This is Mazon Monday post #291.  What’s your favorite Mazon Creek fossil?  Tell us at email:esconi.info@gmail.com.

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Dithyrocaris sp. is a genus of crustacean from the Carboniferous. The Mazon Creek fossil biota includes one undescribed species, although there are other described species from other fossil localities – Bear Gulch, Montana (Dithyrocaris rolfei). Danville, IL (Dithyrocaris carbonarius), Cane Hill, Arkansas (Dithyrocaris quinni), the Allegheny Group, Ohio, and localities in Europe.

Dithyrocaris belongs to Subclass Phyllocarida. Phyllocarids are known from the Cambrian until present time. Leptostraca is the only extant order.

Phyllocarida was established by Alpheus Spring Packard (1839 – 1905) in 1879. Packard was an American entomologist and paleontologist. He is remembered most for his distinguished work on butterflies and moths. He did work on crustaceans, describing the Mazon Creek shrimp Belotelson magister.

W.D. Ian Rolfe the namesake for Dithyrocaris rolfei, wrote the crustacean chapter (12) of the “Richardson’s Guide to the Fossil Fauna of Mazon Creek” with Frederick R. Schram and Andy Hay. The following text appears on pages 165 and 166.

Class Phyllopoda

Carapace, if present, generally covering most of body; thoracic limbs thin and leaflike; abdo-men often lacking limbs in whole or in part.

Subclass Phyllocarida

Thorax with eight segments, abdomen with seven segments plus a telson.

Dithyrocaris new species
Rolfe and Richardson MS
Figures 12.30-12.32

Carapace shield-like with narrow median plate and rostral plate; posterior margin sinuous; mesolateral carina gently arcuate, terminating in a large posteroventral spine; dorsolateral carinae flanking median plate diverge posteriorly in adults; doublure very broad; surface with cusp-like ornamentation; last abdominal segment somewhat longer than those anterior, abdominal segments with a chevronlike ornament on surface; telson and caudal rami subequal and marked by chevronlike ornament seen on abdominal segments. Carapace lengths vary from 5 to 40 mm with a mean of 20 mm. Dithyrocaris from other localities are generally fully marine. This is a form characteristic of the Essex fauna.

A rare fossil, Rolfe only saw 34 specimens in his survey of collections in 1981 and felt that there were probably no more than 50 in all collections. In life this animal was probably convexly arched; and fossils are often preserved with the marginal doublure of the carapace displaced laterally. The creature was most likely benthic. No limbs have been preserved on the specimens at hand, which might suggest that they were poorly sclerotized in life if not rather thin and delicate. Individual carapaces of this animal can be preserved showing either the outer or inner surface.

Jack Witty wrote of Dithyrocaris on page 89 of “The Fossil Fauna of Mazon Creek”.

Dithyrocaris sp.

This animal is a rare Essex crustacean. Its carapace is shield-like, most likely convexly arched in life, up to 50 mm in length, with the rear margin terminating in a large spine. Inner and outer surfaces can be studied on the individual carapaces found preserved. Limbs on fossil specimens are not known. The pleomeres (abdominal segments) are decorated with a chevron-like surface. Dithyrocaris sp. is considered to be a bottom-dweller.

Despite being one of the best-preserved phyllocarids in the fossil record, this form was never formally given a specific name. Most of the early research was done by Dr. W. D. Ian Rolfe, and a name was chosen, but the paper was never completed and the attempt was abandoned. All of his research material has been passed on to Professor Patrick R. Racheboeuf. The effort to fully describe Dithyrocaris sp. continues. Hopefully, this animal will get its planned name which honors a researcher whose work is cited throughout this book and who is one of the most prolific contributors to the knowledge of Mazon Creek animals.

Specimens

From “The Fossil Fauna of Mazon Creek”