The Bromide Formation and the Ordovician Echinoderm Explosion
20th January 2008

The Ordovician shallow marine fauna is very well represented in the Upper Ordovician (roughly 450 - 460 ma) Bromide Formation of Oklahoma, USA. This is thought to be the most diverse echinoderm fauna in Earth history. The small collection illustrated here brings together a representative selection. It mostly comes from the Poolville Member of the Bromide Formation exposed in the Dunn Quarry, Criner Hills, Carter County, Oklahoma. Descriptions of this exposure can be found in Sprinkle (1982, ed). The matrix in the exposed succession here consists of alternating light grey to tan biomicrite with shaly micrite in thin beds. Echinoderms occur in thin intervals or biostromes throughout the succession.

The Bromide fauna is highly illustrative of the first major faunal diversity peak of the Palaeozoic (Raup & Sepkowski 1986, Sepkowski 1990), between an earlier Ordovician radiation and the end Ordovician extinction. It is also an excellent example of exceptional preservation of articulated echinoderms and arthropods beneath storm-deposited layers of sediment.

An additional group of Ordovician echinoderms of similar (slightly older) age from the Bobcaygeon Formation of Ontario, Canada is shown.

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A sketch reconstruction including all species represented in this collection.
A sketch reconstruction including all species represented in this collection.
 Myeinocystites natus Strimple. 25 mm carpoid. Poolville Member, Bromide Formation, Dunn Quarry.
Myeinocystites natus Strimple. 25 mm carpoid. Poolville Member, Bromide Formation, Dunn Quarry.
 Anatifopsis papillata, a “tunicate mitrate”. 29 mm long. Poolville Member, Bromide Formation, Dunn Quarry. This small stylophoran comprised about 12% of the fauna at this location.
Anatifopsis papillata, a “tunicate mitrate”. 29 mm long. Poolville Member, Bromide Formation, Dunn Quarry. This small stylophoran comprised about 12% of the fauna at this location.
 Quadrocystis graffhami Sprinkle, 26 mm. Some brachioles are preserved in this specimen. Poolville Member, Bromide Formation, Dunn Quarry.
Quadrocystis graffhami Sprinkle, 26 mm. Some brachioles are preserved in this specimen. Poolville Member, Bromide Formation, Dunn Quarry.
Praepleurocystites watkinsi Strimple. A 75 mm cystoid with Chaulistomella brachiopods. Three pectinirhombs are visible, typical of the Class Rhombifera. Poolville Member, Bromide Formation, Dunn Quarry.
Praepleurocystites watkinsi Strimple. A 75 mm cystoid with Chaulistomella brachiopods. Three pectinirhombs are visible, typical of the Class Rhombifera. Poolville Member, Bromide Formation, Dunn Quarry.
 Praepleurocystites watkinsi Strimple. 68 mm long complete individual showing the full length of the stem.
Praepleurocystites watkinsi Strimple. 68 mm long complete individual showing the full length of the stem.
 Tanaocystis watkinsi Sprinkle, 50 mm. Poolville Member, Bromide Formation, Dunn Quarry.
Tanaocystis watkinsi Sprinkle, 50 mm. Poolville Member, Bromide Formation, Dunn Quarry.
 Pirocystella strimplei (Sprinkle), 50 mm. Mountain Lake Member. Bromide Formation. Johnston County, Oklahoma, USA.
Pirocystella strimplei (Sprinkle), 50 mm. Mountain Lake Member. Bromide Formation. Johnston County, Oklahoma, USA.
Glyptocystella loeblichi (Ulrich), 14 mm. Mountain Lake Member. Bromide Formation. Johnston County, Oklahoma, USA.
Glyptocystella loeblichi (Ulrich), 14 mm. Mountain Lake Member. Bromide Formation. Johnston County, Oklahoma, USA.
 Sinclairocystis praedicta Bassler, two calyces, 16 mm and 10 mm. Mountain Lake Member, the lower unit of the Bromide Formation, Murray County, Oklahoma.
Sinclairocystis praedicta Bassler, two calyces, 16 mm and 10 mm. Mountain Lake Member, the lower unit of the Bromide Formation, Murray County, Oklahoma.
 Globulocystites (Platycystites) levatus (Bassler), 16 mm. Mountain Lake Member. Bromide Formation. Johnston County, Oklahoma, USA.
Globulocystites (Platycystites) levatus (Bassler), 16 mm. Mountain Lake Member. Bromide Formation. Johnston County, Oklahoma, USA.
 Bothriocidaris kolati Kier, 13 mm complete, free of matrix. Poolville Member, Bromide Formation, Dunn Quarry. Two ambulacral zones and two interambulacral zones can be seen.
Bothriocidaris kolati Kier, 13 mm complete, free of matrix. Poolville Member, Bromide Formation, Dunn Quarry. Two ambulacral zones and two interambulacral zones can be seen.
Bromidechinus rimaporus Smith & Savill 2002 (topotype), 35 mm. Poolville Member, Bromide Formation, Dunn Quarry.
Bromidechinus rimaporus Smith & Savill 2002 (topotype), 35 mm. Poolville Member, Bromide Formation, Dunn Quarry.
 Drawing of above Bromidechinus, with interpretation of plates. A curved ambulacral zone (light blue) with central column of perradial plates (lilac) can be seen in the central part of the specimen. Interambulacral plates are coloured green. This specimen is an example of a topotype, which is a specimen collected from the same locality as the Holotype (in this case described by Smith & Savill 2002).
Drawing of above Bromidechinus, with interpretation of plates. A curved ambulacral zone (light blue) with central column of perradial plates (lilac) can be seen in the central part of the specimen. Interambulacral plates are coloured green. This specimen is an example of a topotype, which is a specimen collected from the same locality as the Holotype (in this case described by Smith & Savill 2002).
 Carabocrinus treadwelli Sinclair. 60 mm. Mountain Lake Member, Bromide Formation, Blackriverian, Ordovician, Johnston County, Oklahoma.
Carabocrinus treadwelli Sinclair. 60 mm. Mountain Lake Member, Bromide Formation, Blackriverian, Ordovician, Johnston County, Oklahoma.
 Peltacrinus sculptatus. 30 mm crinoid crown and stem. Poolville Member, Bromide Formation, Dunn Quarry.
Peltacrinus sculptatus. 30 mm crinoid crown and stem. Poolville Member, Bromide Formation, Dunn Quarry.
Hybocrinus nitidus Sinclair 1945. Order HYBOCRINIDA Jaekel 1918. 22 mm crown on matrix. Poolville Member, Bromide Formation, Blackriverian, Ordovician, Dunn Quarry, Criner Hills, Carter County, Oklahoma.
Hybocrinus nitidus Sinclair 1945. Order HYBOCRINIDA Jaekel 1918. 22 mm crown on matrix. Poolville Member, Bromide Formation, Blackriverian, Ordovician, Dunn Quarry, Criner Hills, Carter County, Oklahoma.
 Pararchaeocrinus decoratus Strimple & Watkins and Anthracocrinus primitivuus Strimple (with crown towards bottom of the image). 65 mm. Poolville Member, Bromide Formation, Dunn Quarry. Crinoids at this location occurred in “gardens” about 1 m across and are found articulated at the bases of biomicrite beds.
Pararchaeocrinus decoratus Strimple & Watkins and Anthracocrinus primitivuus Strimple (with crown towards bottom of the image). 65 mm. Poolville Member, Bromide Formation, Dunn Quarry. Crinoids at this location occurred in “gardens” about 1 m across and are found articulated at the bases of biomicrite beds.
 Pararchaeocrinus decoratus Strimple & Watkins, 9 cm. Poolville Member, Bromide Formation, Dunn Quarry.
Pararchaeocrinus decoratus Strimple & Watkins, 9 cm. Poolville Member, Bromide Formation, Dunn Quarry.
 Calceocrinoid, Cremacrinus ramifer Brower, two individuals to about 15 mm. Poolville Member, Bromide Formation, Dunn Quarry. These form part of a group of five individuals associated with a bryozoan colony.
Calceocrinoid, Cremacrinus ramifer Brower, two individuals to about 15 mm. Poolville Member, Bromide Formation, Dunn Quarry. These form part of a group of five individuals associated with a bryozoan colony.
Urasterella sp. 97 mm across. Poolville Member, Bromide Formation, Dunn Quarry.
Urasterella sp. 97 mm across. Poolville Member, Bromide Formation, Dunn Quarry.
 Cyathocystis americanus Bassler, 8mm edrioasteroid. Poolville Member, Bromide Formation, Dunn Quarry.
Cyathocystis americanus Bassler, 8mm edrioasteroid. Poolville Member, Bromide Formation, Dunn Quarry.
 Eoceraurus trapezoidalis Esker, 33 mm excellent enrolled specimen. Poolville Member, Bromide Formation, Dunn Quarry.
Eoceraurus trapezoidalis Esker, 33 mm excellent enrolled specimen. Poolville Member, Bromide Formation, Dunn Quarry.
 “Encrinuroides” capitonis. Complete, outstretched, 13 mm. Poolville Member, Bromide Formation, Dunn Quarry.
“Encrinuroides” capitonis. Complete, outstretched, 13 mm. Poolville Member, Bromide Formation, Dunn Quarry.
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