High-latitude Assemblages Research Articles

Community Assembly and Climate Mismatch in Late Quaternary Eastern North American Pollen Assemblages.

Plant community response to climate change ranges from synchronous tracking to strong mismatch. Explaining this variation in climate change response is critical for accurate global change modeling. Here we quantify how closely assemblages track changes in climate (match/mismatch) and how broadly climate niches are spread within assemblages (narrow/broad ecological tolerance, or "filtering") using data for the past 21,000 years for 531 eastern North American fossil pollen assemblages. Although climate matching has been strong over the last 21 millennia, mismatch increased in 30% of assemblages during the rapid climate shifts between 14.5 and 10 ka. Assemblage matching rebounded toward the present day in 10%-20% of assemblages. Climate-assemblage mismatch was greater in tree-dominated and high-latitude assemblages, consistent with persisting populations, slower dispersal rates, and glacial retreat. In contrast, climate matching was greater for assemblages comprising taxa with higher median seed mass. More than half of the assemblages were climatically filtered at any given time, with peak filtering occurring at 8.5 ka for nearly 80% of assemblages. Thus, vegetation assemblages have highly variable rates of climate mismatch and filtering over millennial scales. These climate responses can be partially predicted by species' traits and life histories. These findings help constrain predictions for plant community response to contemporary climate change.

Declines in both redundant and trace species characterize the latitudinal diversity gradient in tintinnid ciliates.

The latitudinal diversity gradient is a well-known biogeographic pattern. However, rarely considered is how a cline in species richness may be reflected in the characteristics of species assemblages. Fewer species may equal fewer distinct ecological types, or declines in redundancy (species functionally similar to one another) or fewer trace species, those occurring in very low concentrations. We focused on tintinnid ciliates of the microzooplankton in which the ciliate cell is housed inside a species-specific lorica or shell. The size of lorica oral aperture, the lorica oral diameter (LOD), is correlated with a preferred prey size and maximum growth rate. Consequently, species of a distinct LOD are distinct in key ecologic characteristics, whereas those of a similar LOD are functionally similar or redundant species. We sampled from East Sea/Sea of Japan to the High Arctic Sea. We determined abundance distributions of biological species and also ecological types by grouping species in LOD size-classes, sets of ecologically similar species. In lower latitudes there are more trace species, more size-classes and the dominant species are accompanied by many apparently ecologically similar species, presumably able to replace the dominant species, at least with regard to the size of prey exploited. Such redundancy appears to decline markedly with latitude in assemblages of tintinnid ciliates. Furthermore, the relatively small species pools of the northern high latitude assemblages suggest a low capacity to adapt to changing conditions.

Morphological evidence for geologically young thaw of ice on Mars: A review of recent studies using high-resolution imaging data

Liquid water is generally only meta-stable on Mars today; it quickly freezes, evaporates or boils in the cold, dry, thin atmosphere (surface pressure is about 200 times lower than on Earth). Nevertheless, there is morphological evidence that surface water was extensive in more ancient times, including the Noachian Epoch (∼4.1 Ga to ∼3.7 Ga bp), when large lakes existed and river-like channel networks were incised, and early in the Hesperian Epoch (∼3.7 Ga to ∼2.9 Ga bp), when megafloods carved enormous channels and smaller fluvial networks developed in association with crater-lakes. However, by the Amazonian Epoch (∼3.0 Ga to present), most surface morphogenesis associated with liquid water had ceased, with long periods of water sequestration as ice in the near-surface and polar regions. However, inferences from observations using imaging data with sub-metre pixel sizes indicate that periglacial landscapes, involving morphogenesis associated with ground-ice and/or surface-ice thaw and liquid flows, has been active within the last few million years. In this paper, three such landform assemblages are described: a high-latitude assemblage comprising features interpreted to be sorted clastic stripes, circles and polygons, non-sorted polygonally patterned ground, fluvial gullies, and solifluction lobes; a mid-latitude assemblage comprising gullies, patterned ground, debris-covered glaciers and hillslope stripes; and an equatorial assemblage of linked basins, patterned ground, possible pingos, and channel-and-scarp features interpreted to be retrogressive thaw-slumps. Hypotheses to explain these observations are explored, including recent climate change, and hydrated minerals in the regolith ‘thawing’ to form liquid brines at very low temperatures. The use of terrestrial analogue field sites is also discussed.

Chapter 11 Biodiversity, biogeography and phylogeography of Ordovician rhynchonelliform brachiopods

Abstract The phylogeographical evolution and the consequent changing distribution and diversity of rhynchonelliform brachiopods through the Ordovician are linked to the dynamic palaeogeography of the period. The Early Ordovician (Tremadocian and Floian) is characterized by globally low-diversity faunas with local biodiversity epicentres, notably on the South China Palaeoplate; low-latitude porambonitoid-dominated faunas with early plectambonitoid and clitambonitoid representatives, as well as high-latitude assemblages mostly dominated by orthoids, can be recognized, but many taxa are rooted in Late Cambrian stocks. The Early Ordovician displays a steady increase in rhynchonelliformean biodiversity, which was mostly driven by the increasing success of the Porambonitoidea and Orthoidea, but the billingsellids and early plectambonitoids also contributed to this expansion. During the Early to Mid Ordovician (Dapingian–Darriwilian), marine life experienced an unprecedented hike in diversity at the species, genus and family levels that firmly installed the suspension-feeding benthos as the main component of the Palaeozoic fauna. However, this may have occurred in response to an early Darriwilian annihilation of existing clades, some of which had been most successful during the Early Ordovician. New clades rapidly expanded. The continents were widely dispersed together with a large number of microcontinents and volcanic arcs related to intense magmatic and tectonic activity. Climates were warm and sea-levels were high. Pivotal to the entire diversification is the role of gamma (inter-provincial) diversity and by implication the spread of the continents and frequency of island arcs and microcontinents. The phylogeographical analysis demonstrates that this new palaeogeographical configuration was particularly well explored and utilized by the strophomenides, especially the Plectambonitoidea, which radiated rapidly during this interval. The porambonitoids, on the other hand, were still in recovery following the early Darriwilian extinctions. Orthides remained dominant, particularly at high latitudes. Biodiversity epicentres were located on most of the larger palaeoplates, as well as within the Iapetus Ocean. Provincial patterns were disrupted during the Sandbian and early Katian with the migration of many elements of the benthos into deeper-water regimes, enjoying a more cosmopolitan distribution. Later Katian faunas exhibit a partition between carbonate and clastic environments. During the latest Katian, biogeographical patterns were disrupted by polewards migrations of warm-water taxa in response to the changing climate; possibly as a consequence of low-latitude cradles being developed in, for instance, carbonate reef settings. Many clades were well established with especially the strophomenides beginning to outnumber the previously successful orthides, although this process had already begun, regionally, in the mid to late Darriwilian. At the same time, atrypoid and pentameroid clades also began to radiate in low-latitude faunas, anticipating their dominance in Silurian faunas. The Hirnantian was marked by severe extinctions particularly across orthide-strophomenide clades within the context of few, but well-defined, climatically controlled provincial belts. Supplementary material: The individual localities and a reference list for the data sources are provided at: http://www.geolsoc.org.uk/SUP18667

Calcareous nannoplankton ecology and community change across the Paleocene-Eocene Thermal Maximum

The Paleocene-Eocene Thermal Maximum (PETM; ca. 55.8 Ma) is thought to coincide with a profound but entirely transient change among nannoplankton communities throughout the ocean. Here we explore the ecology of nannoplankton during the PETM by using multivariate analyses of a global data set that is based upon the distribution of taxa in time and space. We use these results, coupled with stable isotope data and geochemical modeling, to reinterpret the ecology of key genera. The results of the multivariate analyses suggest that the community was perturbed significantly in coastal and high-latitudes sites compared to the open ocean, and the relative influence of temperature and nutrient availability on the assemblage varies regionally. The open ocean became more stratified and less productive during the PETM and the oligotrophic assemblage responded primarily to changes in nutrient availability. Alternatively, assemblages at the equator and in the Southern Ocean responded to temperature more than to nutrient reduction. In addition, the assemblage change at the PETM was not merely transient—there is evidence of adaptation and a long-term change in the nannoplankton community that persists after the PETM and results in the disappearance of a high-latitude assemblage. The long-term effect on communities caused by transient warming during the PETM has implications for modern-day climate change, suggesting similar permanent changes to nannoplankton community structure as the oceans warm.

Global patterns of organic‐walled phytoplankton biodiversity during the late Silurian to earliest Devonian

Numerous environmental factors as well as oceanic circulation patterns and geographic constraints all contribute to the abundance, distribution, and diversity of present‐day marine phytoplankton assemblages. These same factors presumably affected the Paleozoic marine phytoplankton, which was dominated by organic‐walled acritarchs and prasinophytes. During the Late Silurian (Gorstian, Ludfordian, and Prídolf) and earliest Devonian (Lochkovian), important paleogeographic, paleooceanographic, and geochemical changes were occurring as well as major compositional changes and diversity fluctuations in the marine organic‐walled phytoplankton. Innovative morphologies appeared during the Late Silurian, in both low and high latitude assemblages, but with significant quantitative differences. This was followed by a turnover in assemblage composition during the Silurian/Devonian transition, and an initial radiation of new acritarch and prasinophyte taxa in the Early Devonian. Observed changes in total phytoplankton diversity during the Gorstian through earliest Lochkovian are based on organic‐walled microphytoplankton data derived from published and unpublished key stratigraphic sections where independent age control has been firmly established. These key sections are from: Missouri and Oklahoma, U.S.A. and western Newfoundland, Canada (Laurentia); Gotland, Sweden, and Podolia, Ukraine (Baltica); the Welsh Basin and Borderland (Avalonia); northern France and northern Spain (Armorica); and Libya in northern Africa, and Argentina and Bolivia, South America (Gondwana). Regional biodiversity changes for the organic‐walled microphytoplankton were determined for the warm low latitude areas (Baltica, Laurentia, and Avalonia) and temperate to cool higher latitude areas (northern and southern Gondwana). The Late Silurian‐earliest Devonian organic‐walled phytoplankton was divided into three major categories to facilitate comparison of compositional fluctuations, both within stratigraphic sections as well as between geographic areas. The three categories, based on overall morphology, are marine chlorophytes and prasinophytes, marine acritarchs, and nonmarine types, including coenobial forms. This triparate grouping is both broad and detailed enough to mark critical changes in both the phytoplankton assemblages, as well as the paleoenvironment. In general, high phytoplankton diversity peaks occurred during the Early and Late Gorstian in the warm low latitude areas, followed by varying fluctuations during the Ludfordian and Prídolí for both the warm low latitude and cool high latitude areas. An initial radiation of new phytoplankton taxa and the appearance of more cosmopolitan assemblages mark the beginning of the Lochkovian.

GLOBAL PATTERNS OF ORGANIC-WALLED PHYTOPLANKTON BIODIVERSITY DURING THE LATE SILURIAN TO EARLIEST DEVONIAN

Abstract Numerous environmental factors as well as oceanic circulation patterns and geographic constraints all contribute to the abundance, distribution, and diversity of present-day marine phytoplankton assemblages. These same factors presumably affected the Paleozoic marine phytoplankton, which was dominated by organic-walled acritarchs and prasinophytes. During the Late Silurian (Gorstian, Ludfordian, and Přidoli) and earliest Devonian (Lochkovian), important paleogeographic, paleooceanographic, and geochemical changes were occurring as well as major compositional changes and diversity fluctuations in the marine organic-walled phytoplankton. Innovative morphologies appeared during the Late Silurian, in both low and high latitude assemblages, but with significant quantitative differences. This was followed by a turnover in assemblage composition during the Silurian/Devonian transition, and an initial radiation of new acritarch and prasinophyte taxa in the Early Devonian. Observed changes in total phytop...

Antarctic sessile marine benthos: colonisation and growth on artificial substrata over three years

The development of sessile invertebrate assemblages on hard substrata has been studied extensively in temperate and tropical latitudes. Such studies provide insights into a range of ecological processes, and the global similarity of taxa recruiting to these assemblages affords the potential for regional-scale comparisons. However, few data exist for high latitude assemblages. This paper presents the first regularly resurveyed study of benthic colonisation from within the Antarctic Circle. Acrylic panels were deployed horizontally on the seabed at 8 and 20 m depths at each of 3 locations in Ryder Bay, Adelaide Island, SW Antarctic Peninsula (67° 35’ S, 68° 10’ W). Assemblages colonising upward- and downward-facing panel surfaces were photographed in situ from February 2001 to March 2004. Assemblages were dominated by bryozoans and spirorbid polychaetes. Total coverage after 3 yr ranged from 6 to 100% on downward-facing surfaces but was <10% on all upward-facing surfaces. Overall colonisation rates were up to 3 times slower than comparable temperate latitude assemblages but showed unexpected similarities with a tropical assemblage. Growth in most taxa was highly seasonal and maximum growth rates of encrusting bryozoans were 5 to 10 times slower than literature values for temperate species, suggesting rate limitation by cold rather than food availability. Assemblage development was controlled predominantly by post-settlement disturbances, and there was considerable variability between locations associated with differences in disturbance history. Ice impact was significant only at 8 m but biotic disturbances exerted a stronger and more consistent influence on assemblage development at all sites. It is suggested that the combination of slow growth rates and strong environmental seasonality results in succession being more predictable than in comparable temperate or tropical assemblages.

Early Ordovician bivalves from Dali, West Yunnan, China

A bivalve fauna of Early Ordovician (late Arenig) age is described from the Hsiangyang Formation of the eastern part of West Yunnan, China. The fauna contains elements in common with Early Ordovician faunas of southern Gondwanan areas such as the Montagne Noire and Morocco and with those of Avalonia, together with several previously undescribed taxa. The following taxa are new: Biseriodonta simplex gen. et sp. nov.; Glyptarca sinensis sp. nov.; Trigonoglyptarca magna gen. et sp. nov.; Erhaiconcha xiangyangensis gen. et sp. nov.; Fasciculodonta impressa gen. et sp. nov.; Yunnanoredonia laevis gen. et sp. nov.; Daliella gen. nov.; Goniophorina (Goniophorina) contracta sp. nov.; Haidongoconcha radialis gen. et sp. nov.; Eopterinea aequiconcha gen. et sp. nov. The bivalve fauna includes the most diverse glyptarcid fauna and the earliest nuculanid and paracyclid known hitherto. Eastern West Yunnan belonged to the Indochina terrane and it is concluded that the bivalve fauna represents a high‐latitude assemblage and that the Indochina terrane should be considered a component part of the Peri‐Gondwanan continent in the Ordovician; its bivalve faunas contrast with those of neighbouring terranes which have affinities with those of lower latitudes.

The evolutionary history of size variation of planktic foraminiferal assemblages in the Cenozoic

The iterative evolutionary radiation of planktic foraminifers is a well-documented macroevolutionary process. Here we document the accompanying size changes in entire planktic foraminiferal assemblages for the past 70 My and their relationship to paleoenvironmental changes. After the size decrease at the Cretaceous/Paleogene (K/P) boundary, high latitude assemblages remained consistently small. Size evolution in low latitudes can be divided into three major phases: the first is characterized by dwarfs (65–42 Ma), the second shows moderate size fluctuations (42–14 Ma), and in the third phase, planktic foraminifers have grown to the unprecedented sizes observed today. Our analyses of size variability with paleoproxy records indicate that periods of size increase coincided with phases of global cooling (Eocene and Neogene). These periods were characterized by enhanced latitudinal and vertical temperature gradients in the oceans and high diversity (polytaxy). In the Paleocene and during the Oligocene, the observed (minor) size changes of the largely low-diversity (oligotaxic) assemblages seem to correlate with productivity changes. However, polytaxy per se was not responsible for larger test sizes.

Biogeography of terminal Cretaceous benthic foraminifera: deep-water circulation and trophic gradients in the deep South Atlantic

The biogeographic distribution of terminal Cretaceous (late Maastrichtian) deep-sea benthic foraminifera are analysed from the South Atlantic Ocean. The data quantified derive from six DSDP sites representing a west-to-east transect in mid-latitudes and three high-latitude ODP sites.Correspondence analysis revealed five benthic foraminiferal assemblages that are representative of bathymetrically and latitudinally different environmental settings within the South Atlantic: (1) a Shallow Mid-Latitude Assemblage [Bolivinoides draco, Eouvigerina subsculptura, Gaudryina pyramidata,Scheibnerova ? sp., Spiroplectammina spp. (calcerous forms) and Tritaxia aspera]; (2) an Intermediate Mid-Latitude Assemblage [Cibicidoides hyphalus, Nuttallides truempyi, Paralabamina lunata, Praebulimina spp., Sitella cushmani and Valvalabamina sp. (involute form)]; (3) a Deep Mid-Latitude Assemblage (Bulimina velascoensis, Gyroidinoides beisseli, Nuttallinella sp. A,Oridorsalis -complex, Osangularia ? sp., Paralabamina hillebrandti, Quadrimorphina camerata,Reussella szajnochae szajnochae and Sitella cf. plana); (4) a Shallow High-Latitude Assemblage (Alabamina creta, Brizalina incrassata, Osangularia texana, Pullenia coryelli, Pyramidina rudita and Spiroplectammina‘crassa’); and (5) a Deep High-Latitude Assemblage [Gavelinella beccariiformis, Gyroidinoides quadratus, Nuttallides sp. A, Osangularia velascoensis,Paralabamina sp. (intermediate form), Valvalabamina ? praeacuta and Spiroplectammina dentata].Comparison of the proportions of epibenthic/endobenthic morphotypes within each of the five assemblages resulting from correspondence analysis suggests clear trends between sites of the mid- and high latitudes respectively, and along bathymetric gradients among sites of similar latitudes. These trends are inferred to represent environmental (such as trophic and oxygenation) gradients when placed within a framework of hypothesized surface circulation and upwelling patterns in the late Maastrichtian South Atlantic.

Reworked Jurassic-Neogene calcareous nannofossils in the central Arctic

Over 130 different reworked calcareous nannofossil taxa, ranging from the Lower Jurassic to the Neogene, are recorded in Quaternary sediments from the central Arctic Ocean. Species with Mesozoic and Tertiary stratigraphic ranges occur together. This suggests that the reworked specimens are not primarily derived from the local bedrock, but are transported to the central Arctic Ocean from the surrounding shelves and landmasses. Sea ice provides a possible means of transport. The reworked nannofossil assemblages in the Arctic are a result of geologic and climatic developments in the source areas, both during the time of their deposition and during their subsequent erosion and transportation in the Quaternary. Only two specimens restricted to the Lower Jurassic were observed and none restricted to the Middle and Upper Jurassic. The Lower Cretaceous is represented by at least four species restricted to that interval, together with other long ranging taxa. The presence of Micrantholithus speetonensis Perch-Nielsen is the first record of this species outside northwest Europe. The other Lower Cretaceous species observed are all typical of temperate to high latitude assemblages of both the southern and northern hemispheres. The nannofossils reworked from the Upper Cretaceous strata are the dominant component of the assemblages. Nephrolithus corystus Wind is recorded in the northern hemisphere for the first time. Some of the distinctive high latitude species present in the southern hemisphere have not been observed in the Arctic. Helioliths, discoasters and sphenoliths indicate relatively warm surface water conditions in the Arctic-subarctic areas during the Paleocene and Eocene.

Origin of the subgenera Cyclampterium, Paralampterium and Sciadiopeplus from Lophocyrtis ( Lophocyrtis) (Radiolaria, Theoperidae)

Work on the exceptionally well-preserved, rapidly accumulating Bath Cliff Section, Barbados and supplementary Deep Sea Drilling Project samples, has revealed the evolutionary origins of three stratigraphically useful species in the Cryptoprora ornata Zone straddling the Eocene/Oligocene boundary and demonstrated the origin of the genus Cyclampterium. Elucidation of the origin of Cyclampterium milowi necessitates a revision of the genera Lophocyrtis and Cyclampterium. Lophocyrtis ( Lophocyrtis) jacchia is the ancestor of L. ( Cyclampterium) hadra, the earliest member in the subgenus Cyclampterium which comprises the anagenetic lineage leading from L. ( C.) hadra to L. ( C.) neatum. The monotypic subgenus Sciadiopeplus branches off from an early member in the Cyclampterium lineage. The new species L. ( L.) exitelus and L. ( S.) oberhaensliae terminate the subgenera Lophocyrtis and Sciadiopeplus, respectively. During the investigation it also became clear that morphotypes resembling early L. ( C.) milowi could be found in mid and high latitude assemblages in the late Early and late Middle Eocene. The origin of one these morphotypes was also traced to L. ( Lophocyrtis) jacchia giving rise to the new subgenus Paralampterium. This lineage includes the new species L. ( Paralampterium) dumitricai and two species questionably assigned to it, L. ( Paralampterium)? longiventer and the new species L. ( Paralampterium) ? galenum. The relationship of L. ( P.) dumitricai to L. ( P.) ? longiventer and L. ( P.) ? galenum is unknown.

Late Cretaceous deep-water agglutinated foraminiferal assemblages from the North Atlantic and its marginal seas

The stratigraphic and biogeographic distribution of more than 170 species of deep-water agglutinated benthic foraminifers (DWAF) from the North Atlantic and adjacent marginal seas has been compared with paleoenvironmental data (e.g. paleobathymetry, oxygenation of the bottom waters, amount of terrigenous input and substrate disturbance). Six general types of assemblages, in which deep water agglutinated taxa occur, are defined from the Turonian to Maastrichtian times: 1. High latitude slope assemblages 2. Low to mid latitude slope assemblages 3. Flysch-type assemblages 4. Deep water limestone assemblages (»Scaglia«-type) 5. Abyssal mixed calcareous-agglutinated assemblages 6. Abyssal purely agglutinated assemblages Latitudinal differences in faunal composition are observed, the most important of which is the lack or extreme paucity of calcareous forms in high latitude assemblages. East-to-west differences appear to be of comparatively minor importance. Most DWAF species occur in all studied regions and are thus considered as cosmopolitan. Biostratigraphic turnovers in the taxonomic content of assemblages are observed in the lowermost Turonian, mid- Campanian and in the upper Maastrichtian to lowermost Paleocene. These datum levels correspond to inter-regional and time-constant paleooceanographic events, which probably also affected the deep-water benthic biota. This allows us to use deep-water agglutinated foraminifers for biostratigraphy in the North Atlantic sequences deposited below CCD and to geographically extend the currently used zonal schemes which have been established in the Carpathian and Alpine areas.

Mesozoic-cenozoic history of calcareous nannofossils in the region of the southern ocean

The Mesozoic-Cenozoic evolution of high southern latitude calcareous nannofossil assemblages developed in parallel with that of the Southern Hemisphere ocean basins and the attendant progressive changes in global climate. The equitable Middle to Late Jurassic climates are reflected in a cosmopolitan zonation although distinctive high latitude taxa developed in both polar regions. Monospecific or low diversity provincial assemblages characterized the incipient Early Cretaceous South Atlantic Basins until the introduction of Tethyan elements during the Aptian. Bipolar or austral provincial taxa are useful in erecting a biostratigraphic subdivision for the remainder of the Cretaceous sequence on the Falkland Plateau. In contrast to the middle Cretaceous, the global sample coverage of DSDP holes for the Campanian-Maestrichtian is sufficiently broad to demonstrate a distinct latitudinal distribution of species and assemblages. Provincial austral or bipolar taxa are relatively minor components of the Paleocene-Eocene assemblages, but quantitative methods document the existence of definable high latitude assemblages which shifted latitudinally in response to climatic changes. Indirect evidence suggests that calcareous nannofossils were deposited in the interior basins of Antarctica during this interval. Species diversities declined progressively through the Oligocene-Miocene epochs in response to the deterioration of Neogene climates and glacial episodes on the Antarctic continent, finally resulting in low diversity assemblages generally dominated by high latitude taxa. Sharp migrations of these assemblages occurred in response to glacial-climatic events. Plio/Pleistocene sediments deposited beneath the expanding Antarctic water mass are essentially barren of calcareous nannofossils, but coccoliths are widely distributed in the Subantarctic region as a result of the amelioration of Holocene climate and the Quaternary descent of the carbonate compensation depth. Two new taxa are described: Stephanolithion bigotii brevispinus n. ssp. from the Upper Jurassic and Gephyrobiscutum diabolum n.g., n. sp. from the lower Campanian.

Comparison of Foraminiferal, Coccolithophorid, and Radiolarian paleotemperature equations: Assemblage coherency and estimate concordancy

The Imbrie-Kipp method of paleotemperature estimation is rigorously tested by comparing Atlantic temperature equations independently derived from the microfossils of three biotic groups: the Foraminifera, Coccolithophorida, and Radiolaria. This method consists of two steps: factor analysis of the modern sea-bed data of the individual groups which resolves discrete biogeographic assemblages and regression analysis of the modern assemblage data with observed sea-surface temperature data to obtain paleotemperature equations. Assemblage biogeography shows a simple subdivision into warm (low latitude) and cold (high latitude) for all biotic groups. Between biotic groups there is greater similarity among high-latitude assemblages than low-latitude ones. Correlating the assemblage data with observed sea-surface temperatures to produce temperature distribution patterns shows differences of less than 2°C in their optimum and critical temperatures. Regression analysis produced accurate temperature equations for each biotic group, all with standard errors of estimate of less than or equal to 2°C. Multiple correlation coefficients were all greater than 0.970. Applying these equations to two multiple biotic data sets (the modern and ice-age sea-bed data) and comparing their temperature estimates using the standard error pooled, shows over 87% concordancy for both data sets. Unlike the modern data, the discordancy among temperature estimates of the ice-age data shows a distinct geographic distribution; its cause is believed to be oceanographic, a difference in the water-mass structure between the modern and ice-age ocean.