Trilobites

Se estudia un nuevo yacimiento de la base de la Formación Oville (Cámbrico medio) localizado en el núcleo de la ventana tectónica del
Cueto Negro (Asturias, en la Zona Cantábrica). En este yacimiento se han identificado seis especies de trilobites, una de las cuales es
nueva para la ciencia: Badulesia cautumensis. La edad del yacimiento es Caesaraugustiense inferior (equivalente a la parte alta del piso
5 del Cámbrico) y, probablemente, pertenece a la parte alta de la zona de Badulesia tenera.

Traditionally, the evolutionary scenarios of Asteropyginae have been organized in two major clades involving four pygidial
patterns. The first cladistic analysis performed on the subfamily maintained the organization in two clades, though the
phylogenetic relationships between genera were unexpected compared to the traditional scenarios. Moreover, the previous
systematic scheme based on pygidial segmentation was rendered obsolete. In this study, we performed a new phylogenetic
analysis from well-known taxa and recent discoveries. Sixty species assigned to 36 genera have been analysed from a
dataset of 72 characters. Three more species are used as the outgroup. The 79 most parsimonious trees have a length of
492 steps and a retention index of 0.735. Our analysis confirms the monophyly of Asteropyginae excluding the genus
Protacanthina. The phylogenetic pattern is unconventional in that a largely pectinate topology is resolved, rather than two
clades corresponding to formerly delimited pygidial morphs. Nevertheless, most relationships between genera suggested in
the traditional evolutionary scenarios of the subfamily have been recovered, the main differences being the origin of the
group. Whereas Treveropyge was usually considered as the origin of the remaining Asteropyginae, the present results instead
identify Destombesina as the sister group to all remaining members of the subfamily. From the new phylogenetic pattern,
the diagnoses of genera are rewritten in a standard way and to delimit clades more accurately. This work implies modified
generic assignments for some species and the erection of four new genera: Minicryphaeus gen. nov., Gandlops gen. nov.,
Morzadecops gen. nov. and Pennarbedops gen. nov. The systematic position of Erbenochile is also discussed, the genus no
longer being assigned to Asteropyginae.

Documentation of non-or weakly biomineralizing animals that lived during the Furongian is essential for a comprehensive understanding of the diversification dynamics of metazoans during the early Palaeozoic. However, the fossil record of 'soft'-bodied metazoans is particularly scarce for this critical time interval, consisting of rare fossils found at a dozen or so localities worldwide. Here we report new occurrences of exceptional preservation in Furongian (Jiangshanian) strata of the McKay Group near Cranbrook, British Columbia, Canada. This locality had already yielded trilobites with phosphatised guts, with all specimens representing the same species and occurring within a 10-m-thick interval. Two stratigraphically higher horizons with soft-tissue preservation are reported herein; one has yielded a ctenophore and an aglaspidid arthropod, the other a trilobite with a phosphatised gut belonging to a different species than the previously described specimens. The ctenophore represents the first Furongian record of the phylum and the first reported occurrence of Burgess Shale-type preservation in the upper Cambrian of Laurentia. The aglaspidid belongs to a new species of Glypharthrus, and is atypical in having twelve trunk tergites and an anteriorly narrow 'tailspine'. These features suggest that the tailspine of aglaspidids evolved from the fusion of a twelfth trunk segment with the telson. They also confirm the vicissicaudatan affinities of these extinct arthropods. Compositional analyses suggest that aglaspidid cuticle was essentially organic with a thin biomineralised (apatitic) outer layer. The trilobite reveals previously unknown gut features, such as medial fusion of digestive glands, possibly related to enhanced capabilities for digestion , storage, or the assimilation of food. The new fossils demonstrate that conditions conducive to soft-tissue preservation repeatedly developed in the outer shelf environment represented by the Furongian strata near Cranbrook. Future exploration of the c. 600-m-thick, mudstone-dominated upper part of the section may result in more abundant discoveries of exceptional fossils.

The monophyly of the order Proetida, the only trilobite group to survive the end- Devonian mass extinction, has been regularly questioned since its erection almost three decades ago. Through analysis of a novel phylogenetic dataset comprising 114 characters coded for 55 taxa, including both traditional members of the Proetida along with a number of other trilobite groups, the monophyly of proetide trilobites is rigorously tested for the first time. Proetida is shown to be monophyletic, united by the initial compound eye formation in early protaspids occurring at the lateral margin rather than the anterior margin, and the form of the protaspid glabella being tapering with a preglabellar field. A number of adult characters, including the possession of a quadrate or shield-shaped hypostome with angular posterior margins, the hypostome median body being divided by a deep groove that entirely traverses the median body, the presence of an enlarged thoracic spine on the sixth tergite, and a tergite count of between 7 and 10, also define the basal node. Hystricurid and dimeropygid trilobites are shown to resolve at the base of the group, while the remaining proetide taxa are divided between large proetoid and aulacopleuroid clades. Some taxa previously allied with Aulacopleuroidea, such as rorringtoniids and scharyiids, are retrieved as basal members of the Proetoidea.

The palaeontological species concept – a rather subjective concept – is based on morpho- logical criteria and carries a notion of time. The delimitation of a species among trilobites does not break this rule and is based on morphological and ontogenetic features. Thus, among phacopid trilobites, characters such as the visual complex and the vincular furrow are diagnostic. Furthermore, quantitative studies of the morphological disparity and onto- genetic trajectories allow us better to define the species and its variability, and to identify the evolutionary patterns established in Phacopidae during 100 Ma of existence.

Silurian (Llandovery-Ludlow) Encrinurinae from Wisconsin, Indiana, and Illinois include species of Balizoma Holloway, 1980, Curiella Lamont, 1978, Distyrax Lane, 1988, Encrinurus Emmrich, 1844, Mackenziurus Edgecombe and Chatterton, 1990a, and Nucleurus Ramsköld, 1986. Mackenziurus lauriae n. sp. is described from Wenlock strata of the Racine and Sugar Run Dolomites; nine segments in the holaspid thorax are the fewest known for any encrinurid. A square rostral plate is diagnostic of Mackenziurus. New morphological data are provided by Illinois specimens of Balizoma indianensis (Kindle and Breger, 1904) from the Wenlock-Ludlow Racine Dolomite, and of Curiella tuberculifrons (Weller, 1907) from the Llandovery Elwood-Wilhelmi Formations. Nucleurus n. sp. is possibly from Llandovery strata of Wisconsin. Distyrax n. sp. occurs in the Brandon Bridge Member (late Llandovery-early Wenlock) of the Joliet Dolomite in Illinois. The type pygidia and possible topotype material of Encrinurus nereus Hall, 1867, confirm assignment to that genus as currently viewed; this reefal species is distinct from the closely related inter-reef species E. egani Miller, 1880, and appears to be distinct from reefal E. reflexus Raymond, 1916. Lectotypes are selected for those Encrinurus species.

Recent investigation of the historical Mont d’Haurs section near Givet yielded
numerous trilobites from Middle Devonian carbonate deposits. The trilobite fauna described in the
present paper comprises a number of taxa from the basal Givetian, including two new ones:
Dechenella givetensis sp. n.; Dechenella calxensis sp. n.; Dechenella ziegleri Struve, 1992; Goldius cf.
capitellum (Archinal, 1994); and Nyterops cf. hollandi van Viersen, 2007a. This fauna confirms the
previously recognised taxonomic diversity pattern and the Dechenella and Nyterops Association
from the middle Middle Devonian in the Ardenne area.

Phacopid trilobites are relatively widespread in Devonian deposits of north Gondwana and
some have been collected from several sections of the Saoura Valley in SWAlgeria. New occurrences
of phacopids assigned to Trimerocephalus, Dianops and Phacops sensu lato are described from this
area and comparisons are made with closely allied species from Morocco and Europe. The trilobite
assemblages of the ‘Argiles de Marhouma’ Formation are considered to be Frasnian–Famennian in age.
These new occurrences have been integrated into an analysis of Upper Devonian phacopid biodiversity.
Diversity fluctuations reflect environmental changes, bioevents and stratigraphic turnovers throughout
the Upper Devonian. Peak diversity was attained after the post-Kellwasser event.