This is Mazon Monday post #88. What's your favorite Mazon Creek fossil? Tell us at email:[email protected].
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Hesserella shermani is the earliest known isopod in the fossil record. Isopods are crustaceans, which includes shrimp, crabs, and lobsters. Modern day rolly-pollys are isopods, They have many common names like pill bugs, woodlice, and doodle bugs. They are the only crustaceans that spend their whole life on land.
H. shermani was described in 1970 by Frederick Schram, while he was at the Field Museum. Frederick Schram is an absolute giant in fossil crustaceans having written over 200 papers on the subject. He described many of the newer Mazon Creek shrimp species, including Kallidecthes, Essoidia, and more recently Lobetelson. For more on him, checkout "Dinner With Dr, Frederick Schram". The paper describing Hesserella was simply called "Isopod from the Pennsylvanian of Illinois".
Abstract
Hesslerella shermani is described as the oldest representative of the crustacean superorder Peracarida, order Isopoda, suborder Phreatoicidea. This description is based on a single specimen of exceptional preservation from the Middle Pennsylvanian of Illinois. The existence of isopods in the Pennsylvanian raises some questions concerning peracarid and eumalocostracan evolution.
H. shermani appears in Jack Wittry's "The Mazon Creek Fossil Fauna".
Hesslerella shermani is a member of the Isopods. This present-day group is composed mostly of marine and land dwelling crustaceans (woodlice, pill bugs, etc.) that live as scavengers. H. shermani has a round head with prominent eyes on the side and a single pair of long antennae. The body lacks a carapace, and the legs appear similar in size and structure.
The subgroup to which H. shermani belongs exhibits a Gondwanan distribution today, and dwells in freshwater habi tats. It appears that this animal was a near-shore sea-dweller. Most fossils have come from the marine off-shore area of Pit 11, and when found, preservation is often excellent.
The "Richardson's Guide to the Fossil Fauna of Mazon Creek" by Charles Shabica and Andrew Hay mentions H. shermani in chapter 12, which was written by Frederick R. Schram, W. D. Ian Rolfe, and Andrew A. Hay.
Hesslerella shermani Schram, 1970
Head short, antennules and antennae with long single flagella, body without a carapace covering, eyes sessile on sides of head; thoracic segments with anterior and posterior ridges, thoracic limbs equally developed and composed of one endopodal ramus except for the first limb, which is reduced to a large maxillipede; four anterior abdominal segments with rounded pleural lobes and bladelike pleopods (abdominal limbs), fifth segment large and elongate, sixth segment fused with telson and bearing a pair of biramous uropods.Though not frequently encountered in collections of Mazon Creek fossils, the quality of preservation of this species is usually excellent. The rounded head capsule with its protruding eyes on the side of the head is easily recognized. This is the earliest known isopod crustacean. It is a member of the subgroup of "pill bugs" that was widely spread in Paleozoic seas and is today restricted to habitats in Australia and Tasmania.
Specimens
