Echinoderms are marine animals. They are recognized by their five-point radial symmetry, and include such well-known animals as starfish, sea urchins, and sand dollars. Echinoderms are very common in North Texas, and we have found three different kinds on our property in Hood Co. First and most common is the Heteraster texanus, that is heart shaped, and has a star shape on the top. Second is the Leptosalenia Mexicana, which is typically smaller and more round in shape. It has a very ornate shell structure with double lines circling the outside of the urchin. And lastly, we have found the Holectypus engerrandi, which is the largest of the specimens, and is round in shape with a beautiful star shape on the top. These echinoderms are index fossils and are commonly found in the Commanche Peak and Walnut formation in Hood Co. which formed about 100 million years ago. See examples of all three below.
In addition, below you will see the Crinoids from Jacksboro, in Jack Co., TX and from Mineral Wells Fossil Park in Palo Pinto Co., TX. Crinoids are also echinoderms and have a five point shape in the middle of their stem. Crinoids were filter feeders, attaching themselves to the sea floor and filtering food as it passed by. Pictured below are parts of the stem that grew in sections, and has the distinct pattern in the center. They were located in the Finis Shale formation of the Pennsylvanian in Jack Co., TX or in the Pennsylvanian in Palo Pinto Co., TX, making them much older than fossils found in Hood Co. These specimens are about 300 million years old.
From Tarrant Co., south of Fort Worth, we are showing a Macraster, a large sea urchin that is heart shaped, but much larger than the Heteraster. It is approximately 3 inches long and 1.5 inches thick.