The Cassiduloida: Morphological Evolution, Biogeography, Diversity Dynamics
Cassiduloids are irregular echinoids closely related to sand dollars, living mostly in shallow, tropical waters. Only about 35 species survive today, but their fossil record tells a much richer story, stretching back over 100 million years. I study their anatomy, biodiversity, and evolutionary relationships to understand the processes that have shaped this group since it first appeared in the Cretaceous.
Cassiduloids have long been considered morphologically conservative, changing remarkably little over deep time. But look closer, with the right tools, and that picture starts to unravel. Using microCT scanning, I discovered that bourrelets, the bulged plates around the mouth that expand the surface area used for feeding on sediment, are actually built in two completely different ways: some by depressing existing plates, others by adding new skeletal material. In other words, the same external structure evolved independently, not once, but twice, in separate lineages. This finding also revealed that the genus Eurhodia builds its bourrelets differently than the rest of Cassidulidae, meaning it belongs in its own family entirely, one closely related to the extinct Faujasiidae.
The cassiduloids that survived the Cretaceous-Paleogene extinction didn't just persist. They thrived, rapidly diversifying and spreading from the Tethys Ocean into oceans around the world. I'm now tracing that expansion, piecing together how and why this group conquered such a wide range. I'm also investigating the other side of that story: why their diversity has been steadily declining since the Oligocene.
The Cassiduloida: Natural History of Oligopodia epigonus from N. Sulawesi (von Martens, 1865)
Oligopodia epigonus is the most puzzling living cassiduloid. Its conserved morphology has made it difficult to pin down its phylogenetic placement within the Cassiduloida, and living specimens are notoriously hard to find, so surprisingly little is known about this species.
To improve our understanding of the genus Oligopodia, I'm using high-resolution 3D imaging to study the body morphology of specimens from around the world, alongside fossil species. Beyond describing new species, I hope to explain the genus's remarkably broad geographic distribution.
In collaboration with Prof. Charles Marshall (UC Berkeley) and partners at the University of Manado (Indonesia), I've been studying a living population in North Sulawesi, learning about its burrowing behavior, predatory drill holes, sexual dimorphism, and more. We also hope to generate DNA sequences from this population. It's a unique opportunity not just to learn about living cassiduloids in general, but to finally understand this enigmatic species.