First UMMP Blog post - Understanding respiration in fossil and living crinoids.
Welcome to the official blog of the University Of Michigan Museum Of Paleontology! This is where museum folks will post brief descriptions of and updates on their research. I’m James, a second-year Ph.D. candidate, and as a(n incipient) biologist/paleontologist I’m interested in things like functional morphology, biogeography, and inferring the relationships among organisms. The subject of my dissertation is the evolution of crinoids, a group of charismatic marine invertebrates closely related to the perhaps better-known starfish and sea urchins. Crinoids feed by filtering food particles out of the water with their long arms, and the stalkless ones – featherstars – are common on coral reefs in the Caribbean and the Indo-West Pacific. Last summer I participated in a dig in Aragon, Spain, where my collaborators and I discovered some exceptionally-preserved fossils of the Early Cretaceous (about 120 million years ago) featherstar Decameros ricordeanus. I noticed intricate markings on the insides of some of the fossils, and even though I originally went to Spain to study something else (paleoecology), I thought these markings were so interesting that I spent the next few months trying to figure them out. Using CT scanning (made possible by the University of Michigan’s relatively new facility), I visualized the internal anatomy of Decameros, revealing a complex system of canals within the center of the body. After scanning some of Decameros’s living relatives for comparison, I found that these canals (part of the body cavity) are present in modern crinoids, too. In the larger species they can be contorted into complex shapes, although not as complex as what’s seen in Decameros. Since large animals (say, bigger than a few millimeters) tend to have special adaptations for breathing, these structures might be used for flushing oxygen-rich fluid through the center of the body, and the network of internal canals seen in Decameros are probably adaptations for large body size. Decameros was larger than any living featherstar, with arms that might have been up to a meter in length, so maybe it’s not surprising that its respiratory system was more elaborate than those of living crinoids. Something I hope to explore in the future is whether the complexity of these internal canals corresponds to environmental conditions like ambient oxygen supply. We tend to think of information from the fossil record as being degraded relative to what we can learn from living organisms, but I think this research provides a nice example of how fossil organisms, especially those with extreme forms not seen today, can reveal genuinely new biological processes.
Left: the living featherstar Heterometra from the Red Sea. PC: Michael Reich. Top right: Central part of the fossilized skeleton of the Cretaceous featherstar Decameros ricordeanus. Side view (left) and view of the inside (right). PC: Note the impressions of canals on the inside of the skeleton. Bottom right: 3D model of the system of canals within the skeleton of Decameros, generated from a CT scan.