51813_Sturgeon biodioversity an.PDF

Figure 18.Dorsal bones of the rostrum of †Paleopsephurusand representatives of three genera of Acipenseridae: Dorsal rostral bon ...

face of the neurocranium without a cartilage cover (Figure 17a, b). These taxa also lack an ethmoid-or- bital angle as the ventr ...

Figure 19.Ventral rostral bones in †Paleopsephurusand representatives of all genera of Acipenseridae: The series is shown in ven ...

Figure 20.Lateral view of the orbit and ethmoid regions ofthe neurocranium inPolyodonand representatives of three genera of Acip ...

sess thin jaws. † Paleopsephurusis not preserved correctly to see the prearticular. † Chondrosteus possesses a large, flat prear ...

Figure 22. Dermopalatine of † Paleopsephurusand representa- tivesof Huso andAcipenser:The dermopalatine is flat along the antero ...

ing the rostral nerves (grn). The lateral ethmoid shelves are penetrated several millimeters from the lateral edge by foramina c ...

lost discrete spines, but a ridge is present in pho- tographs in Williams & Clemmer (1991) and prob- ably represents a resid ...

ever, inAcipenserthey are not as dominantly elon- gate and are thin. Similarly, Husoand all polyodon- tids (Grande & Bemis 1 ...

Character49.Dorsal head of the hyomandibula is cylindrical-Scaphirhynchini The dorsal head of the hyomandibula of scaphi- rhynch ...

Figure24.Ventral axial skeleton of representatives ofAcipenserandScaphirhynchus: Ontogeny of the haemal arch is shown inA. brevi ...

Universal presence of these scales in all other aci- penserids and their outgroups suggests that this loss defines Scaphirhynchi ...

Figure25.Gill rakers of representatives of all genera of Acipenseridae: The gill rakers ofHuso(a), primitive polyodontids, and † ...

Figure26. Ventral views of the dermal pectoral girdle of representatives ofHuso, Acipenser,andPseudoscaphirhynchus: The anterome ...

more elongate than a small, inner tip (Figure 25d). Larger rakers may possess only an outer tip, but the base remains expanded w ...

and dorsoventrally flattened with a rectangular cross-section. Elongation occurs suddenly and rap- idly in small juveniles to ac ...

Chavacter 66. Cleithralwallpresent Scaphirhynchus cardiacshield. The cleithral wall of the scapulocoracoid is a trian- gular s ...

Figure27.Proposed interrelationships of the genera of Acipenseridae:Husois defined by two synapomorphies forming the subfamily H ...

tentially untenable. Characters typically ascribed to Acipenserin the literature are plesiomorphic for Acipenserinae. Interspeci ...

allowing mobile benthic foraging. This proposed Feeding behavioral styleIterm benthic cruising is unique to As benthic cruisers, ...