Few workers ever accepted the Aldinger-Nielsen
hypothesis (see Yakovlev 1977 for history and a de-
tailed critique), and it was rendered even more un-
likely by the cladistic definition of Acipenseroidei
(Grande & Bemis 1991).
Several additional extinct genera of Acipenseri-
formes based on relatively complete skeletons were
described in the 20th century, and more are being
found at the time of writing of this paper. New aci-
penseriforms include a Jurassic paddlefish, †Pro-
topsephurusLu 1994; a Cretaceous paddlefish, †Pa-Figure 2.A partial growth series ofScaphirhynchus platorynchus leopsephurusMacAlpin 1941a (also see MacAlpin
larvae showing allometric lengthening of the rostrum. Like other 1941b, 1947); a Cretaceous sturgeon, †Protoscaphir-
living acipenseriforms, growth of the rostral region is positively hynchusWillimovsky 1956; two Jurassic (or earliest
allometric during early life. Scale marks are millimeters. Cretaceous) genera, †Stichopterus Reis 1910 (also
see Yakovlev 1977,1986) and †PeipiaosteusLiu &
the group, Cope (1883) described the first fossil pad- Zhou 1965 (also see Bai 1983, Zhou 1992, Grande &
dlefish, †Crossopholis magnicaudatus, and Wood- Bemis 1996; see Jin 1995 and Jin et al. 1995 for more
ward (1891,1895a,b,c, 1909) reviewed the fossil his- taxa described since this paper was accepted). Most
tory of sturgeons in papers which remain useful to authors of the type descriptions of these fossil taxa
this day. included comparisons with recent acipenseriforms,
With the exception of Berg’s remarkable synthe- but the descriptions of all four genera pre-date the
tic works (e.g., Berg 1940, also see Birstein & Bemis widespread application of cladistics to frame phylo-
1997 this volume), 20th century ichthyologists rare- genetic questions and organize character informa-
ly incorporated paleontological data into their tion. Another problem with some of these papers is
ideas about acipenseriform systematics. Thus, the that reconstruction of the fossils was based on ex-
ichthyological tradition of this century emphasized tant sturgeons and paddlefishes, which makes it dif-
regional faunas and keys for sturgeons and paddlef- ficult to separate observation from interpretation.
ishes, such as for territories of the former Soviet Comments on relationships were provided by Liu
Union (Berg 1911,1933,1948a), the western North & Zhou (1965), Nelson (1969) and Jollie (1980), but
Atlantic (Bigelow & Schroeder 1953, Vladykov & none of these treatments explicitly traced relation-
Greeley 1963), eastern Atlantic and Mediterranean ships of living and fossil forms, nor did they include
(Svetovidov 1984), and European freshwaters synapomorphy schemes. It was not until later, when
(Holcík 1989). Other collected works, such as Bin- Gardiner (1984b) published the first generic level
kowski & Doroshov (1985), Williot (1991), and Ger- cladogram including fossil and recent Acipenseri-
shanovich & Smith (1995) summarized much basic forms, that interest in their phylogenetic interrela-
biological and distribution data, but did not attempt tionships began to grow. Gardiner’s (1984b) analy-
to examine acipenseriform interrelationships. sis was controversial because he suggested that pad-
During the 1930s and 1940s, a period in which di- dlefishes were diphyletic, a conclusion rejected by
phyletic origins were proposed for several groups Grande & Bemis (1991). More recently, Zhou
(e.g., tetrapods; Holmgren 1933, Jarvik 1942), Ald- (1992) provided a different tree, which we criticize
inger (1937) proposed that paddlefishes and stur- in our analysis below.
geons were derived from separate early Mesozoic Molecular and karyological approaches to sys-
ancestors. In a detailed study of a Triassic species of tematics of Acipenseriformes are still at the level of
†Birgeriafrom east Greenland, Nielsen (1949) ex- initial surveys (e.g., Fontana & Colombo 1974, Din-
amined and supported Aldinger’s hypothesis that gerkus & Howell 1976, Birstein & Vasiliev 1987), al-
this genus is closely related to living paddlefishes. though increasingly comprehensive (e.g., Birstein