Zacanthoides sp
Name: Zacanthoides
n. sp. |
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following comments on this specimen are courtesy of Fred Sundberg and
James Cook: The box shape pygidium with numerous spines is common in the Zacanthoides from the Glossopleura and Ehmaniella Biozone (these may need to be made a different genus). Dr. Sundberg is currently working on Z. sampsoni Resser, 1938, from the Lakeview Limestone of Idaho, Glossopleura Biozone. The species here is similar, but the frontal area does not have the strongly divergent anterior branches of the facial sutures typical of Z. sampsoni or Z. divergens Rasetti (Ehmaniella Biozone). This specimen is also similar to Zacanthoides sexdentatus Rasetti, 1951 (Albertella Biozone), but lacks the well developed pleural and interpleural furrows on the pygidium and has a more rectancular shape pygidium. When comparing with Resser, 1939 on the Spence Shale and its fauna, this specimen looks like Z. serratus Resser, 1939. Also, it has similarities to Zacanthoides spinosus (Walcott, 1884) figured in Palmer, 1954. Palmer discusses the similarity of Z. spinosus to Z. typicalis, but mentions an expanding frontal lobe and a rectangular pygidium. The specimen here does not have a pygidium that is as rectangular. It is also similar to the pygidium of Zacanthoides variacantha, that is reported in the Nevada Test Site, Albertella Zone, Zacanthoidid Zonal. The pygidium of Z.variacantha has one outer long pair of marginal spines, and four pairs of very short marginal spines. The pygidium the Chisholm trilobite has the four pairs of inner spines, but the outer spine pair does not appear to be big/long. So, is this specimen from the Chisholm a new species? Perhaps, but the cranidium is too crushed to distinguish some important features. Dr. Sundberg recommends to perhaps refer the species as Zacanthoides cf. spinosus (Walcott, 1884) until further specimens are recovered. It is also possible it could be Zacanthoides cf. serratus Resser, 1939, although the original photos of this species are poor. With the collection of more specimens (including cranidia and pygidia), the assignment of this species from the Chisholm may be narrowed down. |
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 Name: Zacanthoides sp. Trilobites Order Corynexochida, Family: Zacanthoididae Locality: Pioche, Nevada Stratigraphy: Chisholm Formation, Middle Cambrian Compliments of: G. Ast Collection Comments: Recent finds and sophisticated preparation techniques have established that this species had a number of long axial spines. |
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