Figure 19.Ventral rostral bones in †Paleopsephurusand representatives of all genera of Acipenseridae: The series is shown in ventral view
with anterior to top. The first ventral rostral bone (most posterior) is paired in polyodontids andHuso(a, b), but singleinacipenserines (c,
d, e; Character 30). This bone is elongate in scaphirhynchines (d, e; Character 42), with the remaining bones clustered at the anterior tip of
the rostrum.
pineal bones are present and the frontal lacks der-
mal ornament medially, suggesting that closure oc-
curs by frontal expansion. There are often two
openings in polyodontids (Grande & Bemis 1991),
but only one in Huso. These outgroups possess
frontals making medial contact, and the frontals of
†Chondrosteus(Traquair 1887, Hennig 1925) and
†Peipiaosteus(Liu & Zhou 1965) uniformly close in
the skull roof.
joint.Polyodonis similar, but less strikingly since its
elongate jaws coincidentally flatten all jaw features.
The dentary of all fossil polyodontids (Grande &
Bemis 1991 and †Chondrosteus(Traquair 1887) is
angled, suggesting that an angled lower jaw is ple-
siomorphic within Acipenseriformes. Zhou (1992)
reconstructs the dentary of †Peipiaosteus with a
slight angle and I accept an angled lower jaw as ple-
siomorphic for Acipenseridae.Character33.Lower jaw is straight-Acipenserinae
The lower jaw of all acipenserines examined is short
and transverse under the head. Meckel’s cartilage
curves slightly opposite the upper jaw to define the
mouth near the symphysis, but the lateral end of
Meckel’s cartilage and the dentary is almost entire-
ly linear throughout its length (Figure 21c).
The posterior end of Meckel’s cartilage and the
dentary of HusoandPsephurus(Grande & Bemis
1991) angles dorsally (Figure 21a, b) toward the jaw
Character 34. Dermopalatine sheIf present-Acipen-
serinaeThe medial dermopalatine broadens as a ventral
shelf in all acipenserines examined (Figure 22c).
This dermopalatine shelf deepens the upper jaw as
an anteromedial surface often opposing a protrud-
ing dentary shelf (Figure 21c). The dermopalatine
shelf is consistently present, but the dentary shelf is
not universal and not used as a character here. The
dermopalatine shelf occurs where the dermopala-