FIGURE 1. Location of study area in South Dakota. A, paleobiogeographic map of most of North America during the Late Cretaceous (late Campanian) with the locality indicated by a red dot (modified from Sampson et al., 2010, figure 1). B, photo of the locality in Pennington County, South Dakota, USA, where the studied crab specimen was discovered. A massive limestone from the upper Campanian Didymoceras cheyennense ammonite Zone is located at the top of the hill on the right and many limestone pieces are found downslope. See PDF for higher resolution version of this figure.
FIGURE 2. The crab Secretanella sp. (ALMNH:Paleo:6522) from an upper Campanian methane seep limestone in Pennington County, South Dakota. A, carapace in dorsal view. B, closeups of the preserved gills in left branchial chamber. C, carapace in ventral view. D, carapace in frontal view. See PDF for higher resolution version of this figure.
FIGURE 3. Exposed gills of the crab Secretanella sp. (ALMNH:Paleo:6522) from an upper Campanian methane seep limestone in Pennington County, South Dakota and an interpretative drawing. 1-4: inferred number of gills; ?af: possible afferent vessel. See PDF for higher resolution version of this figure.
FIGURE 4. MicroCT (µCT) scan results of the crab Secretanella sp. (ALMNH:Paleo:6522) from an upper Campanian methane seep limestone in Pennington County, South Dakota. The external surface of the crab is translucent to show the position of the preserved internal structures that the scan detected. Blue: cardiac stomach; yellow: esophagus; red: apodemes and mandibles. A, dorsal view. B, frontal view. C, right lateral view. D, closeup of dorsal view. E, closeup of frontal view. F, closeup of right lateral view. G, closeup of left lateral view. See PDF for higher resolution version of this figure.
FIGURE 5. Rotating illustration (spin around the dorsal and ventral sides) of the microCT (µCT) scan results of the crab Secretanella sp. (ALMNH:Paleo:6522) from an upper Campanian methane seep limestone in Pennington County, South Dakota. Blue: cardiac stomach; yellow: esophagus; red: apodemes and mandibles.
