Complex axial growth patterns in an early Cambrian trilobite from South Australia

The exceptional fossil record of trilobites provides our best window on developmental processes in early euarthropods, but data on growth dynamics are limited. Here, we analyse post-embryonic axial growth in the Cambrian trilobite Estaingia bilobata from the Emu Bay Shale, South Australia. Using threshold models, we show that abrupt changes in growth trajectories of different body sections occurred in two phases, closely associated with the anamorphic/epimorphic and meraspid/holaspid transitions. These changes are similar to the progression to sexual maturity seen in certain extant euarthropods and suggest that the onset of maturity coincided with the commencement of the holaspid period. We also conduct hypothesis testing to reveal the likely controls of observed axial growth gradients and suggest that size may better explain growth patterns than moult stage. The two phases of allometric change in E. bilobata , as well as probable differing growth regulation in the earliest post-embryonic stages, suggest that observed body segmentation patterns in this trilobite were the result of a complex series of changing growth controls that characterized different ontogenetic intervals. This indicates that trilobite development is more complex than previously thought, even in early members of the clade.

Furongian (upper Cambrian) trilobites and agnostoids from the Alum Shale Formation of Bornholm, Denmark: revised taxonomy and biostratigraphy

The Furongian (upper Cambrian) trilobite-agnostoid fauna from the Alum Shale Formation of Bornholm, Denmark, is reviewed and revised. The study is based on the museum material stored at the Natural History Museum of Denmark, including the material originally monographed by C. Poulsen (1923) [Bornholms Olenuslag og deres fauna. Danmarks Geologiske Undersøgelse II. Række, Vol. 40, 83 pp]. A total of 8502 specimens, mostly disarticulated sclerites, have been registered. The taxonomy of all species is updated and the best preserved specimens are illustrated. A total of 39 olenid and 5 agnostoid taxa (incl. the Miaolingian Agnostus pisiformis) are recorded including one new species, Ctenopyge magna n. sp. Two specimens of Ctenopyge, treated in open nomenclature as Ctenopyge sp. 1 and sp. 2, may also rep-resent new species. 14 taxa have not been previously reported from Bornholm, viz. Ctenopyge ahlbergi, Ctenopyge tumidoides, Eurycare brevicauda, Leptoplastus abnormis, Leptoplastus crassicornis, Olenus transversus, Parabolina lobata praecurrens, Peltura acu-tidens, Peltura minor, Peltura westergaardi, Protopeltura planicauda, Protopeltura praecursor, Pseudagnostus leptoplastorum? and Sphaerophthalmus drytonensis. Ctenopyge pecten and Ctenopyge affinis are also new to Bornholm as the material formerly described under these names represent Ctenopyge tenuis and C. magna n. sp., respectively. Lotagnostus americanus, Ctenopyge fletcheri, Sphaerophthalmus alatus and Triangulopyge humilis were described under different names by C. Poulsen (1923). Peltura westergaardi and Ctenopyge tenuis are elevated from subspecies to species rank. A redescription of Leptoplastus bornholmensis is presented; the species is transferred to Eurycare. The identification of isolated skeletal parts of L. abnormis and Leptoplastus ovatus and Sphaerophthalmus flagellifer and S. drytonensis are remarked on. The presence of three agnostoid and 14 trilobite zones is confirmed by fossils and all six Furongian superzones are developed on Bornholm. At least the Leptoplastus paucisegmentatus and Leptoplastus raphidophorus zones seem to be absent. Other undocumented zones may be unfossiliferous, not exposed or truly absent. Three different trilobite assemblages (potential subzones) are discerned in the Peltura acu-tidens–Ctenopyge tumida Zone; Ctenopyge tumidoides and Sphaerophthalmus angustus range into the basal part of this zone. All exposures of the Furongian Alum Shale Formation along the Læså and Øleå streams on southern Bornholm are briefly described including GPS coordinates.

Absolute axial growth and trunk segmentation in the early Cambrian trilobite Oryctocarella duyunensis

A short stratigraphic interval near Bulin in western Hunan (China) yields multiple specimens of the ~514-Myr-old oryctocarine trilobite Oryctocarella duyunensis. Size data obtained from these specimens indicate that, from meraspid degree 1 onward, degrees represent successive instars. Meraspid growth persisted until a terminal stage was reached, providing the first example of determinate growth in trilobites and, notably, in an early Cambrian species. The sample contains three varieties of such terminal stages, recognized as holaspids, with 9, 10, or 11 thoracic segments, respectively. During the meraspid phase, growth rates were not constant in this species. The pattern of growth seen in the Bulin assemblage differs modestly from that reported in the same species from two other localities, attesting to microevolutionary variation in developmental patterns among these collections.

Ontogeny of the trilobite Redlichia from the lower Cambrian (Series 2, Stage 4) Ramsay Limestone of South Australia

Studies that reveal detailed information about trilobite growth, particularly early developmental stages, are crucial for improving our understanding of the phylogenetic relationships within this iconic group of fossil arthropods. Here we document an essentially complete ontogeny of the trilobite Redlichia cf. versabunda from the Cambrian Series 2 (late Stage 4) Ramsay Limestone of Yorke Peninsula in South Australia, including some of the best-preserved protaspides (the earliest biomineralized trilobite larval stage) known for any Cambrian trilobite. These protaspid stages exhibit similar morphological characteristics to many other taxa within the Suborder Redlichiina, especially to closely related species such as Metaredlichia cylindrica from the early Cambrian period of China. Morphological patterns observed across early developmental stages of different groups within the Order Redlichiida are discussed. Although redlichiine protaspides exhibit similar overall morphologies, certain ontogenetic characters within this suborder have potential phylogenetic signal, with different superfamilies characterized by unique trait combinations in these early growth stages.

Trilobite fauna (Wuliuan Stage, Miaolingian Series, Cambrian) of the lower Lakeview Limestone, Pend Oreille Lake, Idaho

The Lakeview Limestone is one of the westernmost Cambrian exposures in the northwestern United States and occurs on the western edge of the Montania paleotopographic high. These deposits occur between the deeper water deposits to the west and carbonate banks and intracratonic basins to the east and provide critical link between the regions. A re-investigation of the Cambrian trilobite faunas from the lower portion of the Lakeview Limestone, Pend Oreille Lake, Idaho, is undertaken due to the inadequate illustrations and descriptions provided by Resser (1938a). Resser's type specimens and additional material are figured and described. The trilobite assemblages represent the Ptychagnostus praecurrens Zone, Wuliuan Stage, Miaolingian Series and including two new taxa: Itagnostus idahoensis n. sp., and Utia debra n. sp. Because of the similarity between some species of Amecephalus from the Lakeview Limestone to specimens from the Chisholm Shale, Nevada, the type specimens of Amecephalus piochensis (Walcott, 1886) and Am. packi (Resser, 1935), Walcott's and Resser's type specimens are re-illustrate and their taxonomic problems are discussed. Utia curio Walcott, 1924 from the Spence Shale, Utah, have never been re-illustrated since Walcott (1925), these type specimens are also re-illustrated and compared to Utia debra n. sp.UUID: http://zoobank.org/5ef6ee5e-bddc-4395-becf-9bcea54c679c