FOSSIL RECORD AND THE EVOLUTIONARY HISTORY OF INIODEA - Biology, Evolution and Conservation of River Dolphins Within South America and Asia - page 199

exhibit only partially overlapping morphologies, available material is sufficient to
differentiate the three species.
According to the analysis of Barnes (1985), the parapontoporiids are morphologically
intermediate between Pontoporia and Lipotes . He revised the taxonomy of the family
Pontoporiidae accordingly. He recognized three species in the subfamily Pontoporiinae: the
Late Miocene Argentine Pontistes , the Pliocene Peruvian Pliopontos, and the Recent
Pontoporia , distinguished mainly by the apomorphy of a symmetrical cranial vertex. He
erected the subfamily Parapontoporiinae for the three species of that genus, which differ from
the Pontoporiinae and resemble Lipotes by their asymmetrical cranial vertex offset to the left
side. Barnes (1985) considered several other cranial characters which diagnose this
subfamily, such as braincase proportions, construction of bones around nares, and orientation
of occipital shield, as intermediate between Pontoporiinae and Lipotes . To reflect this close
relationship, he suggested a new rank and context for Lipotinae (Zhou et al., 1979) by placing
it as the third subfamily of the Pontoporiidae.
Barnes' taxonomic arrangement was recognized by subsequent authors (Brownell, 1989).
However, several issues cast doubt on Barnes' interpretation. The relationships among the
three proposed pontoporiid subfamilies were unresolved by Barnes' analysis of cranial
characters. While he stated that comparative specimens of all four extant river dolphin
species, Inia , Lipotes, Pontoporia, and Platanista were used in formulating the descriptions
and diagnoses, only the five taxa are included in his phylogeny: the three parapontoporiids,
plus Lipotes and Pontoporia. A thorough methodological approach should include at least
Pontistes , Pliopontos and Inia in any analysis of pontoporiid relationships. More recent
cladistic analysis of both molecular and morphological characters are rather conclusive in
establishing that, among extant cetaceans, Inia and Pontoporia are sister taxa (see below).
Muizon (1985, 1988c) presents evidence that Parapontoporia belongs in the family
Lipotidae, the sister lineage to Inia + Pontoporia . In an analysis of the auditory region of all
fossil and living non-platanistid river dolphins (Muizon, 1988c), he suggested that
Parapontoporia is allied to Lipotes , and not to Inia nor Pontoporia. Muizon regards
characters of the auditory region of greater diagnostic value than the cranial characters that
Barnes used to unite Parapontoporia and Pontoporia, some of which are subject to strong
parallelisms (Muizon, 1988c). Interestingly, Barnes (1985) assigned 7 periotics found in SD
formation to Parapontoporia sternbergi based on their resemblance to Lipotes . Clearly the
overdue systematic analysis of the Pontoporiidae should include rigorous cladistic
comparisons with the fossil parapontoporiids and Lipotes.
Superfamily Inioidea (Sensu Lato)
Family BRACHYDELPHIDAE Muizon, 1988c
Brachydelphis mazeasi Muizon, 1984 and Brachydelphis sp from Peru and Chile
This genus was described as the earliest member of the Pontoporiid lineage. It comes
from the Pisco formation, along the southern Peruvian coast. It ranges in age from Middle
Miocene (Santa Rosa level, 14-16 mya) to Late Pliocene (Sacaco level, 3.5 mya) (Muizon,
1988a). The Pisco formation is rich in both vertebrate and invertebrate marine fossils, where
fossil cetaceans are represented, with over 40 taxa described.