morphic features because the bones more or less
closely ensheath the underlying endochondral ros-
trum. For now we accept these as separate charac-
ters.
Discussion of clade Acipenseroidi
The monophyly of Acipenseroidi sensu Grande &
Bemis (1991) was questioned by Zhou (1992).
Zliou’s tree is shown in Figure 21, as well as a table
summarizing the nine characters he identified to
challenge the monophyly of Acipenseroidei.
Zhou’s (1992) analysis is problematic for three
basic reasons. First, the polarity of change in the
proposed characters was not explained and cannot
be assessed without explicit outgroup comparisons
to non-acipenseriforin taxa not included in Zhou’s
paper. This problem applies in particular to charac-
ters Z1 (quadratojugal sickle shaped) and 22 (in-
fraorbital canal ‘L’ shaped). Second, apparently
only some of the taxa included in Zhou’s phylogeny
were examined for all characters. For example,
Zhou interpreted characters Z6 (the presence of
fewer than 7 opercular boncs) and Z7 (branched
opercular bones) as synapomorphies of a clade in-
cluding †Peipiaosteidae + Acipenser. But both of
these characters are also present inPoIyodonand
†Paleopsephurus, so Zhou’s tree requires these two
characters to be derived at least twice. Third,
Zhou’s scoring or definitions for at least three char-
acters are problematic. Character 23 (loss of man-
dibular canal) applies toPoIyodonand †Paleopse-
phurusas well as to all of the other taxa in Zhou’s
analysis (see our character 9 above). The definition
of character Z8 (broad opercular-pectoral gap) is
vague, and in any event problematic to score in fos-
sils. Finally, character Z9 (hook-like rostral bones
in juveniles) is an ontogenetic feature with un-
known development in extant taxa. Zhou’s rostral
bones seem to be canal boncs bearing rostral por-
tions of the infraorbital canal, and we doubt that
this shape character is actually sufficiently similar in
Acipenserand †Peipiaosteusto warrant recognition
as a synapomorphy.
We scored characters Z1-Z9 as well as we could
determine (Figure 21), and found that Zhou’s pro-
posed tree is two steps longer than the tree we
would propose for these taxa (CI: 1.00 versus CI:
0.78). In view of this and our five well investigated
synapomorphies (characters 14-18 above), we re-
tain Acipenseroidei sensu Grande & Bemis (1991).Characters of PoIyodontidaeIn this section, we simply list the characters de-
scribed by Grande & Bemis (1991) with minor mod-
ifications. Figure 17 shows the same branching pat-
tern within Polyodontidae as reported by Crande &
Bemis (1991). The recent description of a new fossil
polyodontid, †ProtopsephurusLu 1994, raises some
questions that can only be answered by a side-by-
side analysis of specimens. This discovery pushes
back to the Mesozoic the presence of polyodontids
in Asia. Based on current information, however, we
cannot specify the phylogenetic placement of †Pro-
topsephurusrelative to the other members of the
family, and so indicate it as a basal multichotomy
within Polyodontidae.Character19. Many small stellate bones make up lat-
eral supports for the paddle
This character was delined by Grande & Bemis
(1991, character 15) as a synapomorphy of Polyo-
dontidae. These bones may be present in †Protop-
sephurus(Lu 1994), but additional clarification and
illustration is needed.Character 20. Series of very elongate dorsal and ven-
tral medial rostral bones, with cylindrical cross-sec-
tions
This character was defined by Grande & Beinis
(1991, character 16) as a synapomorphy of Polyo-
dontidae. Findeis (1993) proposed that the cylindri-
cal cross sectional shape should also be noted to
help differentiate these bones from the elongate
rostral bones present in some sturgeons. Elongate
rostral bones are present in †Protopsephurus(Lu
1994).Character 21. Unique shape of subopercle
This character was defined by Grande & Bemis
(1991, character 17) as a synapomorphy of Polyo-
dontidae. The anterior arm of the subopercle, al-
though more elongate in Polyodontidae than in any