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Morphological disparity and taxonomic richness are two major aspects of evolution used to understand biodiversity changes. These metrics are often decoupled in time, particularly during the early history of clades. To assess the pervasiveness of this pattern during the post-acme of a clade, both morphological disparity and taxonomic diversity of the well-documented Devonian trilobites from North Africa were analysed. Morphospace occupancy and body size were estimated and compared to genus richness through time. This study highlights that, during the Early Devonian, morphological disparity of the pygidium and the cephalon strongly increased, whereas cranidium disparity remained low. Interestingly, the pygidium and cephalon morphological dynamics were decoupled. Taxonomic diversity also increased. Then, the Middle Devonian anoxic events affected the trilobite communities with simultaneous drastic loss of both morphologies and taxonomic richness. This coupling between diversity and disparity dynamics could be explained by either the intensity of extinctions or strong internal constraints. Finally, the weak Famennian recovery of both disparity and diversity did not reach the Early Devonian levels, thus making trilobites a 'dead clade walking' during their late evolutionary history. Devonian trilobite families are thus identified as 'Bottom-Heavy Clades', characterised by a diversity peak at the end of their history. [ABSTRACT FROM AUTHOR]

This study provides a taxonomic treatment and comparison of lower Gorstian (Silurian) radiolarians recovered from two sections of the Cape Phillips Formation in the Canadian Arctic that accumulated in two different paleoenvironmental settings. Twilight Creek is more basinal, located ~100 km from the paleo-shelf margin, whereas Snowblind Creek is located within 1 km of the paleo-shelf break, on Cornwallis Island. The fauna, like other material from the Cape Phillips Formation, is extremely well preserved and was recovered from four samples at two localities, all from the Lobograptus progenitor graptolite Zone, an interval that has few published studies regarding radiolarians. A total of 28 species are recognized, of which two are new and described herein (Fusalfanus bilateralis n. sp. and Pseudospongoprunumparvispina n. sp.), belonging to the Haplotaeniatidae, Inaniguttidae, 'Sponguridae', Ceratoikiscidae, Entactiniidae, Palaeoscenidiidae, and Secuicollactidae. Based on these new data, the stratigraphic ranges of some taxa are extended. The species concepts of several closely related inaniguttid species are re-evaluated. As a result, Inanihella tarangulica Nazarov and Ormiston, 1984 is transferred to the genus Fusalfanus Furutani, 1990 based on cortical shell structure, and Inanihella duroacus, Inanihella legiuncula, and Inanihella perarmata are synonymized under Fusalfanus tarangulica sensu lato. Aciferopylorum admirandum is transferred to Fusalfanus and considered a junior synonym of Fusalfanus osobudaniensis. The comparative analysis of taxonomic richness and composition reveals that the more distal sample from Bathurst Island exhibits a slight, but statistically significant, higher alpha diversity at the species rank than the more proximal basin/platform samples from Snowblind Creek. Biodiversity indices at the genus rank produced mixed results, indicating that differences between sites are at best slight. There is also a strong taxonomic separation between the fine and coarse size radiolarian fractions recovered during the sieving of each sample. The siliceous sponge spicule assemblages from these faunas show an inverse diversity relationship to the radiolarians in that Snowblind Creek contains greater alpha diversity than Twilight Creek. This study provides the first documentation of facies-controls in Silurian radiolarian diversity and is useful in evaluating the role of taxa used in biostratigraphy. L'etude presente le traitement taxonomique et la comparaison de radiolaires du Gorstien (Silurien) inferieur recuperes de deux sections de la Formation de Cape Phillips, dans l'Arctique canadien, accumulees dans deux contextes paleoenvironnementaux differents. Twilight Creek s'apparente plus a un milieu de bassin situe a ~100 km de la bordure de la paleoplateforme, alors que Snowblind Creek est situe a moins de 1 km de la bordure de cette derniere, dans l'ile Cornwallis. La faune, comme d'autre materiau de la Formation de Cape Phillips, est extremement bien preservee et a ete recuperee de quatre echantillons provenant de deux localites, tous de la zone a graptolite Lobograptus progenitor, un intervalle caracterise par peu d'etudes publiees sur les radiolaires. Un total de 28 especes sont reconnues, dont deux nouvelles decrites dans la presente etude (Fusalfanus bilateralis n. sp. et Pseudospongoprunum parvispina n. sp.), appartenant aux Haploteniatides, Inaniguttides, <>, Ceratoikiscides, Entactiniides, Paleoscenidiides et Secuicollactides. A la lumiere de ces nouvelles donnees, les repartitions stratigraphiques de certains taxons sont elargies. Le concept d'espece pour plusieurs especes d'inaniguttides etroitement reliees est reevalue et, en consequence, Inanihella tarangulica Nazarov and Ormiston, 1984 est transfere au genre Fusalfanus Furutani, 1990 a la lumiere de la structure corticale de sa coquille, et Inanihella duroacus, Inanihella legiuncula et Inanihella perarmata sont etablis comme des synonymes de Fusalfanus tarangulica sensu lato. Aciferopylorum admirandum est transfere a Fusalfanus et considere comme etant un synonyme junior de Fusalfanus osobudaniensis. L'analyse comparative de la richesse et de la composition taxonomiques revele que l'echantillon plus distal de l'ile Bathurst presente une diversite alpha legerement, bien que significativement, plus forte au rang de l'espece que les echantillons plus proximaux de bassin/plateforme de Snowblind Creek. Les indices de biodiversite au rang du genre produisent des resultats mitiges, indiquant que les differences entre localites sont, au mieux, minimes. Il y a egalement une separation taxonomique marquee entre les fractions fines et grossieres de radiolaires produites par le criblage de chacun des echantillons. Les assemblages de spicules d'eponges siliceux de ces faunes presentent une relation de diversite inverse a celle des radiolaires, en cela que l'assemblage de Snowblind Creek contient une plus grande diversite alpha que celui de Twilight Creek. Cette etude fournit la premiere documentation d'un controle de la diversite de radiolaires siluriens par le facies et est utile pour l'evaluation du role des taxons utilises en biostratigraphie. [Traduit par la Redaction], Introduction Since their appearance in the lower Cambrian (Pouille et al. 2011), Polycystine radiolarians diversified during the entire Phanerozoic (De Wever et al. 2001); they thus have the potential to [...]

Fossils of Devonian ammonoids are abundant and well-preserved in the Anti-Atlas of Morocco; as such they provide an invaluable record of regional morphological disparity changes (diversity of shapes) that characterise the first steps of ammonoid evolution. However, they were rarely analysed quantitatively with respect to their morphological spectrum. Here, we investigated the morphological disparity of the Early-Middle Devonian ammonoids of the Moroccan AntiAtlas by analysing the shape of their whorl profile. A geometric morphometric approach based on the acquisition of outline semilandmark coordinates was used to analyse the whorl profiles. For comparison, morphometric ratios based on classical conch measurements were also analysed to investigate the overall conch geometry. Several standard disparity estimators were computed to measure different aspects of morphological disparity fluctuations through time. It appears that a major increase in disparity occurred throughout the Early Devonian, followed by fluctuating disparity during the Middle Devonian constituting a general decreasing trend. Only the end-Eifelian Kačák Event shows a significant decrease in disparity. Thus, the ammonoids explored the range of possible shapes fairly quickly during their initial radiation; however, we found no evidence for an early burst of shape diversity (i.e., the rise does not exceed the expectations given diversity). Nevertheless, correlation tests between diversity and disparity time series support that they are partially decoupled. The highly resolved biozone record highlights that the increase in disparity began earlier than the increase in diversity that characterises the late Emsian. [ABSTRACT FROM AUTHOR]

The Taidon and Fomin formations of the Kuznetsk Basin (SW Siberia, Russia) were sampled in three sections, Old Belovo quarry, Artyshta village and Starobachaty village. The carbonate beds revealed microfacies of bioclastic wackestone and packstone, deposited in the distal parts of inner ramps and the proximal parts of mid ramps. Relatively rare plurilocular foraminifers occur in bioclastic neomicrosparitized wackestone deposited in the shallower parts of the carbonate ramp. The other microfacies only contain the bilocular foraminifer genus Earlandia. The plurilocular foraminifers permit the dating of the lower part of the Taidon Formation and the distinction of a biozone characterized by Tuberendothyra, Pseudoplanoendothyra, and Granuliferella. This local biozone can be correlated with the MFZ4 reference-biozone established in Belgium, which is late Hastarian (i.e., latest early Tournaisian) in age. Conodonts of the upper Siphonodella crenulata Zone in the lower part of Taidon Formation are consistent with this late Hastarian age. The Fomin Formation cannot be directly dated by its foraminifers Earlandia. As it is overlain by previously dated lower Visean beds, the Fomin Formation corresponds to all or part of the entire Ivorian (i.e., late Tournaisian) and of the MFZ5 to MFZ8 biozones. The same uncertainty on the late Tournaisian age exists with the conodonts, which belong to the lower Siphonodella crenulata Zone and isosticha-upper crenulata/typicus/anchoralis-latus zones, respectively. As a taxonomical result, Septabrunsiinoidea n. superfam. is introduced, in order to explain some poorly known lineages of the Tournaisian. Palaeobiogeographically, SW Siberia is proposed as the radiation centre of the Septabrunsiinoidea during the Tournaisian, and especially during the Hastarian, and their migration centre toward three directions: North America, South China and western Tethyan areas.

The end-Permian mass extinction removed more than 80% of marine genera. Ammonoid cephalopods were among the organisms most affected by this crisis. The analysis of a global diversity data set of ammonoid genera covering about 106 million years centered on the Permian-Triassic boundary (PTB) shows that Triassic ammonoids actually reached levels of diversity higher than in the Permian less than 2 million years after the PTB. The data favor a hierarchical rather than logistic model of diversification coupled with a niche incumbency hypothesis. This explosive and nondelayed diversification contrasts with the slow and delayed character of the Triassic biotic recovery as currently illustrated for other, mainly benthic groups such as bivalves and gastropods.

Abstract Background A major goal in evolutionary biology is to understand the processes that shape the evolutionary trajectory of clades. The repeated and similar large-scale morphological evolutionary trends of distinct lineages suggest that adaptation by means of natural selection (functional constraints) is the major cause of parallel evolution, a very common phenomenon in extinct and extant lineages. However, parallel evolution can result from other processes, which are usually ignored or difficult to identify, such as developmental constraints. Hence, understanding the underlying processes of parallel evolution still requires further research. Results Herein, we present a possible case of parallel evolution between two ammonoid lineages (Auguritidae and Pinacitidae) of Early-Middle Devonian age (405-395 Ma), which are extinct cephalopods with an external, chambered shell. In time and through phylogenetic order of appearance, both lineages display a morphological shift toward more involute coiling (i.e. more tightly coiled whorls), larger adult body size, more complex suture line (the folded walls separating the gas-filled buoyancy-chambers), and the development of an umbilical lid (a very peculiar extension of the lateral shell wall covering the umbilicus) in the most derived taxa. Increased involution toward shells with closed umbilicus has been demonstrated to reflect improved hydrodynamic properties of the shell and thus likely results from similar natural selection pressures. The peculiar umbilical lid might have also added to the improvement of the hydrodynamic properties of the shell. Finally, increasing complexity of suture lines likely results from covariation induced by trends of increasing adult size and whorl overlap given the morphogenetic properties of the suture. Conclusions The morphological evolution of these two Devonian ammonoid lineages follows a near parallel evolutionary path for some important shell characters during several million years and through their phylogeny. Evolution of some traits (involution, umbilical lid) appears to be mainly driven by adaptation to improve the hydrodynamic properties of the shell, whereas other characters (sutural complexity) evolved due to covariation with features that play a central role in the morphogenesis of mollusc shells. This example provides evidence that parallel evolution can be driven simultaneously by different factors such as covariation (constructional constraints) and adaptation (natural selection).