A NEW AND UNUSUAL MIDDLE DEVONIAN ECHINODERM FAUNA FROM THE BOYLE FORMATION IN MADISON COUNTY, KENTUCKY THAT EXTENDS THE RANGE FOR DIPLOPORAN CYSTOIDS

Blastozoan echinoderms are generally minor elements of Middle Devonian faunas. Blastoids are locally common and callocystitid rhombiferans are known from a few scattered localities in North America. However, all other blastozoans were considered to be extinct by the Middle Devonian. A newly discovered blastozoan-dominated fauna from the Middle Devonian Boyle Formation near Waco, Madison County, Kentucky demonstrates that this is not the case. This fauna occurs in a 0.4- 2.0 m-thick, basal succession of echinoderm pack- to grainstones that rests unconformably upon the Silurian Bisher or Estill Formations and grades upward and laterally into typical laminated, fine calcarenites with white chert nodules. The age of the occurrence is constrained biostratigraphically by the presence of Phacops cf. rana and Mucrospirifer in the beds yielding blastozoans. Laterally equivalent, fine calcarenites of the lower Boyle yielded the conodonts Icriodus latericrescens and Polygnathus linguiformis, (D.J. Over, pers. com.), long-ranging, but diagnostic Givetian age taxa. Blastozoans are the most common identifiable megafossils and include blastoids, callocystitid rhombiferans, and dactylocystid diploporans. The blastoid, known from thirteen complete and partial specimens, is a new genus and species of small, obconical, spiraculate. This taxon is distinct in having larger hypodeltoids than regular deltoids and lancet plates that are completely covered by side plates in slightly concave ambulacra. The glyptocystitoid rhombiferan is a small callocystitid known only from a small collection of isolated plates that bear half-rhombs with high vestibule rims. The lack of floor plate scars on these plates suggests that it has short and/or unbranched ambulacra. The diploporan is a large (up to 5 cm), globular, diplopore-covered dactylocystid, known from several nearly complete specimens. It differs from other known taxa by bearing large, fused cover plates over the peristome and an extremely proximal periproct. Dactylocystidae was previously known only from Middle to Upper Ordovician rocks of Europe making this occurrence both a major geographic and temporal (~70 My) range extension for the family. This occurrence also forms a major age-range extension (nearly 30 My) for the entire Class Diploporita.