Data from: Modelling enrolment in Cambrian trilobites

Trilobites were capable of enroling in different ways based on the
flexible articulation of thoracic segments and associated interlocking
devices; the type of enrolment (spiral or sphaeroidal) is thought to have
largely depended on the coaptative devices that each trilobite used to
enclose the body. Based on X-ray microtomography scans of complete
enrolled specimens from the Cambrian, we created three-dimensional (3D)
computer models to assess the kinematics needed to achieve both enrolment
types. We demonstrate that closely related trilobites with little
morphological variation (Bailiaspis?, Conocoryphe and Parabailiella)
developed different enrolment types as a result of small variations in the
number of thoracic segments and the angle between adjacent segments.
Moreover, our models indicate that sphaeroidal enrolment, which is
associated with a smaller number of thoracic segments, enabled faster
encapsulation. This supports the hypothesis that there was a trend in the
evolution of trilobites towards reduction in the number of thoracic
segments in phylogenetically derived taxa in order to enhance the
efficiency of enrolment.