51813_Sturgeon biodioversity an.PDF

Environmental Biology of Fishes 48: 73 - 126,1997.

© 1997Kluwer Academic Publishers. Printed in the Netherlands.

Osteology and phylogenetic interrelationships of sturgeons (Acipenseridae)

EricK.Findeis

Department of Biology, University of Massachusetts, Amherst, MA 01003-0027, U.S.A.

Current address: Department of Biology, Wake Forest University, Winston-Salem, NC 27109, U.S.A.

Received18.8.1995 Accepted22.3.1996

Key words:Actinopterygii, cladistics, evolutionary morphology, benthic fishes, peramorphosis, Huso, Aci-
penser, Pseudoscaphirhynchus, Scaphirhynchus

Synopsis

Sturgeons (Acipenseridae) are an ancient and unique assemblage of fishes historically important to discus-

sions of actinopterygian evolution. Despite their basal position within Actinopterygii, rigorous comparative

morphological studies of acipenserids have never been made, and most ideas about acipenserid evolution

hinge on an untested impression that shovelnose sturgeons (Scaphirhynchini) are phylogenetically primitive.

This impression promoted ideas that: (1) the earliest acipenserids were highly benthic and evolved secondarily

into pelagic predators, and (2) paedomorphosis has dominated mechanisms affecting their morphological

change. Using cladistic methods, this study examines generic level interrelationships within Acipenseridae.

Representatives of the four acipenserid generaHuso, Acipenser, Pseudoscaphirhynchus, andScaphirhyn-

chus,as well as their acipenseriform outgroups Polyodontidae, †Peipiaosteidae, and †Chondrosteidae, were

surveyed for skeletal characters. Sixty-nine characters are identified and described to support the first generic

level cladogram of Acipenseridae.Husois phylogenetically primitive within Acipenseridae and the sister

group to a redefined subfamily Acipenserinae.Acipenseris not supported by any characters identified in this

study, but the tribe Scaphirhynchini comprisingScaphirhynchusandPseudoscaphirhynchusis found to be

monophyletic. The cladogram contradicts historical ideas about acipenserid evolution becauseHusodefines

an outgroup morphology and life history founded on pelagic habitats and piscivory. In contrast, acipenserines,

and more markedly scaphirhynchines, are benthic predators possessing character complexes for benthic feed-

ing, respiration, locomotion, and protection. Also, the pattern of character acquisition within Acipenseridae

suggests that peramorphosis played a central role in acipenserid evolution. Peramorphic addition and en-

largement of the skeleton and scalation defines most characters at all nodes within Acipenseridae, and repu-

diates paedomorphosis as a major trend in evolution within the family Acipenseridae.

Introduction (†ChondrosteusEgerton, 1858). Acipenserids are

distinctive inmorphology andbehavior,with nu-

The family Acipenseridae includes 25 species in merous features such as armoring trunk scutes, a

four currently recognized genera in a Holarctic dis- ventral mouth, rostral chemosensory barbels, and a

tribution. This is an ancient assemblage with recog- flattened body contributing to their benthic hab-

nizable acipenserid fossils known from the Upper itats and behaviors. Their commercial importance,

Cretaceous and fossil relatives extending the origin uniqueness, and almostuniversalendangered sta-

of Acipenseriformes into the Lower Jurassic tus (see Birstein 1993) has promoted a modern