Materials and methods
Phylogenetic methodsInterrelationships among genera of Acipenseridae
were examined using cladistic methods as generally
espoused by Hennig (1966) and Wiley (1981). Skele-
tal features identified as potentially relevant char-
acters for phylogenetic reconstruction were coni-
pared with outgroup taxa to: (1) determine which
subgroups possess or lack the character: and (2) de-
fine the polarity of change in character states. Polar-
ity assessments were made through comparison
with all genera of Acipenseridae, Polyodontidae
(personal observations; Grande & Bemis 1991), Scaphirhynchus
†Chondrosteus(Traquair 1887, Woodward 1889,
Watson 1925, 1928, Hennig1925),†Peipiaosteus Scaphirhynchusplatorynchuswas accepted as gen-
(Liu & Zhou 1965, Bai 1983, Zhou 1992), and mul- erally typical for the genus in this study. Nine newly
tiple non-acipenseriform taxa such as †Mimiand collected adult specimens were hand cleaned and
†Moythomasia (Gardiner 1984a), †Cheirolepis multiple preserved specimens were examined ex-
(Pearson & Westoll 1979), † Birgeria(Nielsen 1949), ternally and through dissection. Two large adult
†Saurichthys(Rieppel 1992),Polypterus,Lepisos- specimens from the Shedd Aquarium (FMNH
teus,andAmia(personal observations). Characters 98285, 98286) were prepared with dermestid bee-
were accepted only when skeletal features were tles. An extensive developmental series ranging
consistent within ingroups compared to outgroups from prehatching embryos to small juveniles was
(for respective polarities). Rather than provide a cleared and double stained with addition of a larger
matrix with proposed character states, putative syn- juvenile (AMNH 4485) with slightly more ad-
apomorphies are defined and directed to specific vanced skeletal development. Scaphirhynchus al-
phylogenetic nodes. Character descriptions pro- buswas examined externally and non-invasively to
vide information on character morphology of in- confirm skeletal characters of the genus (see Bailey
groups and outgroups to unambiguously define & Cross 1954, Carlson 1985). No specimens of S.
apomorphic and plesiomorphic character states. suttkutsiwere available for examination, but this
species is very similar to S. platorynchus (Williams
& Clemmer 1991).mens were prepared with dermestid beetles result-
ing in near total loss of cartilage, but leaving intact
dermal skeletons. Many small specimens were pre-
pared by clearing and double staining (Dingerkus
& Uhler 1977) to examine intact skeletons. Specific
osteological structures were examined in preserved
specimens of multiple taxa to confirm or deny puta-
tive characters identified from skeletons. Develop-
mental series mere examined in cleared and double
stained preparations to clarify structural interpreta-
tions amidst morphological variation and to inter-
pret homology recognition.Specimens and preparationSpecimens examined included representatives of Pseudoscaphirhynchus
all four acipenserid genera. Skeletal characters gen-
erally focus on bone since most taxa possess ossified Only two specimens of the dwarf morphotype ofP.
endoskeletons (and fossils are predicated on pres- kaufmanniwere available for examination of the
ervation of bone), but cartilage is dominant in the genus in this study. One was cleared and double
acipenserid endoskeleton. Conventional tech- stained (MCZ 27653) and one was examined exter-
niques of skeletal preparation can damage or de- nally with additional description from Ivanzoff
stroy cartilage, so several techniques were used to (1887) and Sewertzoff (1926a, 1928). This species is
assess morphology of specimens examined in this accepted as representative for the genus in this
study. Large, newly collected specimens were hand study, althoughP hermannidiffers markedly from
cleaned to preserve cartilages. Several adult speci- P.kaufmannni(Berg 1948a) and is assumed to be spe-