This is Mazon Monday post #92. What's your favorite Mazon Creek fossil? Tell us at email:[email protected].
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Illilepas damrowi is a gooseneck barnacle from the Mazon Creek biota, found in Essex localities like Pit 11. Barnacles are crustaceans thus they are related to crabs and lobsters. They are fairly rare in the fossil record with the oldest known from the Middle Cambrian about 510 million years ago. I. damrowi was described by Frederick Schram in 1975. It is named for ESCONI member Dan Damrow, whom you might remember from his Rib River Fossil booth at ESCONI shows for many years. Originally, it was placed under the genus Praelepas, but in 1986 Schram moved it to a new genus named Illilepas.
Schram, F.R. (1975) A Pennsylvanian lepadomorph barnacle from the Mazon Creek area, Illinois. Journal of Paleontology, 49(5), 928–930.
Schram, F.R. (1982) The fossil record and evolution of the Crustacea. In Biology of Crustacea. (Ed. L.G. Abele), 1, 93–147. Academic Press, New York.
Schram, F.R. (1986) Crustacea. Oxford University Press, New York. 606 pp.
I. damrowi appears in Jack Wittry's "The Mazon Creek Fossil Fauna".
Illilepas damrowi Schram, 1975
Barnacles are crustaceans, although they do not appear or behave like other crustaceans. Illilepas damrowi is a member of the Gooseneck Barnacles. In this group, I. damrowi probably started life as a free-swimming larva, then would change its form as it settled and metamorphosed. In the last stage of metamorphosis, it became stationary and a strong, flexible stalk containing a cement gland formed from the head. The animal then attached itself permanently to an object, perhaps a rock or a piece of driftwood. Some I damrowi specimens have been discovered attached to mollusks. (See Associations, page 169.) Modern forms are colonial filter-feeders more often found on exposed intertidal substrates as they depend, unlike most other types of barnacles, on water motion rather than the movement of their cirri for feeding.
Schram first described I. damrowi in 1975 under the genus Praelepas. It was later determined that this was not a good fit and a new genus, Illilepas, was erected.
There is a short paragraph about I. damrowi in the "Richardson's Guide to the Fossil Fauna of Mazon Creek".
Illilepas damrowi (Schram, 1975) Figures 12.42-12.44
Capitulum well developed, scutum large and subrectangular, tergum moderate in size and oval, together covering almost the entire capitulum, capitular margin marked by a row of fine spines and a large platelike spine between the scutum and tergum (originally thought to be a reduced tergum); peduncle well developed and without any armature.
This barnacle species was originally placed in the family Praelepadidae and related to Praelepas jaworskii of the Soviet Carboniferous. Subsequently, the form of the fossil was reevaluated and found to be closer to that seen in the living Iblidae, stalked barnacles of problematic affinities.
Specimens
These two specimens were contributed by Dan Damrow. Thanks, Dan! The first one is from Chowder Flats.
This specimen is from Pit 11. Dan has both halves, only the positive side is shown.
