APPENDIX 1.
Detailed description of characters and character states for cladistic analysis herein.
1. Pegma or pegma-like structure.
Description: projection angled inward from near the apex.
States: (0) Absent; (1) Present.
Notes: Pseudomyona and Tuarangia appear to have tooth-like structures projecting from the dorsal margin of their shell plates (Runnegar and Pojeta 1992, fig. 3c). It is unclear to what extent these structures might be homologous to the pegma, and thus these two genera are coded for this character with "?" (unknown state).
2. Development of pegma.
Description: extent of inward projection of pegma or pegma-like structure.
States: (-) Not applicable (for those without pegma); (0) Weak (wide but short extension inward); (1) Moderate (greater extension inward, reflected on internal moulds as a groove); (2) Strong (extensive development inward as a sheet).
3. Divided shell.
Description: univalved or bivalved adult shell, regardless of state of larval shell.
States: (0) Absent (univalved shell); (1) Present (bivalved shell).
4. Degree of coiling.
Description: extent of coiling, whether just in apical region or throughout the shell.
States: (0) Up to one complete coil; (1) One or more coils.
5. Raised sub-apical aperture lip.
Description: raised edge of aperture underneath the apex, allowing part of the aperture to face horizontally.
States: (0) Absent; (1) Present.
6. Internal shell ridges.
Description: comarginal ridges on the inner surface of the shell, reflected in internal moulds.
States: (0) Absent or very faint; (1) Present.
7. Curved ventral margin.
Description: ventral (aperture) margin raised at anterior and posterior ends.
States: (0) Absent (no significant curvature); (1) Present.
8. Univalved or bivalved larval shell.
Description: whether larval shell is split into two or is univalved, regardless of state of adult shell.
States: (0) univalved; (1) bivalved larval shell.
Notes: Watsonella is coded as having a bivalved larval shell, even though there is some doubt as to how widespread such a state is for this genus (see main text).
9. Lateral compression.
Description: shell with much greater height than width.
States: (0) Absent; (1) Present.
10. Ratio of length: height.
Description: whether l:h of shell is less or greater than 1.5.
States: (0) Less than 1.5; (1) 1.5 or greater.
11. Prismatic shell layer.
Description: prismatic microstructure in one of the shell layers. Prismatic shell microstructure consists of "mutually parallel, adjacent polygonal columns that do not strongly interdigitate along their mutual boundaries, and which may be separated by organic matrix" (Carter et al. 1990, p. 654).
States: (0) Absent; (1) Present.
Notes: taxa coded as 1 in this analysis have distinct imprints of prismatic shell microstructure somewhere on the internal moulds. Others are coded as "?" (uncertain) because prismatic shell microstructure is typically in the outer shell layer of molluscs, and consequently many species that have it will not typically show it on internal moulds.
12. Inner laminar layer.
Description: inner shell layer (reflected on most regions of surface of internal mould) is a laminar (layered) form wherein "rods, laths, blades or tablets comprise sheets which are oriented parallel or nearly parallel to the depositional surface" (Carter et al. 1990, p. 611).
States: (0) Absent; (1) Present.
13. Inner calcite layer.
Description: inner shell layer with calcitic mineralogy.
States: (0) Absent; (1) Present.
14. Shell pores.
Description: shell pores, reflected on internal moulds as tubercles.
States: (0) Absent; (1) Present.
15. Lamello-fibrillar (spiny)
Description: presence within shell of layers that consisted of organized fibres where "the horizontal fibers in successive laminae differ in orientation by irregularly varying angles" (Carter et al. 1990, p. 611). This is the "spiny" shell microstructure of Kouchinsky (1999).
States: (0) Absent; (1) Present.
16. Stepwise inner layer.
Description: inner shell layer with unusual laminar shell microstructure named 'stepwise' by Kouchinsky (1999).
States: (0) Absent; (1) Present.
17. Calcitic semi-nacre.
Description: presence in the shell of laminae made up of calcite rhombs that laterally grew together.
States: (0) Absent; (1) Present.
18. Prismatic best preserved near apex.
Description: expression of the most distinct prismatic shell microstructure on the inner surface of the shell (hence reflected on internal moulds) near the apex rather than elsewhere on the surface.
States: (0) Absent; (1) Present.
19. Coiling loss; straight dorsal margin.
Description: whether coiling of the adult shell continues from the initial coiling of the larval shell or whether the coiling is lost, forming a straight dorsal margin instead.
States: (0) Absent (coiled); (1) Present (forming straight margin).
20. Aperture constriction.
Description: lateral constriction (pinching) of shell aperture near sub-apical margin, with a widening of the aperture front and back of it.
States: (0) Absent (1) Present (pinched).
21. Aperture shape.
Description: whether the greatest width of aperture occurs more towards the anterior or posterior end. However, because anterior and posterior are still somewhat speculative with these fossils, this character is defined with respect to the apex.
States: (0) Sub-apical width greatest; (1) Supra-apical width greatest.