The partial exoskeleton of a large trilobite
was recovered from an underwater exposure
of the Maquoketa formation of
Green Bay, Wisconsin.
This specimen, probably a species of Isotelus, was found on the shore of Green Bay about three miles south of the Edgewater Beach Road Maquoketa exposure which contains only trace fossils. On different dates, several short sections of a straight cephalopod were found nearby. This is tantalizing evidence that there is a stratum containing well-preserved fossils very close to, or just under, the surface of the bay along the eastern shore. The genal spine of this specimen, along its longest edge, is 4.25 cm.
Edrioaster bigsbyi. Although edrioasteroids appear occasionally in the De Pere quarry, they are usually flattened and in a coarse matrix that disintegrates quickly on exposure. This specimen from the Duck Creek Quarry, however, is fully inflated. In life, it was attached at its base to a piece of bryozoa, to which it adheres yet. An echinoderm, the edrioasteroid is a related to both crinoids and cystoids (diameter: 2.25 cm).
Unidentified nautiloid. While enormous Endoceras straight-cephalopod sections are quite common in the Galena, ranging up to five feet in length (and thus impossible to extract), other genera are scarce. This is the inner mold of a member of a different genus, showing well-defined septa and a central siphuncle. The specimen is attractively imbued with calcite crystals and comes from the lowest level of the Duck Creek Quarry, where fossils are otherwise rare (length: 7.5 cm).
Ceraurus species. Though markedly different from the specimen on the previous page, this Ceraurus comes from the same level in the De Pere quarry. It has a rounder profile and pygidial spines that are less spread apart. In the literature, widely divergent forms are labeled Ceraurus pleurexanthemus, and perhaps that identification is appropriate to both specimens. However, this common Trentonian trilobite comes in several different shapes and sizes, and I hesitate to identify variant forms as one species. On this reverse carapace, the hypostoma is clearly visible (length: 2.5 cm).
This trilobite is included here not because it is very special or rare, or even because I can identify it (I can't), but because it is so small that I am always losing it. In fact, I haven't seen it in months. Somewhere, virtually invisible on one of the slabs in my collection, it languishes unnoticed. This photograph may well become its only proof of existence and chance at virtual redemption (.25 cm, if that). Update: Xavier Riu wrote from Spain to suggest that this specimen might belong to the genus Harpidella.
This Calyptaulax callicephalus was found just after the snow melted in the depths of the De Pere quarry. The species is barely distinguishable from the Calliops shown on the preceding page, but for a bulbous termination of the axial lobe of the pygidium and its narrower, more elongated three-quarter-moon eyes. Even so, terminology in the literature is somewhat interchangeable, both Calyptaulax callicephalus and Calyptaulax (Calliops) appearing to identify a single type. Because there is a difference between this specimen and my Calliops, and it was found in a different matrix/level, I have chosen to identify it, at least temporarily, by these subtle distinctions (2.25 cm).
Dimeropyge species (one of two complete specimens from the De Pere quarry). Note that this trilobite is lodged under a piece of a bryozoan up to, and stopped by, its median spine which stems from the middle of the fifth thoracic segment. Dimeropyge bear a "stout backwardly directed median spine", and on the other specimen (picture pending) it extends well beyond the pygidium. There is a profile drawing (showing the spine) of Dimeropyge in Moore's "Treatise on Invertebrate Paleontology" (page O411) (.7 cm).
Arthropod trackways are common in the Maquoketa exposures north of Green Bay. Here, one or two critters touched bottom briefly (lower center and left), one to dig in for a sharp turn. Extending straight upwards just to the right of the center track is another, but very faint and barely discernible impression of an even smaller creature's progress (track width: 1.25 cm).
Another trackway left by a larger animal making sedate progress along a rippled-marked sea floor across the direction of the water flow. Only one side of the trackway is visible, the other presumably remaining covered by matrix on one of the matching slabs (both positive and negative impressions were recovered) (half-track width: .8 cm).
Coronocystis durandensis. One cystoid is buried under another on this slab which contains three whole specimens, along with partials and detached plates. Identification of this species and the Coronocystis angulatus on the previous page is based on Dennis R. Kolata's Paleontological Society Memoir 7, "Middle Ordovician Echinoderms from Northern Illinois and Southern Wisconsin," a Journal of Paleontology supplement dated May, 1975 (length: 4.75 cm).
Ceraurus pleurexanthemus, tentatively identified by Michael Ryan as to species. This and the following trilobite appear as found, showing nice relief. The pygidial spines are missing from this specimen, but the upper genal spine is a prominent feature, while the lower one is partially missing. The two trilobites were found on adjacent slabs in a stratum at the very top of a newly blasted expansion to the De Pere quarry (length: 2 inches).
Ceraurus pleurexanthemus. This is a complete specimen, though well buried in its matrix. Both genal and pygidial spines appear to be present, but can only just be distinguished under the covering matrix. This may well turn out to be a magnificent trilobite, but, as the surrounding rock is extremely hard, it will not be resurrected easily (length: 2.5 to 3 inches).