bluuebunny/crossref_metadata_2025 huggingface dataset:
Jaw geometry and molar morphology in marsupial carnivores: analysis of a constraint and its macroevolutionary consequences
Authors: Werdelin Lars
Published: July 2016

In both jaw geometry and molar morphology, eutherian carnivores (order Carnivora) as a whole display greater diversity (plasticity in evolution from the primitive type) than marsupial carnivores (order Dasyurida). This is related to the difference in tooth replacement between the two taxa. In Carnivora, the permanent carnassial is preceded by a deciduous carnassial; the permanent tooth can erupt in its (geometrically) permanent position, and the post-carnassial molars are free to evolve for specialized functions or be reduced. In Dasyurida, there is relative molar progression, each erupting molar in turn functioning as a carnassial, and subsequently being pushed forwards in the jaw by the next erupting molar. Thus, all molars have carnassiform morphology, and none are free to develop for other functions. The greater plasticity of Carnivora has led to their adaptive zone being broader (as a group they are relatively more eurytopic than Dasyurida), which in turn has led to greater taxonomic diversity within Carnivora than Dasyurida. The resulting pattern from a macroevolutionary point of view is that, even in the absence of direct competition, Carnivora have had greater evolutionary “success” than Dasyurida.
The taphonomy of gastropod shell accumulations in large lakes: an example from Lake Tanganyika, Africa
Authors: Cohen Andrew S.
Published: July 2016

An investigation of shell morphometrics of the prosobranch genusParamelaniafrom Lake Tanganyika shows striking contrasts between some live and dead populations from identical localities. Living populations and surficial dead shells were collected from 15 sublittoral-profundal localities along the east side of the lake. Interpopulation variability in this endemic gastropod is clinal (N-S) for several shell characters. Intrapopulation variability of dead shell populations frequently exceeds that of live populations. Distinctive morphs may be present in a local dead shell population which are absent in the live population from the same locality. However, the phenodeviant dead shell morphology may occur among live snails elsewhere in the lake. Phenodeviant shells may be encrusted, but are unabraded and show no preferred orientation.

Radiocarbon ages of >2000 yr b.p. on dead phenodeviants suggest that surficial shell accumulations in Lake Tanganyika are strongly time-averaged. Although wave activity and biogenic concentration are important processes in Lake Tanganyika, neither is sufficient under modern lake conditions to account for these admixed assemblages. Winnowing andin situstratigraphic condensation during periods of lowered lake levels is the most likely explanation for the occurrence of phenodeviant surficial shells. This hypothesis is consistent with the observation that extensive shell lags are exposed on the lake floor in areas currently inhabited by the same snails.

A model of biogeographic range fluctuations for particularParamelaniamorphs during the Holocene, in concert with lake level fluctuations, can account for the shell assemblages seen on the lake floor today. The complex history of these accumulations suggests that taphonomic admixtures may obscure the interpretation of evolutionary sequences in the lacustrine stratigraphic record.
Paedomorphosis, Aristotle's lantern, and the origin of the sand dollars (Echinodermata: Clypeasteroida)
Authors: Mooi Rich
Published: July 2016

Convincing hypotheses of the origin of major invertebrate groups are difficult to make in the absence of phylogenetic analyses. In spite of this, several scenarios exist for the origin of the unusual echinoid order Clypeasteroida. I expand upon the most probable of these models by performing a phylogenetic analysis on three clypeasteroid suborders, the enigmatic fossil genusTogocyamus, and the extinct Oligopygoida. This analysis shows that the oligopygoids are the sister group of the Clypeasteroida plusTogocyamus. The latter is here considered a plesion (extinct sister group) to the crown group Clypeasteroida. Within that order, the suborder Clypeasterina is the sister group to the Laganina plus Scutellina. A new classification of all these taxa is presented. The phylogeny is based on 47 characters and incorporates data on external appendages, Aristotle's lantern anatomy, and test structure of irregular echinoids, as well as new information on the morphology ofTogocyamus. The earliest clypeasteroids had a lantern similar to that of adult oligopygoids, which in turn inherited their lantern from a cassiduloid-like ancestor that retained the lantern into adulthood. This lantern is absent in adult cassiduloids. Subsequent changes, including modification of the lantern into a crushing mill, extreme flattening of the test, and proliferation of food-gathering tube feet have allowed clypeasteroids to become epifaunal inhabitants of environments characterized by fine, shifting substrates, a habitat previously inaccessible to most other irregular echinoids.
Angiosperm diversification and Cretaceous floristic trends: a comparison of palynofloras and leaf macrofloras
Authors: Lidgard Scott , Crane Peter R.
Published: July 2016

Fossil leaves and palynomorphs represent different phases of the plant life cycle, are studied as systematically independent entities, and are subject to different taphonomic, sampling, and recognition biases in the paleobotanical record. They thus provide parallel, and largely independent, documentation of long-term trends in land plant diversity, and the palynological record may be used as a comparative test of floristic trends inferred from macrofossil evidence. Analyses of relative “species” richness in 91 macrofossil and 860 palynomorph Cretaceous “floras” (assemblages) from between 25° and 65° N paleolatitude show a major mid-Cretaceous increase in the within-flora diversity of angiosperms, from near 0% prior to the Aptian (120 Ma) to 50–80% by the end of the Maastrichtian (65 Ma). This level of diversity is attained rapidly in macrofloras, but more slowly in palynofloras. In the latest Cretaceous, macrofloras and palynofloras both indicate that “pteridophytes,” conifers, and other “gymnosperms” are generally less diverse than angiosperms. In both data sets, “pteridophyte” diversity shows a clear decline through the Cretaceous, whereas conifer diversity shows no marked temporal trend. Broad congruence of these patterns, in spite of different biases in the macrofossil and palynomorph records, indicates that they provide a robust reflection of floristic trends through the Cretaceous. Nevertheless, discrepancies between the patterns do occur and underline the importance of complementary macrofossil and palynological analyses for accurate resolution of long-term vegetational change.
A reassessment of the enigmatic Burgess Shale fossil Wiwaxia corrugata (Matthew) and its relationship to the polychaete Canadia spinosa Walcott
Authors: Butterfield Nicholas J.
Published: July 2016

The enigmatic fossil Wiwaxia corrugata is organically preserved in the Burgess Shale (Middle Cambrian, British Columbia) and is therefore extractable by careful acid maceration of the mineralic matrix. High magnification transmitted light microscopy and SEM of macerated Wiwaxia sclerites reveal a substantial amount of previously undescribed structural and microstructural detail. Anatomical and histological comparison with modern organisms indicates that Wiwaxia sclerites are polychaete paleae (flattened setae) and that Wiwaxia was a jawed annelid broadly related to the extant polychaete families Chrysopetalidae and/or Aprhoditidae (Palmyra). Canadia spinosa, an uncontested fossil polychaete from the same beds, shows a paleal microstructure identical to that of Wiwaxia, as well as a closely comparable gross anatomy and taphonomic grade. The unique combination of taxonomically significant characters shared by Wiwaxia and Canadia suggest that they are more closely related to each other than either is to any other fossil or extant polychaete. Thus they constitute a separate superfamily, Canadiacea superfam. nov., in the order Phyllodocida.
Effects of late Cenozoic sea-level fluctuations on the bivalve faunas of tropical oceanic islands
Authors: Paulay Gustav
Published: July 2016

The frequent late Cenozoic glacial ages were accompanied by sea-level falls of 100–150 m amplitude. These falls stranded the complex inner-reef platforms and lagoons of tropical Pacific islands, while outer-reef-slope habitats persisted, although displaced downslope. The effects of glacial regressions on bivalves were studied by examining the zonation of species across reef systems and species composition on tectonically uplifted islands, islands with, effectively, local low sea stands. I show that qualitative habitat loss (the stranding of inner-reef habitats) was responsible for the local extinction of about one-third of the bivalve species that inhabit central Pacific islands during high sea stands, whereas quantitative loss of habitat area and climatic effects were inconsequential. Soft-sediment habitats, and consequently soft-bottom bivalves, were more drastically affected by sea-level fluctuations than were hard-bottom habitats and bivalves.

Although many bivalve species were extirpated in the central Pacific during low sea stands, they survived in the western Pacific, where the different geomorphology of many marine systems provided refugia for lagoonal species. Thus, a large proportion of Pacific bivalve species has very dynamic distributions, undergoing great range reductions and expansions with falls and rises of sea level, and much of the present central Pacific lagoonal fauna is of Holocene age. Several implications of these findings are discussed.
The effect of random range truncations on patterns of evolution in the fossil record
Authors: Springer Mark S.
Published: July 2016

Both fossil preservation and sampling methods affect perceived patterns of biotic diversity. Artificial range truncations, for example, may lead to incongruences between apparent- and actual-diversity curves. Thus, a catastrophic extinction event may appear gradual. Recent advances in biostratigraphic-gap analysis provide models for the distribution of gap lengths between fossil occurrence horizons and provide methods to place confidence intervals on local taxon ranges and remove the biases caused by artificial range truncations. Confidence intervals for a set of local taxon ranges may then be evaluated collectively to test a hypothesis of co-extinction/co-emigration or co-origination/co-immigration. In the case of terminal Cretaceous ammonites from Seymour Island, range-chart data are compatible with an abrupt extinction event, although the test statistic is not minimized at the stratigraphic horizon that was suggested by Macellari (1986).
Living and fossil scallop shells as airfoils: an experimental study
Authors: Hayami Itaru
Published: July 2016

Selected shell specimens of extant and fossil streamlined pectinids, which have or presumably had level-swimming ability, were examined experimentally to elucidate their hydrodynamic properties, in particular, airfoil efficiency estimated by lift-drag ratio. Using a stationary water tank for nautical engineering, lift and drag forces were measured at various attack angles. Of the examined species, Amusium japonicum, which is characterized by an unusually shiny surface, upward-cambered commissure and sharpened trailing edge, is the most efficient level swimmer and has the lowest drag coefficient and the highest value of lift-drag ratio at any attack angle. Amussiopecten praesignis from the Plio-Pleistocene may have swum horizontally because its airfoil efficiency is superior to that of a living level swimmer, Placopecten magellanicus. Although its shell shape is analogous to that of Placopecten, Camptonectes (Maclearnia) cinctus from the Lower Cretaceous shows a much inferior efficiency and a significant flow separation from the surface. Bernoulli's effect in convex-upward species may contribute to increase lift, but a certain attack angle is always required for level flight. The strategy of level swimming probably evolved independently in several pectinacean lineages in which swimming rather than shell robustness became the preferred defense against predators. One problem that must be solved is that some feedback mechanism is required to check pitching, rolling, and yawing of the shell to attain stability in level flight.
Dickinsoniaas a polypoid organism
Authors: Valentine James W.
Published: July 2016

Dickinsoniais reconstructed as a benthic polypoid of generally cnidarian design. The oral surface was without tentacles but contained a median oral slit that probably led through a pharynx into an enteron, which was divided into digestive diverticulae by radiating mesenteries; feeding may have been via ciliary tracts. The mesenteries and body wall contained a stiff form of mesogloea. There seems to be no need to postulate a novel constructional grade for this organism, bringing the concept of the Vendozoa into question.
Nonprogressive evolution in a clade of CretaceousMontastraea-like corals
Authors: Budd Ann F. , Coates Anthony G.
Published: July 2016

A phylogeny of CretaceousMontastraea-like corals was constructed and used to evaluate the importance of differential speciation, selective extinction, and developmental constraints in the evolutionary history of the clade. Colonies assembled from localities across the central and western Tethyan region were subdivided into four stratigraphic levels: (1) Neocomian to lower Albian, (2) upper Albian to Cenomanian, (3) Turonian to Campanian, and (4) Maastrichtian. Ten corallite characters were measured on transverse thin sections of each colony, and analyzed following a three-step procedure: (1) species were recognized using all-inclusive average linkage cluster analyses (UPGMA) and a series of iterative canonical discriminant analyses; (2) species were separated by stratigraphic level and linked between levels by comparative analysis of the resulting discriminant scores; and (3) ancestor-descendant relationships were interpreted within and among adjacent levels using phenetic and cladistic approaches. A composite tree was then examined with respect to biogeography.

The results suggest that a total of 16 species existed during the Cretaceous, only 2 of which extended between stratigraphic levels. Speciation events between levels 1 and 2 were associated with the radiation of “small-corallite” forms from a “large-corallite” form, as its distribution expanded southward into the Tethyan realm. Limited speciation and stasis predominated among species within the clade between levels 2 and 3. Speciation events between levels 3 and 4 were associated with the radiation of predominantly “large-corallite” forms from a “small-corallite” form, as the clade became restricted to the Caribbean. Extinction initially focussed on “small-corallite” forms, but later shifted to “large-corallite” forms. Morphologic change was constrained between two extremes, the lower limit of which involved a minimum corallite diameter possibly set by developmental or ecological constraints, and the upper by limitations to increases in number of septa. The overall net result was that of nonprogressive evolution within the clade.
The Phylum Vendobionta: a sister group of the Eumetazoa?
Authors: Buss Leo W. , Seilacher Adolf
Published: July 2016

We offer an alternative interpretation of the Kingdom Vendobionta as a monophyletic sister group to the Eumetazoa. We hypothesize that the Vendobionta are cnidarian-like organisms that lacked cnidae. Cnidarians are held to have arisen by acquisition of cnidae by symbiosis with a microsporidian. Our analysis differs from existing interpretations of the Ediacaran fossils as ancestors of extant cnidarians in that we do not regard any of these forms as either polypoid or medusoid. This interpretation requires the erection of a new metazoan phylum, the Vendobionta.
The paradox of the first tier: an agenda for paleobiology
Authors: Gould Stephen Jay
Published: July 2016

Nature's discontinuities occur both in the hierarchical structuring of genealogical individuals and in the distinct processes operating at different scales of time, here called tiers. Conventional evolutionary theory denies this structuring and attempts to render the larger scales as simple extrapolation from (or reduction to) the familiar and immediate—the struggle among organisms at ecological moments (conventional individuals at the first tier). I propose that we consider distinct processes at three separable tiers of time: ecological moments, normal geological time (trends during millions of years), and periodic mass extinctions.

I designate as “the paradox of the first tier” our failure to find progress in life's history, when conventional theory (first tier processes acting on organisms) expects it as a consequence of competition under Darwin's metaphor of the wedge. I suggest a resolution of the paradox: whatever accumulates at the first tier is sufficiently reversed, undone, or overriden by processes of the higher tiers. In particular, punctuated equilibrium at the second tier produces trends for suites of reasons unrelated to the adaptive benefits of organisms (conventional progress). Mass extinction at the third tier, a recurring process now recognized as more frequent, more rapid, more intense, and more different than we had imagined, works by different rules and may undo whatever the lower tiers had accumulated.
Species in the fossil record: concepts, trends, and transitions
Authors: Gingerich Philip D.
Published: July 2016

Morphological continuity in the fossil record is the principal evidence favoring evolution as a historical explanation for the diversity of life. Continuity is usually discussed on scales broader than the species level. Patterns of morphological variation characteristic of living species are useful in recognizing species on time planes in the fossil record, but the fossil record is rarely complete enough temporally or geographically to preserve more than a fraction of species living in a given interval. Transitions between known species are even rarer. Where transitions are preserved, new species appear to arise through anagenesis (transformation of an ancestral stock producing a modified descendant) and through cladogenesis (subdivision of an ancestral lineage where one or more descendants differ from the ancestral stock). Evolutionary species are often necessarily bounded arbitrarily in the dimension of time.

Orthogenesis and punctuated equilibrium lie at opposite poles in a spectrum of speciation modes. Orthogenesis, highly constrained anagenesis, is probably rare. Cladogenesis appears to differ little from anagenesis once ancestral stocks are segregated. Limited evidence suggests that morphological differentiation during cladogenesis postdates genetic isolation. Hence punctuated equilibrium may be rare as well. Patterns of gradual change over time indicate that morphological evolution is reasonably viewed as continuous within and between species. Rates of evolution vary greatly (continuity does not require constancy). Rate distributions are truncated and biased by limits of stratigraphic completeness and time resolution: moderate to high rates of morphological evolution and species turnover are rarely recorded by fossils. Species durations are poorly characterized, but they appear to be so variable that there is no suggestion of periodicity. Species longevity is unpredictable. The episodic nature of faunal turnover suggests that extrinsic environmental factors rather than intrinsic homeostatic factors govern evolution at the species level.
Estimation of locomotory forces and stresses in the limb bones of Recent and extinct equids
Authors: Thomason J. J.
Published: July 2016

The locomotory stresses acting at the midshaft of the third metacarpal ofEquusare estimated from a geometrical model of the manus during peak loading, which is derived from in vivo data. The stress results compare favorably with those from in vivo strain gage experiments. The model is then modified to account for the anatomical and inferred functional differences in the feet of the two extinct, tridactyl equidsMerychippusandMesohippus, incorporating assumptions from earlier functional studies. Estimates of the stresses in the fossil metacarpals are derived, and fall within the range of values obtained in vivo for limb bones of a wide size range of mammals. The results indicate that the third metacarpal ofMerychippuswas the most highly stressed and that ofMesohippusthe least, with stresses forEquusfalling between. Thus the anatomical and functional changes in the manus betweenMesohippusandEquusare not simply a result of the difference in body size.
Mass extinction patterns of marine invertebrate groups and some implications for a causal phenomenon
Authors: McKinney Michael L.
Published: July 2016

A nonparametric analysis of the extinction patterns of 10 major marine invertebrate groups at the five most profound mass extinction events leads to five observations: (1) At each event some taxonomic groups were affected much more than others. (2) There is little consistency among events in terms of which taxonomic groups were most or least affected; however, adaptive groupings do exhibit consistency: benthic, mobile organisms suffered significantly fewer extinctions than sessile suspension feeders, while the pelagic organisms apparently suffered the most. (3) There are no convincing patterns of interrelated extinctions among taxonomic groups. (4) No group exhibits a persistent tendency through time for a relative increase or decrease in their extinction rate at the events. (5) Some relationships are seen between the extinction patterns of three pairs of events; the Late Ordovician and Late Devonian events exhibit a significantly similar pattern (the same taxonomic groups suffered the most extinction in both cases) as do the Late Triassic and Late Cretaceous events. The Late Permian and Late Cretaceous events show a significantly inverse pattern (the most affected groups in the former were among the least affected in the latter). Upon examination, these observations, notably 1, 2, and 5, are consonant with current scenarios of the effects of catastrophic bolide impacts on marine fauna.
The use of paleontology in systematics and biogeography, and a time control refinement for historical biogeography
Authors: Grande Lance
Published: July 2016

Four main potential contributions of fossils to phylogenetic systematics and historical biogeography are (1) to provide additional taxa which (when sufficiently well preserved) can give new morphological and ontogenetic data in addition to those provided by Recent species; (2) to provide additional taxa which can increase the known biogeographic range of a taxon; (3) to help establish a minimum age for a taxon; and (4) to present fossil biotas that can be examined for biogeographic patterns not recognizable in younger (including the Recent) or older biotas.

The first three points have been expressed or at least implied by other workers and are only briefly reviewed. The fourth point is proposed as a method of using fossil biotas to provide time controls to cladistic studies of historical biogeography. Previously, cladistic vicariance biogeographers have used fossilplusRecent biotas, or the Recent biota alone, for the geographic areas of study. Such investigations that lack any time control in the data base cannot effectively deal with areas that have complex histories as, for example, an earlier area of endemism in which area relationships are later complicated through the addition of exotic taxa by dispersal. By using time controls provided by fossil biotas, we may learn more about the relationships of areas with complex histories and may reveal biogeographical information that is sometimes unavailable through examination of the Recent biota.
On the expected distribution of species' ranges
Authors: Koch Carl F. , Morgan John P.
Published: July 2016

A method is provided to calculate the expected distribution of species' ranges for use as a basis of comparison for paleontological interpretation of species' range charts. If the method is used for such studies, the possibility of suggesting an environmental or biological cause for observed patterns, when in fact no such cause exists, will be diminished. The method is applied to a large, well-studied fossil data set to illustrate some possible species' range patterns which result only from sample size inequities. As examples, stepwise extinction and species richness patterns are predicted for situations where, in reality, none exist.
Survivorship analysis of Cambrian and Ordovician trilobites
Authors: Foote Mike
Published: July 2016

Cohort analysis is used to investigate survivorship of trilobites originating during the Cambrian and Ordovician. Using a time-homogeneous branching model, it is estimated that trilobite genera and species originating during the Ordovician survived three times longer than Cambrian genera and species. Monte Carlo simulation of survivorship is used to show that (1) Cambrian and Ordovician survivorship are significantly different, (2) Ordovician cohorts conform more closely to the time-homogeneous model than do Cambrian cohorts, and (3) deviations from temporal homogeneity are more often produced by extraordinary extinction than by unusually slow turnover.

When Early Ordovician cohorts are decomposed into genera within families that originated in the Cambrian versus the Ordovician, no evidence that Cambrian and Ordovician survivorship differences are clade-specific can be found. Ordovician genera of Cambrian affinity and of Ordovician affinity become extinct at similar rates.

Some of the ultimate causes of these differences in survivorship include (1) taxonomic inconsistency, (2) greater environmental stability in the Ordovician, and (3) more highly structured ecosystems in the Ordovician that may have led to the weeding out of extinction-prone taxa.
The decline and extinction of Plesiadapiformes (Mammalia: ?Primates) in North America: displacement or replacement?
Authors: Maas Mary C. , Krause David W. , Strait Suzanne G.
Published: July 2016

Plesiadapiforms were among the most diverse and abundant of North American mammalian groups during the Paleocene epoch. Their decline and extinction has been attributed to a variety of causes, including competitive exclusion by rodents and/or by primates of modern aspect (euprimates), and the effects of late Paleocene–early Eocene climatic warming. However, analyses of generic and species richness and relative abundance patterns indicate that the decline of plesiadapiforms was more complex than usually supposed. The two major superfamilies, Plesiadapoidea and Microsyopoidea, exhibited very different patterns of decline. Microsyopoids and paromomyid plesiadapoids do not exhibit a pronounced decline in taxonomic richness and relative abundance during the Early Tertiary. Non-paromomyid plesiadapoids do decline markedly, but, when their taxonomic richness and relative abundance patterns are compared with those of potentially competing taxa (rodents and euprimates) only non-paromomyid plesiadapoids and rodents show the inverse relationship consistent with taxonomic displacement. Euprimates appear in North America after non-paromomyid plesiadapoids were virtually extinct. Analyses of body size, diet, diel activity patterns, and locomotion support the hypothesis that rodents and non-paromomyid plesiadapoids may have competed for the same resources; their paleobiogeographic histories also are consistent with the competition argument.

Currently available paleoclimatological data for the Early Tertiary largely pertain to global temperature trends and are not detailed enough to demonstrate unequivocally whether the decline of non-paromomyid plesiadapoids coincided with climatic change. A more complete record of paleoclimatic indicators, especially from the Western Interior of North America, is needed to test the climate hypothesis adequately. The several independent lines of evidence considered here and elsewhere in reference to other mammalian taxa strongly support the hypothesis that competition with rodents was an important factor in a major restructuring of Early Tertiary mammalian communities in North America.
Rarefaction analysis of morphological and taxonomic diversity
Authors: Foote Mike
Published: July 2016

Our assessment of morphological diversity is influenced by morphological extremes and therefore depends on sample size (taxonomic richness). Rarefaction predicts the morphological diversity that would probably be observed in a sample of reduced size, thereby allowing both compensation for differences in sample size that may be strictly preservational, and analysis of diversity structure, that is, the relationship between morphological and taxonomic diversity. Middle and Late Cambrian trilobites exhibit a diversity structure characterized by many variations on a few morphological themes. In contrast, Middle and Late Ordovician trilobites occupy a larger range of morphospace per unit of species richness. Diversity structure in the Devonian is similar to that in the Middle and Late Ordovician, but the magnitude of morphological diversity is lower in the Devonian, as many fewer species are observed. For blastoids, different aspects of morphological diversity (range of morphospace occupied, number of character states possessed, and number of different regions in morphospace occupied) exhibit different relationships to taxonomic richness. In all cases Permian blastoids are characterized by a diversity structure in which morphological diversity per unit of taxonomic richness is greater than for Devonian blastoids. Changes in morphological diversity in fissiculate blastoids appear to reflect evolution of continuous variation in thecal morphology more than changes in the number of character states. Saunders and Swan's data on Namurian ammonoids illustrate some significant differences in diversity structure among stratigraphic levels, but many apparent differences in morphological diversity are consistent with the possibility that they reflect the sampling of different numbers of species from the same underlying diversity structure. Rarefaction curves are also presented for idealized increases and decreases in diversity, and these are compared to some of the observed changes in trilobites, blastoids, and ammonoids.
Generic longevity in Lower Ordovician trilobites: relation to environment
Authors: Fortey Richard A.
Published: July 2016

The longevity of genera living at the edge of the early Ordovician North American plate is related to their position on the former shelf, that is preserved in richly fossiliferous sections of Spitsbergen. Genera which endure for a long period (SO Myr or more) tend to be confined to shallow-water sites associated with algal mounds at the edge of the carbonate platform (illaenid-cheirurid community type) or deep-water sites with low oxygen concentration, and probably beneath the thermocline (olenid community type). The latter includes “conservative” forms that have survived from the Cambrian. The long ranges of the olenid community type are attributed to the adaptation of only a few genera to a highly specific, stressed environment. The endurance of the illaenid-cheirurid genera is due to the persistence of the tropical shelf-edge habitat, with high predictability of resources, to which the Ordovician forms became adapted early on. The nileid community type, which occurred between the platform edge and olenid-bearing environment, was the site of rapid generic turnover and may have been the source for subsequent recruitment into other environments. The inner shelf also had rapid generic replacement, dominated by a single family, the Bathyuridae. Rapidity of evolution in this site may be due to the spatial heterogeneity of the epeiric environment, as in the Devonian phacopids studied by Eldredge (1974).
Crises in the Devonian history of the rugose corals
Authors: Oliver William A. , Pedder A. E. H.
Published: July 2016

Detailed analysis of the stratigraphic ranges of Devonian rugose coral genera within the Old World and Eastern Americas Realms gives new information on faunal extinctions and other bioevents in both realms. Various origination and extinction metrics are calculated from tabulations of occurrences in each stage. The most significant faunal changes were near or at the ends of the Lochkovian and Frasnian stages. The former marks the gradual transition from dominance by Silurian families and genera to the characteristic Devonian coral assemblages; the latter marks the virtual extinction of the Devonian families and genera. Other coral events are related to the two major changes.

The data provide new bases for comparing the histories of the two realms. Most of the events are recorded in both, giving support to previous suggestions that the causes were worldwide. The coral record shows an increase (probably episodic) in environmental deterioration persisting through the Middle Devonian and culminating in extinction at the end of the Frasnian. Eustatic sea level fluctuations may have caused the precursor events and a bolide impact may have caused the end-Frasnian extinction.
Effects of the Mesozoic Marine Revolution on the taxonomic, morphologic, and biogeographic evolution of a group: aporrhaid gastropods during the Mesozoic
Authors: Roy Kaustuv
Published: July 2016

The mid-Mesozoic time was characterized by massive reorganization of the ecological structure of benthic marine communities. Although the general pattern of this “Mesozoic Marine Revolution” has been extensively documented, little is known about how it affected the taxonomic and morphologic diversities of individual lineages of organisms. Here I document group-level dynamics of the Mesozoic change using the fossil record of aporrhaid gastropods, a diverse and widespread family during that time. Using data gathered through field and museum work and extensive literature search, I compare and contrast patterns of taxonomic and morphologic change during the Jurassic and Cretaceous within a geographic framework. I also examine how the changes were manifested at different ecological and geographic scales.

The Mesozoic history of the Aporrhaidae includes two major radiations separated by a period of overall stability. While both radiations increased the taxonomic diversity of the family, they had very different morphologic consequences, resulting in a striking discordance between morphologic and taxonomic diversity patterns. The initial radiation during Bajocian-Bathonian times established two large morphologic groups within the aporrhaids based mainly on differences in the shape of the apertural margin. The second, post-Albian, radiation saw higher origination rates and increased taxonomic and morphologic diversity among genera having simpler apertural margins, while genera with elaborate multidigitate apertures declined in taxonomic diversity but not in morphologic diversity. During post-Albian times the group with simpler apertural margins also tended to be more widespread compared to the group with multidigitate apertures. Comparison of regional and global taxonomic diversities reveals a discordance between regional and global taxonomic patterns: while diversities within certain geographic areas increased in concert with the global radiation, those for other areas decreased substantially, resulting in a remarkably constant average taxonomic diversity within geographic areas.
Demise of the middle Paleozoic crinoid fauna: a single extinction event or rapid faunal turnover?
Authors: Ausich William I. , Kammer Thomas W. , Baumiller Tomasz K.
Published: July 2016

Macroevolutionary change from the Middle to the Late Paleozoic crinoid fauna was not the result of mass extinction. The presumption that the decline of the middle Paleozoic crinoid fauna was from a single mass extinction event was tested using seriation, multidimensional scaling (MDS), binomial analysis, and bootstrapping simulations on a data set which is a comprehensive revision of old faunal lists. The data for these analyses were based on temporal distributions of 214 species from 69 late Osagean and early Meramecian localities from the midcontinental United States. The time under consideration is subdivided into seven informal intervals using MDS in conjunction with biostratigraphy. Seriation of species ranges into these intervals results in a gradual pattern of faunal turnover, and sampling bias can be eliminated as a cause for this more gradual pattern. MDS analysis of the crinoid range data is similar to MDS simulations using data with continuous, monotonic species turnover and dissimilar to a simulated mass extinction. Binomial analysis and bootstrapping demonstrate that the observed number of extinctions at the putative extinction boundary were not unusually high. All methods agree that extinctions throughout this time were high but spanned several time intervals and that rapid, monotonic faunal turnover describes the data better than mass extinction. Macroevolutionary processes other than mass extinction and microevolutionary processes must have dictated the character and composition of this remarkable faunal transition among the Crinoidea.
Stable isotopic signals and photosymbiosis in Late Paleocene planktic foraminifera
Authors: D'Hondt Steven , Zachos James C. , Schultz Gretchen
Published: July 2016

Late Paleocene planktic foraminifera exhibit strong positive correlations between carbon isotopic values and test mass, but negative correlations between oxygen isotopic values and test mass. Based on analogy with modern taxa, these trends are probably ecotypic and may or may not apply to an ontogenetic series. AmongAcarininaandMorozovellaspecies, the magnitude and direction of these trends resemble those of modern planktic foraminifera with dinoflagellate photosymbionts. This is consistent with current models of photosymbiosis and calcification in planktic foraminifera and suggests thatAcarininaandMorozovellarelied heavily on photosymbionts for nutrition.

AcarininaandMorozovellaspecies resemble modern, strongly photosymbiotic taxa in their association with low and mid latitude nearsurface water masses. However, their test morphologies differ greatly from those of extant taxa that bear obligate photosymbionts. Earliest Paleocene taxa that exhibit a similar paleohabitat association and similar size-related isotopic trends are characterized by still different test morphologies. These comparisons suggest that (1) throughout geologic time, strong reliance on photosymbiont activity has been closely linked to habitat, but not to test morphology; (2) photosymbiosis has been a common and convergently evolved strategy of planktic foraminifera over geologic time, and (3) modern relationships between planktic foraminiferal test morphology and photosymbiont dependence are largely an artifact of geologically recent phylogenetic relationships and shared ecologic strategies.

Intersite comparison suggests that the stable isotopic signals of narrowly constrained size fractions of a late PaleoceneAcarininaorMorozovellaspecies can be used to reconstruct the magnitude and direction of relative variation in equilibrium stable isotopic values throughout its geographic and temporal range. This is supported by analogy with extant photosymbiotic taxa. However, since photosynthetic depletion of12C leaves13C-enriched HCO3-for calcification, the carbon isotopic values ofAcarininaandMorozovellatests may have been consistently greater than paleoseawater values. Failure to account for this effect could lead to overestimation of late Paleocene marine productivity.
Phylogeny reconstruction and the tempo of speciation in cheilostome Bryozoa
Authors: Jackson Jeremy B. C. , Cheetham Alan H.
Published: July 2016

We compared phylogenies derived from morphological data for two cheilostome bryozoan genera,StylopomaandMetrarabdotos,with genetic differences between species (Stylopoma) and the stratigraphic occurrence of fossils (both genera). Correspondence between species ofStylopomadefined by protein electrophoresis and on preservable skeletal morphology is excellent, despite great morphological variability within colonies and the predominance of quantitative over discrete characters. Moreover, agreement between genetic and morphological classifications increased greatly when morphological discrimination was pushed to the limit, despite inability to consistently assign all specimens to species with high confidence. This “splitting” strategy also maximized the correlation between genetic distances and the distances between species in cladistically derived phylogenies.

Fossil and living species of both genera are sufficiently abundant and widespread to provide credible limits for inferred ancestral relationships. Inclusion of fossils in cladistic analyses ofStylopomaincreased the consistency of cladistic hypotheses by up to 30% and provided a more effective means of rooting trees than comparison with living species of the most closely related genus (“outgroup”). Moreover, in the case ofMetrarabdotos,failure to incorporate stratigraphic information turned the cladogram virtually upside down, so that postulated ancestors first appear in the fossil record 6–16 m.y. after their putative descendants became extinct.

Stratigraphically rooted trees suggest that most well-sampledMetrarabdotosandStylopomaspecies originated fully differentiated morphologically and persisted unchanged for > 1 to > 16 m.y., typically alongside their putative ancestors. Moreover, the tight correlation between phenetic, cladistic, and genetic distances among livingStylopomaspecies suggests that changes in all three variables occurred together during speciation. All of these observations support the punctuated equilibrium model of speciation.
Were the Ediacaran fossils lichens?
Authors: Retallack Gregory J.
Published: July 2016

Ediacaran fossils are taphonomically similar to impressions of fossil plants common in quartz sandstones, and the relief of the fossils suggests that they were as resistant to compaction during burial as some kinds of Pennsylvanian tree trunks. Fossils of jellyfish are known from siderite nodules and fine-grained limestone, and even in these compaction-resistant media were more compressed during burial than were the Vendobionta. Vendobionta were constructed of materials that responded to burial compaction in a way intermediate between conifer and lycopsid logs. This comparative taphonomic study thus falsifies the concept of Vendobionta as thin soft-bodied creatures such as worms and jellyfish.

Lichens, with their structural chitin, present a viable model for the observed preservational style of Vendobionta, as well as for a variety of other features that now can be reassessed from this new perspective. The diversity of Ediacaran body plans can be compared with the variety of form in fungi, algae, and lichens. The large size (ca. 1 m) of some Ediacaran fossils is reasonable for sessile photosynthetic symbioses, and much bigger than associated burrows of metazoans not preserved. Microscopic tubular structures and darkly pigmented cells in permineralized late Precambrian fossils from Namibia and China are also compatible with interpretation as lichens. The presumed marine habitat of Ediacaran fossils is not crucial to interpretation as lichens, because fungi and lichens live in the sea as well as on land.
Sympatric speciation and phyletic change inGloborotalia truncatulinoides
Authors: Lazarus David , Hilbrecht Heinz , Spencer-Cervato Cinzia , Thierstein Hans
Published: July 2016

Speciation processes are only rarely studied with fossil materials, even though in principle hypotheses of speciation patterns are most directly testable in the fossil record. We quantitatively document in two widely separated South Pacific DSDP holes the mid-Pliocene speciation of the planktonic foraminiferGloborotalia truncatulinoides.Speciation, with continuous geographic co-occurrence of ancestor and descendant forms, occurred simultaneously at both localities over a period of ~500,000 years. This suggests a sympatric speciation process that involved a large, geographically extensive population.Globorotalia truncatulinoidesunderwent its most rapid and extensive evolutionary change between ~2.8 and 2.5 Ma. This time interval corresponds to the development of northern hemisphere glaciation, suggesting that climate-controlled paleoceanographic change may have played a significant role in the evolution ofG. truncatulinoides.
Laurussian land-plant diversity during the Silurian and Devonian: mass extinction, sampling bias, or both?
Authors: Raymond Anne , Metz Cheryl
Published: July 2016

In phytogeographic data sets, the number of assemblages or floras from each interval may provide a test of the influence of sampling intensity on land-plant diversity. Using a data set of Silurian and Devonian compression-impression plant genera from Laurussia and the Acadian terrain, regression of five measures of land-plant diversity (total diversity, mean genus richness of floras, median assemblage diversity, most diverse assemblage, and standing diversity at interval boundaries) against the number assemblages or floras from thirteen intervals suggests that sampling bias influences all of the diversity measures to some extent, including within-habitat measures. The standing diversity of land plants at interval boundaries, the measure least influenced by sampling (r= 0.65,p= 0.05), increased steadily from the Middle Silurian to the late Givetian/early–middle Frasnian boundary, fell sharply in the early–middle Frasnian and remained low throughout the late Frasnian–middle Famennian. Standing diversity rose dramatically in the late Famennian and Strunian (latest Devonian): the Frasnian–Famennian extinction event may have affected land plants. The standing diversity of Silurian and Devonian microspore genera at interval boundaries mirrors that of compression-impression genera: neither record supports a land-plant diversity equilibrium during the Devonian.
Stratigraphic tests of cladistic hypotheses
Authors: Wagner Peter J.
Published: July 2016

Cladograms predict the order in which fossil taxa appeared and, thus, make predictions about general patterns in the stratigraphic record. Inconsistencies between cladistic predictions and the observed stratigraphic record reflect either inadequate sampling of a clade's species, incomplete estimates of stratigraphic ranges, or homoplasy producing an incorrect phylogenetic hypothesis. A method presented in this paper attempts to separate the effects of homoplasy from the effects of inadequate sampling. Sampling densities of individual species are used to calculate confidence intervals on their stratigraphic ranges. The method uses these confidence intervals to test the order of branching predicted by a cladogram. The Lophospiridae (“Archaeogastropoda”) of the Ordovician provide a useful test group because the clade has a good fossil record and it produced species over a long time. Confidence intervals reject several cladistic hypotheses that postulate improbable “ghost lineages.” Other hypotheses are acceptable only with explicit ancestor-descendant relationships. The accepted cladogram is the shortest one that stratigraphic data cannot reject. The results caution against evaluating phylogenetic hypotheses of fossil taxa without considering both stratigraphic data and the possible presence of ancestral species, as both factors can affect interpretations of a clade's evolutionary dynamics and its patterns of morphologic evolution.