Contributions to Zoology, 67 (4) 237-256 (1998)G. A. Bishop; R. M. Feldmann; F. Vega: The Dakoticancridae (Decapoda, Brachyura) from the Late Cretaceous of North America and Mexico

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Paleoautecology of Dakoticancer overanus

The morphological characteristics of Dakoticancer overanus including its equant, rectangular shape, long. slender equally-sized legs P2-P4, equant claws held free from the carapace margin with modest-sized, small-toothed downturned fingers, and functional-sized corneas on the eye stalks is consistent with the conclusion that Dakoticancer was a generalized epifaunal crawler that lived on the soft substrates of the mud bottoms of the Western Interior Cretaceous Seaway. Reduction of P5, the hind- most legs may be evidence for a possible carrying and covering behavior exhibited by some modern crabs with reduced hind legs. Dactyli on P2-P4 are elongate and triangular, fully capable of folding over into "snow shoes" for walking across the soft substrate. Of all the observable characteristics, none can be cited which clearly establish the mode of life of this primitive crab.

Dakoticancer overanus is associated with a few concentrically layered straight burrows. Not only are they not abundant enough to have been Dakoticancer domiciles, they are too small. The preservation of burrows (probably assignable to the thalassinoid Protocallianassa cheyennensis) in the Dakoticancer assemblages indicates that if Dakoticancer overanus was a burrow dweller, its burrows would likely be preserved in some abundance. Because they were not, Bishop (1981) concluded that Dakoticancer overanus was not an obligatory burrower.

The consistent association of Dakoticancer overanus with segmented burrows and fecal pellet packed burrow trails led Bishop (1987: 325) to the conclusion that the presence and preservation of Dakoticancer overanus was linked through a positive feedback cycle to population explosions of benthic worm populations. If this conclusion is valid, benthic worms may have been the preferred food item for Dakoticancer overanus; a conclusion further supported by this decapod‘s delicate downturned fingers armed with small teeth that would be useful in capturing and pulling worms from the substrate. As with most crabs, Dakoticancer overanus was not an obligatory feeder, but rather would have been a generalized omnivorous browser capable of rapidly responding to periodically burgeoning food resources.

Lithologic evidence from the bentonitic claystone of the Pierre Shale in which Dakoticancer overanus is preserved, usually in phosphatic concretions distributed through one to three meters of section and the associated fauna including inoceramid bivalves, baculitid cephalopods, often diverse foraminiferal suites (over 100 species at some localities) and mosasaurs all indicate Dakoticancer overanus lived in brackish to fully marine water of the Western Interior Cretaceous Seaway.