also cited in the list of characters by their page and
character numbers.
Only cranial and mandibular characters were used because of the lack of uniform
information about postcranial bones for many of the taxa. Similarly, although characters of
the petrosal and the tympanic bulla are pivotal in recognizing and defining the superfamily
Platanistoidea
(sensu
Muizon, 1994; Fordyce, 1994) and the family Platanistidae
(sensu
Barnes, 2002a, 2002b, 2006), because these bones are not known for all species, their
characters were with one exception (the anterior bullar spine) omitted from this analysis.
Definitions of morphologic characters used in the phylogenetic analysis:
The following
characters are those that we found to be useful among the Platanistoidea. The numbers of the
characters are the same that appear in the matrix (Table 1). Character states are: [0] indicates
a plesiomorphic character state, and [1] indicates an apomorphic character state.
1.
Mesorostral groove
absent [0]; or present [1]. The mesorostral groove is formed
dorsal to the vomer bone, and is flanked on either side by the premaxillae (see
Rommel, 1990: Figure 2). In life the mesorostral groove holds the anteroposteriorly
elongated mesethmoid cartilage. In some derived species of Odontoceti, notably in
some species of the family Ziphiidae, the groove is occupied by a mesorostral
ossification. The mesorostral groove occurs in no species of the Archaeoceti, and this
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