51813_Sturgeon biodioversity an.PDF

basitrabecular process medially (Findeis 1993) is

This morphology contrasts with the inferred ple-
siomorphic condition of Psephurusand several spe-
cies ofAcipenser(e.g.,A. ruthenus,A.transmonta-
nus) with basitrabecular processes that protrude
ventrally (Figure 15b) and are isolated by deep
grooves medially. Basitrabecular morphology va-
ries widely among other taxa. Some species ofAci-
penser(e.g.,A.oxyrinchus) possess basitrabecular
processes that curl medially over the palatine
groove to occasionally complete a nerve canal. Aci-
penser brevirostrum possesses stubbier processes
that flare laterally unlike other species ofAcipenser
examined (Figure 15c). Scaphirhynchines possess
small processes and a basitrabecular cartilage (Fig-
ure 15d, e; Character 43). Variation withinAcipen-
ser makes basitrabecular morphology a difficult
character to analyze, but the morphology of Husois
unique.

Character26.Nopalatoquadrate-interhyaljoint

thin and shallow. -Huso

The interhyal (ih)ofHusodoes not contact the pa-

latoquadrate, articulating only with Meckel’s cartil-

age (mk, Figure 16c). It is unexpanded anterodor-

sally and the palatoquadrate lacks a corresponding

interhyal process (Figure 16c). This character was

described by Tatarko (1936) and has been used as a

Husocharacter by other authors (e.g., Berg 1948a,

Antoniu-Murgoci 1936b).

All other extant acipenseriforms possess jaw-in-

terhyal joints with mutual contact of the interhyal,

Meckel’s cartilage, and palatoquadrate (Figure 16a,

b, d, e). Osteologically, contacting extensions of the

interhyal (ihpa) and palatoquadrate (pq) are found

in extant polyodontids (Figure 16a, b), all species of

Acipenserexamined (Figure 16d; Tatarko 1936, An-

toniu-Murgoci 1936b), and scaphirhynchines (Fig-

ure 16e), but ratio of Palatoquadrate/Meckel’s car-

tilage contact with the interhyal varies. Meckel’s

Figure 14.Scales of the pectoral girdle inPsephurus,†Peipiaosteus,and representatives ofHusoandAcipenser: The pectoral scales of

acipenserids (c, d) possess multiple recurved tips overhanging an elliptical base (Character23).Polyodontids (a-redrawn from Grande

& Bemis 1991) possess pectoral scales with a single process and the scales of †Peipiaosteus(b-redrawn from Liu & Zhou1965) possess

three processes fanning from a flat base.