Ontogeny of a New Species of the Cambrian Series 3 (Middle Cambrian) Trilobite Genus Liostracina Monke, 1903 from North China and the Taxonomic Position of the Superfamily Trinucleoidea

Abstract

The Order Asaphida was grouped by the presence of a ventral median suture and a globular protaspis. The Superfamily Trinucleoidea has been assigned to the Order Asaphida, based on the recognition of a globular protaspis in the Ordovician representatives of the group, and the presence of a ventral median suture in the middle Cambrian genusLiostracinawhich has been regarded as a primitive sister-group to the post-Cambrian trinucleoideans. Recent studies demonstrate that the ventral median suture and the globular protaspis could have evolved multiple times in the trilobite evolutionary history, casting doubt on the traditional concept of the Order Asaphida. Inclusion of the Trinucleoidea into the Order Asaphida, therefore, has to be tested. It has recently been revealed thatLiostracina simesiJago and Cooper, 2005 did not possess a ventral median suture, implying that there could have been variable types of ventral suture within the genusLiostracina. Here we report the ontogeny ofLiostracina tangwangzhaiensisn. sp. from the Cambrian Series 3 (middle Cambrian) strata of Shandong Province of North China. The material for this study includes protaspides, which are of flat, benthic morphology, contrasting to the globular protaspid morphology of the Ordovician trinucleoideans. The benthic protaspid morphology ofL. tangwangzhaiensisindicates an independent evolution of the globular protaspis within the Superfamily Trinucleoidea. Together with the variable types of ventral suture within the genusLiostracina, the benthic protaspid morphology ofLiostracinaleads us to propose that the Superfamily Trinucleoidea be excluded from the Order Asaphida.

Ontogeny of the Furongian (late Cambrian) trilobite Proceratopyge cf. P. Lata Whitehouse from northern Victoria Land, Antarctica, and the evolution of metamorphosis in trilobites

“…In order to test these hypotheses, a cladistic analysis for the Order Asaphida ( sensu Park et al . ) was performed based on the new information on the protaspid morphology. The phylogenetic relationships were analysed using TNT version 1.1 (Goloboff et al .…”

“…Emending the concept of the Order Asaphida, Park et al . () concluded that the Order Asaphida contains five families (Ceratopygidae, Asaphidae, Taihungshaniidae, Nileidae and Cyclopygidae) which can be grouped by the presence of petaloid facet and pre‐occipital tubercle. Although the pre‐occipital tubercle is seen in trilobite groups other than Asaphida, such as the Trinucleaoidea (see Chatterton et al .…”

“…Interestingly, while the Ordovician representatives of Trinucleoidea and Remopleuridioidea had bulbous protaspides which metamorphosed into flat meraspides, the Furongian (late Cambrian) representatives of the two lineages did not undergo metamorphosis at the transition between protaspid/meraspid phases (Park & Choi ; Park et al . ). For the Asaphida, several Ordovician asaphid trilobites are known to have had commutavi protaspides (see Fortey & Chatterton ; Chatterton & Speyer ), but ontogeny of the Cambrian representatives of the Asaphida has not been documented, and thus whether there was metamorphosis at the protaspid/meraspid transition in Cambrian asaphide trilobites has remained unknown.…”

“…In turn, superfamilies Asaphoidea and Cyclopygoidea (Taihungshaniidae + Nileidae + Cyclopygidae) form the current Order Asaphida (see Park & Choi , , ; Park et al . ). Ceratopygidae spans the Cambrian Series 3 to the Furongian, whereas the oldest members of the Asaphidae occur no earlier than the middle Furongian (see the generic list in Jell & Adrain ).…”

“…Subsequently however, following the emendation of the concept of the Order Asaphida, it has been revealed that the bulbous commutavi protaspides independently evolved in Remopleuridioidea, Trinucleoidea, and Asaphida (Park & Choi ; Park et al . ; Park & Kihm ).…”