Color banding in the Triassic terebratulid brachiopod Coenothyris from the Muschelkalk of Central Europe

Abstract

The Triassic terebratulid brachiopod Coenothyris frequently displays preserved color patterns; such patterns have commonly been recorded from Paleozoic terebratulid brachiopods. Despite the frequency with which color patterns are preserved in Coenothyris, there has been no recent investigation of the cause and significance of this phenomenon. Shell material is well-preserved; energy-dispersive spectroscopy and microprobe analysis has been unable to detect compositional differences between colored and noncolored shell. This supports the organic origin of the color patterns as suggested for Devonian terebratulids by Richter (1919); color patterns originate from organic pigment in the primary shell layer.Three subtypes of radial color banding are identified: subtype A with a relatively large number (up to 80) of delicate color bands on each valve; subtype B with fewer and generally wider color bands (less than 20) on each valve of adult specimens; subtype C with faint to fairly wide but very short color bands along the anterior margin (ranging from a few to more than 50 in number). Serial sections prepared from subtypes A and B confirm their congeneric status.As shell form (length/width/thickness ratio) and maximum size varies, color pattern types differ in various stratigraphic horizons and also in isochronous populations from different geographic localities, indicating different facies. However, the variation in color patterns is not due to systematic differences at the species or subspecies level but rather reflects a tendency among Coenothyris vulgaris to respond to different environmental parameters. This variation in color patterns is ecophenotypic.