Acipenseriformes
Acipenseroidei
Figure 1.proposed phylogenetic relationships within Acipenseriformes: Characters defining this cladogram are from Grande & Bemis
(1991), Findeis (1993), and Bemis et al. (1997 this volume). These characters support a monophyletic Acipenseroidei comprising Acipen-
seridae and Polyodontidae. The Acipenseroidei forms an unresolved trichotomy in Acipenseriformes with the fossil taxa †Peipiaosteidae
and †Chondrosteidae. For outgroup comparison with Acipenseridae, all (three families are used when possible. Illustrated taxaare
†Chondrosteus acipenseroides Agassiz 1844,†PeipiaosteuspaniLiu & Zou 1965,Psephurus gladius(Martens 1862), andHuso huso
(Linnaeus 1758).
been made of the Acipenseridae at any level, two midwater environments. Second, classic ideas
themes dominate evolutionary studies of the family. about acipenserids focus on paedomorphosis as the
The first suggests that shovelnose sturgeons (Sca- dominant mechanism in their evolution (Wood-
phirhynchini) represent the primitive condition ward 1889, Goodrich 1909, Gregory 1933). These
among acipenserids (Schmalhausen 1991,Birstein persisting hypotheses have never been examined
1993).In this scenario, sturgeons evolved initially as rigorously and the results from this phylogenetic
benthic predators, with Husoand the more preda- study contradict them.
ceous species of Acipenserrising subsequently into