lost discrete spines, but a ridge is present in pho-
tographs in Williams & Clemmer (1991) and prob-
ably represents a residual spine. When present,
spines are present on the parietal, posttemporal, su-
pracleithrum, and multiple anterior dorsal rostral
Character 40. Ampullary bones present-Scaphi- bones.
rhynchini Spines ofScaphirhynchusare shallow and ridge-
like, but elevate into sharp posterior points. They
Ampullary bones compose an ossification group are prominent in juveniles, but become allometri-
covering the endochondral rostrum between the cally smaller in adults as dermal ornament thickens
dorsal rostral series and peripheral border rostral and obscures them. Spines of the posttemporal and
bones (Figure 18d). They are small, rounded (Sca- supracleithrum are the largest inScaphirhynchus,
phirhynchus) or larger, rectangular (Pseudosca- with posteriorlycurved tips identical to and in series
phirhynchus) plates that interweave among the with the flank scutes. Spines ofP.kaufmanniare
dorsal rostral ampullary field. Ampullary bones de- large, with posttemporal and supracleithrum spines
velop as a group well after appearance of the dorsal similar to Scaphirhynchus accompanied by huge
rostral series (Findeis 1993) and anterior to the si- parietal and frontal spikes (see Character 55).
multaneously developing border rostral bones Weak spines occur occasionally on the supratempo-
(brb, Figure 18c,d)to cover the broad scaphirhyn- ral ofScaphirhynchus,but they are rarely visible
chine rostrum (see Character 39). and not present inP. Kaufmanni
The border rostral series is a putative synapo- Some skull bones ofAcipenserpossess central
morphy of the Acipenserinae (Character 29) dis- ridges, but never manifest spines and anterior dor-
tinct from the ampullary series. Border rostral sal rostral bones are plates without raised ridges or
bones of Acipenserare positionally separate from spines. Husonever possesses spines or strong ridges
dorsal rostral bones in early ontogeny and usually in in any skull bones and polyodontids possess little
adults (Figure 18c). No interior rostral bones fill this dermal ornament on the skull roof and no discrete
gap in small juveniles of any species ofAcipenser ridges (Grande & Bemis 1991). †Chondrosteus
examined, suggesting that the ampullary series is (Hennig 1925) and †Peipiaosteus(Liu & Zhou 1965)
missing in Acipenser.Broadening of the rostrum in possess obvious dermal ornament, but no spines.
scaphirhynchines (see Character 39) opens it dor-
sal surface unlike any outgroup and this area is cov-
ered by a novel ampullary series.
gests that the generally cylindrical skulls and rostra
typical of most species ofAcipenserare plesiomor-
phic.
Character 42. First ventral rostral bone is elongate -
ScaphirhynchiniThe first ventral rostral bone of scaphirhynchines is
elongate, accounting for over two-thirds the length
of the ventral rostral series (vrb1, Figure 19d, e). It is
a wide, Flat bone slightly keeled centrally with addi-
tional, smaller bones of the ventral rostral series
clustered anteriorly .Scaphirhynchustypically pos-
sesses four or five additional ventral rostral bones
(Findeis 1993), whilePseudoscaphirhynchus kauf-
mannican possess twice as many (nine in Figure
19c).
This is a qualitative character since first ventral
rostral bones of all species of Acipenserexamined
are also the longest of the series (Figure 19c). How-Character 41. Central spines present on the parietal,
postiemporal, supracleithrum, and anterior dorsal
rostral bones–ScaphirhynchiniCentral spines are present inScaphirhynchus plato-
rynchus,S.albus,andPseudoscaphirhynchus kauf-
manni, variably present in P. fedtschenkoi (Berg
1948a), but absent in S. suttkusi andP. hermanni
(Berg 1948a). Within Pseudoscaphirhychus, P.
kaufmanniis most simiIar toScaphirhynchusand
seems to be representative for the basal morpho-
type of the genus, with presence of spines pulatively
plesiomorphic. Scaphirhynchus suttkusi may have