MAZON CREEK LAGERSTÄTTE
One of the most remarkable soft-bodied fossil deposits
(lagerstätten) on Earth is the Pennsylvanian-aged Mazon Creek Lagerstätte near
Chicago, Illinois. In the Mazon Creek area, the Francis Creek Shale
consists of concretionary gray shales. The Francis Creek concretions are ironstone,
and can be fossiliferous or unfossiliferous. The fossiliferous
concretions contain land plants and terrestrial & marine animals, including
nonmineralizing organisms.
Stratigraphy: Francis Creek Shale Member, Carbondale Formation, Desmoinesian Stage
(= Westphalian D), upper Middle Pennsylvanian
Essexella asherae Foster, 1979 (above & below) - fossil jellyfish
in concretions (above: concretion is 6.5 cm tall; below:
concretion is 7.1 cm tall) from the Mazon Creek Lagerstätte (Middle
Pennsylvanian) of Illinois, USA. Jellyfish are extremely rare in the fossil
record. This is hardly surprising, considering they completely lack hard
parts, and the tissues they do possess are gelatinous. The most abundant
marine organisms in the Mazon Creek biota are jellyfish. Many Mazon Creek
jellyfish specimens do not have many diagnostic features, and are
affectionately referred to as “blobs” by local fossil collectors (“blob A”,
“blob B”, “blob with character”, etc.). Essexella asherae
jellyfish fossils consist of a bell and a relatively long skirt.
Sometimes, well-defined tentacles extend below the level of the skirt (see
specimen above).
Classification: Animalia, Cnidaria, Scyphozoa, Scyphomedusae
Generously donated by the Geology Department of the
Field Museum of Natural History (Chicago, Illinois, USA).
Ode to a Blob
(Rob Shula, 2002)
Oh, lowly blob,
Whose grave I did not rob.
On the ground you sit
So round and nicely split.
Were you but a few,
I'd bend to pick up you.
But alas, you're not so rare.
And although I wish I'd care,
I left you lying there.
Anthracomedusa turnbulli Johnson & Richardson, 1968 - fossil jellyfish in
concretion from the Mazon Creek Lagerstätte (Middle Pennsylvanian) of Illinois,
USA (FMNH PE 38977, Field Museum of Natural History, Chicago, Illinois,
USA). This is a rare example of a fossil cubozoan jellyfish.
Cubozoans are also called “box jellyfish” for having a subquadrate bell
shape. Some of the most venomous marine animals in modern oceans includes
species of box jellyfish.
This specimen has been compressed perpendicular to the
oral-aboral axis of the jellyfish body. The central structure is the
bell. Anthracomedusa had four tufts of tentacles near the
periphery of the body - those are the irregularly linear structures near the margin
of the concretion.
Classification: Animalia, Cnidaria, Cubozoa, Carybdeida, Carybdeidae
Kallidecthes richardsoni Schram, 1969 - laterally compressed fossil shrimp in
concretion from the Mazon Creek Lagerstätte (Middle Pennsylvanian) of Illinois,
USA (FMNH PE 37598, Field Museum of Natural History, Chicago, Illinois, USA).
Classification: Animalia, Arthropoda, Crustacea, Malacostraca,
Hoplocarida, Aeschronectida
Acanthotelson stimpsoni Meek & Worthen, 1865 - dorso-ventrally compressed
fossil shrimp in concretion from the Mazon Creek Lagerstätte (Middle
Pennsylvanian) of Illinois, USA (FMNH PE 37647, Field Museum of Natural
History, Chicago, Illinois, USA).
Classification: Animalia, Arthropoda, Crustacea, Eumalacostraca,
Syncarida, Acanthotelsonidae
Belotelson magister Packard, 1886 - laterally compressed fossil shrimp in
concretion from the Mazon Creek Lagerstätte (Middle Pennsylvanian) of Illinois,
USA (FMNH PE 45648, Field Museum of Natural History, Chicago, Illinois, USA).
Classification: Animalia, Arthropoda, Crustacea, Eumalacostraca, Belotelsonidea,
Belotelsonidae
Bandringa rayi Zangerl, 1969 - fossil shark in concretion (~10.7 cm
across) from the Mazon Creek Lagerstätte (Middle Pennsylvanian) of Illinois,
USA (FMNH PF 5686, Field Museum of Natural History, Chicago, Illinois,
USA). This is the holotype specimen of a bizarre looking juvenile
shark. It has an extremely elongated snout, well-preserved eyespots, and
a set of very small teeth arranged in a V-pattern (discernible as two light-grayish
lines extending in the 2-o’clock and 3:30 directions from the lower
eyespot). This rare species has been reported from the Mazon Creek
deposit of Illinois and from Cannelton, Pennsylvania, USA.
Classification: Animalia, Chordata, Vertebrata, Chondrichthyes,
Elasmobranchii, Eusealchii, Ctenacanthiformes, Ctenacanthoidea, Bandringidae
Annularia stellata Wood, 1860 - fossil horsetail in concretion from the
Mazon Creek Lagerstätte (Middle Pennsylvanian) of Illinois, USA (FMNH PP 29326,
Field Museum of Natural History, Chicago, Illinois, USA). This is one of
the most common Mazon Creek plant fossils. The horsetails are the sphenophytes,
of which only one genus survives in the Holocene - Equisetum.
Annularia is an easily-recognizable foliage genus of fossil calamitacean
sphenophyte. It consists of a central axis (stem) with whorls of
elongated-spatulate leaves originating from widely-spaced nodes.
Depending on the species, there may be from 5 to 32 leaves per whorl/per
node. The leaf whorls of Annularia were probably not perpendicular
to the upright axis/stem.
Classification: Plantae, Sphenophyta, Equisetales, Calamitaceae
Neuropteris flexuosa Sternberg, 1823 - fossil seed fern from the Mazon
Creek Lagerstätte (Middle Pennsylvanian) of Illinois, USA (FMNH PF 46204, Field
Museum of Natural History, Chicago, Illinois, USA). The seed ferns are not
true ferns. They typically grew into trees (arborescent). Seed
ferns were odd plants that had woody trunks, large fronds bearing fern-like
foliage, and reproduced using seeds (not the spores of true ferns).
Classification: Plantae, Pteridospermophyta, Medullosales