51813_Sturgeon biodioversity an.PDF

Figure 22. Dermopalatine of † Paleopsephurusand representa-
tivesof Huso andAcipenser:The dermopalatine is flat along the
anteroventral edge in † PaleopsephurusandHuso(a. b). but ex-
panded medially in acipenserines (arrows in c: Character 34).
The dermopalatine (dp)and ectopterygoid (ecp1)fuse in Sca
phirhynchus (Character 69). but are separate elements inall
other acipenseriforms (as shown in a. b c).

The in terhyal-posterior ceratohyal joint of Huso

and extant polyodontids (Grande & Bemis 1991)

occurs anteriorly on the interhyal (Figure 16a, b, c).

This is a cartilaginous character not scorable in fos-

sil acipenseriforms. but the anterior joint is consis-

tent in all extant outgroups.

Character 37. Loss of median cartilage posterior to

branchial arches –Acipenserinae

The ventralmidlineofthe branchialarchskeleton

of all acipenserines examined includes a large ba-

sibranchial one and one or two small posterior ba-

sibranchials (Figure 13c), but no other elements.

The posterior basibrachials are paired serially with

ceratobranchial lour and five (e.g., bb2associated

withcb4in Figure 13).

The branchial arch skeleton ofHusoand extant

polyodontids possesses a median cartilage posteri-

or to the serial basibranchials (ug). The median car-

tilage ofHusois thin and short (Figure 13b), but

forms a plate in PolyodonandPsephurus (Figure

13a). Grande & Bemis (1991) named it an unidenti-

fied median cartilage and it has no postional affinity

with any branchial arch. This element is cartilagi-

nous and not scorable in fossils, but is present in all

extant outgroups.

Character 38. Loss of haemal spines anterior to the

caudal fin-Acipenserinae

Elongate basiventrals with haemal spines are pre-

sent in a short span of the vertebral column entering

the caudal fin, but are missing in the caudal pedun-

cle. In all acipenserines examined, three to four ba-

siventrals with haemal spines (bvh) are typically

found anterior to the hypurals (hyp, Figure 23b)

supporting the anterior fin rays of the caudal fin as

an anterior shelf characteristic of Acipenseriformes

(Findeis 1993, Bemis et al. 1997). More anterior ba-

siventrals neverpossesshaemal spines (bv, Figure

23b).

Polyodontids (Grande & Bemis 1991) andHuso

(Figure 23a) possess haemal spines throughout the

caudal peduncle and extending anteriorly over the

anal fin. Elongate haemal spines may be dependent

on a deep peduncle, with the flattened peduncle of

acipenserines too spatially restricted to accommo-

datethem.

Character 39. Lateral ethmoid shelves present-Sca-

phirhynchini

The lateral ethmoid ridges of scaphirhynchines are

broad and ventrally flat, forming lateral ethmoid

shelves (les, Figure 17d) lateral to the groove carry-