Wood-fall associations from Late Cretaceous deep-water sediments of Hokkaido, Japan

Sunken wood (wood-fall) in the deep sea today is colonized and consumed by diverse invertebrate communities that show phylogenetic relationships to the chemotrophic fauna on whale carcasses, hydrothermal vents and hydrocarbon seeps. Here we document Late Cretaceous examples of wood-fall communities from deep-water sediments of the Yezo Group on Hokkaido, Japan, consisting of provannid, skeneiform, and patelliform gastropods, and thyasirid and nuculanid bivalves. These species are similar or identical to those found on plesiosaur bones and at hydrocarbon seeps in the same sediments, showing that many members of the modern chemotrophic deep-sea fauna colonized this range of habitats at least since Late Cretaceous time. We also document for the first time faecal chimneys in boreholes in these wood fragments, which were presumably built by xylophagain bivalves.     

Methane-flux-dependent lateral faunal changes in a Late Cretaceous chemosymbiotic assemblage from the Nakagawa area of Hokkaido, Japan

A Late Cretaceous carbonate body (2 m in maximum diameter) surrounded by clastic rocks, recently discovered in the Nakagawa area (Hokkaido, Japan), is interpreted as a methane‐seep deposit, on the basis of negative carbon isotopic composition (as low as ?43.5‰), variable sulphide sulphur isotopic composition, high carbonate content, and in situ fractures. It most likely formed owing to methane‐bearing pore‐water diffusion. We estimate that the concentration of methane decreased toward the margin of the carbonate body, and that only small carbonate concretions were precipitated at a certain distance from the methane‐seep centre. These spatial characteristics coincide well with the observed pattern of faunal distribution. The gastropod‐dominated association (indeterminate abyssochrysids and ataphrids and the acmaeid limpet Serradonta sp. are most common) co‐occurs with lucinid and thyasirid bivalves (Thyasira sp., Myrtea sp., and Miltha sp.), and was found within and just above the methane‐derived carbonate body. Acharax and Nucinella (solemyoid bivalves) are more typical of the peripheral part of the methane‐influenced sediments. We suggest that this pattern of faunal distribution reflects the decreasing concentration of methane and apparently also hydrogen sulphide when moving from the centre of discharge toward the periphery of the methane seep.     

Intraspecific variation in behaviour: effects of evolutionary history, ontogenetic experience and sex

Geographical variation in behaviour within species is common. However, how behavioural plasticity varies between and within locally adapted populations is less studied. Here, we studied behavioural plasticity induced by perceived predation risk and food availability in pond (low predation - high competition) vs. coastal marine (high predation - low competition) nine-spined sticklebacks (Pungitius pungitius) reared in a common garden experiment. Pond sticklebacks were more active feeders, more risk-taking, aggressive and explorative than marine sticklebacks. Perceived predation risk decreased aggression and risk-taking of all fish. Food restriction increased feeding activity and risk-taking. Pond sticklebacks became more risk-taking than marine sticklebacks under food shortage, whereas well-fed fish behaved similarly. Among poorly fed fish, males showed higher drive to feed, whereas among well-fed fish, females did. Apart from showing how evolutionary history, ontogenetic experience and sex influence behaviour, the results provide evidence for habitat-dependent expression of adaptive phenotypic plasticity.     

Two early eudicot fossil flowers from the Kamikitaba assemblage (Coniacian,Late Cretaceous) in northeastern Japan

Two new fossil taxa referable to the basal eudicot grade are described from the Kamikitaba locality (ca. 89 MYBP, early Coniacian: Late Cretaceous) of the Futaba Group in Japan. These charcoalified mesofossils exhibit well-preserved three-dimensional structure and were analyzed using synchrotron-radiation X-ray microtomography to document their composition and internal structure. Cathiaria japonica sp. nov. is represented by infructescence segments that consist of an axis bearing three to four fruits. The capsular fruits are sessile and dehiscent and consist of a gynoecium subtended by a bract. No perianth parts are present. The gynoecium is monocarpellate containing two pendulous seeds. The carpel is ascidiate in the lower half and conduplicate in the upper part, and the style is deflected abaxially with a large, obliquely decurrent stigma. Pollen grains are tricolpate with a reticulate exine. The morphological features of Cathiaria are consistent with an assignment to the Buxaceae s. l. (including Didymelaceae). Archaestella verticillatus gen. et sp. nov. is represented by flowers that are small, actinomorphic, pedicellate, bisexual, semi-inferior, and multicarpellate. The floral receptacle is cup shaped with a perigynous perianth consisting of several tepals inserted around the rim. The gynoecium consists of a whorl of ten conduplicate, laterally connate but distally distinct carpels with a conspicuous dorsal bulge, including a central cavity. The styles are short, becoming recurved with a ventrally decurrent stigma. Seeds are ca. 10 per carpel, marginal, pendulous from the broad, oblique summit of the locule. Pollen grains are tricolpate with a reticulate exine pattern, suggesting a relationship to eudicots. The morphological features of Archaestella indicate a possible relationship to Trochodendraceae in the basal grade of eudicots. The fossil currently provides the earliest record of the family and documents the presence of Trochodendraceae in eastern Eurasia during the middle part of the Late Cretaceous.     

Ephedroid fossil pollen from the Lower Cretaceous (Upper Albian) of Hokkaido,Japan

This paper presents eight ephedroid palynomorphs from the Lower Cretaceous (Upper Albian) of Hokkaido, Japan. The ephedroid palynomorphs are ellipsoid and polyplicate pollen grains that show a wide range of variation in pollen size, shape, and plication. These ephedroid palynomorphs suggest a wide range of diversity in Gnetales at mid- or high-paleolatitude in the eastern side of Lauresia during the Upper Albian.     

Irregular calcareous sheets preserved in a conch of the Cretaceous ammonoid Hypophylloceras from Hokkaido,Japan

The mantle tissue is essential for understanding the diverse ecology and shell morphology of ammonoid cephalopods. Here, we report on irregular calcareous sheets in a well-preserved shell of a Late Cretaceous phylloceratid ammonoid Hypophylloceras subramosum from Hokkaido, Japan, and their significance for repairing the conch through the mantle inside the body chamber. The sheets are composed of nacreous layers arranged parallel to the irregularly distorted outer whorl surface. The nacreous sheets formed earlier are unevenly distributed and attached to the outer shell wall locally, whereas the last formed sheet covers a wide area of the outer shell wall. The absence of any interruption of ribbing around the irregular area suggests that these sheets were secreted inside the body chamber from the inner mantle. Gross morphological and X-ray computed tomography observations revealed that the spacing of septal formation was not affected by this event. The complex structure of the irregular sheets suggests a highly flexible mantle inside the body chamber.     

Support from early juvenile Jurassic,Cretaceous and Holocene thecideoid species for a postulated common early ontogenetic development pattern in thecideoid brachiopods

Abstract: The analysis of morphological characters exhibited by the earliest ontogenetic stages of Middle Jurassic, Cretaceous and Holocene thecideoid species, together with the application of techniques that reveal the presence of early juvenile morphological characters buried in the shell fabric of adult representatives of the species concerned, reinforce the idea of a development pattern common to thecideoids from the early Middle Jurassic to the present day. Basic and long‐standing differences in the architecture of the brachidial skeleton of thecidellinids and lacazellins may be correlated with the morphology of thecospiroids and indicate that the Thecidellinidae and Thecideidae may have emerged as sister groups as early as the Triassic.     

Experimental analysis of an early life‐history stage: avian predation selects for larger body size of hatchling turtles

One common life‐history pattern involves an elevated rate and nonrandom distribution of neonatal mortality. However, the mechanisms causing this pattern and the specific traits that confer a survival benefit are not always evident. We conducted a manipulative field experiment using red‐eared slider turtles to test the hypothesis that diurnal avian predators are a primary cause of size‐specific neonatal mortality. Body size was a significant predictor of recapturing hatchlings alive and of finding hatchlings dead under natural conditions, but was unimportant when diurnal predators were excluded from the field site. Overall recapture rates also more than doubled when predators were excluded compared to natural conditions (72.4 vs. 34.9%). We conclude that birds are an important cause of size‐specific mortality of recently emerged hatchling turtles and that ‘bigger is better’ in this system, which has important implications for life‐history evolution in organisms that experience size‐specific neonatal mortality.     

A new Bennettitalean trunk with unilacunar five-trace nodal structure from the Upper Cretaceous of Hokkaido, Japan

A new species of Bucklandia is described based on a permineralized fossil trunk that was obtained from sediments of Upper Cretaceous age from Hokkaido, Japan. The quality of preservation is exquisite, and anatomical and morphological features are preserved at the cellular level. The specimen is clearly bennettitalean because of the cycadeoidean-type arrangement of vascular bundles in the petiole. However, this specimen is unique among previously described progymnosperms and gymnosperms in possessing a unilacunar five-trace type of nodal structure. The fossil thus contributes to a more complete understanding of the variation of nodal structure in bennettitalean trunks.     

A new look at genome size,evolutionary duration and genetic variation in salamanders

Salamanders have some of the largest genomes among vertebrates, and also some of the lowest reported levels of genetic diversity. Paedomorphs, in particular, have the largest genomes on average among urodela, and display exceptionally low levels of nucleotide and protein variation. Here, we address the question of genetic variation in relation to genome size in eight different salamander families. Using the rag1 gene as a probe for evolutionary rates, we found that rates of substitution are exceptionally low in obligate paedomorphs (neotenes) and other salamander species. Substitution rates in some cases are as low as those reported for cartilaginous fish, which have the slowest mutation rates recorded so far in vertebrates. Confirming and extending an earlier study, we also found that genome size is correlated with phylogenetic age in Plethodontidae, indicating a more general trend in genome size evolution in urodela. The Plethodontidae, furthermore, display much higher levels of genetic variance than the obligate neotene families, consistent with greater habitat heterogeneity in terrestrial salamanders. Finally, we present the first direct evidence of a gene, rag1, whose substitution rate is negatively associated with genome size. Based on these and other observations, we propose a hypothesis according to which mutation rates in nuclear genes tend to increase as genome size decreases during the course of vertebrate evolution.     

Sheltered preservation: a peculiar mode of ammonite occurrence in the Cretaceous Yezo Group, Hokkaido, north Japan

Maeda, H. 1991 01 15: Sheltered preservation: a peculiar mode of ammonitc occurrence in the Cretaceous Yeto Group, Hokkaido. north Japan. Lethaia , Vol. 24, pp. 69–82. Oslo. ISSN 0024–1164.
'Sheltered preservation', in which many small ammonites ('refugees') arc preserved in the inside and/or the lower umbilical void of a large ammonite shell ('shelter'), is a common preseivational style in the Cretaceous Yezo Group in Hokkaido, north Japan. The best example is large Calycoceras of Middle Cenomanian age, attaining 300 to 500 mm diameter, whose shell usually hours more than 100 individuals of Desmoceras comprising mainly juveniles less than 12 mm in diameter. In contrdst with other preservational styles of Desmoceras from the same horizon. the shells of refugee ammonites have not suffered phragmoeone collapse, and the inner whorls and a protoconch are intact. Many refugee ammonites are allochthonous, as indicated by the incomplete preservation of their living chamber and the absence of a jaw apparatus. The sheltered preservation is, therefore, a kind of 'Konzcntrat Lagerstatten' completed by both pre- and post-burial processes. Acting as a 'concentration trap' on the sea floor, a large empty ammonite shell probably triggered off such accumulation of the small ammonite shells in post-mortem transport across the sea floor. This biostratinomical process biased the original thanatococnosis of ammonites, so that its immature specimens were selectively accumulated and preserved in the shelter. Ammonoidea, taphonomy, Konzentrat Lagerstätten'. differenrial preservation, Cretuceous. Hokkaido .     

Intraspecific variation in space use, group size, and mating systems of caviomorph rodents

Intraspecific variation in social systems is widely recognized across many taxa, and specific models, including polygamy potential, resource defense, and resource dispersion, have been developed to explain the relationship between ecological variation and social organization. Although mammals from temperate North America and Eurasia have provided many insights into this relationship, rodents from the Neotropics and temperate South America have largely been ignored. In this review we focus on reports documenting intraspecific variation in spacing systems, group size, and mating systems of caviomorphs. This large group of New World hystricognath rodents occupies a diverse array of habitats; thus, members of the same species potentially exhibit different social systems in response to different ecological conditions. Spatial patterns vary in response to a diverse array of factors, including predation, food availability, population density, and soil characteristics. Changes in group size typically correlate with changes in resource availability, particularly food. Mating systems generally reflect the ability of males to control access to females, which may depend on population density or food distribution. In general, social organization in caviomorphs fits predictions of resource-based models; however, most studies have been purely observational, involving small numbers of animals over short time periods and reporting qualitative rather than quantitative levels of ecological correlates. In future studies the use of molecular techniques and controlled, experimental manipulations can increase our understanding of intraspecific variation in caviomorph social systems. This understudied group of rodents offers excellent opportunities to provide insights into the influence of ecological conditions on behavior such as social systems.     

Intraspecific variation in body size and sexual size dimorphism,and a test of Rensch's rule in bats

The magnitude and direction of sexual size dimorphism (SSD) may vary considerably within and among taxa, and the primary causes of such variation have not been thoroughly elucidated. For example, the effect of abiotic factors is frequently attributed to explain intra‐ and interspecific variation in SSD. Rensch's rule, which states that males vary more in size than females when body size increases, has rarely been tested in bats. Therefore, whether bats follow Rensch's rule remains unclear, particularly when females are larger than males. We investigated whether four bat species presented SSD, as well as whether their body sizes varied within each sex across localities, testing the hypothesis that intraspecific SSD varies substantially depending of sampling localities. We finally examined whether bats followed Rensch's rule by simultaneously using intraspecific and interspecific approaches. Although SSD was not observed for most bat species within each locality, the females of three of the four captured species exhibited differences in body size between particular localities. Usually the females varied more in size than did males across localities, mostly exhibiting a female‐biased SSD. Significant differences in SSD were observed (i.e. mean values of the sexual dimorphism index), even though Rensch's rule was not followed.     

Craniometric variation of the Ainu: an assessment of differential gene flow from northeast Asia into northern Japan, Hokkaido

In and after the latest Neolithic period in Japan (approximately B.P. 2,300 years), there were two distinct waves of migration from eastern Asia. One is well known as successive episodes in which indigenous inhabitants of main-island Japan were intruded on by new arrivals with advanced technology, and of a different genetic stock. Another migration of people and culture, identified as the Okhotsk culture, reached the northeastern part of Hokkaido. As opposed to main-island Japan, the morphological continuity from the Neolithic to recent inhabitants in Hokkaido (Ainu) is notable, so that the evidence of admixture easily could have escaped notice. In this study, the effects of gene flow from an outside source on the pattern of among-group variation of Hokkaido Ainu are examined by means of two models. One is the R-matrix model comparing observed and expected craniometric variation for estimating differential external gene flow into a region. The other is a simple simulation model that estimates admixture in a population with two parental populations. The two approaches give similar results. The results suggest the possibility of admixture between the migrants from Northeast Asia, the Okhotsk culture people, and the indigenous inhabitants in Hokkaido during the 5th to 12th centuries A.D., at least in northeastern Hokkaido. Such gene flow may have a certain degree of effect on the genetic structure of recent Ainu. The findings further suggest morphological heterogeneity in Northeast Asia during the Holocene that has relevance for understanding the morphological heterogeneity seen through time in the New World.     

Pinus MUTOI (Pinaceae), a new species of permineralized seed cone from the upper Cretaceous of Hokkaido,Japan

Pinus mutoi is described as a new species on the basis of a permineralized seed cone from the Upper Cretaceous of Hokkaido, Japan. The cone is at least 20 cm long and up to 6 cm in diameter, consisting of a cone axis and numerous cone-scale complexes that are arranged helically around the axis. Two winged seeds are borne on the adaxial surface of each ovuliferous scale. Each complex receives a single trace from the vascular cylinder of the cone axis. In the scale base, all the resin canals occur abaxially to the vascular strand. The spatulate bract of the fossil is unique to the specimen among the cones of both living and fossil Pinus. The central umbo, broad sclerotic cortex of cone axis, and absence of serotinous features of the fossil cone suggest affinity with the subsection Sylvestres of the section Pinus, subgenus Pinus. This is the first record of permineralized preserved Pinus cone from the Cretaceous of Eastern Eurasia.     

A second hadrosauroid dinosaur from the early Late Cretaceous of Zuoyun,Shanxi Province,China

A second basal hadrosauroid dinosaur, Zuoyunlong huangi gen. et sp. nov., is reported from the early Late Cretaceous Zhumapu Formation in Zuoyun County, Shanxi Province, northern China. Zuoyunlong preserves a partial right ilium and ischium and is unique in having a very short postacetabular process 50% as long as the iliac central plate. Our cladistic analysis recovers Zuoyunlong as the most basal Late Cretaceous hadrosauroid, with a sister taxon relationship with Probactrosaurus from the late Early Cretaceous of Inner Mongolia. Including Zuoyunlong, four Cenomanian basal hadrosauroids have been recorded, and the two taxa in North America (Eolambia and Protohadros) represent the earliest known hadrosauroids outside of Asia. In the light of the proposed phylogenetic topology and biogeographic data, the discovery of Zuoyunlong indicates that the first dispersal of hadrosauroids from Asia to North America probably happened around the boundary between the Early and Late Cretaceous.