51813_Sturgeon biodioversity an.PDF

tapers ventrally inHusoand all speciesAcipenser

examined (Figure 11b, c) to a ventral position form-

ing a flat edge in scaphirhynchines (Figure 11d;

Character 50). The ventral end is cartilaginous, but

the ossified core reflects the wedge by posterior

flaring and thinning of the perichondral center.

The hyomandibula ofPsephurusis slender, with

a ventral head tapering with a continuously curved

posterior edge (Figure 11a). The ossified center of

Psephurus and †Crossopholis expands ventrally

(Grande & Bemis 1991), but not as sharply as in aci-

penserids and with a rounded posterior edge. The

hyomandibula of †Paleopsephurus is incomplete

and not well known (Grande & Bemis 1991, MacAl-

pin 1947).Theossified cores of †Chondrosteus(Tra-

interpretation on shape or composition is made

here.

No palatal complex is present in other extant aci-

penseriforms or actinopterygians, but as a cartilagi-

nous character its presence or absence is unknown

in †Chondrosteusor †Peipiaosteus.

Character 19.Posteroventraledge of hyomandibula
forms a wedge–Acipenseridae

The hyomandibulae of all acipenserids examined

are expanded posteriorly to form a posterior wedge

in the ventral cartilaginous head (Figure 11).Posi-

tion of thewedgevaries from a dorsal position that

Figure 11.Hypomanbibula ofPsephurusand respresentatives of three genera of Acipenscridae: The hyomandibula is shown in lateral view

in all taxa and also inanterior view in Acipenser(c) and Scaphirhynchus(d). The hyomandibula of Psephurus(a) possesses a convex

posterior edge, but is expanded posteriorlyinall acipenserids examined (heavy arrow in b, c, d; Character 19).Theposterior wedge is

dorsal inHuso(b) andAcipenser(c), but ventral in scaphirhynchines (hollow arrow; Character 50). Also, the dorsal tip is board inHuso

andAcipenser,but thin in scaphirhynchines (thin arrows; Character 49).