the circumorbital series, docs not apply to the ante-
rior process of the jugal of acipenserids. The ex-
tended jugal braces the dermal skull roof against
the neurocranium anterior to the orbit (Findeis
1993) and conforms the dermal skull to the expand-
ed neurocranium of acipenserids. Ethmoid expan-
sion of the neurocranium coincides with a broad-
ened postnasal wall as a probable character of the
Acipenseridae not scorable in fossil taxa, but coin-
cident jugal expansion restricted to acipenserids
suggests that ethmoid expansion is an acipenserid
character.
No polyodontid possesses homologizable cir-
cumorbital bones as the infraorbital canal is carriedCharacter 3. Jugal possesses an anterior process-
Acipenseridae
The jugal of all acipenserids examined extends a
prominent anterior process undercutting the orbit
(atp, Figure3).It is small inHuso(Figure 3a), but
large in all species ofAcipenserexamined andSca-
phirhynchus, and massive in Pseudoscaphirhyn-
chus(Character 57). The anterior process extends
anterolaterally to contact the neurocranium.
Theanterior process does not bear the infraorbi-
tal canal that curls anteromedially within a sepa-
rate, smaller canal process of the jugal(cnp, Figure
3). Thus, passage of the infraorbital canal, typical of
Figure 4.Antorbital of representatives of all genera of Acipenseridae: a –Huso huso,b–Acipenser oxyrinchus,c–A.brevirostrm,d-
Pseudoscahirhynchus kaufmanni, c – Scaphirhynchus platorynchus. The antorbital lies betweentheorbitandoIfactory opening dorsally
in the dermal skull (top in black; Character 4). It lacks any portion of the supraorbital canal and extends ventrally as a variably sized
wedge-shaped process. The ventral wedge is small inHuso(a), variably sized inAcipenser(b, c), but elongate in scaphirhynchines (arrows
in d, e; Character46).It contacts an enlarged postrostral bone (prb)inScaphirhynchus(Character 61).