This is Mazon Monday post #89. What's your favorite Mazon Creek fossil? Tell us at email:[email protected].
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Of all the millions (yes, millions!) of Mazon concretions that have opened over the years, only two specimens of Jeletzkya douglassae are known. That might make it the rarest of species in the Mazon Creek biota. It's considered to be a squid. Talk about soft bodied animals... its only hard parts are the radula and the pen. For as rare as it is, it has a Wikipedia page!
It was described in 1968 by Ralph Gordon Johnson and Eugene S. Richardson, Jr. The description appeared in the journal Science "Ten Armed Fossil Cephalopod from the Pennsylvanian of Illinois". Both men are giants in Mazon Creek paleontology. At that time, they worked at the Field Museum in Chicago and fostered relationships with amateur collectors who were all to happy to show them what they had found.
Abstract
Jeletzkya douglassae Johnson and Richardson is described as the oldest known representative of an extant squid group. The species is known from a single specimen from the Middle Pennsylvanian of Illinois. This very unusual fossil consists of the complete tentacular crown and a fragile shell. The arms bear hooks in double rows.
The animal is named for June Douglass, the mother of Dave Douglass who would eventually open "Dave's Down to Earth Rock Shop" in Evanston, IL in 1970. June and her family, husband Lincoln and son Dave, started collecting Mazon Creek fossils in 1958. All three of them have species named for them. Lincoln has Mischoptera douglassi, a winged insect that Eugene Richardson called "one of the most important fossil insects ever found." And, Dave was the namesake for Titanoscorpio douglassi, a 3 inch scorpion claw. When June found the squid fossil in Pit 11, it pushed back the fossil history of squid 100 million years to the Pennsylvanian Period. The original specimen is on display in the basement museum at Dave's.
The other specimen was donated to the Field Museum by amateur collector Dave Young.
J. douglassae appears in "The Mazon Creek Fossil Fauna" by Jack Wittry.
Jeletzkya douglassae is generally considered to be a squid, though it has been argued that it may be a belemnite. Assignment remains problematic. It has ten arms, and an internal shell similar to the gladius (pen) of present-day squid. Made of a chiton-like material, the pen is a feather-shaped internal structure that supports the squid's mantle and serves as a site for muscle attachment. However, the double rows of hooks on each arm may be a feature more similar to belemnites. It has been suggested that the internal shell rep resents a belemnitid prostracum with only the final phragmocone chamber attached. The radular pattern of J. douglassae is the same as modern coleoids, though belemnoid radulae are not known. Single rows of arm hooks occur in modern squid, and it has been thought that perhaps double rows as well as undifferentiated arms are primitive characteristics of these coleoid cephalopods. Fossil ink sacs are are found in the Essex Biota, but are known from both squid and belemnoids.
A rare Mazon Creek cephalopod, J. douglassae was erected based on the two fossils shown below. The first is the holotype, which displays the nine elements of the radula, and ten equal-sized arms, each having two rows of hooks. The second is of an internal shell that is missing part of the apex. This area at the apex is still not well known. The internal shell is decorated with longitudinal parallel lines near the apex.
Specimens
