the sense of Gans 1986) which we hope will provoke (1833) and Fitzinger & Heckel (1836) to subdivide
further basic work on the group. Additional recent the genusAcipenserinto several subgenera, how-
treatment of many of these taxa can be found in ever, were less successful.
Grande & Bemis (1991, 1996a) and Findeis (1997 It was also in the middle of the 19th century that
this volume). the first important fossil acipenseriform, †Chon-
Acipenseriforms are central to historical ideas drosteus, was named by Agassiz (1844) and de-
about theclassification and evolution of fishes. scribed by Egerton (1858). Increasingly synthetic
Sturgeons were often the largest freshwater ani- works on higher relationships of fishes also ap-
mals in a fauna and quite naturally attracted atten- peared, exemplified by Müller (1846), who defined
tion from early naturalists and systematists. Aci- three grades of bony fishes Chondrostei, Holostei
penseriforms also are noteworthy because of their and Telcostei--on the basis of increasing degrees of
unusual mixture of characters, which caused early ossification. In doing this, Müller rejected the clas-
debate about their classification. Two aspects of liv- sical idea that sturgeons are closely related to
ing Acipenseriformes were especially problematic sharks and accepted them as osteichthyans. Sewert-
for early ichthyologists:(1)reduced ossification of zoff (1925, 1926b, 1928) was the only 20th century
the endoskeleton combined with presence of an ex- ichthyologist to seriously consider a closer link be-
tensive dermal skeleton: and (2)the presence of a tween sturgeons and chondrichthyans. Sewertzoff
hyostylic jaw suspension and protrusible palato- (1925) presented his conclusions as a phylogenetic
quadrate recalling the jaws of sharks. The current tree, in which chondrosteans are shown as the sister
conventional view (developed and refined by many group of all other bony fishes, and emphasized the
authors, including Muller 1846, Traquair 1877, presence of a protrusible palatoquadrate in both
Woodward I891, 1895 a,b, Regan 1904, Goodrich elasmobranchs and sturgeons. We now regard pala-
1909,Watson 1925, 1928, Gregory 1933, Berg 1948b, toquadrate protrusion as derived independently
Yakovlev 1977) holds that Acipenseriformes within chondrosteans (see additional discussion in
evolved from a ‘paleonisciform’ ancestor via pae- the final section of this paper). Norris (1925) and
domorphic reduction of the skeleton and special- others noted neuroanatomical similarities between
ization of the feeding system. hut there is much sturgeons and sharks, but these are almost certainly
more to the history of ideas about the systematics of plesiomorphic features (see Northcutt & Bemis
this group. 1993), and few workers ever accepted Sewertzoff’s
Figure 1 highlights contributions to the system- view (see Berg 1948b and Yakovlev 1977 for addi-
atics of Acipenseriformes over the last 250 years. tional history and critique).
From the time of Linnaeus through the early part of Representatives of two of the six extant genera of
the 19th century, descriptions ofmost of thecurrent- Acipenseriformes , Psephurus gladius (Martens
ly recognized species and genera were made, in- 1862) and Pseudoscaphirhynchus fedtschenkoi
cludingAcipenserLinneausaus 1758,PoIyodonLacé- (Kessler 1872) were discovered in the latter part of
pède 1797, and Scaphirhynchus Heckel 1836. the 19th century, but apart from early papers (e.g.,
Throughout this period most workers adhered to Handyside 1875a,b, Ivanzoff 1887), they remained
the classical idea that sturgeons must be closely re- poorly studied for decades. Also in the latter part of
lated to sharks because they appeared to share a the 19th century paleontologists described and in-
largely cartilaginous endoskeleton and similar jaw terpreted fossil taxa relevant to Acipenseriforms.
suspension. An obvious example of this was Wal- Traquair (1877,1887) considered that extant acipen-
baum’s (1792) description ofPolydon spathulaas seriforms were derived from ‘paleoniseiforms’. Tra-
‘Squalus spathula’.By the 1830s, the first serious at- quair’s (1887) ideas were the source for many sub-
tempts to synthesize and revise the systematics of sequent interpretations of acipenseriform evolu-
Acipenseriformes began, including Heckel’s (1836) tion, although we still do not sufficiently under-
definition of Scaphirhynchus as a genus distinct stand ‘paleoniseiforms‘ to allow us to make strong
fromAcipenser.Attempts by Brandt & Ratzeberg phylogenetic hypotheses about relationships within
martin jones
(Martin Jones)
#1