Sphaeroidal enrolment in middle Cambrian solenopleuropsine trilobites






Jorge Esteve, Samuel Zamora & Eladio Liñán [jorgeves@unizar.es], [samuel@unizar.es], [linan@unizar.es] Área y Museo de Paleontología-IUCA, Departamento de Ciencias de la Tierra, Universidad de Zaragoza, E-50009 Zaragoza, Spain; Rodolfo Gozalo [rodolfo.gozalo@uv.es], Departamento de Geología, Universitat de València, C/Dr Moliner 50, E-46100- Burjassot (Valencia), Spain; manuscript received on 15/1/2009; manuscript accepted on 23/9/2009.


Esteve, J., Zamora, S., Gozalo, R. & Liñán, E. 2010: Sphaeroidal enrolment in middle Cambrian solenopleuropsine trilobites. Lethaia, 10.1111/j.1502-3931.2009.00205.x

Fifty specimens belonging to species of Solenopleuropsis and Pardailhania from Spain and France demonstrate sphaeroidal enrolment in Cambrian trilobites for the first time. These solenopleuropsines show novel coaptative structures in different regions of the exoskeleton: in the cephalon there are vincular furrows and notches; in the thorax an articulating facet is developed at the pleural margins, with a ball and socket connection on the adaxial most portion, and an articulating half-ring axially; the pygidium possesses an articulating facet. The interaction of these coaptative structures resulted in a sphaeroidal enrolment that was a progressive act from the first articulation between the occipital ring and the first segment to the pygidial articulating facet. A similar type of sphaeroidal enrolment is observed in the Devonian trilobite Phacops. Both Cambrian and Devonian trilobites developed a vincular furrow in the ventral surface of the cephalon to close their bodies tightly. In both cases, this is probably a convergent adaptation to protect against predators and obrution. Indeed, the enrolled trilobites are very common in obrution deposits restricted to shallow and soft muddy substrates. □Coaptative structures, convergence, Murero Formation, Pardailhania, Solenopleuropsinae, Solenopleuropsis.