Figure 7. Aspects of the feeding system of the Chinese paddlefish, Psephurus gladius: a -A preserved specimen with its jaws in the
projected position. This projection system is shared by all living and fossil Acipenseriformes except for North American paddlefish
(Polyodon). b-View of the first typical gill arch to show gill rakers. The gill rakers ofPsephurusare short, stubby and unsuited for filter
feeding. This is the plesiomorphic condition for Polyodontidae (see Grande & Bemis 1991, fig. 26).
linked with Acipenseriformes are †Saurichthys (a
widespread and speciose genus from the Triassic
and Early Jurassic, see Rieppel 1992 for review) and
†Birgeria(particularly the species from the Triassic
of east Greenland; see Nielsen 1949 and Yakovlev
1977). In their summary phylogeny, Gardiner &
Schaeffer (1989, their fig. 12; their ‘chondrostean
group’ is equivalent to Acipenseriformes here)
show a group containing †Saurichthysas the imme-
diate sister group of Acipenseriformes. This posi-
tion, however, is only one of several equally parsi-
monious possibilities from their cladistic analysis,
and so must be regarded as uncertain. Rieppel
(1992), in a review of the genus †Saurichthys, con-
cluded that Acipenseriformes, †Saurichthys, and
†Birgeriaform an unresolved trichotomy.
In selecting the outgroup taxa listed in Table 1, we
were guided by their putative phylogenetic posi-
tions, the availability of detailed osteological de-
scriptions, and the general desirability of including
a spectrum of taxa. Better understanding of the re-
lationships of Acipenseriformes to other groups of
Actinopterygii can be achieved by a detailed speci-
men-based review of these and other taxa, includ-
ing preparation of many of the known fossils (see
Grande &Bemis 1996 for example of †Peipiaos-
teus), but this is far beyond our present purposes.Diversity of fossil and recent Acipenseriformes and
specification of ingroup taxaInthis section, we briefly review the known taxa
and their geographic and geological ranges. We also
identify which taxa were the sources of character
information for our analysis. The text is supple-Table 4. Species and biogeographic ranges of fossil and extant Polyodontidae Bonaparte 1838.†ProtopsephurusLu 1994 - China
†P. liuiLu 1994
†PaleopsephurusMacAlpin 1941a - North America
†P. wilsoniMacAlpin 1941a
PsephurusGünther 1873 - China
P. gladius(Martens 1862)
†CrossopholisCope 1883 -North America west of Rocky Mountains
†C. magnicaudatusCope 1883
PolyodonLacépède 1797 -North America east of Rocky Mountains
P. spathula(Walbaum 1792)
†P. tuberculataGrande & Bemis 1991
Upper Jurassic -China
Upper Cretaceaus -Montana
Yangtze River drainage, ChinaLower Eocene -Wyoming
Mississippi River drainage
Lower Paleocene -Montana