This is Mazon Monday post #157. What's your favorite Mazon Creek fossil? Tell us at email:[email protected].
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Figure 141.1, Platysomus circularis; modified after Eastman (1903). Scale bar = 10 mm.
The list of truly rare, desirable Mazon Creek animals is long. It includes spiders, scorpions, insects, tetrapods, cephalopods, and fish. Of the fish, one of the holy grail species is Platysomus circularis. Many refer to it as the "panfish" as it resembles some modern day fresh water fish which are known by the same nickname.
P. circularis is a ray-finned fish that lived during the Carboniferous and the Triassic periods. While Platysomus is known from fossil worldwide, P. circularis is only known from Mazon Creek. It was named by John Strong Newberry and Amos Henry Worthen in 1870.
John Newberry (December 22, 1822 – December 7, 1892) was an American physician, geologist and paleontologist. He served as a surgeon and a naturalist for a few exploratory expeditions to explore and survey the western United States. During the Civil War, Newberry was secretary of the western department of the US Sanitary Commission. Later, he was professor of geology and paleontology at the Columbia University School of Mines.
A. H. Worthen was the second state geologist of Illinois and the first curator of the Illinois State Museum. He had an extensive fossil collection, which now resides at the Prairie Research Institute PRI at the University of Illinois.
P. circularis appears on Page 141 of Jack Wittry's "The Fossil Fauna of Mazon Creek".
Platysomus circularis Newberry and Worthen, 1870
This is a relatively small disc-shaped fish approximately 6 cm in size. Platysomus circularis is similar in appearance to the discus fish found in the Amazon basin today. It likely was a slow swimmer inhabiting still and brackish waters, and is thought to have fed on plants or possibly plankton. Platysomus as a group went extinct during the Early Triassic Period.
P. circularis has a laterally compressed body with a rounded outline. The head is deep with a flattened snout. The scales are rectangular, becoming more elongate ventrally and run in vertical rows. They are rare and considered to be one of the most highly prized of all Mazon Creek fish by collectors.
P. circularis is mention on page 236 of the "Richardson's Guide to the Fossil Fauna of Mazon Creek".
Order Bobasatriiformes
Platysomus circularis Newberry and WorthenTwo species of Platysomus, P. circularis and P. lacovianus, have been described from the Mazon Creek fauna. Zidek (1992) places the latter in synonymy. He describes P. circularis as a small species, perhaps not over 6 cm in standard length. Specimens show approximately 40 dorsal fin rays, 30 to 35 anal fin rays, and 28 to 30 caudal fin rays. There are 20 to 22 vertical scale rows between the back of the shoulder girdle and start of the caudal peduncle. Zidek (1992) recognizes nine specimens from the Braidwood and Essex faunas.
Specimens
Field Museum specimen FMNH PF 7333 (from Pit 11)
