No abstract

Several thousand disarticulated remains together with a few complete enrolled specimens of the lower Cambrian eodiscoid trilobite Calodiscus lobatus (Hall, 1847) have been collected at two outcrop areas in Sweden. The material reveals new details of morphology and morphogenesis during ontogenetic development. Size-frequency analyses show that the material from the Fånån rivulet in Jämtland, central Sweden, represents a natural population dominated by juveniles, whereas the material from Gislövshammar in Scania, southern Sweden, has been sorted during postmortem transport. Three stages of protaspid development can be traced and defined as well as all subsequent ontogenetic stages for the cephalon, hypostome and pygidium. The early meraspid pygidium has a pronounced larval notch, which persists, though becoming progressively less distinct in later meraspides. The number of axial rings in the transitory pygidium increases throughout meraspid development until a third and final thoracic segment is liberated. During ontogeny the articulating half-rings are strongly developed, and both meraspides and holaspides were capable of full sphaeroidal enrollment and outstretched postures. The hypostome undergoes some dramatic modifications; in M0 the anterior margin is axe-shaped, by M1 the area of attachment greatly decreases and the hypostome becomes more elongated and pear-shaped, before attaining its adult form, which has an overall resemblance to that of polymerid trilobites. During ontogeny, the hypostome changes from a conterminant attachment to a natant condition, thereby mirroring hypostomal evolution within trilobites generally. The morphology, ontogeny, enrollment, hypostomal development and the presence of calcified protaspides suggest polymerid rather than agnostoid affinities of the eodiscoids.

A lower Cambrian eodiscoid trilobite fauna and an associated holmiid trilobite,Holmiasp., are described from a bioclastic limestone at the top of the Torneträsk Formation in the Luobákti section, south of Lake Torneträsk, northern Sweden. Other associated polymerid trilobites includeOrodes?lapponicaandStrenuaeva inflata. The precise age of the trilobite fauna cannot be determined, but its generic composition and stratigraphical position at the top of the lower Cambrian suggest that it was recovered from theOrnamentaspis?linnarssoniAssemblage Zone. Two species of eodiscoids are present:Neocobboldiaaff.dentataandChelediscus acifer. The latter species is known previously from England and southeastern Newfoundland, and provides a novel link between upper lower Cambrian successions in Baltica and Avalonia.

Shallow marine, nearshore strata of earliest Campanian (Gonioteuthis granulataquadrata belemnite Zone) and latest Early Campanian (informal Belemnellocamax mammillatus belemnite zone) age in the Kristianstad Basin, southern Sweden, have yielded isolated leptoceratopsid teeth and vertebrae, representing the first record of horned dinosaurs from Europe. The new leptoceratopsid occurrence may support a European dispersal route for the Leptoceratopsidae, or may represent an entirely endemic population. The presence of leptoceratopsid teeth in shallow marine deposits contradicts previous hypotheses suggesting that basal neoceratopsians mainly preferred arid and ⁄ or semi-arid habitats far from coastal areas.

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.