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The Nord-Pas-de-Calais Coalfield is formed by an almost continuous succession of upper Carboniferous deposits, from which an extremely diverse macroflora has historically been described. Recent evidence has highlighted a clear pattern of changing species diversity, showing some differences from what is seen in other coalfields of Variscan Euramerica. We further study this significant macroflora, focusing on the biostratigraphical changes and their palaeoecological implications. Clustering and ordination analyses have indicated key floral discontinuities that enable the standard regional macrofloral biozones to be recognized in the Nord-Pas-de-Calais Coalfield. By combining these results with the previous diversity studies, six distinct phases in the evolution of the coal swamp vegetation in north-eastern France can be identified: (1) an initial invasion of peat substrate vegetation in the earliest Langsettian; (2) a rapid diversification of the clastic substrate vegetation in the early-middle Langsettian; (3) a more gradual diversification of the vegetation of both clastic and peat substrates during the late Langsettian to middle Duckmantian glacial phase C3; (4) the appearance of more characteristically late Westphalian, but less diverse floras during the late Duckmantian to early Bolsovian C3-C4 interglacial phase; (5) a marked increase in species diversity in the middle-late Bolsovian, coinciding with the onset of the C4 glacial phase; and (6) a marked reduction in species diversity, and the appearance of new medullosaleans and marattialeans in the Asturian, possibly linked to climate change. The evidence clearly shows how this palaeotropical swamp vegetation was responding to climate change and orogenic landscape changes during Westphalian times. [ABSTRACT FROM AUTHOR]

Phacopidae were a successful family of the Silurian–Devonian period. Although their diversity trends are well identified, their shape evolution is unknown; their morphology often considered to be conservative. We have quantified these morphologies using geometric morphometrics (landmarks) and investigated their evolution using morphological disparity indices. Results identified morphological variations between the genera, and through time. Phacopids differ from each other by the position of the facial suture linked to the size of the visual complex, the shape of the genal angle and the elongation of both cephalon and pygidium. The morphological disparity of cephala was high from the Silurian, contrary to that of pygidia. Subsequently, the morphological disparity increased in the Early Devonian with the development of narrow cephala and triangular pygidia. Morphological disparity was greater in the Emsian for both cephala and pygidia, more than 50 myr after the origination of phacopids. It constituted a perfect example illustrating that a peak of biodiversity does not necessarily happen in the early history of a clade. Subsequently, a strong decrease of morphological disparity occurred in the Middle Devonian, in conjunction with sea‐level changes and anoxic events. Taxonomic richness and morphological disparity declined strongly in the Givetian, in a non‐random extinction affecting particularly blind genera. The morphological disparity remained low in the Frasnian despite progressive eye reduction influenced by environmental changes. An extensive recovery occurred in the Famennian with an important increase of both taxonomic and morphological diversity. The Hangenberg event caused the final extinction of phacopids. [ABSTRACT FROM AUTHOR]

The Silurian–Devonian plant radiation was a critical development in the evolution of early terrestrial ecosystems. Characterizing the diversity dynamics of this radiation has been a focus of numerous studies. However, little is known about the impact of geological bias on our perception of this biodiversification. Here, we use a new, comprehensive compilation of plant occurrences from North America, together with a Macrostrat lithological dataset, to elucidate the relationships between the palaeobotanical and geological records of early land plants. Results show that observed raw diversity patterns at both species and genus rank are significantly correlated with fluctuations of sedimentary rock volume, especially of non‐marine fossiliferous deposits. The lack of terrestrial sedimentary deposits before the Emsian (Early Devonian) makes it difficult to obtain an accurate depiction of the pre‐Emsian plant diversification in North America. However, complementary analyses reveal that sampling‐standardized diversity patterns partially correct the raw trajectories, especially at the genus‐level if enough preserved non‐marine sediments are available for sampling. Our findings highlight that geological incompleteness remains a fundamental bias for describing early plant diversification. This indicates that, even when sampling is extensive, observed diversity patterns potentially reflect the heterogeneity of the rock record, which blurs our understanding of the early history of land vegetation. [ABSTRACT FROM AUTHOR]

The Devonian was a time of drastic environmental change that shaped the morphology of trilobites. This study aims to investigate their morphological evolution and to show the influence of some abiotic and biotic factors (bathymetry, feeding habits and visual abilities) on their shape. A dataset was compiled to investigate the shape of three structures (cephalon as a whole, central part of the cephalon, and pygidium) of Devonian trilobites from North Africa, using a geometric morphometric approach. Based on empirical morphospaces, the morphological changes were quantified through the Devonian stages. The results reveal important variations in the morphological disparity of the glabella shape, the facial suture location, the pygidial length and the presence of spines. In the Lochkovian, morphological disparity was low, subsequently increased in the Pragian with numerous innovations, and reached a maximum in the Emsian. If the morphospace occupancy remained until the Eifelian, a severe loss of disparity occurred in the Givetian, a time known for important environmental changes. Disparity then remained low in the Late Devonian. The shapes inherited from the Silurian persisted throughout the Devonian whereas Pragian novelties were most affected by losses. These persistent shapes were more versatile for environmental adaptation, helping those trilobites to survive the environmental events. Similarly, the trilobite orders that survived Devonian events had a wide morphological spectrum and were better adapted to withstand environmental change. [ABSTRACT FROM AUTHOR]

Abstract: The family Prionitidae Hyatt represents a major component of ammonoid faunas during the Smithian (Early Triassic), and the genus Anasibirites Mojsisovics is the most emblematic taxon of this family. Its stratigraphical range is restricted to the beginning of the late Smithian (Wasatchites distractus Zone). The genus is also characterized by an unusual cosmopolitan distribution, thus contrasting with most earlier Smithian ammonoid distributions that were typically restricted by latitude. Because the late Smithian witnessed an extinction of the nekton (e.g. ammonoids, conodonts) whose amplitude is equal to or larger than that of the end‐Permian crisis, the number of valid species that should be included in the genus Anasibirites becomes a highly relevant question when addressing this extinction at the highest possible taxonomic resolution. Based on a new extensive collection from Timor, the composition of the genus Anasibirites is herein revised with respect to its intraspecific and ontogenetic variations. Comprehensive morphological and biometric studies (c. 950 measured specimens) indicate that, of the c. 60 available species names, only two are valid, namely A. kingianus (Waagen) and A. multiformis Welter. Continuous ranges of intraspecific variation enable us to synonymize A. nevolini Zakharov, and A. angulosus (Waagen) with A. kingianus. The contribution of Anasibirites to species diversity during the late Smithian extinction is thus significantly less than previously estimated, therefore accentuating the severity of this event. [ABSTRACT FROM AUTHOR]

Directed evolution of life through millions of years, such as increasing adult body size, is one of the most intriguing patterns displayed by fossil lineages. Processes and causes of such evolutionary trends are still poorly understood. Ammonoids (externally shelled marine cephalopods) are well known to have experienced repetitive morphological evolutionary trends of their adult size, shell geometry and ornamentation. This study analyses the evolutionary trends of the family Acrochordiceratidae Arthaber, 1911 from the Early to Middle Triassic (251-228 Ma). Exceptionally large and bed-rock-controlled collections of this ammonoid family were obtained from strata of Anisian age (Middle Triassic) in north-west Nevada and north-east British Columbia. They enable quantitative and statistical analyses of its morphological evolutionary trends. This study demonstrates that the monophyletic clade Acrochordiceratidae underwent the classical evolute to involute evolutionary trend (i.e. increasing coiling of the shell), an increase in its shell adult size (conch diameter) and an increase in the indentation of its shell suture shape. These evolutionary trends are statistically robust and seem more or less gradual. Furthermore, they are nonrandom with the sustained shift in the mean, the minimum and the maximum of studied shell characters. These results can be classically interpreted as being constrained by the persistence and common selection pressure on this mostly anagenetic lineage characterized by relatively moderate evolutionary rates. Increasing involution of ammonites is traditionally interpreted by increasing adaptation mostly in terms of improved hydrodynamics. However, this trend in ammonoid geometry can also be explained as a case of Cope's rule (increasing adult body size) instead of functional explanation of coiling, because both shell diameter and shell involution are two possible paths for ammonoids to accommodate size increase. [ABSTRACT FROM AUTHOR]

The family Acrochordiceratidae Arthaber, 1911 ranges in age from latest Spathian to the middle/late Anisian boundary, and it represents a major component of ammonoid faunas during that time. The middle Anisian genus Acrochordiceras Hyatt, 1877 is the most widespread taxon of the family and occurs abundantly worldwide within the low paleolatitude belt. However, there is a profusion of species names available for Acrochordiceras. This excessive diversity at the species level essentially results from the fact that sufficiently large samples were not available, thus leading to a typological approach to its taxonomy. Based on new extensive collections obtained from the Anisian (Middle Triassic) Fossil Hill Member (Star Peak Group, north-west Nevada) for which a high resolution biostratigraphic frame is available, the taxonomy and biostratigraphy of the genus Acrochordiceras Hyatt, 1877 is herein revised with respect to its intra-specific variation. Morphological and biometric studies ( c. 550 bedrock-controlled specimens were measured) show that only one species occurs in each stratigraphic level. Continuous ranges of intra-specific variation of studied specimens enable us to synonymize Haydenites Diener, 1907, Silesiacrochordiceras Diener, 1916 and Epacrochordiceras Spath, 1934 with Acrochordiceras Hyatt, 1877. Three stratigraphically successive species are herein recognized in the low paleolatitude middle Anisian faunas from Nevada: A. hatschekii (Diener, 1907), A. hyatti Meek, 1877 and A. carolinae Mojsisovics, 1882. Moreover, an assessment of intra-specific variation of the adult size range does not support recognition of a dimorphic pair ( Acrochordiceras and Epacrochordiceras) as previously suggested by other workers ( Epacrochordiceras is the compressed and weakly ornamented end-member variant of Acrochordiceras). The successive middle Anisian species of Acrochordiceras form an anagenetic lineage characterized by increasing involution, adult size and intra-specific variation. This taxonomic revision based on new bedrock-controlled collections is thus an important prerequisite before studying the evolution of the group. [ABSTRACT FROM AUTHOR]