51813_Sturgeon biodioversity an.PDF

Northcutt 1978, New & Bodznick 1985) or by a com-
bination of physiological and behavioral approach-

As in all of the groups enclosed by dotted outline
in Figure 3, the ampullary organs of Acipenseri-
formes are restricted to the head. There are two
types of exceptions which prove this rule. First, in
some taxa, such as skates of the genus Raja,very
long ampullary organs radiate onto the broad pec-
toral fins from sensory capsules located on the head
(Raschi 1986). In this case, the ampullary organ
tube has been lengthened so that the organ may be
sampling a different environment, but the sensory
epithelium is still based in the head region. Second,
in taxa such as the Australian lungfish, Neocerato-
dus forsteri, the presence of ampullary organs on
the trunk is linked to a recurrent branch of the ante-
rior lateral line nerve (Northcutt 1986). The func-
tional significance of locating the sampling portion
of an electroreceptor caudal to head in each of the
two cases (taxa) is untested, but perhaps it allows
better localization of point electrical fields by trian-
gulation (Kalmijn 1974). If this idea is correct, then
it may help explain the unusual body shape of
paddlefishes. Weproposethat thelongrostrum and
trailing opercular tipofpaddlefishesreflect ex-
treme specialization for electroreception. In a
juvenile paddlefish, therostrum and operculum to-
gether extend formore thanone half the body

Family†ChondrosteidaeEgerton 1858

Genus †Chondrosreus Agassiz 1844

Genus †Gyrosteus Agassiz 1844

es. Suborder Acipenseroidei sensu Grande &Bemis 1991

Family Polyodontidae Bonaparte 1838

incertae sedis

Subfamily †Paleopsephurinae Grande &Bemis 1991

Genus †Protopsephurus Lu 1994

Tribe †Paleopsephurini Grande &Bemis 1991

Genus†Paleopsephurus MacAlpin 1941a

Subfamily Polyodontinae sensuGrande&Bemis 1991

Tribe Psephurini Grande &Bemis 1991

Tribe Polyodontini sensuGrande&Bemis 1991

GenusPsephurus Günther 1873

Genus †CrossopholisCope 1883

GenusPolyodon Cope 1883

SubfamilyHusinaesensuFindeis 1993

SubfamilyAcipenserinaesensuFindeis 1993

FamilyAcipenseridae Linnaeus 1758

GenusHusoBrandt 1869

Tribe Acipenserini sensu Findeis 1993

GenusAcipenser Linnaeus 1758

Tribe Scaphirhychini Bonaparte 1846

GenusScaphirhynchus Heckel 1836

GenusPseudoscaphirhynchus Nikolskii 1900

Genus †Protoscaphirhynchus Wilimovsky 1956

Conclusions

We have fourbasic conclusions:

(1) The phylogeny for Acipenseridae is still in

need of additional testing. A more detailed analysis

length,sothat thelongtrailing tip of theoperculum

functionallyplaceselectroreceptors far moretau-

dal thanmightotherwise bepossible given that

of acipenserid phylogeny is needed for planning for

the conservation of sturgeons and forunderstand-

ing their evolutionary history andbiogeography.

electroreceptors areplesiomorphicallyrestricted to

to the dominanceofthissensorysystem in Polyo-

dontidae.

Therefore, it is very important to conduct broad,

molecular studies of the species of Acipenseridae.

Ideally, a future comparative morphological inves-

tigation should emphasize completeness by includ-

ing all well-preserved fossil and extant species of

Acipenseridae. Fossil taxa are, in most cases, known

only from the type descriptions and a number of

undescribed. In addition to reexamining the pat-

terns of generic interrelationships proposed by

Findeis (1997 this volume) and reviewed here, fu-

ture work should specifically target the question: Is

Acipensermonophyletic? There should be a serious

effort to examine all existing specimens, particular-

the head. Wethink toolittleattention has beenpaid comparative morphological developmental and

Nomenclaturalrecommendations

Our currentclassification of the generaofAcipenseriformes fol- newly discovered nearly complete skeletons remain

lows:

OrderAcipenseriformes Berg 1940

incertae sedis

Family †PeipiaosteidaeLiu&Zhou 1965

Genus †StichopterusReis 1910

Genus †PeipiaosteusLiu&Zhou 1965

Suborder†chondrosteoideisensuGrande&Bemis 1991