51813_Sturgeon biodioversity an.PDF

tentially untenable. Characters typically ascribed to
Acipenserin the literature are plesiomorphic for
Acipenserinae. Interspecific variability in morpho-
logical features withinAcipenseris rampant, cloud-
ing the applicability of most characters used in phy-
logenetic reconstruction. It is possible thatAcipen-
seris paraphyletic and closer examination of the ge-
nus is warranted.

phirhynchusa local remnant of the original radi-

ation; and (2) the observation that scaphirhyn-

chines are heavily scaled, ancient looking sturgeons

easily interpreted as primitive. That the earliest aci-

penserid fossils are from the upper Cretaceous of

North America (not Europe or Asia), and that pu-

tatively primitive aspects of scaphirhynchine mor-

phology have never been examined phylogenetical-

ly have not impeded such hypotheses. Typically, the

interpretation that scaphirhynchines are plesio-

morphic within Acipenseridae is accepted a priori,

and has driven evolutionary discussions of the fam-

A second dominant tenet to historical perspec-

tives on acipenserid evolution is paedomorphosis.

In recognizing chondrosteans with cartilaginous en-

doskeletons and a reduced dermal skeleton as sec-

ondarily de-ossified compared to their palaeoniscid

ancestors (e.g., Traquair 1887, Woodward 1891,

subfamilyHusinaenew name Goodrich 1909, Gregory 1933), early authors initi-

genusHusoBrandt 1869 ated a persistent theme presenting sturgeons as de-

subfamilyAcipenserinaenew usage generate and primitive among extant actinoptery-

tribeAcipenseriniundefined gians. Although acipenserids possess extensive

scalation, they remain perceived as paedomorphs.

The phylogeny and characters presented in this

study allow for new interpretations about the evo-

lution of the Acipenseridae. The cladogram sup-

ported here reverses classic evolutionary scenarios

for Acipenseridae, suggesting instead that acipen-

serids show progressive layering of peramorphic

characters in phylogeny and have evolved into in-

Taxonomic recommendations

Order Acipenseriformes Berg 1940 ily.

suborder †Chondrosteodei sensu Grande

suborder Acipenseroidei sensu Grande

& Bemis 1991

& Bemis 1991

family Polyodontidae Bonaparte 1838

family Acipenseridae Linnaeus 1758

taxon

genusAcipenserLinnaeus

1758

tribeScaphirhynchini

Bonaparte 1846

genusPseudoscaphirhynchus

genusScaphirhynchusHeckel

Nikolskii 1900

1836 creasingly benthic fishes.

Evolutionary patterns within Acipenseridae Benthic cruising as a scenario in

acipenserid evolution

Based on this cladogram, scaphirhynchines are de-

rived sturgeons, withHusothe most phylogeneti- Based on this phylogeny of Acipenseridae, a major

cally primitive genus within Acipenseridae (Figure trend in acipenserid evolution was to become in-

27). This counters widely held interpretations that creasingly benthic. However, acipenserids never

implicate scaphirhynchines as representing the achieved the extreme benthic specializations exhib-

primitive condition within Acipenseridae (Schmal- ited by some fishes exemplified by such features as

hausen 1991, Birstein 1993). Scaphirhynchines are flattened bodies, extensive camouflage, and sta-

generally accepted as phylogenetically primitive for tionary behaviors. Instead, acipenserids remain cy-

two reasons: (1) the premise that acipenserids orig- lindrical in cross-section and are relatively active

inated in freshwater basins of Triassic northern fishes that interact with the substrate focally for

Asia (Berg 1948b, Yakovlev 1977) withPseudosca- predation, while developing locomotory abilities