PhD Defense: John Moore

Event Date: 

Friday, December 6, 2013 - 10:00am

Event Location: 

  • Webb Hall 1025

ABSTRACT:
At the dawn of the Phanerozoic, for the first time in the history of  the Earth, the seas teemed with diverse creatures with skeletal hard parts. The remains of these animals are the small shelly fossils--a variety of spines, shells, plates, and tubes that occur in great profusion in some early Cambrian rocks. Certain of these fossils can be recognized as the earliest representative of major groups that still exist today, such as molluscs, sponges, or brachiopods, but many remain enigmatic, often representing long-extinct groups of bizarre appearance. I will briefly present the results of four studies on different groups of small shellies. First, I'll talk about Cambrothyra, an animal with an external armor of many pieces (termed sclerites) preserved as tiny jar-shaped fossils. It appears to be related to the chancelloriids, strange Cambrian animals whose bag-like bodies were covered with rosettes of spines, so that they looked like barrel cacti living on the seafloor, but Cambrothyra differs from chancelloriids in having simple rather than compound sclerites. In the second part, I will focus on the chancelloriids themselves; in particular, I will show that different species can be identified from their isolated spines alone. One of the species I examined is among the oldest well-characterized chancelloriids, and it shows similarities with Cambrothyra and other strange fossils. In the third part, I will discuss two strange fossils (a cap-shaped fossil with a spine on is lower surface and a spine that often bears little barbs) that also appear to be sclerites, but the animals that produced them remain entirely mysterious. Finally, I will discuss the hyoliths, a group of animals with conical calcareous shells; I will describe some beautiful fossils that preserve very fine details, showing that the shell wall was made of  aragonite fibers arranged in a plywood-like structure.

John Moore