Biology Reference
In-Depth Information
families are from marine deposits. Fossils of the extant family Platanistidae are from
marine, estuarine, and fresh water deposits.
3.
Species in the extinct platanistoid family Allodelphinidae are known only from
marine deposits around the margin of the North Pacific Ocean, their fossils having
been found in California, Oregon, Washington, and Japan. They are known from the
earliest Miocene, approximately 23 million years ago, to the Late Miocene,
approximately 10 to 12 million years ago. Allodelphinids had skull lengths of
approximately one meter or more, 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.
4.
An extinct odontocete named
Squalodon errabundus
Kellogg, 1931, was named on
the basis of isolated petrosal bones from the middle Middle Miocene age Sharktooth
Hill Local Fauna in the Sharktooth Hill Bonebed, in Kern County, California, U. S.
A. A complete skull, found with this same type of petrosal associated with its
basicranium, demonstrates that this species is not a member of the Squalodontidae,
but is actually an allodelphinid platanistoid, and the species therefore needs a new
generic assignment. The new genus name
Zarhinocetus
is proposed here for this
species, yielding the new combination
Zarhinocetus errabundus
(Kellogg, 1931).
5.
The members of the extinct family Squalodontidae were large odontocetes with large
teeth, and had extreme heterodonty, with the teeth differentiated as incisors, canines,
premolars, and molars. They are known from Oligocene and Miocene deposits and
from all of the world's major ocean basins.
6.
The extinct family Waipatiidae includes marine odontocetes with relatively short and
stout rostra and mandibles, symmetrical cranial vertices, and dentitions that are less
prominently heterodont than those of squalodontids. Included are
Waipatia
maerewhenua,
of Late Oligocene age from New Zealand, and possibly
Sulakocetus
dagestanicus,
of Late Oligocene age from the Caucasus, and
Sachalinocetus
cholmicus,
of Early or Middle Miocene age from Sakhalin Island, Russia.
7.
A more derived family, the extinct Squalodelphinidae, includes platanistoids that
have stout rostra and mandibles in which the cheek teeth have single roots (the result
of the original two roots having coalesced), dorsoventrally thickened supraorbital
processes, asymmetrical cranial vertices, and transversely compressed zygomatic
processes of the squamosals. Members of this family include Early Miocene
Squalodelphis
fabianii
from Italy, Early Miocene
Notocetus
vanbenedeni
from
Patagonia, Argentina, and probably
Notocetus
marplesi
and
“Microcetus” hectori
,
both of Late Oligocene age from New Zealand, and
Phocageneus
venustus,
of
Middle Miocene age from Virginia, Maryland, and North Carolina in the U. S. A.
8.
The highly derived platanistoid family Platanistidae includes dolphins that have
exceptionally narrow rostra and symphyseal portions of their mandibles,
asymmetrical cranial vertices, and transversely compressed zygomatic processes of
their squamosals. This is the family that includes the living, river-dwelling members
of the genus
Platanista,
but fossil members of this group are found in deposits of
marine, brackish, and fresh water origin. Fossils are known only from the Northern
Hemisphere, and demonstrate that members of this family were much more
widespread in the past than they are now. The most primitive named member of the
Search WWH ::
Custom Search