首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 203 毫秒
1.
Two associated partial skeletons, one from the McCarty ranch (MOTTU site 0690) near Kalgary, Texas, Tecovas Formation, and the other from the Petrified Forest Member of the Chinle Formation, outside the Petrified Forest, Arizona, represent the most complete specimens ofPoposaurus gracilis found to date, and increase our understanding of the osteology of this rare pseudosuchian archosaur. The cervical centrum of TTUP-10419 possesses an accessory dorsal parapophyseal rib facet, as in “Lythrosuchus”. The ilia of these new fossils are the first ofPoposaurus to preserve the complete preacetabular blade, which is long and “blade-like” rather than “paddle-shaped” as previously thought. These specimens also confirm that isolated elements previously referred toPoposaurus (fused sacral vertebrae, the pubes and the ischia), but not present in the holotype indeed belong to that taxon. The morphology of the cervical centrum and the preacetabular blade of the ilium are identical to the much larger type of“Lythrosuchus” langstoni, suggesting that “Lythrosuchus” is a junior synonym ofPoposaurus. However, we retain the speciesPoposaurus langstoni nov. comb. on the basis of larger size, absence of a distinct ridge on the lateral surface of the ilium, and the lack of a pit on the proximal end of the ischium. A phylogenetic analysis suggests a monophyletic Poposauroidea and a paraphyletic “Rauisuchia”.  相似文献   

2.
There is now a considerable body of evidence to suggest that the phthiocerol-containing lipids, including the phenolic glycolipids, comprise the so-called “peribacillary substance”, “spherical droplets”, “foamy structures” and “capsular materials” ofMycobacterium leprae. Thus, the phthiocerol-containing lipid capsule may be directly responsible for the intracellular survival ofMycobacterium leprae.  相似文献   

3.
4.
Two skulls, two mandibles and some postcranials ofMesopithecus from the locality “Vathylakkos 2” of Axios Valley (Macedonia, Greece) enlarge our knowledge about the genus and its differentiation. The new material together with an old skull from the same locality is compared with the Pikermi, “Ravin des Zouaves 5” (Axios Valley), and Maramena (Serres basin) samples. It is concluded that the VathylakkosMesopithecus resemblesM. pentelicus from Pikermi, as wellM. delsoni from “Ravin des Zouaves 5” and it is referred asMesopithecus sp. aff.M. pentelicus. The biochronological age of “Vathylakkos 2” has been considered as MN 12, while recent magnetostratigraphic data indicate an age of about 7.5 Ma. This age confirms the position of the VathylakkosMesopithecus between Pikermi and “Ravin des Zouaves 5”. Some dental indices compared with those of the RecentCercopithecus suggest that the Vathylakkos sample is monospecific.   相似文献   

5.
A method based on the Fourier analysis is proposed, which describes and analyzes the contour morphology of carpal bones by separating morphology into factors of shape and size. Here, “size” refers to the average diameter of the contour. The “shape” is expressed byshape factors which are derived from the Fourier series and the “shape” of a monkey is expressed by ashape index which is calculated fromshape factors. The age change in the morphology of the lunate and capitate ofMacaca fuscata fuscata was analyzed by this method. The development of “shape” approximately completes by 3 years of age, whereas increase in “size” begins its spurt at that age as do body weight and anterior trunk length. By applying this method to other macaque species, it was found thatM. mulatta, M. f. yakui andM. cyclopis exhibit similar patterns of growth and development of carpal bones to those ofM. f. fuscata. Patterns found inM. fascicularis differ in that its bones develop faster than in the other macaques with respect to the “shape,” but remain small with respect to the “size.”  相似文献   

6.
The Role of Organic Acids in the Domestication of Oxalis tuberosa: A New Model for Studying Domestication Resulting in Opposing Crop Phenotypes. Though few crops display directly opposing domesticated phenotypes, these crops may be the key to understanding domestication processes that address conflicting selective pressures in the agricultural ecosystem. Two relatively well-known examples are cassava (Manihot esculenta Crantz), which has high-cyanide and low-cyanide varieties, and potato (Solanum section Petota). Among the potatoes are several species, including the common potato (Solanum tuberosum L.), that have low levels of glycoalkaloids and there are other species of “bitter potato” with elevated levels of glycoalkaloids. We propose that Oxalis tuberosa Molina, “oca,” may represent a third example of such a crop system, with opposing high organic acid and low organic acid cultivars. Each cultivar set has different cultural food preparation practices (“use-categories”), similar to the “use-categories” that have been described for potatoes in the Andes (Brush et al. Economic Botany 35;70–88, 1981; Zimmerer Journal of Biogeography 18;165–178, 1991). Our initial analyses suggest that organic acids in tubers may be an important biochemical difference between use-categories, based on both oxalic acid and pH data. Here, we review our understanding of organic acids in oca tubers, while highlighting areas that merit further investigation.  相似文献   

7.
Regarding the arts as something peopledo — as behaviors, rather than the residue or artifacts of behavior — makes possible a theoretical grounding about their nature and importance, an endeavor that current anthropology of art has largely abandoned. A reconsideration of the suspect and largely discarded terms “functionalism” and “evolutionism” is presented in light of current evolutionary thinking. It is suggested that a contemporary reformulation of these concepts, illustrated by the author's Darwinian or “adaptationist” perspective on art, supports aims and claims of current anthropology of art, and contributes new focus and direction to its endeavors.  相似文献   

8.
Rocket line immunoelectrophoresis was used to study the taxonomy ofAzotobacter andAzomonas assessed by reaction with antiserum to the AVO2 strain ofAzotobacter. Forty-five cultures, comprising seventeen species in five genera, showed that antigen “β”, like high-titer somatic agglutination, was restricted to all 11 strains ofAzotobacter vinelandii and to one strain which has been namedAzotobacter macrocytogenes (10EM). A thermoresistant antigen (“γ”) was found to be shared by all strains and species ofAzotobacter andAzomonas investigated.  相似文献   

9.
Summary The light emitting photocytes ofChaetopterus variopedatus larvae are bilaterally situated within the ectoderm of the post-trochal region. Their histological appearance is similar to that of the adult photocytes. The larval photocytes contain a large quantity of membranous secretory vesicles (photosomes), which probably contain the photoluminescent protein. The two-cellChaetopterus embryo contains a small AB and a large CD blastomere. Previous studies have shown that only the “larvae” resulting from isolated CD blastomeres are able to luminesce. Consistent with these findings, morphologically distinct photocytes are only found in the CD larvae. The removal of the small polar lobe that forms during first cleavage leads to the production of a “larva” that is unable to produce light. All delobed larvae contain morphologically distinct photocytes, which are identical to those in normal larvae except they appear to contain only a small quantity of photosomes. Experimental equalization of first cleavage leads to the production of a double embryo. While photocytes are found in both of the duplicated post-trochal regions, usually only one of these is capable of emitting luminescence. Apparently, the highly localized vagetal material (determinants) responsible for functional light emission is distributed to both halves in only a few cases when first cleavage is experimentally “equalized”. These results indicate that the determinative action of the polar lobe is not required for the formation of the photocytes themselves, but rather for their ability to function as emitters of light. The determinants in the polar lobe ofChaetopterus may control some aspect of the photoluminescence reaction itself, such as the production of the photoprotein.  相似文献   

10.
11.
A reevaluation of floral and vegetative morphology together with data from analysis of floral fragrance and flavonoid co-pigment chemistry suggest that specific status is warranted for the two kinds ofPhalaenopsis violacea Witte known informally as the “Bornean type” and the “Malayan type.”Phalaenopsis violacea var.bellina Rchb.f. is elevated to specific rank, providing a name for the “Bornean type” plants.  相似文献   

12.
Podocopid ostracods have a calcified carapace encasing their uncalcified body parts like an envelope. A marginal infold (calcified inner lamella) develops along the free margin of both valves, notably in the adult stage. Radial pore canals, which often exhibit a distinct branched shape, can be seen in the free margin and they connect to the space between the outer and inner calcified cuticles called “vestibule.” These characters associated with the marginal infold have been recognized as important criteria both taxonomically and anatomically, but the calcification process of the marginal infold has never been investigated. In this study, we observed the calcification process of the anterior free margin in Leptocythere species. The free margin of the adult specimen starts its calcification just after ecdysis, but the degree of calcification remains the same as in the juvenile until approximately 35 h after ecdysis. The marginal infold of the adult specimen then begins to calcify from its distal part around 40 h postecdysis, and short simple pore canals can still be observed in the free margin. Marginal pore canals become more branched and narrower as calcification proceeds beyond 100 h postecdysis. These results indicate that the calcification of the free margin in a podocopid carapace occurs in two steps, and needs much time to complete the process even in small species of Leptocythere. In addition, these observations provide a basis for discussion on the correlation of the carapace size, environmental factors of the habitat, and the development of the vestibule in some Krithe species, “Krithe problem.”  相似文献   

13.
Pre-dispersal seed predators of quickly maturing inflorescences of Asteraceae are constrained by shortage of development time. At seed dispersal, they should pupate or, if still immature, relocate into another inflorescence. To investigate how dominant coleopteran predators of dandelion seed, Glocianus punctiger (Curculionidae) and Olibrus bicolor (Phalacridae), cope with time limitation we combined observation (development and temperature of dandelion capitulum, thermal constants of predator development, age structure of larval populations at seed dispersal) and analogy (“rate isomorphy” in predator development, comparing “model” coleopteran species with similar temperature requirements). Development of a dandelion capitulum takes 21 days. The time available to G. punctiger (140–190 day degrees, development threshold 6.3°C) is sufficient to complete development and pupate after seed dispersal. By contrast, only 30–50 day degrees are available to O. bicolor (threshold 13.5°C) and this is not enough to complete development and consequently immature larvae should move to other capitula to continue feeding until pupation. These contrast strategies which are determined by this thermal adaptation, are accompanied by differences in larval morphology. The “cold adapted” G. punctiger has an apodous larva not capable of migrating between capitula while the “warm adapted” O. bicolor has a mobile campodeiform larva capable of migration.  相似文献   

14.
The life cycle ofCandida tropicalis has been elucidated by nuclear staining. We were able to distinguish 5 stages: (1) the sexually active unstable haplophase which either can mutate directly to (2) the sexually inactive haplophase, or is converted to (3) the diplophase by “autoploidization”. The unstable diplophase changes into the sexually inactive haplophase, which is stable, by “budding meiosis’. Chlamydospores (4), which are possibly formed by sexually inactive haploid cells, are true resting spores, and during their germination only mitosis takes place. The buds formed during germination may develop into either the sexually active, or the inactive haplophase. During budding meiosis in the diplophase, multinucleate giant cells (5) may occur. The authors do not consider the latter to be metabasidia. Instead, they might in some way be homologus with asci, and their daughter nuclei might be comparable with the nuclei of ascospore initials. These new nuclei migrate successively into new buds which process results in a short chain of haploid cells. True ascospores have not been found. From these findings it is likely thatC. tropicalis is closely related to the ascomycetes rather than to the Hemibasidiomycetes.  相似文献   

15.
A method for estimating the complexity of behavioral patterns of ants based on the Kolmogorov complexity is considered. Behavioral sequences are presented as “texts” compressed with the KGB Archiver (v. 1.2). The elements of behavior (a total of 10) singled out from video records served as an alphabet. The comparison of “successful” and “incomplete” hunting behaviors in Myrmica rubra showed that successful hunting patterns were characterized by less complexity than “incomplete” ones. It was assumed that complete patterns had less redundancy and better predictability. The smallest complexity was revealed in complete hunting patterns of naive (laboratory reared) ants in comparison with members of a natural colony. In perspective, quantitative evaluation of complexity of behavioral patterns will help to evaluate the level of discrete variability within ant colonies.  相似文献   

16.
On fixed precision level sequential sampling   总被引:1,自引:0,他引:1  
Summary It is proposed that the sequential sampling design ofKuno (1969) for estimating populations with a fixed level of precision be modified by using σ2=am b for the variance-mean relationship for most field distributions of organisms. This function yields a straight line “stop line” rather than a curve. An example is calculated and used with field data.  相似文献   

17.
Hybridization of gametophytes, continuous self-crossing and targeted selection were utilized to breed a new Laminaria variety. After five-generation selection breeding, the new variety “Rongfu” was obtained. Its male parent “Yuanza No.10” was the high-yield cultivation variety, and its female parent was variety “Fujian” which could tolerate relatively high seawater temperature. “Yuanza No.10” and “Fujian” were different but complement in their morphological characteristics and biological habits. Variety “Rongfu” was bred through their hybridization which exhibited high-yield potential and high seawater temperature tolerance. The results of traits evaluation in consecutive years showed that “Rongfu” attained higher yields by 24–27% compared to the control (widely used commercial variety) and also contained considerable amounts of iodine, mannitol, and algin. When seawater temperature was 18–21°C, the blade growth of “Rongfu” was maintained and tissue loss by abrasion was significantly lower than the control. Since the adoption of variety “Rongfu” in 2001, its cultivation areas have been extended to Shandong, Fujian and Guangdong province and have reached 14,133 ha currently, i.e., almost one-tenth of the total cultivation areas of Laminaria in China. The results of Random Amplified Polymorphic DNA analysis showed that the relationship between “Rongfu” and other cultivation varieties in China was very close.  相似文献   

18.
Light state transition is a physiological function of oxygenic organisms to balance the excitation of photosystem II (PSII) and photosystem I (PSI), hence a prerequisite of oxygen-evolving photosynthesis. For cyanobacteria, phycobilisome (PBS) movement during light state transition has long been expected, but never observed. Here the dynamic behavior of PBS movement during state transition in cyanobacterium Synechocystis PCC6803 is experimentally detected via time-dependent fluorescence fluctuation. Under continuous excitation of PBSs in the intact cells, time-dependent fluorescence fluctuations resemble “damped oscillation” mode, which indicates dynamic searching of a PBS in an “overcorrection” manner for the “balance” position where PSII and PSI are excited equally. Based on the parallel model, it is suggested that the “damped oscillation” fluorescence fluctuation is originated from a collective movement of all the PBSs to find the “balance” position. Based on the continuous fluorescence fluctuation during light state transition and also variety of solar spectra, it may be deduced that light state transition of oxygen-evolution organisms is a natural behavior that occurs daily rather than an artificial phenomenon at extreme light conditions in laboratory.  相似文献   

19.
New osteological material of the endemic deer from Lunel-Viel and l’Igue des Rameaux (France) reveals its evolutionary specialization, and gives reason for establishing a new genus,Haploidoceros, with a single speciesH. mediterraneus (Bonifay, 1967). The cranial proportions and morphology suggest thatH. mediterraneus is close to the Late Villafranchian speciesMetacervocerus rhenanus, which may be a possible forerunner of the deer under study. The evolutionary origin ofH. mediterraneus took place in the Iberian glacial refugia during the “Mindel glaciation” of the early Middle Pleistocene. The North-East distribution ofH. mediterraneus was limited by unfavorable climate influence of the Arctic and Alpine Ice Shields.   相似文献   

20.
Mobile genetic elements constitute a substantial part of eukaryotic genome and play an important role in its organization and functioning. Co-evolution of retrotransposons and their hosts resulted in the establishment of control systems employing mechanisms of RNA interference that seem to be impossible to evade. However, “active” copies of endogenous retrovirus gypsy escape cellular control in some cases, while its evolutionary elder “inactive” variants do not. To clarify the evolutionary relationship between “active” and “inactive” gypsy we combined two approaches: the analysis of gypsy sequences, isolated from G32 Drosophila melanogaster strain and from different Drosophila species of the melanogaster subgroup, as well as the study of databases, available on the Internet. No signs of “intermediate” (between “active” and “inactive”) gypsy form were found in GenBank, and four full-size G32 gypsy copies demonstrated a convergence that presumably involves gene conversion. No “active” gypsy were revealed among PCR generated gypsy ORF3 sequences from the various Drosophila species indicating that “active” gypsy appeared in some population of D. melanogaster and then started to spread out. Analysis of sequences flanking gypsy variants in G32 revealed their predominantly heterochromatic location. Discrepancy between the structure of actual gypsy sites in G32 and corresponding sequences in database might indicate significant inter-strain heterochromatin diversity. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号