RESIDUAL COLOR PATTERNS IN THE ECHINOID HEMIPATAGUS CAROLINENSIS FROM THE NORTH CAROLINA OLIGOCENE

Many specimens of the extinct echinoid Hemipatagus carolinensis from the River Bend Formation (middle and upper Oligocene) found on North Topsail Beach, NC after offshore dredging show evidence of color patterns. 709 specimens are particularly striking, with colors ranging from light purple to deep mauve. Patterns are considered original, with large numbers of specimens displaying markings in identical positions on the tests.

Petaloid ambulacral coloration occurs in two forms. “Lined”, with colored striping of various widths on plates inside the adradiad sutures of petals (leaving the perradiad sutures clear of color), and “Filled”, with petals being entirely color filled, (496 outlined, 213 filled).

Coloration of the upper portion of the test including the non-petaloid ambulacrum (Amb III), the anterior sulcus, and the interambulacral (IA) areas 2 and 3 occurs in three forms. 1) “Shaded”, with the area around the perradiad suture within the sulcus (Amb III) being colored and IA 2 and IA 3 showing color density decreasing from the apex towards the margin with no color loss along latitudinal plate sutures (338 specimens). 2) “Dashed”, with both ambulacral and interambulacral plates showing color but all meridional sutures (interradiad, perradiad and adradiad) fading or lacking color (207 specimens). 3) “Mixed”, which displays a combination of patterns 1 and 2 above (164 specimens).

Specimens with “Lined” ambulacra on the aboral side correlate strongly with adoral patterning showing light coloration on primary tuberculate areas of IA 1-4 and sternal and episternal plates of IA 5, and tuberculate areas of the trivium (Amb II, III, and IV). No coloration on naked areas of ambulacra, or adradiad or interradiad sutures. Color density varies inversely with primary tubercle size. Specimens with “Filled” ambulacra on the aboral side do not show a corresponding pattern on the adoral side.

Specimens with “Filled” ambulacra correlate strongly with “shaded” upper test areas (176 specimens) while “Lined” ambulacra have a mix of upper test coloration, “Dashed” (190 specimens), “Mixed” (144 specimens) and “Shaded”(162 specimens).

Coloration on the rest of the test varies widely. Tests are ongoing to try to determine the nature and timing of the coloration.