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Artist's rendering of Crateraster mccarteri - StarfishCrateraster mccarteri
Starfish

TMM BEG 34041
Cretaceous
Travis County, Texas


These starfish were found in a large block of “float” in Bouldin Creek, here in Travis County. This is one of two pieces that were cut out of the 1200-pound slab. The starfish were first exhibited in 1936, and they have been gems of the Texas Memorial Museum´s collections ever since.

These particular specimens are embedded in a type of rock known as limestone, the “Austin Chalk”. This layer of rock was formed from the settling of fine layers of sediment onto the sea floor during the Late Cretaceous, about 85 million years ago.

Starfish (also know as sea stars) are invertebrates that can be found in oceans all over the world. They live in a wide range of marine environments, from rocky shores to kelp beds, tidal pools to depths of more than 9000 meters. They vary greatly in size and shape. Their size can range from that of a penny to as big as a bathtub. In fact, there are about 1800 different species of starfish alive today, and hundreds more are known from the fossil record.

The body form of a starfish is stellate (star-shaped) with central disc and typically five radiating, symmetrical, arms (rays). The dimension is measured for the center of the central disc to the tip of one of the rays. Did you know that, occasionally, a “five-rayed” starfish is born with only four rays? Variation like this occurs in all natural populations. However, it´s very rare that enough individuals are preserved together for us to see this variation in fossils. Can you find the four-rayed specimen on this slab? At the other end of the spectrum there is a modern species of starfish that has 50 rays. And just to add more confusion, starfish can regenerate severed rays, or intentionally remove rays.

The robust starfish have retained much of their detailed structure on this slab but have lost all their vibrant color. Modern starfish pigments include yellow, red, purple, orange, brown, gray, and blue. Original color is only very rarely preserved in the fossil record.

Modern starfish have diverse eating habits. Some are carnivorous, eating sponges, corals or shellfish, others are scavengers and some are cannibals. Others are deposit feeders extracting their food from the mud, or suspension feeders sifting food from the water column.


 

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