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Home ranges of sympatric shrews, Sorex unguiculatus Dobson, 1890 S. gracillimus Thomas, 1907 and S. caecutiens Thomas, 1907 were studied by a mark-recepture method during the non-snow covered seasons in northern Hokkaido, 1988 and 1989. Home range size of S. unguiculatus, the largest species (15.1 g for adult males), was not significantly different from that of S. gracillimus, the smallest species (4.4 g for adult males). Both S. unguiculatus and S. gracillimus had more exclusive home ranges within species than between species. Tolerance of home range overlap may be related to the reduction of dietary overlap. No reliable information of home range for S. caecutiens was obtained in this study.
Ammonoid biodiversity changes from shallow to offshore environments across the Cenomanian–Turonian (C–T) boundary are reconstructed in the Yezo Group, Hokkaido, Japan. This group was probably deposited at approximately 35–45ºN along a westward subduction margin in the northeastern Asian continent. Temporal changes in species richness in the Yezo Group, which show persistently high values during the middle Cenomanian and then decline stepwise from near the middle–late Cenomanian boundary, resemble those in Europe, but not those in Tunisia and the Western Interior. These differences suggest that the Cenomanian–Turonian “mass extinction” was not a global event for ammonoids but was restricted to mid−palaeolatitudinal regions (Europe and Japan). Sea level and climate changes probably influenced ammonoid faunas in the Yezo Group as well as those in Europe. However, it is unlikely that a single, simple cause led to the C–T boundary “mass extinction” because various abiotic changes in the Cenomanian–Turonian transition have been detected, and biotic and abiotic change are interrelated.
The feeding habits and hoarding behaviour of the Eurasian red squirrel Sciurus vulgaris Linnaeus, 1758 were examined during autumn in Nopporo Forest Park (43°20'N, 141°30'E), in western Hokkaido, Japan. The diet consisted of 32 plant species. Twelve species were both eaten and hoarded (the two most common of which were Abies sachalinensis and Pinus koraiensis), and 20 species were eaten but not hoarded. The distance from where a food item was found to the hoarding spot averaged 50 m and differed significantly according to food type. Walnuts Juglans regia were transported farthest, and chestnuts Castanea crenata to the second farthest from the site of origin. Most food was hoarded beneath the ground surface (95%), but some were hoarded in forks of trees and in small tree holes. Squirrels selected food items of high energy content for hoarding, in preparation for winter and the breeding season.
The Campanian (Upper Cretaceous) seep carbonate at Omagari (Hokkaido, Japan) yields a monospecific association of the terebratulide brachiopod Eucalathis methanophila Bitner sp. nov. The association is the only occurrence of brachiopods known from the post−Early Cretaceous history of chemosynthesis−based communities. Unlike many earlier rhynchonellide−dominated hydrocarbon seep associations—which disappeared in Aptian times—this association is composed of chlidonophorid terebratulides. It is hypothesised here that large rhynchonellide brachiopods have been outcompeted from chemosynthesis−based associations by large chemosymbiotic bivalves (especially lucinids) and that this seep association containing numerous terebratulide brachiopods originated as a result of immigration from the background fauna settling in a seep that lacked numerous large bivalves but offered some hard substrates for brachiopod attachment. Some living chlidonophorids are known to settle around seep/vent localities or more generally in deep−water hard−substrate settings. We review occurrences of brachiopods in chemosynthesis−based associations and show that brachiopods immigrated repeatedly to seep/vent environments. Eucalathis methanophila Bitner sp. nov. represents the oldest and single Mesozoic record of the genus. The new species is similar in ornamentation to three living species, Indo−Pacific E. murrayi, eastern Atlantic E. tuberata, and Caribbean E. cubensis but differs in having a higher beak and wider loop. Additionally the studied species is nearly twice as large as E. tuberata.
Sixteen gastropod species from two Campanian (Upper Cretaceous) hydrocarbon seep localities in Hokkaido, Japan are described. Seven species are new: the acmaeid limpet Serradonta omagariensis; three turbinids: Homalopoma abeshinaiensis, Cantrainea yasukawensis, and C. omagariensis; the trochid Margarites sasakii; the seguenzioid Cataegis nakagawensis; and the provannid Provanna nakagawensis. The most common species in the investigated localities are acmaeid limpets (S. omagariensis), tiny turbinids (H. abeshinaiensis, C. yasukawensis, C. omagariensis), and provannids/hokkaidoconchids (P. nakagawensis and Hokkaidoconcha hikidai). The Upper Cretaceous associations described here do not resemble Lower Cretaceous associations known from other regions but are composed of species similar to gastropods from Recent hydrocarbon seeps and hydrothermal vents in the Northwestern Pacific. This strongly suggest that this region possesses a regional pool of gastropods in chemosynthesis−based communities at least since Late Cretaceous time. The only group of gastropods described here which has no Recent counterpart is the Hokkaidoconchidae. A comparison to gastropods from plesiosaur falls and sunken wood of the same age and region strongly suggest that these invertebrate communities do not differ significantly from the coeval hydrocarbon seep communities described herein.
The origin and phylogenetic relationships of most modern coleoid groups have not yet been explained by reliable fossil evidence, in large part because of the reduction or disappearance of a calcified chambered shell during their evolutionary history. Herein we describe two exceptionally large coleoid lower jaws from the Upper Cretaceous strata in Hokkaido, Japan. On the basis of the comparison of gross morphology and morphometric data of the lower jaws of modern and fossil coleoids, we assigned the two lower jaws to the following new taxa: Nanaimoteuthis hikidai sp. nov. of the order Vampyromorpha (superorder Octobrachia) and Haboroteuthis poseidon gen. et sp. nov. of the order Teuthida (superorder Decabrachia). The lower jaw of N. hikidai is distinguished from other species of the same genus from the Upper Cretaceous of Vancouver Island (Canada) and Hokkaido by having a broader, more anteriorly curved hood of the outer lamella. The lower jaw of H. poseidon seemingly exhibits mosaic features like those of modern teuthids and sepiids but is assigned to Teuthida on the basis of the overall shape of the outer lamella and the development of a distinct fold on the lateral wall. Because of the unusually large lower jaws, these new taxa appear to be comparable in body size to modern giant squids (Architeuthis spp.) and the Humboldt squid (Dosidicus gigas). This and other discoveries of large jaws referable to octobrachian and decabrachian coleoids from the Upper Cretaceous strata of the North Pacific fill the gap in the relatively poor fossil record of mainly soft-bodied coleoids.
Two Campanian methane seep sites in the Nakagawa area of Hokkaido (northern Japan) yield fossils of the limpet genera Serradonta and Bathyacmaea that appear to have had the same substrate preference as do their modern counterparts. Serradonta cf. vestimentifericola was a species having an elongated and strongly compressed shell adapted to living on vestimentiferan tubes, like its modern relatives. Bathyacmaea cf. subnipponica was an acmaeid with a relatively elongated shell but with a more rounded aperture than Serradonta and thus apparently attached to small hard objects other than worm tubes. One Bathyacmaea specimen was found attached in situ to an ataphrid gastropod shell. The restricted present−day distribution of Serradonta possibly reflects its spreading route exclusively through the hot vent and cold seep communities settled by vestimentiferans.
Organic membranes preserved in the rear part of the body chamber of the Late Cretaceous phylloceratid ammonite Phyllopachyceras ezoense were examined with scanning electron microscopy (SEM) on the basis of well−preserved specimens from Hokkaido, Japan. SEM observations revealed that the membranes are continuous with the siphuncular tube wall in the phragmocone and consist of two layers, both of which are made of a dark, primarily conchiolin material; namely, a thinner inner homogeneous layer and a thicker outer layer with gently inclined pillar−like units. Hence, they are interpreted as the precursory siphuncular membranes. The precursory siphuncular membranes are not associated with any other organic components such as the siphuncular sheets reported in some Paleozoic and Mesozoic ammonoids. Unlike the tube−like condition in the phragmocone, the precursory siphuncular membranes in the body chamber of the specimens examined do not form a tube shape; on the ventral side the membranes are truncated and directly contact the outer shell wall. These observations suggest that the inner and outer layers of the precursory siphuncular membranes in the body chamber were respectively formed by the siphuncular epithelium from the inner side and by the invaginated septal epithelium from the outer side. It is also postulated that at the initial stage of septal formation, the rear part of the body moved slowly forward, developing a circumsiphonal invagination of the septal epithelium. Because similar conchiolin membranes are occasionally preserved in the body chambers of other phylloceratids, the above morphogenetic process applies to all members of the Phylloceratina. The tube−shaped structure in the rear part of the body chamber of desmoceratid Damesites consists only of nacreous layer. We interpret it as a pathologically overgrown prochoanitic septal neck.
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Cretaceous cold−seep deposits of the Yezo Group on Hokkaido, Japan, yield a rich and well−preserved mollusk fauna. The systematics of nine bivalve species previously reported from these deposits can now be reevaluated using newly collected fossils. The fossils include a Cenomanian specimen of Nucinella gigantea with a drill hole possibly made by a naticid, by far the oldest record of a drill hole from a cold seep site. In Japan, Cretaceous seep bivalve assemblages are characterized by (i) the unique occurrence of large specimens of Nucinella (Manzanellidae), (ii) the commonly present nuculid Acila (Truncacila), and (iii) a high diversity of lucinids, possibly as many as four distinct genera. Two new species described are the Albian Acharax mikasaensis(Solemyidae) and the Albian to Campanian Thyasira tanabei (Thyasiridae), of which the former had previously been misidentified as the oldest vesicomyid, the latter as the oldest Conchocele.
The taphonomy of the Upper Cretaceous ammonite Anagaudryceras limatum differs from associated ammonites in the same horizon. This differential taphonomy is reconstructed based on fragmentation patterns and structural property of the corrugated shells of their body chamber parts. The characteristic preservation of isolated body chamber parts with corrugations is commonly observed in A. limatum from the upper Turonian of the Oyubari area, central Hokkaido, Japan. This preservation probably results from the differential internal structural properties of the hollow body chamber and septated phragmocone as well as the peculiar corrugation on body chamber of the present species: (1) fracturing along the corrugations against bending force is easier than flat material, because of the concentration of force on the tops or bottoms of corrugations, and (2) high durability against compressive forces. The separated body chamber parts were resistant to being squashed and broke into pieces due to the durability of corrugations against compressive force. The statistic test on the fossil assemblage suggests that selective destruction did not affect the fidelity of species composition and relative abundance of the studied fossil assemblage. Molluscan death assemblages in marine systems consistently show strong fidelity to relative abundances in the live community, suggesting that there was an Anagaudryceras−dominant ammonoid community during the late Turonian in the Oyubari area.
We examined sequence variation in mitochondrial and nuclear genes of seven species of the genus Martes (Mustelidae, Carnivora): Martes americana (American marten), Martes flavigula (yellow-throated marten), Martes foina (beech marten), Martes martes (pine marten), Martes melampus (Japanese marten), Martes pennanti (fisher) and Martes zibellina (sable), focusing on the phylogenetic history of the Hokkaido subspecies of the sable, Martes zibellina brachyura. Nucleotide sequence analysis of the mitochondrial cytochrome b gene confirmed the view that the Hokkaido sable population has lower genetic diversity. In contrast, network analysis of a nuclear gene related to coat colour, melanocortin-1 receptor (Mc1r), revealed two different haplogroups for this population: one shared with that of Russian sables and the other specific to this population but with a close relationship with the American and Japanese martens, implying that these endemic haplotypes are composed of uncharacterised ancestral lineages of a past population. We also examined the sequence variation in a neighbouring nuclear gene, transcription factor 25 (Tcf25), located about 5 kb upstream from the Mc1r gene, and found similar trends. The sable genome leaves the impression that Hokkaido hosted ancient marten lineages, with subsequent recent migrations from the continent. The validity of a candidate Mc1r mutation for the entirely yellow coat observed on Hokkaido sables was also discussed.
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