This is Mazon Monday post #48. What's your favorite Mazon Creek fossil? Tell us at email:[email protected].
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Kalliidecthes richardsoni was described in 1969 by Frederick Schram. It was named for Eugene Richardson, who was then the Curator of Fossil Invertebrates at the Field Museum of Natural History in Chicago, IL. It's an extinct species of shrimp that lived during the Pennsylvanian Period. Additionally, they are one of the more common species of shrimp found in the Essex biota.
Surprisingly, K. richardsoni did not appear in Creature Corner, but it does have an entry in both "The Mazon Creek Fossil Fauna" by Jack Wittry and the "ESCONI Keys to Mazon Creek Animals". Additionaly, it's mentioned in the "Richardson's Guide to the Fossil Fauna of Mazon Creek".
Along with a good description, there are some very nice drawings in the "ESCONI Keys to Mazon Creek Animals".
The body configuration of this moderate sized filter feeder is interesting In profile, it is heaviest in the center and tapered towards the front and rear. Dorsally, it is a think almost tubular creature with long much-branched antennae.
The carapace is almost triangular, with short rostrum and deep optic notch. The abdomen is almost three times the length of the carapace, and the second segment is the largest, the others grow smaller, with the sixth segment the longest and tapered. Uropods are visibly longer than the spade-like telson. The second of the graceful thoracopods is longest and the others are shorter posteriorly; pleopods are sturdy and bristled. It has the structure of a shrimp that would feed, then sink lightly toward the bottom.K. richardsoni is quite often preserved in a flexed, almost doubled position. The gills on the pleopods of this animal are often well preserved, a great rarity in the fossil record.
Here is the text from "The Mazon Creek Fossil Fauna" by Jack Wittry.
In profile, the body configuration of Kallidecthes richardsoni, a moderate-sized filter-feeder, is interesting. It is heaviest in the center and tapers toward the front and rear. Dorsally, it is a thin, almost tubular creature with long, branched antennae. The carapace is rather triangular, with a short rostrum and deep optic notch. The pleon is nearly three times the length of the carapace, and the second segment is the largest. The other segments are smaller, with the sixth being the longest and tapered. Uropods are visibly longer than the spade-like telson. The second of the graceful thoracopods is longest, and the others are shorter posteriorly. Its pleopods are sturdy and bristled. This shrimp has a body structure which suggests that it would feed in open water, then sink lightly toward the bottom.
K. richardsoni is most often preserved in a flexed to almost i doubled over death pose. Pictured below is an unusual example of what is thought to be the animal preserved in life position. The gills on the pleopods of this specimen are also well-preserved, a great Parity in the fossil record.
The Richardson's guide mentions K. richardsoni in Chapter 12, which is called "Crustacea". That chapter was written by Frederick R. Schram, W. D. Ian Rolfe, and Andrew A. Hay.
Kallidecthes richardsoni Schram, 1969
Figures 12.4, 12.5Shrimplike body; antennule with three flagella: Carapace subtriangular in outline with apex toward antennules, distinct optic notch and compound eye tightly affixed in it; thoracic legs
longer anteriorly than posteriorly; abdomen long (about two-thirds the length of the body), abdominal limbs with tufts of branched gills at their base; tail fan with bladelike uropods and
broad, spatulate telson.This species is the second most numerous crustacean in the Essex biota. It represents an entirely extinct radiation of crustaceans whose closest living relatives today are the mantis
shrimp. Originally, these beasts were thought to have been filter feeders; it is suspected now that they may have been carnivores or scavengers. Some of the somewhat larger specimens of this species, seemingly characterized by a slightly longer and deeper abdomen and a more rectangular carapace, may in fact be a separate species.
Here are a few fossil specimens.
