Ausich et al.—Fort Payne Formation Batocrinidae
the two parent species were well resolved where the hybrid spe- cimens were excluded; whereas if analyses included the hybrids, species separation in multidimensional space became blurred resulting in several “misclassified” specimens. Also, we regard Batocrinus laciniosus Miller and Gurley, 1895a to be more cor- rectly described as Eretmocrinus magnificus×E. spinosus, rather than a separate valid species. Hybridization between two species of the same genus is
relatively common in nature among both plants and animals, including echinoderms (e.g., Swan, 1953; Hyman, 1955; Hinegardner, 1975; Menge, 1986; Kwast et al., 1990; Byrne and Anderson, 1994). Hybridization occurs among a three- species complex in the extant echinoid
Strongylocentrous.Itis reasonable to assume that hybrids occurred during the geological past. In addition to the Eretmocrinus example, Nichols (1959) reported hybrids in the fossil echinoid Micraster. We suggest further, that hybridization in the geological past is a vastly underappreciated phenomenon (see Goodfriend and Gould, 1996).
Genus Macrocrinus Wachsmuth and Springer, 1897 Type species.—Actinocrinus konincki Shumard, 1855.
Other species.—Early Viséan species of Macrocrinus are M. casualis, M. mundulus, and M. strotobasilaris. See Ausich and Kammer (2010) for full list of Macrocrinus species.
Diagnosis.—Calyx shape medium to low cone or low bowl, or rarely slightly expanding with concave sides; basal concavity absent; calyx as high as or higher than tegmen; calyx plates smooth, convex, or nodose with radial plate and first interradial plate commonly nodose; median ray ridges absent; plate sutures commonly distinct; basal plates low or high, may be proximally expanded by nodes; radial plates high; first primibrachial tetra- gonal; rays not lobate; regular interrays not in contact with tegmen; CD interray in contact with tegmen; tegmen flat to low inverted bowl, flat to low cone, or flat to low expanding cone with concave sides; tegmen plates smooth, convex, nodose, or spinose; anal tube cylindrical, may be curved or otherwise asymmetrical; arm facets face outward (subvertical); free arms 12–20, unbranched, rarely spatulate distally (from Ausich and Kammer, 2010).
Occurrence.—Macrocrinus occurs in the Tournaisian to early Viséan (Kinderhookian to late Osagean) of North America.
Remarks.—Species characters in Macrocrinus are calyx shape, height of calyx relative to the height of the tegmen, relative height of basal circlet, tegmen shape, anal tube plate sculpturing, relative sizes of anal tube plates, and orientation of arm facets.
Macrocrinus casualis (Miller and Gurley, 1895a) Figure 9.5, 9.6
1895a Batocrinus casualis Miller and Gurley, p. 15, pl. 1, fig. 17.
1896c Batocrinus rudis Miller and Gurley, p. 52, pl. 4, fig. 4.
701
Figure 9. Species of Macrocrinus from the Fort Payne Formation. (1, 2) Macrocrinus mundulus; E-ray lateral view and oral views of theca, respectively (USNM 639939). (3, 4) Macrocrinus strotobasilaris; lateral view and oral views of thecae, respectively (USNM 639940). (5, 6) Macrocrinus casualis; oral and lateral views of theca in matrix, respectively (USNM 639933). (7) Macrocrinus casualis with anal tube preserved (USNM 639935a). Scale bar same for all.
2013 Macrocrinus casualis (Miller and Gurley); Webster and Webster, p. 1782.
2013 Macrocrinus rudis (Miller and Gurley); Webster and Webster, p. 1785.
Complete synonymy list in Supplemental Data 2. Holotype.—FMNH UC 6498.
Diagnosis.—Calyx low to medium cone, higher than tegmen; basals high; tegmen shape low inverted cone with few large plates with large nodes; arm facets subvertical.
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