Echinoids (Urchins) from the Permian Fort Apache Limestone East of Payson Fort Apache Limestone

Updated  9/21/17

 The Fort Apache Limestone contains at least two species of Urchins, a smooth spined and one with barbs. After clams, this is the most common element found in our acid fines, made by dissolving the limestone directly in 5-10% muriatic. Many of the silicified remains are highly crystallized and have lost much of their original detail. Here, we are displaying the best of the lot - hand picked under a microscope with tweezers out of the acid fines and separated according to type.

Every invertebrate is tiny in the Fort Apache Limestone. Permian in age, it represented a brief incursion of the sea onto the Schnebly Hill formation dunes forming a 50 foot thick sequence at our fossil locality along the Highland Trail. I will repeat here what we have said before - Fossils are so very rare in this formation, that any fossils at all are a rare glimpse into this enigmatic brief period of time.

 Spine plates from the body (test) of small urchins. The millimeter scale at the bottom shows the range in sizes we encountered. The test would have been roughly 1 - 2 inches in size.
 Close up of one of the better preserved specimens. The round mound in the center is what a spine rests on and pivots around to move the animal along.
 Two different spine types here. On the left and along the bottom is the smooth spined type, which is a very generic appearance for a spine. The larger spines with smaller points along their length were identified by Winters in 1963 as Echinocrinus trudifer.
 Close up of spiny spines using a 5 layer focus stack method.
 Close up of smooth spine.
 This seems to be a very small spine type, we found a few of these in nearly 200 pounds of limestone fines. Most seem to be very tiny, and this would have been a marble sized echinoid.
 Smooth spine types of unknown echinoid.
 Small plates around the periproct (top) of the urchin, appear to be genital plates with the hole being the gonopore. We found all of this set in the first round of limestones, and never after that.

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