EnvironmentalBiology of Fishes48: 25 - 7 1, 1997.
© 1997 Kluwer Academic Publishers. Printed in the Netherlands.
Anoverviewof Acipenseriformes
WilliamE. Bemis^1 ,EricK.Findeis^1 &LanceGrande^2
(^1) Department of Biology and Graduate Program in Organismic and Evolutionary Biology, Universityof
Massachusetts, Amherst, MA 01003, U.S.A.
(^2) Department of Geology, Field Museum of Natural History, Chicago, IL 60605, U.S.A.
Received15.2.1995 Accepted10.3.1996
Key words:Actinopterygii, Paleonisciformes,Acipenseridae,Polyodontidae.†Chondrosteidae,
†Peipiaosteidae
Synopsis
Acipenseriformes occupy a special place in the history of ideas concerning fish evolution, but in many re-
spects, phylogenetic studies of the group remain in their infancy. Even such basic questions as the monophyly
ofAcipenser(the largest genus) are unanswered. We define relationships based on comparative osteology,
which allows us to incorporate well-preserved fossils into analyses. Acipenseriformes has existed at least since
the Lower Jurassic (approximately 200 MYBP), and all fossil and recent taxa are from the Holarctic. Phyloge-
netic relationships among Paleozoic and Early Mesozoic actinopterygians are problematic, but most workers
agree that Acipenseriformes is monophyletic and derived from some component of ‘paleonisciform’ fishes.
(‘Paleonisciformes’ is a grade of primitive non-neopterygian actinopterygians, sensu Gardiner 1993.) Taxa
discussed in comparison here are: †Cheirolepis, Polypterus,†Mimia.†Moythomasia,†Birgeria,†Saurichthys,
LepisosteusandAmia.We review generic diversity within the four nominal families of fossil and recent Aci-
penseriformes (†Chondrosteidae, †Peipiaosteidae, Polyodontidae, and Acipenseridae), and provide a cla-
dogram summarizing osteological characters for those four groups. Monophyly of the two extant families is
well-supported, but there are no comprehensive studies of all of the known species and specimens of †Chon-
drosteidae and †Peipiaosteidae. As a result, sister-group relationships among †Chondrosteidae, †Peipiaostei-
dae, and Acipenseroidei (= Polyodontidae + Acipenseridae) are unresolved. We discuss five features funda-
mental to the biology of acipenseriforms that benefit from the availability of our new phylogenetic hypothesis:
(1) specializations of jaws and operculum relevant to jaw protrusion, feeding, and ram ventilation; (2) anadro-
my or potamodromy and demersal spawning; (3) paedomorphosis and evolution of the group; (4) the bio-
geography of Asian and North American polyodontids and scaphirhynchines; and (5) the great abundance of
electroreceptive organs in the rostral and opercular regions. Finally, we summarize our nomenclatural recom-
mendations.
Introduction and historical overview
This paper reviews the systematics of sturgeons and
paddlefishes and their immediate fossil relatives in
the order Acipenseriformes. We synthesize historic
and current information in our effort to better un-
derstand the evolution, biogeography, and compo-
sition of the order. We emphasize generic and fam-
ilial comparisons, and summarize information for
all recent and well preserved fossil genera. In keep-
ing with our objective of providing background, this
paper includes several ‘evolutionary scenarios’(in