Modelling enrolment in Cambrian trilobites

Abstract

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.

Predation in the marine fossil record: Studies, data, recognition, environmental factors, and behavior

“…Other enrolled specimens include annelidlike animals from the Cambrian (e.g., Chen and Zhou, 1997;Yang et al, 2014). The best-studied temporal patterns in enrollment (or conglobation) are for trilobites; the percentage of enrolled specimens increased throughout the Paleozoic as trilobite enrollment became more efficient due to skeletal modifications (Esteve et al, 2011(Esteve et al, , 2017. Differentiating environmentally and…”

Evolution of trilobite enrolment during the Great Ordovician Biodiversification Event: insights from kinematic modelling

“…It resembles the spiral enrolment, but differs in the relative position of the anterior part of the pygidium. Recently, Esteve et al (2017) presented two kinematic models of Cambrian taxa with spiral and sphaeroidal enrolment types. The spiral model shows that most of the movement to encapsulate the body is between the cephalon and the first segment (~45°).…”

“…The unrolled spiral type signifies a great novelty in the evolution of trilobites: to enrol a trilobite body with lower angles between adjacent segments is faster and could represent a lower energy expenditure. However, most of the structures seen in N. avus have been reported in Cambrian ptychopariids and Cambrian asaphids (Yuan et al 2014;Esteve et al 2017). On the other hand, although the inverted enrolment type of P. (P.) cambriensis seems to be less efficient than the unrolled spiral type, comparisons with a typical Cambrian trilobite with a similar body pattern suggest a more efficient enrolment.…”

“…Logarithm curve describing the enrolment mechanism of the 3D model created using Neseuretus, unrolled spiral enrolment type (A) and Placoparia, inverted enrolment type (B) and its comparison with kinematics of Cambrian spiral and sphaeroidal models fromEsteve et al (2017) [Colour figure can be viewed at wileyonlinelibrary.com].…”

Protocol for the reconstruction of micromammals from fossils. Two case studies: The skulls of Beremendia fissidens and Dolinasorex glyphodon

“…This has occurred due to the high quantity and variety of applications derived from this type of reconstruction, including the possibility of extracting the fossil data from the rock that contains the fossil, sharing this information, studying the interior cavities, structures and materials of the fossil, characterizing fossils in 3D, retrodeforming fossils that have undergone plastic deformation, digitally reconstructing their palaeobiology, testing the movements and insertions of bones, and performing functional analyses using reverse engineering tools such as finite element analysis or hydrodynamic studies (i.e. [ 1 – 10 ]).…”