Figure 20.Lateral view of the orbit and ethmoid regions ofthe neurocranium inPolyodonand representatives of three genera of Acipen-
seridae: The ventral surface of the neurocranium is flat in Polyodon(a) and rises smoothly in PsephurusandHuso(b), but angled by the
central trabecular process (ctp) in acipenserines (Character 31).oc= olfactory capsule,pnw= postnasal wall,btp=basitrabecular pro-
cess,fII= foramen of the optic nerve.
tine contacts the palatoquadrate medially and bears
teeth in juveniles. Acipenserinae
Dermopalatines ofHuso(Figure 22b), all polyo-
dontids (Figure 22a; Grande & Bemis 1991), †Chon-
drosteus(Traquair 1887), and †Peipiaosteus(Liu &
Zhou 1965) possess flat anteroventral edges. These
taxa also bear teeth along the full edge of the der-
mopalatine, not in a restricted portion. Similarly,
the lower jaws of outgroups lack a dentary shelf
(Figure 21a, b).
Character 35. Prearticular bones are small and thin -
The prearticular is a small, splinter-like bone on the
inner surface of Meckel’s cartilage (Figure 21c).Its
size and shape conforms to the thin, straight jaws of
acipenserines (Character 33). The prearticular is
absent in scaphirhynchines (Character 48).
The prearticular of Psephurus(Grande & Bemis
1991) and Huso(Figure 21a, b) is a flat, triangular
bone covering the posterodorsally angled inner sur-
face of Meckel’s cartilage (see Character 33). This
bone is elongate and thin in †CrossopholisandPo-
lyodon(Grande & Bemis 1991), but these taxa pos-