This is Mazon Monday post #143. What's your favorite Mazon Creek fossil? Tell us at email:[email protected]. Thanks!
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Mamayocaris jaskoskii, sometimes referred to as the "Lobster", was described in 1974 by Frederick Schram in the paper "The Mazon Creek Caridoid Crustacea", which appeared in Fieldiana, Volume 30, No. 2. It was named in honor of Professor B. J. Jaskoski of Loyola University of Chicago.
M. jaskoskii appears on page 86 of Jack Wittry's "The Fossil Fauna of Mazon Creek".
Mamayocaris jaskoskii Schram, 1974a
Mamayocaris jaskoskii is a moderate-sized crayfish-like ani- mal, probably a scavenger or low-level carnivore, and is a member of the marine off-shore Essex community. Characteristics include a smooth carapace, half the length of the animal; a small pointed rostrum; strong walking legs; a sturdy, broad abdomen lacking appendages; and an elaborate tail fan containing well-developed units. Most specimens are well-preserved with ventral or dorsal surfaces exposed upon splitting the concretion. The animal strongly resembles a small lobster.
Another caridoid, Anthracaris gracilis, an inhabitant of the Braidwood Fauna, and M. jaskoskii bear a strong resemblance to each other and were contemporaries, yet A. gracilis is virtually unknown in Essex concretions.
Chapter 12 of the "Richardson's Guide to the Fossil Fauna of Mazon Creek" is entitled "Crustacea" and was written by Frederick Schram, W.D. Ian Rolfe, and Andrew Hay. M. jaskoskii appears on page 161.
Figure 12.19. Mamayocaris jaskoskii, modified from Schram (1974). Scale bar = 5 mm.
Mamayocaris jaskoskii Schram, 1974a Figures 12.18, 12.19
Carapace with well-developed branchial region covering the gills, anterolateral spines short and followed by a row of five marginal ser- rations, gastric spines present cervical groove posteriorly directed; tailfan with well-developed flaplike uropods, exopodal ramus with two seg- ments and the joint between the two (diaresis) s-shaped; telson subtriangular in outline, bearing small lobate caudal furca and an accessory projection of the telson over the lobate caudal spine.
These crayfishlike mysidaceans are rarely en- countered and occur only in the Essex fauna. However, because they were bottom-dwelling scavengers with a cuticle that was originally well sclerotized, they are typically well preserved.
Specimens
From "The Fossil Fauna of Mazon Creek".
The holotype from the original paper
