FOSSIL RECORD AND THE EVOLUTIONARY HISTORY OF INIODEA - Biology, Evolution and Conservation of River Dolphins Within South America and Asia - page 203

has been treated as the geologically youngest of the three taxa and occurs in the same
geographic area as does the living Pontoporia.
The late Miocene date for the Paraná formation, the provenance of Pontistes (at least for
its upper section, the only which outcrops) is supported by the presence of several taxa,
including both invertebrates and vertebrates (Zabert & Herbst, 1977; Cione et al., 2001). Del
Rio (1991) pointed out that the mollusk fauna from the ―Entrerriense‖ of northern Patagonia
(formally Aonikan Stage, including, among others, the Puerto Madryn Formation) is
significantly different from the ―Entrerriense‖ of Paraná (Paranian Stage, Paraná Formation)
at the level of species, indicating a probably diachronism, which agree with the evidence from
vertebrates (see Cione et al., 2001; Cozzuol, 1993). More recently, Scasso et al. (2001)
published radiometric dates (87Sr/86Sr) of fossilized bivalves from Patagonia
(―Entrerriense‖) which gave an average of 10.0 +/- 0.3 My, which is the limit between middle
and late Miocene.
Muizon's (1984) interpretation of the morphological characters upon which this
pontoporiid phylogeny is based is questionable. For example, he lists six synapomorphies
uniting Inia and Lipotes to the exclusion of the Pontoporiidae, rejecting Zhou's 1979 proposal
for a monotypic Lipotidae. A year later, he reversed his position, and was the first since
Flower (1869) to suggest that Inia and Pontoporia are sister taxa. However, this interpretation
of river dolphin phylogeny had more taxa than characters (Muizon, 1985). If Pontistes and
Pliopontos are temporally closer in age than is currently accepted, then it is plausible to argue
on biogeographic grounds a sister relationship between Pontistes and recent Pontoporia.
Family INIIDAE Gray, 1863
Possibly Iniidae of uncertain affinities
Goniodelphis hudsoni Allen, 1941
This species was described on a partial skull, lacking the braincase and anterior portion of
the rostrum (Allen, 1941, Figure 1). Additional referred specimens where described by
Kellogg (1944). Since then, many other specimens where found, mainly rostral and
mandibular fragments.
The origin of the specimens is the outcrops of the Bone Valley formation in central
Florida, with a stratigraphic range from the Middle Miocene to the early Pliocene. The best
known of the Bone Valley vertebrate faunas is the early Pliocene Palmetto Fauna, which has
been correlated with the late Hemphillian North American Land Mammal age (Berta &
Morgan, 1985). Deposition of the Palmetto Fauna sediments was during a time of sea levels
25-35 m higher than present day, in a mix of fluvial, deltaic and nearshore marine
environments (Morgan, 1994).
In this original description, Allen (1941) referred Goniodelphis to Iniidae with some
confidence, stating "The specimen proves to be of unusual interest as the first certain record
of a cetacean of the family Iniidae from eastern North America". Kellogg (1944) agreed and
included an extensive comparison of Goniodelphis with all other fossil and living Iniids
(sensu Simpson) known at that time. Thus Goniodelphis was described by Kellogg (1944) as
"somewhat similar to Ischyrorhynchus in the preserved portion of the type skull". However,