FOSSIL RECORD AND THE EVOLUTIONARY HISTORY OF INIODEA - Biology, Evolution and Conservation of River Dolphins Within South America and Asia - page 201

Discussion on the phylogenetic position of Brachidelphidae
Recent phylogenetic propositions (Geisler & Sanders, 2003) suggested that
Brachydelphys might not be a pontoporiid, but the sister group of Iniidae+Pontoporiidae (i.e.
Inoidea sensu stricto).
A re-study of this genus under the light of several new specimens from Peru and Chile
indicated that some of the characters used in the diagnosis of Brachydelphis , like the
extremely short rostrum, are actually derived from the early ontogenetic age of the specimens.
Also, some specimens that can be referred to this genus based on the morphology of the
posterior part of the skull exhibit longer rostra compared with B . mazeasi. This work found
additional support for the idea of excluding Brachydelphis from Pontoporiidae and place it as
the sister group of Iniidae+Pontoporiidae and consequently obligate a reconsideration of the
superfamily taxonomy (Gutstein et al, in press).
So, under the light of this observation, I do not consider Brachydelphis and allied forms
as belonging to the family Pontoporiidae, but as the sister group of the remaining Iniodea. To
include or not include Brachydelphis and allies in the superfamily Inioidea is more of a matter
of choice. I think it is more economic in terms of classification to maintain it in the Inoidea
and elevate the rank from subfamily to family.
Superfamily Inioidea (sensu stricto)
Family Pontoporiidae Burmeister, 1885
The family Pontoporiidae has a much richer fossil record, with greater stratigraphic and
geographic range than the Iniidae. It has correspondingly received greater attention from
paleocetologists. Fossil pontoporiids were found along the Pacific and Atlantic coasts of
South America, in the late Miocene and Pliocene levels of the Pisco formation (Peru), the late
Miocene Bahia Inglesa formation (Chile) and the late Miocene marine Paraná formation in
Argentina. The isolated periotics that have been reported from several sites in North America
may belong to the brachydelphid Stenasodelphis .
Pontistes rectifrons Burmeister, 1885
The late Miocene Paraná formation is the sedimentary source for the fossil pontoporiid
Pontistes rectifrons . The original description was based on an almost complete skull, now
badly damaged. The orbit is reduced, presumably reflecting adaptation to turbid estuarine
waters. The teeth are very close set. The mandible and rostrum are strikingly depressed,
uniquely so among fossil and living odontocetes. Cozzuol (1985) considered the mandibular
morphology of Pontistes an anatomical, functional, and ecological type that had never been
repeated. However, its placement as a pontoporiid has been mostly acknowledged. Cozzuol
(1985) described several key synapomorphies that link Pontistes with Pontoporia , and
Muizon, while remarking that Pontistes showed no sign of the maxillary crests characteristic
of other pontoporiids (1984:61). This is a possible paedomorphic feature that places Pontistes
in the subfamily Pontoporiinae, along with the fossil Pliopontos (see below) and Recent