Evolution Of Fauna Research Articles

Miocene Cercopithecoidea from the Tugen Hills, Kenya

Miocene to Pleistocene fossiliferous sediments in the Tugen Hills span the time period from at least 15.5 Ma to 0.25 Ma, including time periods unknown or little known elsewhere in Africa. Consequently, the Tugen Hills deposits hold the potential to inform us about crucial phylogenetic events in African faunal evolution and about long-term environmental change. Among the specimens collected from this region are a number of discoveries already important to the understanding of primate evolution. Here, we describe additional cercopithecoid material from the Miocene deposits in the Tugen Hills sequence, including those from securely dated sites in the Muruyur Beds (16–13.4 Ma), the Mpesida Beds (7–6.2 Ma) and the Lukeino Formation (∼6.2–5.7 Ma). We also evaluate previously described material from the Ngorora Formation (13–8.8 Ma). Identified taxa include Victoriapithecidae gen. et sp. indet., cf. Parapapio lothagamensis, and at least two colobines. Specimens attributed to cf. Pp. lothagamensis would extend the species’ geographic range beyond its type locality. In addition, we describe specimens sharing derived characters with modern African colobines (Tribe: Colobina), a finding that is congruent with previous molecular estimates of colobine divergence dates. These colobine specimens represent some of the earliest known members of the modern African colobine radiation and, in contrast to previous hypotheses, suggest that early African colobines were mainly arboreal and that semi-terrestrial Late Miocene and Plio-Pleistocene colobine taxa were secondarily derived in their locomotor adaptations.

Insectivores and bat (Mammalia) from the late Middle Miocene of Gratkorn (Austria): biostratigraphic and ecologic implications

The discovery of a late Sarmatian (latest Middle Miocene) small mammal fauna at the base of the clay pit St. Stefan near Gratkorn is of primary importance for the biostratigraphic and ecologic comprehension of the faunal evolution during the late Middle Miocene of Central Europe. In this paper five species of insectivores and one bat are described. The gymnure Schizogalerix voesendorfensis is the most abundant species of the small mammal fauna. The Gratkorn sample represents the earliest occurrence of the species in the fossil record. A single molar of a second, large-sized Galericinae cannot be attributed to any known species. The new talpid Desmanodon fluegeli n. sp. shares similarities with the Anatolian lineage D. minor / D. major. An exceptionally well preserved mandible of the large shrew Dinosorex cannot be determinate at the species level. In addition, some rare remains of the bat cf. Myotis sp. are also reported. From biogeographical point of view the insectivore fauna can be related to eastern Central European / Anatolian assemblages. Although taphonomic biases are suspected, the environmental conditions proposed on the basis of sedimentary analyzes (open forest with moist soil) can contribute to the low alpha diversity of insectivores in this locality.

Adaptive strategies in the evolution of encrusting tentaculitoid tubeworms

The encrusting tentaculitoid tubeworms (Middle Ordovician to Middle Jurassic) have their acme of diversity in the Middle Paleozoic and they form a part of the Paleozoic evolutionary fauna. Most of the morphological and ecological innovations of encrusting tentaculitoid tubeworms appeared during the initial phase of their evolution in the Ordovician and Silurian, and no innovations appeared after the Devonian. The evolutionarily most successful (long lasting) were general hard substrate encrusters, and the most successful morphologies supported this life mode. The morphologies that lasted the longest appeared in the beginning of tentaculitoid tubeworm evolution (during the Ordovician). The ecological innovations with the shortest durations were associated with highly dependent distorting symbiotic and endosymbiotic life modes. Predation pressure may have led to evolution of defensive morphologies (e.g. spines and thick vesicular walls) and endosymbiotic life mode in cornulitids, trypanoporids, Anticalyptraea and Streptindytes.

Global vertebrate-based palaeozoogeographical subdivision for the Givetian-Famennian (Middle-Late Devonian): Endemism-cosmopolitanism spectrum as an indicator of interprovincial faunal exchanges

The spectrum of proposed endemic-cosmopolitan (E-C) categories is applied to demonstrate faunal interchange between palaeozoogeographic provinces during the Givetian-Famennian, on the assumption that the E-C proportion reflects the isolation rate of the fauna. Mostly endemic groups are useful to establish zoogeographical regionalisation, whereas polydemics and cosmopolitans define the historical trends in the faunal development in various zoogeographical areas. Quantitative and systematic analyses suggest significant isolation of the Laurentian, Baltican, Armorican and East Gondwanan faunas during the Givetian-Frasnian that is possibly due to remoteness of the intracontinental basins from the coastal oceanic areas. North Gondwanan and Siberian faunas, on the contrary, were located close to the coast or in island archipelagos. Laurentian and East Gondwanan faunas were the most isolated during the Givetian. Most often the cosmopolitans include antiarch placoderms, struniiform sarcopterygians, and chondrichthyans; arthrodire and ptyctodont placoderms are more rarely cosmopolitan. These fishes might possess some special eurybiont capabilities. Two realms are recognised for the Givetian: the Ptyctodont and the Phyllolepid-Thelodont Realms. Within the Ptyctodont Realm, the Laurentia and Baltica Provinces form the Psammosteiform-Porolepiform Region. During the Frasnian, the Thelodont Realm including East and North Gondwana, as well as West Yunnan, and the Porolepiform Realm including the Psammosteiform Region (Laurentia + Baltica) are erected. For the Famennian, a single Porolepiform Realm houses the Phyllolepid-Tetrapod Region, including Laurentia, Baltica, and East Gondwana Provinces.

Unravelling extrinsic and intrinsic factors of the early Palaeozoic diversification of blastozoan echinoderms

The Subphylum Blastozoa represents more than one third of the early Palaeozoic echinoderm fauna. A comprehensive database including all records of blastozoans was built to provide quantitative analyses of palaeogeography and diversity patterns and processes, for the 10 classes currently included in this subphylum during the early Palaeozoic. The global pattern of taxonomic diversity shows two peaks during the Cambrian Series 3 and the Late Ordovician intervals. In Cambrian times, the high taxonomic diversity seems to be related with a high turnover rate and a high endemicity of blastozoan genera, whereas in Ordovician times, the rise in diversity is associated with a low endemicity and a low turnover rate. The gradual increase of Ordovician diversity can be explained by the progressive geographic extension of blastozoan genera onto most palaeocontinental margins, associated to the long-term gradual sea level rise. This global pattern is subdivided into local trends to compare the relative influence of regional distributional patterns. Blastozoans occurred mainly on Gondwanan and Laurentian margins during the Cambrian. In both Ordovician and Silurian times, blastozoans colonised different provinces, characterised by varied latitudinal position and environmental conditions: the Laurentian province was mainly located in the equatorial latitudes (temperate to warm waters, mainly carbonate platforms), and both the northwestern peri-Gondwanan and Asian provinces, in the intermediate to high latitudes (temperate to cold water, mainly siliciclastic environments). After the Hirnantian mass extinction, blastozoans finally recovered chiefly on Laurentian margins, where climate and environmental conditions were probably more favourable. The two diversification events recorded for blastozoans in the early Palaeozoic concerned two distinct evolutionary faunas (Cambrian Evolutionary Fauna vs. Palaeozoic Evolutionary Fauna). They were driven by distinct processes, even if the Ordovician diversification had indeed started during the middle Furongian with a medium origination event. Difference in processes might be related to the evolution of global environmental/climatic conditions coupled with the position of continental masses.

Holocene climate variations at the entrance to a warm Arctic fjord: evidence from Kongsfjorden trough, Svalbard

Abstract The North Atlantic Current transports warm and salty water into the Nordic Seas and continues northwards into the Arctic Ocean as the West Spitsbergen Current. This current flows along the west coast of the Svalbard archipelago and into the fjords and troughs on the Svalbard shelf. We have investigated a core (NP05-11-21GC) from the Kongsfjorden trough, which spans the last 12 ka. The core site presently experiences seasonal inflow of Atlantic Water masses, and may therefore provide a record of past variations in Atlantic Water inflow to the Arctic. Lithological analysis and benthic foraminifera have been used to reconstruct the palaeoceanographic development in the area. The results show that cold and harsh conditions prevailed during the late part of the Younger Dryas and that the site was in proximity to glaciers. After 11.8 ka BP the first influence of Atlantic Water is seen in the fauna. This was followed by changes in glacial activity at 11.5 ka BP. During the period 11.5–10.6 ka BP the fauna indicate increased influence of Atlantic Water and the final deglaciation of the fjord after the Younger Dryas period. These initial ameliorated conditions were interrupted by a 250-year long cooling starting at 11.3 ka BP, corresponding to the Preboreal Oscillation. After 10.6 ka BP a marked change from an ice proximal to ice distal environment occurred accompanied by the strong influence of Atlantic Water masses. In the Mid-Holocene at 7 ka BP, the influence of Atlantic Water diminished but no sign of an immediate response of the glaciers to this are found in the core. The evidence suggests that intensification of glacial activity started as late as c . 3.5 ka BP. Comparing the core from Kongsfjorden trough with two shelf records from Svalbard generally shows similar faunal development although some differences exist. These are assumed to be related to the distance of each record to the position of the Arctic front.

Neogene Radiolarian Biostratigraphy and Faunal Evolution Rates in the Eastern Equatorial Pacific ODP Sites 845 and 1241

Radiolarians from Sites 845 and 1241 in the eastern equatorial Pacific were examined in order to evaluate the role of paleoceanographic perturbations upon the general faunal evolutionary pattern of tropical planktonic organisms during the last 17 Ma. Radiolarian appearance and extinction rates indicate no periods of mass extinctions during the past 17 Ma. However, a relatively rapid replacement of the species in the radiolarian assemblages occurs near the middle—late Miocene boundary. This replacement event represents the gradual extinction of a number of radiolarian species and their gradual replacement by evolving new species. The modern equatorial circulation system was formed near the middle—late Miocene boundary due to the closure of the Indonesian seaway. The minor faunal turnover appears to be associated with the formation of the modern equatorial circulation system near the middle—late Miocene boundary. Diatom assemblages in the equatorial Pacific became more provincial in character after about 9 ...

Changes of water level in the Eemian palaeolake at Imbramowice (SW Poland) based on isotopic and cladoceran data

Isotopic and cladoceran investigations of Eemian (MIS 5e) lake sediments from Imbramowice, SW Poland, allow us to reconstruct the environmental conditions, especially changes of water level and trophic status, during the early and middle Eemian Interglaciation. We analyzed the sediments from 6.5 to 11.0 m depth in a core provided by Mamakowa (1989). The upper 6.5 m had insufficient carbonates and cladoceran contents for analyses. The analyzed section consists of sandy and organic silts at the bottom, followed by gyttja characterized by increasing CaCO 3 content. Measured δ 18O values oscillate from ca. – 9 to – 4‰ and δ 13C from – 3.5 to above + 6‰. Based on stable isotope analyses of carbonates, we define and characterize eight isotopic horizons (Is). We identify 26 taxa of subfossil Cladocera and seven zones (CLZ) of faunal development. Probably the greatest depth of the lake occurred with pollen zone E2; shallowing then took place. During pollen zones E2-E3, gradual warming is observed and expressed through a positive trend in both δ 18O and δ 13C values. Pollen zone E4 is characterized by frequent changes of water level. During the Eemian Interglaciation, excluding the initial phase of lake evolution, the lake was meso-eutrophic and eutrophic with high phytoplankton productivity.

Danian cool-water coral reefs in southern Scandinavia localised over seafloor highs

Danian (Paleocene) reefs formed by ahermatypic scleractinian corals in relatively deep water are known in a few localities in southern Scandinavia. Reflection and shallow seismic profiles, and samples from drilling and scuba diving in bridge pier excavations in Øresund, the strait between Denmark and Sweden, for the first time allow interpretation of the factors that controlled the localisation of the reefs. After the mass-extinction at the K/T boundary, reef-building scleractinian corals were absent in the Boreal early Danian in the Danish basin. Faunal evolution after the biotic crisis and a rise in relative sea level are interpreted to have favoured formation of deep-water coral reefs in the Øresund region in mid-Danian time. The reefs were 6–20 m high and 20–200 m long on the seafloor and have a patchy distribution within a bryozoan mound-dominated setting in an area of about 10 km 2. They are composed of the framework-building ahermatypic scleractinian coral Dendrophyllia candelabrum with minor occurrences of bryozoans, echinoderms, gastropods and bivalves. It has been suspected that the reefs were located over contemporaneous seafloor highs but this notion was only based on comparison with similar modern deep-water reefs offshore Norway. The data from Øresund indicate that the Danian reef complex was formed over a late Maastrichtian palaeo-seafloor high, the Saltholm-Malmø High, supporting this interpretation and thus adding fundamentally to the understanding of the factors controlling the formation and localisation of these deep and cool-water coral reefs. Individual reefs were initiated and grew on eroded crests and steep south-dipping flanks of bryozoan mounds and were predominantly situated on the southern part of the high and are interpreted as growing towards NW-flowing bottom currents rich in particulate nutrients.

Temporal Distribution of Diagnostic Biofabrics in the Lower and Middle Ordovician in North China: Clues to the Geobiology of the Great Ordovician Biodiversification Event

Abstract:The temporal distribution of the diagnostic biofabrics in the Lower and Middle Ordovician in North China distinctly illustrates that the sedimentary systems on the paleoplate have been changed markedly as consequences of the Great Ordovician Biodiversification Event (GOBE). The pre‐GOBE sedimentary systems deposited in Tremadoc display widespread microbialite and flat‐pebble conglomerates, and a less extent of bioturbation. Through the transitional period of early Floian, the sedimentary systems in the rest of the Early and Mid‐ Ordovician change to GOBE type and are characterized by intensive bioturbation and vanishing flat‐pebble conglomerates and subtidal microbial sediments. The irreversible changes in sedimentary systems in North China are linked to the GOBE, which conduced the increase in infaunal tiering, the expansion of infaunal ecospace, and the appearance of new burrowers related to the development of the Paleozoic Evolutionary Fauna during the Ordovician biodiversification. Thus, changes in sedimentary systems during the pivotal period of the GOBE were consequences of a steep diversification of benthic faunas rather than the GOBE's environmental background.

A Great Revolution of the Earth-Surface Environment: Linking the Bio-Invasion Onto the Land and the Ordovician Radiation of Marine Organisms

The strontium isotopic composition of the oceans changed markedly at the Cambrian-Ordovician transition, some 500 million years ago. This isotopic shift was greatly affected by the first bio-invasion of the land and the ensuing terrestrial-surface environments in a chain reaction that included: 1) an attenuation of weathering on land, 2) changes in the outflow patterns of fluvial floods and the circulation patterns of groundwater, 3) marked regional differentiation of coastal environments, 4) the formation of soil layers, and 5) the eutrophication of estuaries by nutrient salts of terrestrial-biosphere origin. A series of these environmental changes culminated in the marine Ordovician biodiversification, an explosive flourishing of the Paleozoic evolutionary fauna that is characterized by a variety of filter and suspension feeders. The bio-invasion onto land was one of the greatest geobiological events in the Earth's history.

Sinusichnus,a trace fossil from Antarctica and Venezuela: expanding the dataset of crustacean burrows

The sinusoidal decapod crustacean burrow Sinusichnus sinuosus is documented from the Upper Cretaceous Hidden Lake Formation of James Ross Island (Antarctica), the Upper Oligocene-Lower Miocene Naricual Formation of the Eastern Venezuela Basin, and the Middle Miocene Socorro Formation of the Falcon Basin of Western Venezuela, significantly expanding its geographical and palaeolatitudinal range. These burrows may have served for bacterial farming in relatively stressful settings characterized by deltaic progradation. Sinusichnus sinuosus seems to display a broad latitudinal range, from low latitude tropical settings (Venezuela) to intermediate latitude temperate areas (Spain and France), and high latitude cold waters (Antarctica). The appearance of S. sinuosus in the Cretaceous reveals the acquisition of more sophisticated feeding strategies by decapod crustaceans, reflecting the dominance of the Modern Evolutionary Fauna.

Lopingian (Late Permian) foraminiferal faunal succession of a Paleo‐Tethyan mid‐oceanic carbonate buildup: Shifodong Formation in the Changning–Menglian Belt, West Yunnan, Southwest China

AbstractThis paper deals with a Lopingian (Late Permian) foraminiferal faunal succession of the Shifodong Formation in the Changning–Menglian Belt, West Yunnan, Southwest China, which has been geologically interpreted as one of the closed remnants in East Asia of the Paleo‐Tethys Ocean. The Shifodong Formation is the uppermost stratigraphic unit in thick Carboniferous–Permian carbonates of the belt. These carbonates rest upon bases consisting of oceanic island basalt and are widely accepted as having a Paleo‐Tethyan mid‐oceanic (seamount‐ or oceanic plateau‐top) origin. Sixteen taxa of fusuline foraminifers and 37 taxa of smaller (non‐fusuline) foraminifers are recognized from the type section of the Shifodong Formation located in the Gengma area of the northern part of the Changning–Menglian Belt. Based on their stratigraphic distribution, three fusuline zones can be established in this section: they are, in ascending order, the Codonofusiella cf. C. kwangsiana Zone, Palaeofusulina minima Zone, and Palaeofusulina sinensis Zone. These three biozones are respectively referable to the Wuchiapingian, early Changhsingian, and late Changhsingian, of which the Wuchiapingian is first recognized in this study in the Changning–Menglian mid‐oceanic carbonates. The present study clearly demonstrates that the foraminiferal fauna in a Paleo‐Tethyan pelagic shallow‐marine environment still maintained high faunal diversity throughout the almost entire Lopingian, although the very latest Permian fauna in the upper part of the Palaeofusulina sinensis Zone of the Shifodong section records a sudden decrease in both faunal diversity and abundance. Moreover, the Shifodong faunas are comparable in diversity with those observed in circum‐Tethyan shelves such as South China. The present Paleo‐Tethyan mid‐oceanic foraminiferal faunas are definitely more diversified than coeval mid‐oceanic Panthalassan faunas, which are typically represented by those from the Kamura Limestone in a Jurassic accretionary complex of Southwest Japan. It is suggestive that the Paleo‐Tethyan mid‐oceanic buildups presumably supplied a peculiarly hospitable habitat for foraminiferal faunal development in a pelagic paleo‐equatorial condition.

The double mass extinction revisited: reassessing the severity, selectivity, and causes of the end-Guadalupian biotic crisis (Late Permian)

The end-Guadalupian extinction, at the end of the Middle Permian, is thought to have been one of the largest biotic crises in the Phanerozoic. Previous estimates suggest that the crisis eliminated 58% of marine invertebrate genera during the Capitanian stage and that its selectivity helped the Modern evolutionary fauna become more diverse than the Paleozoic fauna before the end-Permian mass extinction. However, a new sampling-standardized analysis of Permian diversity trends, based on 53731 marine invertebrate fossil occurrences from 9790 collections, indicates that the end-Guadalupian “extinction” was actually a prolonged but gradual decrease in diversity from the Wordian to the end of the Permian. There was no peak in extinction rates; reduced genus richness exhibited by all studied invertebrate groups and ecological guilds, and in different latitudinal belts, was instead driven by a sharp decrease in origination rates during the Capitanian and Wuchiapingian. The global diversity decrease was exacerbated by changes in beta diversity, most notably a reduction in provinciality due to the loss of marine habitat area and a pronounced decrease in geographic disparity over small distances. Disparity over moderate to large distances was unchanged, suggesting that small-scale beta diversity changes may have resulted from compression of bathymetric ranges and homogenization of onshore-offshore faunal gradients stemming from the spread of deep-water anoxia around the Guadalupian/Lopingian boundary. Although tropical invertebrate genera were no more likely than extratropical ones to become extinct, the marked reduction in origination rates during the Capitanian and Wuchiapingian is consistent with the effects of global cooling (the Kamura Event), but may also be consistent with other environmental stresses such as anoxia. However, a gradual reduction in diversity, rather than a sharp end-Guadalupian extinction, precludes the need to invoke drastic extinction mechanisms and indicates that taxonomic loss at the end of the Paleozoic was concentrated in the traditional end-Permian (end-Changhsingian) extinction, which eliminated 78% of all marine invertebrate genera.

BILLENGSELLIDE AND ORTHIDE BRACHIOPODS: NEW INSIGHTS INTO EARLIEST ORDOVICIAN EVOLUTION AND BIOGEOGRAPHY FROM NORTHERN IRAN

Abstract: The eastern Alborz Mountains of Iran comprise a significant peri‐Gondwanan terrane relevant to the early evolution of late Cambrian – early Ordovician brachiopods incorporated into the emerging benthic biota of the Paleozoic Evolutionary Fauna. A low diversity brachiopod assemblage from the late Tremadocian unit of the Lashkarak Formation contains six new species including the polytoechioideans Polytoechia and Protambonites and the orthoideans Paralenorthis, Ranorthis, Tarfaya and Xianorthis. The fauna preserves the earliest records of Polytoechia, unknown previously outside Laurentia and the Uralian margin of Baltica, and of Paralenorthis and Ranorthis, which were widespread along Gondwanan margins and in Baltica from the Floian (Arenig), plus Xianorthis, known hitherto only from the Floian of South China. The enigmatic Tarfaya has an impunctate shell fabric and setigerous perforations along the posterior margin, indicating placement within the Orthoidea in a new Family Tarfayidae. New species of Polytoechia, Protambonites, Paralenorthis, Ranorthis, Tarfaya, Xianorthis are described.

Macrostratigraphy and Its Promise for Paleobiology

Macrostratigraphy is the study and statistical analysis of sediment packages that formed continuously at a specified scale of temporal resolution and that are bound by gaps recognizable at that same scale. The temporal ranges of gap-bound packages, compiled separately for different geographic locations, permit area-weighted, survivorship-based measures of rock quantity and spatio-temporal environmental continuity to be measured. Analytical basin fill models suggest that the parameters controlling sedimentation and sequence stratigraphic architecture, such as base level and sediment supply, can be detected quantitatively by macrostratigraphy.Macrostratigraphic analysis of the marine sedimentary rock record in the United States at a temporal resolution of ~106 years reproduces most of the well-known Sloss sequences, but it also identifies two prominent megasequences, the Paleozoic and Modern megasequences, which are separated by a Permian-Triassic discontinuity and Phanerozoic minimum in rock quantity. Many short- and long-term features of the macroevolutionary history of marine animals are reproduced by macrostratigraphy, including 1) many patterns in genus richness, 2) patterns in rates of genus extinction and, to a lesser degree, rates of origination, and 3) patterns of extinction selectivity and the shifting relative richness of Sepkoski's Paleozoic and Modern evolutionary faunas. The extent to which macrostratigraphy reproduces the macroevolutionary history of marine animals transcends what is expected by geologically-controlled sampling biases. Instead, the processes which control the spatio-temporal dynamics of shelf sedimentation, including expansions and contractions of shallow epicontinental seas, have probably exerted a consistent influence on the macroevolutionary history of marine animals. Exploring the common cause hypothesis by putting fossils back into rocks and rocks into a new quantitative framework for physical environmental change holds considerable promise for paleobiology.

The Ordovician Biodiversification: revolution in the oceanic trophic chain

The Early Palaeozoic phytoplankton (acritarch) radiation paralleled a long-term increase in sea level between the Early Cambrian and the Late Ordovician. In the Late Cambrian, after the SPICE delta C-13(carb) excursion, acritarchs underwent a major change in morphological disparity and their taxonomical diversity increased to reach highest values during the Middle Ordovician (Darriwilian). This highest phytoplankton diversity of the Palaeozoic was possibly the result of palaeogeography (greatest continental dispersal) and major orogenic and volcanic activity, which provided maximum ecospace and large amounts of nutrients. With its warm climate and high atmospheric CO2 levels, the Ordovician was similar to the Cretaceous: a period when phytoplankton diversity was at its maximum during the Mesozoic. With increased phytoplankton availability in the Late Cambrian and Ordovician a radiation of zooplanktonic organisms took place at the same time as a major diversification of suspension feeders. In addition, planktotrophy originated in invertebrate larvae during the Late Cambrian-Early Ordovician. These important changes in the trophic chain can be considered as a major palaeoecological revolution (part of the rise of the Palaeozoic Evolutionary Fauna of Sepkoski). There is now sufficient evidence that this trophic chain revolution was related to the diversification of the phytoplankton, of which the organic-walled fraction is partly preserved.

Evolution, palaeoecology, and palaeobiogeography of the Late Ordovician–Early Silurian brachiopod Epitomyonia

Epitomyonia is characterized by various types of dorsal ridges, which may be transverse, longitudinal, or highly convoluted and probably served as skeletal supports for lophophores of various complexity. Multivariate analyses suggest that the Epitomyonia-bearing brachiopod associations lived in relatively shallow-water environment in the Late Ordovician, and inhabited mainly deep-water environments in the early Wenlock. The temporal and spatial change in the faunal distribution may be explained by three alternative scenarios: (1) Epitomyonia followed the broad evolutionary trend of the Palaeozoic Evolutionary Fauna to shift from shallow- to deeper-water settings over time; (2) the dicoelosiid communities could not compete with the large-shelled pentameride communities in continental shelf settings during the Early Silurian; or (3) only the shallow-water Epitomyonia died out in the Late Ordovician mass extinction event, whereas some poorly known deep-water Late Ordovician forms survived into the Early Silurian. Epitomyonia paucitropida n. sp. from the lower Whittaker Formation (late Katian) of the Mackenzie Mountains, northwestern Canada, is reported as the first known Ordovician species of Epitomyonia from the palaeocontinent of Laurentia, characterized by a small shell with weak, transverse dorsal ridges that are most primitive for the genus.

Evolutionary History of Cambrian Spiculate Sponges: Implications for the Cambrian Evolutionary Fauna

Broad-scale analyses of Cambrian spiculate sponges are scarce. The apparent differences between Cambrian and Ordovician sponge faunas were included in Sepkoski's concept of evolutionary faunas; in these, sponges were regarded as minor contributors to the Paleozoic and modern faunas and insignificant in the Cambrian Evolutionary Fauna. More recent published occurrences of Cambrian and Ordovician spiculate sponges and the inclusion of archaeocyaths in the phylum Porifera, however, have altered our understanding of the significance of sponges among Cambrian faunas. The majority of Cambrian occurrences appear to be segregated into two major associations: lower Cambrian sponges in China, and middle Cambrian sponges in North America, primarily British Columbia and Utah. The main associations of spiculate sponges are in siliciclastic deposits from middle-to-deep muddy shelf and basin environments, whereas orchoclad demosponges are associated with shallow carbonate environments. Four main aspects of sponge biology are considered potential factors dictating the distribution of sponges in the Cambrian: their trophic requirements, hydrodynamic constraints, possible biogeochemical constraints, and the sponge-sediment relationship. A series of critical steps in sponge evolutionary history occurred during the interval from the Proterozoic-Cambrian boundary to the middle– late Ordovician. The lower–middle Cambrian faunas are considered to be a Cambrian evolutionary sponge fauna, with archaeocyaths and diverse monaxonid demosponges as distinctive components. There was a transitional fauna in the upper Cambrian–Lower Ordovician, with orchoclad lithistids dominating shallow environments. Hexactinellids began to colonize nearshore siliciclastic settings during this time. The third interval, Middle–Upper Ordovician, corresponds to the Paleozoic Evolutionary Fauna, which is the interval during which lithistids diversified in several suborders and families and the stromatoporoid and sphinctozoan calcified sponges experienced their first radiation.

Taxon characteristics that promote survivorship through the Permian–Triassic interval: transition from the Paleozoic to the Mesozoic brachiopod fauna

Examination of organismal characteristics which promote survivorship through both background and mass extinctions may reveal general ecological principles potentially critical to modern conservation efforts. This study explores survivorship of brachiopods, a highly diverse and abundant Paleozoic clade, through the mid-Permian to mid-Triassic interval, which includes the greatest mass extinction in the history of metazoan life. This interval of time separates two of the major Phanerozoic evolutionary faunas. In this regard, survivorship across any one extinction during the interval would not have been relevant if the survivor went extinct shortly after the extinction event; surviving background extinction is as important as surviving a mass extinction. Similarly, taxa that survived but failed to rediversify also were not major elements of the Mesozoic evolutionary fauna. Thus, the analysis aims to analyze survivorship not just across a single extinction but across the entire mid-Permian to mid-Triassic; only survivors through the entire interval can be the ancestors of the Mesozoic clades.Fewer brachiopod genera survived the interval than did brachiopod clades, suggesting that pseudoextinction or insufficient sampling could be a problem in analyzing these extinctions; thus, survivorship analysis should be conducted at the clade level. Nine characteristics were examined for generic representatives of 20 North American brachiopod clades, five of which survived both Permian extinctions and the subsequent earliest Triassic transitional interval. Characteristics include both those that operate on global scales and those that operate on the higher-resolution scales of individuals and populations.Survivors were significantly smaller and occurred less frequently than victims. Mean diversity of communities in which survivors were present was significantly greater. The finding that rare taxa belonging to high-diversity communities were more likely to survive runs counter to traditional predictions. However, these results are consistent with recent studies suggesting that higher diversity within a trophic level may create a buffer, as surviving taxa quickly occupy the vacant niche space of the victims. As size, abundance, and community diversity are all statistically related, the small size of survivors may be an artifact of reduced biovolume per taxon in a diverse community.No significant relationship exists between global-scale processes and survivorship of brachiopods through the mid-Permian to mid-Triassic. The results suggest that ecological processes can strongly influence global extinction patterns.