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The effects of sea-level changes and anoxia on Devonian trilobites have been studied for a long time, but the importance of palaeogeographic and tectonic events in this key-period is still not well understood. In the Devonian Period, trilobites invaded many different marine environments and areas in North Africa where important palaeogeographic changes occurred. Distribution patterns of trilobites through time and space have been analysed using a hierarchical cluster analysis and diversity indices. Our examination of the literature suggests that trilobites were scarce during Lochkovian time before an important diversification in Pragian time. Trilobites flourished in many North African regions without there being important taxonomic differences between basins, because of free migration in relatively flat palaeo-topography and homogeneous environments. During Middle Devonian time, early Variscan tectonic movements transformed the eastern Anti-Atlas area into a basin with a platform topography. Geographical barriers such as deep basins prevented trilobite migrations. At the beginning of Eifelian time, the reduction in migration between the different regions of this area coincided with a decrease in diversity. Consequently, tectonic events played an important role in the decline of trilobites during Middle Devonian time, especially when these were combined with sea-level changes and anoxic/hypoxic events. A recovery occurred in Famennian time involving only new genera. As at the global scale, cyrtosymbolines developed in shallow seas, whereas phacopids evolved in deeper environments. The basin and platform system still hampered migrations, although sea-level variations led to episodic exchanges. The late Famennian regression reduced trilobite diversity dramatically in the study area. [ABSTRACT FROM AUTHOR]

During the Devonian the sedimentation on the continental shelves of Ardenne Massif and Boulonnais has changed from a mixed siliciclastic-carbonate ramp (Eifelian), through a carbonate barrier reef (Givetian) and then to a detritic influx with local mud-mounds (Frasnian). Here we analysed the faunistic dynamics of the trilobite associations through the changing environment. We used multivariate analyses (clustering and ordering) to discriminate the trilobite associations within 67 different samples. Three previously known communities and one new were recognised: the Eifelian Mixed association, the Givetian Dechenella association and the two Frasnian Bradocryphaeus and Scutellum-Goldius associations. These trilobite faunas present a progressive ecological specialisation. The Mixed association occurs both in the ramp or carbonated (local reef developed on the ramp) facies without any significant difference in its composition. The Dechenella fauna occurs preferentially close to barrier reefs, but can also survive during short periods of detrital input. The two Frasnian communities show a strong relationship with their environment. The Scutellum-Goldius association is only found in reef systems, whereas the Bradocryphaeus flourishes exclusively in lateral facies. [ABSTRACT FROM AUTHOR]

A recent cladistic analysis of the Asteropyginae led to the recognition of the genus Minicryphaeus as one of the most ancestral of this subfamily. A new species, M. giganteus , is described here from the Ihandar Formation (Pragian, Lower Devonian) of Jbel El Mrakib, southern part of the Mader Basin (Morocco). Among other characteristic features, it is almost three times larger than the other species of the genus. The description of this new species provides information on the ancestral character states of the subfamily and necessitated a revision of the oldest known representatives. Moreover, this recent analysis identified Treveropyge as a derived form of asteropygines, whereas it was traditionally considered as ancestral due to one of its oldest species, now Ganetops ebbae nov. comb., which was formerly included in this genus . In order to offer a better view of the ancestral Asteropyginae, the features of M. giganteus nov. sp. and G. ebbae nov. comb. have been coded following the scheme of the previous cladistic analysis. The updated phylogeny reveals that M. giganteus nov. sp. is the sister-group of the other Minicryphaeus species; a paedomorphic event explains their decreasing size. The new phylogeny confirms the basal position of G. ebbae nov. comb. and distinguishes it clearly from the genus Treveropyge , which necessitates the erection of the new genus Ganetops . It appears that the association of G. ebbae nov. comb. with more derived species within the genus Treveropyge disturbed the previous cladistics analysis of the Asteropyginae. Indeed, considering a derived species as root of the subfamily leads necessarily to the formation of two major clades, as it was usually suggested for the Asteropyginae. [ABSTRACT FROM AUTHOR]

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 genusProtacanthina. 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. WhereasTreveropygewas usually considered as the origin of the remaining Asteropyginae, the present results instead identifyDestombesinaas 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:Minicryphaeusgen. nov.,Gandlopsgen. nov.,Morzadecopsgen. nov. andPennarbedopsgen. nov. The systematic position ofErbenochileis also discussed, the genus no longer being assigned to Asteropyginae. http://zoobank.org/urn:lsid:zoobank.org:pub:C42A54C3-2B8E-439A-8DE0-2F35575F7F40 [ABSTRACT FROM AUTHOR]

Numerous exuviae of three Dechenella species (D. givetensis, D. ziegleri and D. calxensis) from the Middle Devonian (Givetian) of NE France (Ardenne Massif) provide the opportunity to identify the evolutionary modifications of ontogeny of the three Dechenella species and to elaborate a conceptual framework of developmental shape changes. First we used biometric and morphometric approaches to characterize shape modifications. Then we computed ontogenetic trajectories by multivariate regression of geometric shape variables on centroid size in order to compare them. Finally, we compared parallelism between trajectories and rates of development relative to size. These analyses demonstrate a significant difference in the cranidial developmental trajectories of D. givetensis and D. ziegleri indicating an allometric repatterning. However, pygidia of these species share the same allometric pattern with a distinct developmental rate suggesting that heterochrony could be a partial explanation for the body shape evolution. Pygidial ontogeny of D. calxensis corresponds to an allometric repatterning with respect to both other species. This work illustrates the complexity of evolutionary modifications of ontogeny constituting an important process in morphological novelties. [ABSTRACT FROM AUTHOR]

The dalmanitid trilobite Kasachstania Maksimova, 1972, previously reported from the Lower Devonian of Kazakhstan and North America (USA) and the upper Silurian–Lower Devonian of South America (Bolivia and Argentina), is revised. Kasachstania kasachstanica (Balashova in Maksimova,1968) and K. septicostata (Maksimova, 1968) are regarded as junior synonyms of the type species K. saryarkensis (Maksimova, 1960), all from the Lower Devonian of the type locality in central Kazakhstan (northern Balkhash). On the basis of a new diagnosis, K. ulrichi ulrichi (Delo, 1940) from the Emsian of the United States, K. ulrichi asiatica (Maksimova, 1968), K. pristina (Maksimova, 1968), and K. alperovichi Pour et al., 2019, from the Lower Devonian of Kazakhstan, K. andii (Kozłowski, 1923) from the upper Silurian–Lower Devonian of Bolivia, and K. gerardoi Edgecombe and Ramsköld, 1994, from the upper Silurian–Lower Devonian of Bolivia and Argentina are excluded from Kasachstania. This genus, represented only by K. saryarkensis and K. kiikbaica (Maksimova, 1968), is restricted to the Lower Devonian of central Kazakhstan, corresponding to the Balkhash–Mongolo–Okhotsk province in the paleobiogeographic context of the Old World Realm, instead of being nearly cosmopolitan as previously considered. In addition, we provide some remarks about Saryarkella Maksimova, 1978b, a monospecific dalmanitid genus largely overlooked although valid from the Emsian of the same area in central Kazakhstan. [ABSTRACT FROM AUTHOR]