This is Mazon Monday post #140. What's your favorite Mazon Creek fossil? Tell us at email:[email protected]. Thanks!
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Gilpichthys greenei was a jawless fish. They are fairly rare and associated with the Essex fauna of Pit 11. G. greenei was described in 1977 by David Bardack and Eugene Richardson in the paper "New agnathous fishes from the Pennsylvanian of Illinois" appearing in Fieldiana, Vol. 33, No. 26, publication 1261, pp. 489-510. It was named for Frank Greene long time Mazon Creek collector, who is also the namesake for Reticulomedusa greenei.
G. greenei appears in Jack Wittry's "The Fossil Fauna of Mazon Creek" on page 127.
Gilpichthys greenei Bardack and Richardson, 1977
Gilpichthys greenei is a jawless fish ranging in length from 4 cm to about 14 cm. This elongate fish has a height of 5 to 13 mm. Almost all specimens are laterally preserved in a curved or ventrally concave shape. Scales and fins are absent. Small eyes having a dark outline and a clear center are located behind the mouth area. The muscular buccopharynx (mouth and throat) of G. greenei is a unique structure. Located parallel to and in the lower anterior part of the body, it appears as a long (5-10 mm), narrow dark line. Under magnification, the teeth and muscular tissues of the buccopharynx are visible. Equally unusual is the apparent soft tissue preservation of these fish. Four to six gill pouches are located in a region behind and below the eye. Specimens are known that show a long zigzag-shaped digestive tract; a stained area indicating the heart and liver anterior to the digestive tract; and long, darkly stained lines representing blood vessels and the notochord.
G. greenei was likely a bottom-dweller and may have fed on live invertebrates or detritus. It is uncertain if the fossils are juvenile or adult forms. They are associated with the Essex Fauna. Early literature incorrectly listed them as Nudibranchiata or Sea Slugs.
There is a short passage about in the "Richardson's Guide to the Fossil Fauna of Mazon Creek". It mentions the holotype, which resides at the Field Museum as FMNH PE 18703. That specimen was found in Pit 11.
Gilpichthys greenei Bardack and Richardson
An elongate agnathan with a tubular, muscular buccopharynx (mouth and pharynx) bearing teeth. At least six gill clefts. There are no fins. This is a very abundant form; in excess of 200 are known, ranging from about 4 to 15 cm in length. Originally thought to be molluscan, they were often called "nudibranchs" by collectors in the belief that the buccopharyngeal structure was a radula. Gilpichthys is assigned to the vertebrates because it possesses a notochord, gill slits, a dorsal hollow nerve tube, angular metamerism, and a postanal caudal region. On excellently preserved specimens, the buccopharynx shows a series of about 20 segments of decreasing thickness, some of which support sharp, posteriorly directed fanglike teeth. Assignment to the agnatha is based on the lack of jaws and the simple metameric (body segmentation) pattern (Bardack and Richardson, 1977).Gilpichthys occurs only in the brackish marine phase of the Mazonian delta. No fossils or living forms with the specializations of Gilpichthys are known elsewhere.
Holotype. FMNH PE 18703, Pit 11.
Specimens
