Sand Dollar

Associated Smithsonian Expert: Kathy Hollis, M.S.

Kathy Hollis with Triceratops obtusus, collected in 1890 by John Bell Hatcher

Courtesy of Adrienne Block

Kathy Hollis is the collections manager in the Smithsonian National Museum of Natural History Department of Paleobiology. As a kid she would give rocks as gifts, assuming everyone thought rocks were as cool as she did. She majored in geology at the College of Wooster in Ohio and went on to finish a master’s in geology at the Ohio State University in 2005. It was at Ohio State that Kathy realized her love for museum collections. She finished a master’s in Museum Studies at the University of Colorado at Boulder in 2008 specializing in collections care and museum-based research. Kathy has been at the Smithsonian since 2010 and helps to care for one of the largest fossil collections in the world. Her work involves getting the information about what organisms lived when and where out of the collection drawers and making it digital, accessible, and searchable online. Kathy brakes for fossil echinoderms.

Meet our associated expert

This image was obtained from the Smithsonian Institution. The image or its contents may be protected by international copyright laws.
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Fossil echinoid (Heterosalenia brocki) from the Jurassic
Photo by Smithsonian Institution, Department of Paleobiology

About Echinoids (Class Echinoidea): Paleobiology

Echinoids show up in the fossil record from the Ordovician (about 450 million years ago), but their fossils are sparse compared to other organisms like bryozoans and crinoids. They may not fossilize well because the skeleton of the first echinoids was made of thin plates loosely held together by soft flesh (in contrast to modern echinoid plates that interlock to make a rigid skeleton). Many modern echinoids live in places with wave action, but the ancient ones probably lived in calm, sheltered waters. Like modern echinoids, some early echinoids had long spines that they could regrow, and tube feet for feeding or locomotion. Their teeth were weaker than modern echinoid teeth, and they may have lived by scavenging food from the ocean bottom. Echinoids diversified during the Triassic and Jurassic, giving rise to the types we see today, including predatory echinoids.

Body plans of types of fossil echinoderms
Photo by Mary Parrish, Department of Paleobiology, Smithsonian Institution

About Echinoderms (Phylum Echinodermata): Body Plan

Echinoderms stand out as the only organisms on Earth with five arms or other elements spaced evenly around a central point. This pentaradial symmetry (penta = “five;” radial = “around a central point") is obvious in some echinoderms, such as sea stars or brittle stars that have five arms. It’s more subtle on others, such as the five rows of tube feet on a sea cucumber or five grooves on a sand dollar. This unusual symmetry of adult echinoderms is not found in juveniles. In fact, echinoderm larvae have two-sided (bilateral) symmetry like humans, and must undergo a metamorphosis to become pentaradial adults. Body plans of animals during their development often say something about their ancestry. The bilateral bodies of developing echinoderms are a reminder that, aside from other back-boned animals (vertebrates), echinoderms may be our closest relatives. Unlike most living echinoderms, many fossil echinoderms did not have pentaradial symmetry.