• journal_title：PALAIOS
• Contributor：JOHN R. GROVES ; MADISON PIKE ; KASEY WESTLEY
• Publisher：SEPM Society for Sedimentary Geology
• Date：2012-10-01
• Format：text/html
• Language：en
• Identifier：10.2110/palo.2012.p12-057r
• journal_abbrev：PALAIOS
• issn：0883-1351
• volume：27
• issue：10
• firstpage：738
• section：Research Articles

Late Paleozoic fusuline foraminifera are thought to have hosted photosymbionts, as do modern larger foraminifera, but the ancient host-symbiont relationship has never been demonstrated conclusively. Among modern larger foraminifera, deeper-dwelling species exhibit large surface-to-volume ratios in order to maximize the amount of sunlight that can be captured for use by photosymbionts. Shallower-dwelling species exhibit smaller surface-to-volume ratios in order to limit incoming sunlight, especially ultraviolet radiation. If modern symbiont-bearing foraminifera are appropriate analogues for fusulines, then deeper-dwelling fusulines ought to exhibit larger surface-to-volume ratios than shallower-dwelling ones. This prediction was tested by analyzing fusuline shells from the Virgilian (Upper Pennsylvanian) Oread, Lecompton and Deer Creek cyclothems in Kansas. Specimens from deeper-water “middle” limestones exhibit significantly larger surface-to-volume ratios than those from regressive “upper” limestones, and specimens with the smallest surface-to-volume ratios occur in shoaling deposits at or near the tops of regressive limestones. Shell shape does not vary predictably with depth of habitat. Rather, changes in surface-to-volume ratio were accomplished mainly by changes in size, with larger shells always characterized by smaller ratios. The observed trend is significantly nonrandom with respect to depth of habitat (p  =  0.012). The trend is not likely the result of hydrodynamic adaptation, postmortem size sorting or size decrease along a bottom oxygen gradient. It most likely reflects geometric optimization for photosymbiosis.