Humble origins for a successful strategy: complete enrolment in early Cambrian olenellid trilobites

Abstract

Trilobites are typified by the behavioural and morphological ability to enrol their bodies, most probably as a defence mechanism against adverse environmental conditions or predators. Although most trilobites could enrol at least partially, there is uncertainty about whether olenellids-among the most phylogenetically and stratigraphically basal representatives-could perform this behaviour because of their poorly caudalized trunk and scarcity of coaptative devices. Here, we report complete-but not encapsulating-enrolment for the olenellid genus Mummaspis from the early Cambrian Mural Formation in Alberta, the earliest direct evidence of this strategy in the fossil record of polymerid trilobites. Complete enrolment in olenellids was achieved through a combination of ancestral morphological features, and thus provides new information on the character polarity associated with this key trilobite adaptation.

The fossil record of ecdysis, and trends in the moulting behaviour of trilobites

“…He focuses on three species of Redlichia with inverted elements and describes scenarios for each specimen that require partial enrolment of the specimen during ecdysis. This link between ecdysial moult configurations and enrolment behaviour was in contrast to previous suggestions that Cambrian micropygous trilobites were rigid and unable to enrol (Harrington, 1959;Bergström, 1973), although later studies have shown that at least flexing, if not entire enrolment, was possible in these trilobites (Esteve et al, 2011Ortega-Hernández et al, 2013). McNamara (1986) stresses that inversions in Redlichia were "the exception, rather than the rule" (pg.…”

Trilobites, their traces and associated sedimentary structures as indicators of palaeoenvironment of Cambrian of the Ociesęki Range (Holy Cross Mountains, Poland)

“…Well-pre served trilobites, bur ied in life po si tion in heterolithic muddy-silty-sandy rocks in South China were noted by Degan et al (1995). Com pletely pre served and en rolled trilobites were re corded from the Cam brian of Green land (Geyer and Peel, 2011) and Can ada (Ortega-Hernández et al, 2013). Other oc cur rences of trilobites pre served in situ with their burrows, such as Thalassinoides nets with Asaphus raniceps, are known from car bon ate fa cies of the Swed ish Or do vi cian (Cherns et al, 2006).…”

“…This abil ity was very use ful and ef fec tive as de fence against pred a tors and also stress ful en vi ron ment con di tions. Such be hav ior in trilobites has been doc u mented from the Early Cam brian on wards (Ortega-Hernández et al, 2013 and ref er ences cited there).…”

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

“…, , ; Ortega‐Hernández et al . ; Esteve & Yuan ). Herein, we present two common Ordovician trilobites, Neseuretus Hicks (), and Placoparia Hawle & Corda ().…”

“…Barrande 1852; Verneuil & Barrande 1855;Airaghi 1902). Nevertheless, what has not been evident until quite recently is that the group shows numerous different styles of enrolment that evolved separately in various lineages, independently of the basic body plans that characterize the major taxonomic groups (Esteve et al 2010(Esteve et al , 2012Ortega-Hern andez et al 2013;Esteve & Yuan 2017). Herein, we present two common Ordovician trilobites, Neseuretus Hicks (1875), and Placoparia Hawle & Corda (1847).…”