Narrow Molar Research Articles

Biogeochemical characteristics of suspended particulate matter in deep chlorophyll maximum layers in the southern East China Sea

Abstract. Continental shelves and marginal seas are key sites of particulate organic matter (POM) production, remineralization and sequestration, playing an important role in the global carbon cycle. Elemental and stable isotopic compositions of organic carbon and nitrogen are thus frequently used to characterize and distinguish POM and its sources in suspended particles and surface sediments in the marginal seas. Here we investigated suspended particulate matter (SPM) collected around deep chlorophyll maximum (DCM) layers in the southern East China Sea for particulate organic carbon and nitrogen (POC and PN) contents and their isotopic compositions (δ13CPOC and δ15NPN) to understand provenance and dynamics of POM. Hydrographic parameters (temperature, salinity and turbidity) indicated that the study area was weakly influenced by freshwater derived from the Yangtze River during summer 2013. Elemental and isotopic results showed a large variation in δ13CPOC (−25.8 to −18.2 ‰) and δ15NPN (3.8 to 8.0 ‰), but a narrow molar C ∕ N ratio (4.1–6.3) and low POC ∕ Chl a ratio (< 200 g g−1) in POM, and indicated that the POM in DCM layers was newly produced by phytoplankton. In addition to temperature effects, the range and distribution of δ13CPOC were controlled by variations in primary productivity and phytoplankton species composition; the former explained ∼ 70 % of the variability in δ13CPOC. However, the variation in δ15NPN was controlled by the nutrient status and δ15NNO3- in seawater, as indicated by similar spatial distribution between δ15NPN and the current pattern and water masses in the East China Sea; although interpretations of δ15NPN data should be verified with the nutrient data in future studies. Furthermore, the POM investigated was weakly influenced by the terrestrial OM supplied by the Yangtze River during summer 2013 due to the reduced sediment supply by the Yangtze River and north-eastward transport of riverine particles to the northern East China Sea. We demonstrated that the composition of POM around DCM layers in the southern East China Sea is highly dynamic and largely driven by phytoplankton abundance. Nonetheless, additional radiocarbon and biomarker data are needed to re-evaluate whether or not the POM around the DCM water depths is influenced by terrestrial OM in the river-dominated East China Sea.

Stachyops, a new nototanaid genus (Crustacea: Peracarida: Tanaidacea) from New Zealand, with remarks on nototanaid and tanaissuid phylogeny

A new genus and species, Stachyops sebparri, is described from the eulittoral of Cook Strait, New Zealand and is the firstrecord of a nototanaid from one of the main islands. A very small species, it has several morphological characters that areshared with some species of the Tanaissuidae, such as a narrow mandibular molar and fewer pereopods 4–6 carpal spines,yet retains some apparent plesiomorphic features more typical of the Nototanaidae or other ‘basal’ paratanaoideans. Aphylogenetic analysis does group it with the Nototanaidae sensu Bird & Larsen, but more phylogenetic studies of these two families are needed to clarify their composition, relationships, and validity.

A New Species of Fossil <i>Mus</i> (Muridae, Mammalia) from the Late Quaternary Deposits of Narmada Valley, Central India

A new species of fossil Mus (Muridae, Rodentia) is described from the Pleistocene fluviatile deposits of the Narmada valley (Central India). The species, Mus narmadaensis sp. Nov., has a comparatively smaller lower molar which is characterized by a narrow molar with well connected cusps, small anterior expansion of lingual anteroconid, protoconid and metaconid, reduced posterior cingulum in addition to hypoconid and entoconid nearly at the same level. The large M3 has centrally placed bulbous hypoconid. Among the extant species, the present one is closest to M. shortridgei in having similarly placed protoconid and metaconid in M1 and a well developed hypoconid in M3.

Platybelodon (Gomphotheriidae, Mammalia) from the middle Miocene of Linxia Basin, Gansu, China

In this paper, we report on abundant fossils of Platybelodon from the Middle Miocene of the Linxia Basin, China. Most of the fossils were discovered at two localities (Laogou and Zengjia) in the upper Middle Miocene Hujialiang Formation, and possess derived characters for the genus, including a relatively slender upper incisor, the development of a transverse ledge on the narrowest part of the mandibular symphysis, narrow, elongate and hypsodont third molars, the development of fourth loph(id)s on the second molars, and the development of small enamel conules and cementum in the interloph(id)s. Following comparisons with other Eurasian platybelodonts, we assign these remains to Platybelodon grangeri, and demonstrate that they are morphologically intermediate between P. grangeri from the Tunggurian localities of Tarim Nor and Platybelodon Quarry in Inner Mongolia. We suggest that the locality of Laogou may be younger than that of Zengjia, based on the occurrence of platybelodonts showing a suite of more de...

A new species ofChalicotheriumfrom the Upper Miocene of Gansu Province, China

ABSTRACT Chalicotherium wuduensis, n. sp., from the late Miocene of Gansu Province, China, is based on two mandibles, one an adult and the other a juvenile. This species of Chalicotherium has a relatively long diastema, short premolar row, and narrow lower molars. Canines are present, but incisors are completely lacking. The jaw is very robust with a long, thick symphysis. C. wuduensis is closest to C. goldfussi, Nestoritherium sivalense, and N. sinense but is clearly different from all three. It is distinct from C. brevirostris, a medial Miocene Chinese species with an abbreviated snout. Differences between Chalicotherium and Nestoritherium seem to be part of a continuum and may not warrant generic distinction.

Discriminatory Analysis of Divergence in Mandibular Morphology of Odocoileus

Canonical analysis was used to investigate morphologic divergence in the mandible among six samples of adult, male deer of the genus Odocoileus . Two subspecies of O. hemionus and three subspecies of O. virginianus were represented in the study. Seven dental and seven osteological dimensions of the mandible were measured. Three separate analyses were run: the first included all variables, the second only the osteological variables, and the third only the dental variables. The major component of group divergence (general size variation excepted in the first and second analyses) tended to separate the two species. This separation was significant statistically in the first and third analyses. The samples of O. hemionus appeared to have relatively short diastemas and narrow third molars. Discriminant classification was done using each of the three different sets of variables mentioned above. A total of 134 specimens was classified. Correct assignment to species varied in the three sets from 89 to 99 per cent. Correct assignment to subspecies within the species varied from 69 to 98 per cent. These results suggest that under certain conditions metric information from mandibular remains, or from only the mandibular cheektooth row, of past populations might be used effectively to discriminate among closely related taxa.

A New Paleocene Mammal (Condylarthra: Arctocyonidae) from a Well in Alberta, Canada

Prothryptacodon albertensis, new species, was recovered from a well drilled in Paleocene rocks in southern Alberta, Canada. The new species is distinguished by its relatively high molar trigonids, narrow molars and small size. The dental features of P. albertensis are less like Thryptacodon than are those of P. furens (Middle Paleocene, Montana). A Torrejonian age is suggested for P. albertensis.