Outgroup analyzes suggest that gastropods were ancestral among the Tergomya (= multi-worker Monoplacophora) of the Middle or Late Cambrian. I excluded most members of the Bellerophontinae, although some were used as outgroups (see below). Almost all specimens examined fit the diagnoses of previously described species.
In almost planispiral forms, however, there is a carina on the perimeter of the base of the shell. The Early Ordovician species Pararaphistoma qualteriata (Schlotheim, . 1820) is an example of the latter (Fig. 3E). Note that the lower part of the aperture has a steeper slope than the upper part.
However, the elaboration of the characters (together with the use of stratigraphic data as tests of parsimony estimates) should increase the accuracy of the phylogenetic analyses. The growth lines of some species (e.g. Clathrospira subconica (Hall, 1847) (Figure 4C) suggest that the specimens had inconsistent clefts, i.e. the presence or absence of the cleft varied. Knight's definition of the selenizone is also logically complex (since the peripheral bands do not coincide with fissures in either ontogeny or phylogeny).
I also include a numerical ranking of the clades and subclades in Table 3 and in the discussions below.
FAMILY
34;MURCHISON1INAES"
The “Murchisoniinae” contain several important taxa, including the earliest putative theropods and most of the early Paleozoic taxa assigned to the Pleurotomarioidea (Figures 20–35, nodes 109–215). The earliest members of the major subclades all co-occur with H. Isimulatrix, and it was often difficult for me to de-. Seelya ventricosa Ulrich in Ulrich and Scofield, 1897 belongs to the "pletospiroids", but none of the other Ordovician or Silurian species assigned to Seelya Ulrich in Ulrich and Scofield belong to the clade.
Erwin (1992) suggested that the Plethospiridae include the sister taxa of the apo-potamian subulitoids. Accordingly, I call the clade the "straparollinoids," which is appropriate, since species assigned to Straparollina represent some of the least derived members of the clade. Hormotoma confusa Cullison, 1944 is the least derived member of a clade that includes most of the species classified in the Murchisonioidea, Subulitoidea and Loxonematoidea (Figure 8, node 7; Figures 22-26, nodes 119-154).
Many authors have classified the earliest species in this clade in the genus Hormotoma, so I call the clade "hormotomoids". Note that the definition of this clade is much broader than that of Hormotominae sensu Wenz (1938). "Hormotomoids" represent the earliest species in which the left side of the aperture is more prominent than the right, a feature associated with the reduction of the right organs.
One of these (Figure 23, note 126) includes Cyrtostropha coralli (Sowerby i Murchison, 1839) and is diagnosed by a sharp lirum in the middle of the right ramp. 34;GONIOSTROPHINES".—One of the main "cyrtostrophid" subgroups includes species classified in Murchisonia, Hormotoma, Goniostropha Oehlert and Sinuspira Perner (Figure 24, nodes 131-138). This analysis suggests that none of the entries -Caradoc (Middle-Late Ordovician) members of this clade retained Omospira-like morphologies.
The genus Rhabdostropha Donald, 1905 appears to be typical of the group, so I refer to this clade as the "rhabdostrophids" for lack of a more appropriate name. Synapomorphies of the "loxonematids" (Figure 25, nodes 142-145) include the loss of the peripheral band, a thick inductura and a slightly flared opening. Most of the taxa classified in the Pleurotomarioidea by Knight et al. 1960) form a major clade that includes species classified in the Eotomariidae, Gosseletinidae, Lophospiridae, Luciellidae and Phanerotrematidae (Figures 27-35, nodes 155-215).
The second major “eotomarioid” subclade includes the remainder of the taxa previously classified in the Pleurotomario ide (Figures 28–35, nodes 166–215). I label this clade as “liospirinae,” although the clade differs greatly from the definition of Liospirinae sensu Knight et al. The most connate species (i.e., P. mundula clade) have much stronger canals below the peripheral band, a channeled carina at the tip of the right ramp, a left, channeled carina, and a more symmetrical sinus.
Some of the more derived types (node 187) are highly asymmetrical, with a marginal band much closer to the suture and a flared inner margin. These species have strong swellings on either side of the marginal band, flat lunulae, and a gap bordered by a very strong lyre, which is within a much wider marginal band. -derived species of the Crenilunula hallei clade (nodes 200, 201) have a peripheral lyre band developed into a small set.
For example, Oehlertia species possess strong swellings on either side of the peripheral band, which I have coded as unique characters (Appendix 1, character 47). The first members of the clade that I include in this analysis come from the Silurian. The phylogenetic estimates presented herein indicate that none of the early Paleozoic trochoid-like species are derived from cleft species.
34;EUOMPHALINAES"
34;Euomphalinaes"
Bait Bait Bait Laur Laur Laur Laur Laur Laur Laur Laur Laur Laur Laur Laur Laur Laur Laur Laur Gond Laur Laur Laur Laur Laur Laur Laur Laur Laur Laur Laur Laur Laur Laur Laur Laur Laur Laur Laur Gond Gond.
MURCHISONIINAES"
Provincie Laur Laur Laur Laur Laur Laur Laur Laur Laur Laur Laur Bait Laur Laur Laur Gond Laur Laur Laur Laur Laur Laur Laur Laur Laur Laur Laur Laur Gond Gond Gond Laur Gond Laur Gond Gond Laur Gond Gond Laur Gond Gond Gond.
34;MURCHISONIINAES"
A Synopsis of the Classification of the British Palaeozoic Rocks (Sedgwick), with a Systematic Description of the British Palaeozoic Fossils in the Geological Museum of the University of Cambridge (M'Coy).
3BSF
