Archaeocidaris sp.; Delocrinus sp.
Lived around 300 million years ago
Found at the Lake Brownwood spillway, Brown County, Texas
This rare fossil slab is overflowing with sea urchin specimens. Even the spines are preserved, because the mud around them was not disturbed after death. We do not know how these animals died, although it was probably not due to force. Changes in temperature or salinity of the ocean water could have caused their death.
By studying the animals here and how they are grouped together, scientists can learn about all modern day sea urchins. The slab shows that sea urchins were already aggregating, or living in groups, around 300 million years ago. Today sea urchins group together to feed and to breed.
Look closely and you’ll also see a ring shape with flattened plates beside a long, thin stalk. The stalked sea lily Delocrinus was very common during the Paleozoic but now lives only in ocean water more than 100 meters (328 feet) deep.
The sea urchins and sea lily are on permanent exhibit in the Hall of Geology and Paleontology.