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Fossils of Pseudophlegethontia have been found from the Mazon Creek fossil beds in Grundy County , Illinois , a conservation lagerstätte well known for the exceptional preservation of middle Pennsylvanian taxa .
 Grundy County , Illinois
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: location, person, organization 
Text: {0} 
Answer:
 Grundy County , Illinois