Shark Teeth Research Articles

Effects of Food Topographical Features on Attachment and Heat Resistance of Salmonella During Drying

Changes in the topographical features of food during thermal processing, e.g., surface and bulk shrinkage during drying, may protect microbial cells from direct exposure to heat. Knowledge of the effects of the surface topographical features and their changes on microbial cell behavior is thus of interest. The objective of the present study was to investigate the effects of artificially prepared topographical features on the attachment ability and heat resistance of Salmonella on model food surface during hot air drying. Carrot was used as a model food material. Carrot sticks (3 × 1 × 1 cm) were artificially textured on one side with either shark tooth or wavy (crinkle) cut; the cut was artificially made to amplify the possible effect of surface roughness, which resembles topographical features of food surface and their changes, on the bacterial cell behavior. The degree of roughness was varied in the range of 20–80% of the total height of a stick. Approximately 0.2–0.7 log increase in the number of Salmonella was observed on the rough surfaces as compared to smooth control samples since larger surface areas were available for bacterial cell attachment. Salmonella attached on the surfaces with higher wave height also exhibited higher heat resistance (up to 2 h extra drying time was required to achieve 4-log reductions of Salmonella as compared to the time required by the control sample). However, the effect of cut pattern on bacterial cell behavior was not observed.

Nd and Sr isotope compositions in modern and fossil bones – Proxies for vertebrate provenance and taphonomy

Rare earth elements (REE), while not essential for the physiologic functions of animals, are ingested and incorporated in ppb concentrations in bones and teeth. Nd isotope compositions of modern bones of animals from isotopically distinct habitats demonstrate that the 143Nd/ 144Nd of the apatite can be used as a fingerprint for bedrock geology or ambient water mass. This potentially allows the provenance and migration of extant vertebrates to be traced, similar to the use of Sr isotopes. Although REE may be enriched by up to 5 orders of magnitude during diagenesis and recrystallization of bone apatite, in vivo 143Nd/ 144Nd may be preserved in the inner cortex of fossil bones or enamel. However, tracking the provenance of ancient or extinct vertebrates is possible only for well-preserved archeological and paleontological skeletal remains with in vivo-like Nd contents at the ppb-level. Intra-bone and -tooth REE analysis can be used to screen for appropriate areas. Large intra-bone Nd concentration gradients of 10 1–10 3 are often measured. Nd concentrations in the inner bone cortex increase over timescales of millions of years, while bone rims may be enriched over millenial timescales. Nevertheless, ε Nd values are often similar within one ε Nd unit within a single bone. Larger intra-bone differences in specimens may either reflect a partial preservation of in vivo values or changing ε Nd values of the diagenetic fluid during fossilization. However, most fossil specimens and the outer rims of bones will record taphonomic 143Nd/ 144Nd incorporated post mortem during diagenesis. Unlike REE patterns, 143Nd/ 144Nd are not biased by fractionation processes during REE-uptake into the apatite crystal lattice, hence the ε Nd value is an important tracer for taphonomy and reworking. Bones and teeth from autochthonous fossil assemblages have small variations of ±1 ε Nd unit only. In contrast, fossil bones and teeth from over 20 different marine and terrestrial fossil sites have a total range of ε Nd values from –13.0 to 4.9 ( n = 80), often matching the composition of the embedding sediment. This implies that the surrounding sediment is the source of Nd in the fossil bones and that the specimens of this study seem not to have been reworked. Differences in ε Nd values between skeletal remains and embedding sediment may either indicate reworking of fossils and/or a REE-uptake from a diagenetic fluid with non-sediment derived ε Nd values. The latter often applies to fossil shark teeth, which may preserve paleo-seawater values. Complementary to ε Nd values, 87Sr/ 86Sr can help to further constrain the fossil provenance and reworking.

Paleoecología del Alto Guayacan Formación Uscari Mioceno provincia de Limón, Costa Rica

A paleoecological analysys o fossils belonging to Uscari Formation (Miocene-Pliocene] at the Limon Province, Costa Rica is presented, Mollusk, foraminifers, arthopods, shark teeth, ichnofossil and plants led to the conclussion that litoral to infralitoral enviroment was developed in that area with dense communities of suspension feeders and deposit feeders. That association shows characteristics of Skolitos Ichnofacies and Vital lipostrate biofacies.

Multicuspidate shark teeth associated with chondrichthyan and acanthodian scales from the Emsian (Devonian) of southern Algeria

Previously undescribed Emsian vertebrates from southern Algeria (southern Ahaggar) include a new chondrichthyan Tassiliodus lessardi n. gen., n. sp. with multicuspidate teeth and scales with a distinctive histology. This is the first Emsian chondrichthyan taxon reported from the north-western margin of Gondwana. Rare acanthodian scales are assigned to Milesacanthus cf. ancestralis Burrow, Lelièvre & Janjou, 2006, an Emsian species also known from Saudi Arabia, reinforcing the Gondwanan faunal affinity.

Remains of Small Ornithurine Birds from a Late Cretaceous (Cenomanian) Microsite in Russell County, North-Central Kansas

Our analysis of vertebrate remains collected from a Cenomanian microsite in the Lincoln Limestone, the basal-most member of the Greenhorn Formation in Russell County, Kansas, identifies ornithurine (sensu Chiappe, 1996) avian fossils. The specimens presented here are slightly younger than the oldest avian remains known from North America (from the Woodbine Formation, Texas) and of a similar age as the avians from the Asheville Formation in Saskatchewan, Canada. This find thus connects the extensive geographic range of the earliest North American birds from Saskatchewan south through central Kansas and on to Texas. The specimens discussed here are fragmentary, yet show features definitive of ornithurine birds. One specimen is attributable to Ichthyornis, whereas another preserves teeth characteristic of ornithurine birds. In addition to bird bones, the microsite yielded numerous bony fish remains, shark teeth, coniasaur vertebrae, and other lizard bones.

Analysis of an AssociatedCretoxyrhina mantelliDentition from the Late Cretaceous (Smoky Hill Chalk, Late Coniacian) of Western Kansas

Fossil shark teeth are common but are usually represented by shed examples and are seldom in associated or articulated groups. Complete dentition reconstruction from isolated teeth cannot be certain, even when large quantities are available from a single location and horizon. The Smoky Hill Chalk (Late Cretaceous) of western Kansas, U.S.A. has yielded a number of associated, and sometimes articulated, tooth sets of Cretoxyrhina mantelli Agassiz. Teeth from articulated sets are rarely removed from matrix which limits the understanding of positional characteristics to a single perspective. In this paper, we analyze and described an associated set of disarticulated Cretoxyrhina teeth. These teeth were arranged and compared with other disarticulated associated sets, then compared with a known articulated tooth set; resulting in a multi-perspective Cretoxyrhina tooth set. This reconstruction provides characteristics that permit upper and lower lateroposterior teeth to be differentiated and raise questions regarding the number of anterior tooth positions present.

MAMMALIAN BITE MARKS ON JUVENILE FUR SEAL BONES FROM THE LATE NEOGENE PURISIMA FORMATION OF CENTRAL CALIFORNIA

Fossils of extinct fur seals and walruses (Carnivora: Pinnipedia) occur within rich vertebrate fossil assemblages recovered from the shallow marine Mio-Pliocene Purisima Formation, central California. Two isolated postcranial bones—a humerus and a radius—belonging to a juvenile fur seal (Pinnipedia: Otariidae) exhibit circular depressions. These bone modifications are associated with radial and circular fractures, and are characterized by inward displacement of the cortex. These depressions lack features typical of erosive invertebrate borings, trampling damage from media ( = substrate) interaction, puncturing by another object during diagenetic compaction, such as a clast embedded or associated with the modification, or pathologic bone modification. These features are best interpreted as tooth marks. These tooth marks lack certain characteristics of commonly reported marks inflicted by shark teeth, such as linear gouges and subparallel scrapes formed by xiphodont and serrated teeth. These bone modifications instead exhibit a circular shape and inward displacement of the cortex, consistent with puncturing by a conical mammal tooth. The size and distribution of the tooth marks, in concert with the known vertebrate assemblage from the Purisima Formation, indicate several possible producers of the bone modifications: a pilot whale or beluga-like cetacean, a terrestrial carnivore, a dusignathine or odobenine walrus, or a case of infanticide by a conspecific otariid.

Shark predation and tooth wear in a population of northeastern Pacific killer whales

The cosmopolitan killer whale Orcinus orca feeds on a wide variety of prey types over its global range, but in at least some regions, genetically distinct and ecologically specialised lineages of killer whales coexist sympatrically. In coastal waters of the northeastern Pacific, 2 such lineages have been well described: the so-called 'residents' prey on teleost fish, especially salmonids and the other ('transients') on marine mammals. A third lineage in this region ('offshores') appears from chemical tracers to be ecologically distinct from residents and transients, but its diet is very poorly known. Here we describe 2 encounters with offshore killer whales during which multiple predation events involving sharks were observed. Using DNA analysis of tissue samples collected from these predation events, we identified the prey species as Pacific sleeper shark Somniosus pacificus and determined that a minimum of 16 individuals were consumed over the 2 encounters. This represents the first confirmed prey species of offshore killer whales based on field observations of foraging and the first record of any Somniosus species in the prey of Orcinus. We also show quantitatively that api- cal tooth wear is far greater in offshores than in resident and transient killer whales, and propose that such wear is at least in part due to abrasion from dermal denticles embedded in shark skin. Further studies are needed to determine whether offshore killer whales are as specialised ecologically as resident and transient killer whales, and whether sharks play a dominant role in their diet.

The world’s oldest fossil seal record

A femur fragment with an Early Lutetian (early Middle Eocene) age is the world’s oldest fossil record from a seal, and, is described as Praephoca bendullensis nov. gen. nov. spec. This find pushes back the earliest evolution of seals into the Paleocene epoch. The femur has plesiomorphic terrestrial mammal characteristics but has a morphology that is already closer to that of Miocene and present day seals. The Eocene seal femur was found at Fürstenau-Dalum in north-west Germany, in a conglomerate rich in shark teeth that was deposited in a coastal delta environment to the north-west of the central European Rhenish Massif mainland, in the southern pre-North Sea Basin. This discovery has led to a revision of the theory that phocids originated along the coastline of the North American continent. Instead they can now be interpreted to have originated in the tropical Eocene climate of central Europe. Although the fossil records of pinnipeds in Europe during the Eocene, Oligocene and Miocene are extremely sparse, they appear to have inhabited the pre- North Sea basin, within the influence of temperate and arctic upwellings. The distribution of abundant teeth from white and megatooth sharks of two different lineages appears to correlate with that of the seals, which the sharks most probably hunted; providing supporting evidence that the phocids were already adapted as shallow marine coastal inhabitants by this time.

Oxygen isotope analysis of shark teeth phosphates from Bartonian (Eocene) deposits in Mangyshlak peninsula, Kazakhstan

Oxygen isotope analysis of shark teeth phosphates from Bartonian (Eocene) deposits in Mangyshlak peninsula, Kazakhstan We report the results of high-precision (±0.05‰) oxygen isotope analysis of phosphates in 6 teeth of fossil sharks from the Mangyshlak peninsula. This precision was achieved by the offline preparation of CO2 which was then analyzed on a dual-inlet and triple-collector IRMS. The teeth samples were separated from Middle- and Late Bartonian sediments cropping out in two locations, Usak and Kuilus. Seawater temperatures calculated from the δ18O data vary from 23-41°C. However, these temperatures are probably overestimated due to freshwater inflow. The data point at higher temperature in the Late Bartonian than in the Middle Bartonian and suggest differences in the depth habitats of the shark species studied.

Biology meets engineering: The structural mechanics of fossil and extant shark teeth

The majority of studies on the evolution and function of feeding in sharks have focused primarily on the movement of cranial components and muscle function, with little integration of tooth properties or function. As teeth are subjected to sometimes extreme loads during feeding, they undergo stress, strain, and potential failure. As attributes related to structural strength such as material properties and overall shape may be subjected to natural selection, both prey processing ability and structural parameters must be considered to understand the evolution of shark teeth. In this study, finite element analysis was used to visualize stress distributions of fossil and extant shark teeth during puncture, unidirectional draw (cutting), and holding. Under the loading and boundary conditions here, which are consistent with bite forces of large sharks, shark teeth are structurally strong. Teeth loaded in puncture have localized stress concentrations at the cusp apex that diminish rapidly away from the apex. When loaded in draw and holding, the majority of the teeth show stress concentrations consistent with well designed cantilever beams. Notches result in stress concentration during draw and may serve as a weak point; however they are functionally important for cutting prey during lateral head shaking behavior. As shark teeth are replaced regularly, it is proposed that the frequency of tooth replacement in sharks is driven by tooth wear, not tooth failure. As the tooth tip and cutting edges are worn, the surface areas of these features increase, decreasing the amount of stress produced by the tooth. While this wear will not affect the general structural strength of the tooth, tooth replacement may also serve to keep ahead of damage caused by fatigue that may lead to eventual tooth failure.

Neoselachian sharks from the Callovian-Oxfordian (Jurassic) of Ogrodzieniec, Zawiercie Region, southern Poland

Abstract: Callovian and Oxfordian strata in Ogrodzieniec near Zawiercie, southern Poland, have yielded two shark tooth assemblages that collectively include 14 neoselachian taxa. A previously unrecognised member of the Orectolobiformes, Akaimia altucuspis gen. et sp. nov., is described and characterised by a dentition remarkably similar to modern wobbegong sharks (Orectolobidae) by convergence. The assemblages also include the first anterior teeth ever found of the palaeospinacid ‘Synechodus’prorogatus Kriwet, in addition to teeth from two other palaeospinacids, Sphenodus spp., four different orectolobiforms, two hexanchids and Protospinax spp. These shark tooth assemblages contribute to the poorly known Callovian and Oxfordian neoselachian faunas and indicate that the diversity was higher than previously appreciated, particularly within the Orectolobiformes.

Performance of shark teeth during puncture and draw: implications for the mechanics of cutting

The performance of an organism’s feeding apparatus has obvious implications for its fitness and survival. However, the majority of studies that focus on chondrichthyan feeding have largely ignored the role of teeth. Studying the functional morphology of shark teeth not only elucidates the biological role that teeth play in feeding, but also provides insight specifically into the evolution of shark feeding because teeth are often the only structures available in the fossil record. In the present study, we investigate the puncture and draw performance of three general categories of extant teeth, tearing-type, cutting-type, and cutting–clutching type, as well as three fossil morphologies, utilizing a universal testing system. Differences in puncturing performance occurred among different prey items, indicating that not all ‘soft’ prey items are alike. The majority of teeth were able to puncture different prey items, and differences in puncture performance also occurred among tooth types; however, few patterns emerged. In some cases, broader triangular teeth were less effective at puncturing than narrow-cusped teeth. There were no differences between the maximum draw forces and maximum puncture forces. Many of the shark teeth in the present study were not only able to perform draw and puncture equally well, but also many tooth morphologies were functionally equivalent to each other. The findings obtained in the present study lend little support to the belief that shark tooth morphology is a good predictor of biological role. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 100, 271–286.

Ancient Nursery Area for the Extinct Giant Shark Megalodon from the Miocene of Panama

BackgroundAs we know from modern species, nursery areas are essential shark habitats for vulnerable young. Nurseries are typically highly productive, shallow-water habitats that are characterized by the presence of juveniles and neonates. It has been suggested that in these areas, sharks can find ample food resources and protection from predators. Based on the fossil record, we know that the extinct Carcharocles megalodon was the biggest shark that ever lived. Previous proposed paleo-nursery areas for this species were based on the anecdotal presence of juvenile fossil teeth accompanied by fossil marine mammals. We now present the first definitive evidence of ancient nurseries for C. megalodon from the late Miocene of Panama, about 10 million years ago.Methodology/Principal FindingsWe collected and measured fossil shark teeth of C. megalodon, within the highly productive, shallow marine Gatun Formation from the Miocene of Panama. Surprisingly, and in contrast to other fossil accumulations, the majority of the teeth from Gatun are very small. Here we compare the tooth sizes from the Gatun with specimens from different, but analogous localities. In addition we calculate the total length of the individuals found in Gatun. These comparisons and estimates suggest that the small size of Gatun's C. megalodon is neither related to a small population of this species nor the tooth position within the jaw. Thus, the individuals from Gatun were mostly juveniles and neonates, with estimated body lengths between 2 and 10.5 meters.Conclusions/SignificanceWe propose that the Miocene Gatun Formation represents the first documented paleo-nursery area for C. megalodon from the Neotropics, and one of the few recorded in the fossil record for an extinct selachian. We therefore show that sharks have used nursery areas at least for 10 millions of years as an adaptive strategy during their life histories.

Determination of Sr and Ba partition coefficients between apatite from fish ( Sparus aurata) and seawater: The influence of temperature

The Sr/Ca and Ba/Ca ratios in inorganic apatite are strongly dependent on the temperature of the aqueous medium during precipitation. If valid in biogenic apatite, these thermometers would offer the advantage of being more resistant to diagenesis than those calibrated on biogenic calcite and aragonite. We have reared seabreams ( Sparus aurata) in tanks with controlled conditions during experiments lasting for more than 2 years at 13, 17, 23 and 27 °C, in order to determine the variations in Sr and Ba partitioning relative to Ca ( D Sr and D Ba, respectively) between seawater and fish apatitic hard tissues (i.e. teeth and bones), as a function of temperature. The sensitivity of the Sr and Ba thermometers (i.e. ∂ D Sr/∂ T and ∂ D Ba/∂ T, respectively), are similar in bone ( ∂ D b – w Sr /∂ T = 0.0036 ± 0.0003 and ∂ D b – w Ba /∂ T = 0.0134 ± 0.0026, respectively) and enamel ( ∂ D e – w Sr /∂ T = 0.0037 ± 0.0005 and ∂ D e – w Ba /∂ T = 0.0107 ± 0.0026, respectively). The positive values of ∂ D Sr/∂ T and ∂ D Ba/∂ T in bone and enamel indicate that D Sr and D Ba increase with increasing temperature, a pattern opposite to that observed for inorganic apatite. This distinct thermodependent trace element partitioning between inorganic and organic apatite and water highlights the contradictory effects of the crystal-chemical and biological controls on the partitioning of Ca, Sr and Ba in vertebrate organisms. Taking into account the diet Sr/Ca and Ba/Ca values, it is shown that the bone Ba/Ca signature of fish can be explained by Ca-biopurification and inorganic apatite precipitation, whereas both of these processes fail to predict the bone Sr/Ca values. Therefore, the metabolism of Ca as a function of temperature still needs to be fully understood. However, the biogenic Sr thermometer is used to calculate an average seawater temperature of 30.6 °C using the Sr/Ca compositions of fossil shark teeth at the Cretaceous/Tertiary boundary, and a typical seawater Sr/Ca ratio of 0.02. Finally, while the present work should be completed with data obtained in natural contexts, it is clear that Sr/Ca and Ba/Ca ratios in fossil biogenic apatite already constitute attractive thermometers for marine paleoenvironments.

Shark-bitten vertebrate coprolites from the Miocene of Maryland

Coprolites (fossilized feces) preserve a wide range of biogenic components, from bacteria and spores to a variety of vertebrate tissues. Two coprolites from the Calvert Cliffs outcrop belt (Miocene-aged Chesapeake Group), MD, USA, preserve shark tooth impressions in the form of partial dental arcades. The specimens are the first known coprolites to preserve vertebrate tooth marks. They provide another example of trace fossils providing evidence of prehistoric animal behaviors that cannot be directly approached through the study of body fossils. Shark behaviors that could account for these impressions include: (1) aborted coprophagy, (2) benthic or nektonic exploration, or (3) predation.

Variation in composition and abundance of Miocene shark teeth from Calvert Cliffs, Maryland

ABSTRACT Shark teeth are the most common vertebrate fossils found along the western shore of Chesapeake Bay at Calvert Cliffs in Maryland. The stratigraphic distribution of teeth within the cliffs has not yet been documented. We utilized museum collections of in situ teeth to access their distribution within stratigraphic beds and a large selection of float teeth retrieved from Calvert County beaches as a proxy for the distribution of teeth within stratigraphic beds and across underlying beaches. Museum collections provide 1,866 teeth recorded in situ; float collections yield a total of 24,409 teeth. These data sets offer different, but complementary, results. Miocene sediments along Calvert Cliffs comprise the Calvert, Choptank, and St. Marys formations. Over 96% of all teeth in the in situ data set derive from the Calvert Formation, likely due to favorable paleoenvironmental conditions for sharks. The non-uniform stratigraphic distribution of teeth is further supported by an uneven distribution of teeth collected on beaches below the cliffs. Samples from northern localities contained more float specimens; cliffs in this area are composed almost entirely of the Calvert Formation. Fifteen genera are represented in the in situ and float collections. The main constituents are Carcharhinus spp., Hemipristis serra, Galeocerdo spp., Isurus spp., and Carcharias spp. Most of these genera exhibit significant unidirectional trends in the proportional abundance of teeth across Calvert Cliffs beaches. Factors influencing these variations remain unclear, but the overall dominance of carcharhiniforms over lamniform and other sharks observed for the Miocene persists in modern nearshore environments.

A morphometric approach for addressing tooth-based species delimitation in fossil mako sharks, Isurus (Elasmobranchii: Lamniformes)

ABSTRACT Morphological studies of fossil and extant shark teeth have typically been qualitative in nature, with resulting taxonomic problems due to the complicated forms of heterodonty exhibited by many sharks. This is apparent in the designation of fossil species assigned to Isurus (Lamniformes), where the status of the putative Neogene fossil species Isurus xiphodon and I. hastalis is solely based upon supposed differences in tooth morphology. Here we apply the geometric morphometric techniques of Procrustes superimposition, resampling-based Goodall's F-test, and canonical variates analysis to extant Isurus teeth, with the goal of assessing whether these quantitative analytical techniques provide a more objective basis for taxonomic decisions than do traditional qualitative morphological descriptions. These quantitative techniques are then applied to I. hastalis and I. xiphodon to examine whether I. xiphodon should be considered a junior synonym of I. hastalis or a separate species. Results show that geometric morphometric techniques can differentiate between the two extant species as well as the two extinct species, supporting I. xiphodon as a valid taxon. We suggest that this type of analysis is applicable for examining tooth-based species delimitations of sharks with both extant and extinct members, and has the potential to be applied to other fossil shark species as well.

Young's modulus and hardness of shark tooth biomaterials

To date, the majority of studies on feeding mechanics in sharks have focused on the movement of cranial components and muscle function, with little attention to tooth properties or function. Attributes related to mechanical properties, such as structural strength, may also be subjected to natural selection. Additionally it is necessary to characterize these properties in order to construct biomechanical models of tooth function. The goal of this study was to determine hardness and elastic modulus for the shark tooth materials enameloid, osteodentine, and orthodentine. Five teeth each from one carcharhiniform species, the bonnethead Sphyrna tiburo, and one lamniform, the sand tiger shark Carcharias taurus, were utilized for nanoindentation testing. Each tooth was sectioned transversely, air-dried, and polished. Both enameloid and dentine were tested on each tooth via a Berkovich diamond tip, with nine 2 μm deep indentations per material. t-Tests were used to determine if there were differences in hardness and Young's modulus between the tooth materials of the two species. There was no significant difference between the two species for the material properties of enameloid, however both hardness and Young's modulus were higher for osteodentine than for orthodentine. This may be due to differences in microanatomy and chemical composition, however this needs to be studied in greater detail.

Variations in V Model for Software Development

V Model Represents one-to-one relationship between the documents on the left hand side and the test activities on the right. This is not always correct. System testing not only depends on Function requirements but also depends on technical design, architecture also. Couple of testing activities is not explained in V model. This is a major exception and the V-Model does not support the broader view of testing as a con-tinuously major activity throughout the Software development lifecycle. Paul Herzlich introduced the W-Model approach in 1993. The W-Model attempts to address shortcomings in the V-Model. Rather than focus on specific dynamic test stages, as the V-Model does, the W-Model focuses on the development products themselves. In its most generic form, the W-Model presents a standard development lifecycle with every develop-ment stage mirrored by a test activity. On the left hand side, typically, the deliverables of a development activity (for example, write require-ments) is accompanied by a test activity test the requirements and so on. If your organization has a different set of development stages, then the W-Model is easily adjusted to your situation. The important thing is this: the W-Model of testing focuses specifically on the product risks of concern at the point where testing can be most effective. The main contribution in this paper is Sawtooth model and Sharktooth model. Sawtooth model is another variation of the V model. The Sawtooth model is actually an extension of the V-model. The only difference between the Saw-tooth and the V-model is that prototypes are created and shown to the client for validation. Sharktooth model is more detailed view of the saw-tooth model. In contrast to the sawtooth model the sharktooth model puts the manager into account. By presenting the manager a certain abstrac-tion it also introduces new activities. Keywords: Quality software through V Model; Overcome W Model on V Model; Sawtooth & Shartooth model