Biology Reference
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Family Allodelphinidae
Species in the extinct platanistoid family Allodelphinidae are known only from marine
sedimentary deposits around the margin of the North Pacific Ocean. Their fossils have been
found in California, Oregon, Washington, and Japan. The presently known geochronologic
range of the Allodelphinidae, currently represented by two named species and several
undescribed species, is from the earliest Miocene, approximately 23 million years ago, to the
Late Miocene, approximately 10 to 12 million years ago.
Their fossils indicate that in life allodelphinids attained adult body lengths ranging from
slightly less than four meters to possibly as much as five meters, and had skull lengths of
approximately one meter or larger, very long and slender rostra with the lower jaw reaching
the same length as the rostrum, many small and single-rooted teeth, and unusually long
cervical vertebrae. The more derived and later-occurring species developed wide braincases,
cranial asymmetry, cranial tuberosities and crests (see Figure 2), and even longer and larger
neck vertebrae. This latter evolutionary trend is the opposite of virtually all other cetacean
groups, in which the cervical vertebrae became shorter, smaller, and in many cases fused
together. The brain cases of these animals are in several characters more primitive than
squalodontids (anteriorly positioned nasal openings, anteroposteriorly elongate nasal bones),
and their primitively constructed zygomatic arches distinguish them from some of the
similarly long-snouted species in the family Platanistidae.
The family Allodelphinidae was named by Barnes (2006), having as its type and only
included genus
Allodelphis
Wilson, 1935. The type and only included species of
Allodelphis
is
Allodelphis pratti
Wilson, 1935 (Figure 1), which is known only from earliest Miocene
sediments in the San Joaquin Valley of California, U.S.A. After it was named in 1935, this
species was rarely cited in the scientific literature, although it is a valid taxon, and as its name
implies, it is a very strange dolphin. Wilson (1935) originally classified it in the modern
oceanic dolphin family Delphinidae, but it was reassigned by Barnes (1977) to the
Platanistidae.
Deering et al. (2003) and Barnes et al. (2003) reported the discovery of an
Allodelphis
-
like platanistoid from the Early Miocene age Vaqueros Formation in Orange County,
southern California, U. S. A. Barnes & Reynolds (2007) reported another species of early
allodelphinid from elsewhere in the same formation in southern California. Kimura and
Ozawa (2001) reported a partial skeleton of a long-snouted platanistoid of late Early Miocene
age from Japan, and we now identify this animal as an unnamed taxon of the family
Allodelphinidae.
The Middle Miocene age
Squalodon errabundus
Kellogg, 1931, from the Sharktooth Hill
Local Fauna in central California, was originally named on the basis of isolated petrosals, and
was assigned by Barnes (1977) to the family Platanistidae. This species is now known by a
complete cranium (Figures 2 and 3) from the same deposit, associated with a mandible,
petrosal, and tympanic bulla of the same individual, which demonstrate that this species is a
member of the family Allodelphinidae. Because it is not a species of
Squalodon,
in the
following text we propose a new genus name for it. Barnes (1977:320) reported an isolated
petrosal of a closely related species from the Late Miocene Santa Margarita Formation near
Santa Cruz in coastal central California, and this is the geochronologically youngest known
occurrence of any allodelphinid.
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