Moulting, ontogeny and sexual dimorphism in the Cambrian ptychopariid trilobite Strenuaeva inflata from the northern Swedish Caledonides

Abstract

Three thousand seven hundred disarticulated remains together with several articulated specimens of the Cambrian Series 2 ptychopariid trilobite Strenuaeva inflata Ahlberg and Bergström, 1978 have been collected from the Torneträsk area, northern Sweden. The material provides significant new data on the morphology, ontogeny, moulting and enrolment of the species. Two distinct morphotypes, possibly an expression of sexual dimorphism, are recognized. The morph with a pair of bulbs in the frontal area, interpreted as brood pouches, is considered to represent females. Statistical treatment of the length ⁄ width ratio in cranidia reveals isometric growth during ontogeny for both morphotypes. The transition from the meraspid to holaspid ontogenetic period has been established through recognition of the successive development of the number of thoracic segments in articulated late meraspides. Throughout its life cycle, S. inflata went through 11 meraspid degrees and at least 17 holaspid growth stages. Inferred moult ensembles and exuviae reveal the successive opening of cephalic sutures and the function of the rostral plate during exuviation. As in other ellipsocephalid trilobites in which enrolment is known, the pygidium and two or three thoracic segments of S. inflata are concealed beneath the cephalon (spiral enrolment) during complete enrolment.

Cambrian microfossils from the Tethyan Himalaya

“…The overall form of this small, evidently early meraspid cranidium is broadly similar to that seen among "ptychopariid" trilobites (e.g. Chatterton, 2005a, 2005b;Cederström et al, 2011;Laibl, Fatka, Cronier, and Budil, 2014) in that the glabella expands anteriorly, the glabella lacks axial carination, and the occipital lobe is inflated. Notable differences are the wide anterior border and the stubby spines on the posterior border neither of which are typical for a ptychoparioid meraspid, and look more like the form seen in the protolenid Ichangia inchangensis (see Zhang and Pratt, 1999).…”

The ontogeny ofEllipsocephalus(Trilobita) and systematic position of Ellipsocephalidae

“…ALCHERINGA TRILOBITE ONTOGENY 7 described by Cederström et al (2011Cederström et al ( , 2012. Rushton (1966) illustrated cranidia of early ontogenetic stages of Ellipsostrenua from England, and Suvorova (1956) described numerous meraspides belonging to the protolenids Lermontovia, Bergeroniellus and Bergeroniaspis from Siberia.…”

“…However, the systematic position of this family remains a subject of discussion. Ellipsocephalidae, together with several other families of the superfamily Ellipsocephaloidea, have been considered representatives of the order Redlichiida Richter, 1932(e.g., Geyer 1990, Geyer & Landing 2001, Dies Álvarez et al 2013, Żylińska 2013a or Ptychopariida Swinnerton, 1915(e.g., Ahlberg & Bergström 1978, Fortey 1990, Cederström et al 2011. Ellipsocephalus Zenker, 1833 is a frequently studied taxon of the family.…”

Morphology, ontogeny and distribution of the Cambrian Series 2 ellipsocephalid trilobiteStrenuaeva spinosafrom Scandinavia

“…1, area 1), northern Lapland (Føyn 1967;Ahlberg 1980;Thelander 1982;Axheimer et al 2007;Cederström et al 2011b); (2) the Laisvall mining district (Fig. 1, area 2), central Lapland (Kautsky 1945;Willdén 1980;Kulling 1982;Ahlberg 1984a;Vidal & Moczydłowska 1996;Moczydłowska et al 2001) and (3) the Lake Storuman area (Fig.…”

“…Moczydłowska et al 2001;Ebbestad et al 2003;Axheimer et al 2007;Cederström et al 2009Cederström et al , 2011b. The trilobite faunas include olenelline (holmiid) and ptychopariid (ellipsocephalid) trilobites, together with a few eodiscoids (Moberg 1908;Kiaer 1917;Ahlberg 1980Ahlberg , 1984aAhlberg , 1984bAhlberg & Bergström 1983;Axheimer et al 2007;Cederström et al 2009Cederström et al , 2011b.…”