This study was to analyze the inquiry characteristics of preservice teachers as they classify trilobites. For the study, 70 preservice teachers attending teacher training university participated. The classification tasks used in the study were 9 photos of trilobite fossils. The preservice teachers' inquiry activity was to classify the evolutionary processes of trilobites after observing trilobite fossils by group and then to construct a phylogenetic tree. The results of the study are as follows. First, preservice teachers observed the external features of the trilobites and constructed systematic classification results based on their observed contents. Second, preservice teachers classified trilobites using various classification criteria. Third, the phylogenetic tree of preservice teachers and the phylogenetic tree of scientists were very similar. The preservice teachers constructed a sphylogenetic tree based on the observation and inference of the change from a simple form to a complex form, which is a general evolution process of the trilobite fossil claimed by scientists. These results suggest that group-based inquiry activities with sufficient time are very effective and that the experience of inquiry activities is very important for preservice teachers.