A “typical” dwarfed assemblage, the limonitic Pennsylvanian “Dry shale fauna”, was studied. Approximately 4000 specimens were collected in Lyon, Greenwood, and Elk counties, Kansas. The fauna consists of 21 species. The ecology of the Dover shale and Dry shale seas is reconstructed on the basis of lithologic and faunal data. The gray argillaceous muds deposited in such seas contain the limonitic fauna. In Elk County limonitic fossils occur above the coal. Catastrophic death and restricted environment are postulated.
Seven thousand measurements were made on usable fossils. These were then tallied on the Wentworth scale, permitting an effective size-grade analysis. The major grade size was thus determined. Juveniles and adults were distinguished by morphologic criteria, graphic analysis, and the use of the known upper size limit for any given genus or species. The evidence on dwarfism for 15 species is conclusive. For six species, because of small sample or poor preservation, it is inconclusive. Only adult imitoceratids appear to be true dwarfs. All other faunal components consists of immature forms and/or undwarfed adults.
The assemblage is termed a “pebble necrocoenosis” (4–8 mm) indicating that sedimentary processes (sorting) and not biological processes (growth retardation) have led to the observed relative size uniformity.