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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]

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]