Age determination in the dugong, Dugong dugon (Müller)

Mitchell, J. F. O.

doi:10.1016/0006-3207(76)90070-7

Cited by 13 publications

(10 citation statements)

References 9 publications

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“…A rare exception was found in one specimen (mm 19) in which the anterior part of lower M2 opposed upper M1 and the posterior part of lower M2 opposed the anterior part of upper M2 so that lower right M3 had erupted ahead of upper M3. This exceptional condition, of development in the upper jaw lagging behind that in the lower jaw, has been documented previously (Mitchell, 1973; Marsh, 1980).…”

Section: Resultssupporting

confidence: 73%

“…Three premolars (presumably the posterior three deciduous premolars) are erupted at birth. The molars progressively erupt posteriorly during growth, whereas the premolars progressively fall out or are partially resorbed (Fernand, 1953; Mitchell, 1973), the sockets filling with bone, until usually only M2 and M3 (occasionally M1) are present in each quadrant in old animals. Thus the cheekteeth are never simultaneously all erupted and in wear (Mitchell, 1973) (Fig.…”

Section: Resultsmentioning

confidence: 99%

“…Rather, their cheekteeth, of which there is a finite number, erupt sequentially in a monophyodont series (Petit, 1955). Dugong cheekteeth have been reported to undergo some forward migration (Mitchell, 1973; Sanson, 1977). Some authors have suggested that this migration may constitute molar progression (e.g.…”

Section: Discussionmentioning

confidence: 99%

“…Males also have significantly wider snouts (at the anterior end of the premaxillae) than females (Mitchell, 1973;Spain & Heinsohn, 1974). It has been suggested that this sexual difference results from eruption and development of the males' tusks at the onset of puberty (Spain & Heinsohn, 1974;Nishiwaki & Marsh, 1985).…”

Section: Tooth Size-body Size Allometrymentioning

confidence: 99%

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Degenerate dentition of the dugong (Dugong dugon), or why a grazer does not need teeth: morphology, occlusion and wear of mouthparts

Lanyon

Sanson

2005

Journal of Zoology

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The morphology and functional occlusion of the cheekteeth of 57 dugongs Dugong dugon of both sexes were examined using reflected light and scanning electron microscopy, radiography, hardness testing and skull manipulation. The functional morphology of the horny oral pads was also described. Mouthparts and body size allometry was examined for ontogenetic and gender-related trends. We found that the worn erupted cheekteeth of the dugong are simple flat pegs composed of soft degenerative dentine. During occlusion, the mandible moves in a mainly anterolingual direction, with the possibility of mandibular retraction in some individuals. Anterior parts of the cheektooth row may become non-functional as a dugong ages. As a function of body size, dugong cheekteeth are extremely small compared with those of other mammalian herbivores, and with other hindgut fermenters in particular. The morphology, small size and occlusal variability of the cheekteeth suggest that there has not been strong selective pressure acting to maintain an effective dentition. In contrast, great development of the horny pads and associated skull parameters and their lower size variability suggest that the horny pads may have assumed the major role in food comminution.

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Section: Resultssupporting

confidence: 73%

Section: Resultsmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Section: Tooth Size-body Size Allometrymentioning

confidence: 99%

See 2 more Smart Citations

Degenerate dentition of the dugong (Dugong dugon), or why a grazer does not need teeth: morphology, occlusion and wear of mouthparts

Lanyon

Sanson

2005

Journal of Zoology

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“…(Mitchell 1976(Mitchell , 1978 Lockyer emphasised the longevity of sirenians and the very similar GLG patterning in teeth of monodontids. In some respects the dugong tusk in males has similarities to the tusks of male narwhals.…”

Section: Discussionmentioning

confidence: 99%

Report of the Workshop on Age Estimation in Monodontids

Hohn

Lockyer²,

Acquarone³

2016

NAMMCOSP

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EXECUTIVE SUMMARY The workshop was a 2-day event organised immediately before the Society for Marine Mammalogy biennial conference in Tampa. Funding from the North Atlantic Marine Mammal Commission (NAMMCO) enabled participation of 4 invited experts and also supported the organization and logistics associated with the workshop. The breadth and depth of the workshop presentations made it clear that most issues concerning monodontid age estimation are not unique. Many researchers investigating many taxa have considered a diversity of methods and tissues to reveal biological records of age. Aside from the biological materials, accuracy and precision of the counts or metric have been considered, as well as their interpretation. Relative age can be estimated using biological or chemical changes if the rate of change is known. Attempts to use genetic telomere length to estimate relative age show telomere lengths provide a measure of individual body fitness and condition rather than age, as environment, migration, health and reproduction affect telomere length. The method has potential but is still under investigation. Reviews of aspartic acid racemization (AAR) aging techniques on eye lenses from harp seals (Pagophilus groenlandicus), fin whales (Balaenoptera physalus), harbour porpoises (Phocoena phocoena), and bowhead whales (Balaena mysticetus), indicated potential for producing relative ages but warned that the presence of cataracts in the eye lens could seriously bias the age estimation upward. In narwhal (Monodon monoceros), tusk growth layer groups (GLG) correlated well with AAR age. The AAR method is relatively accurate, but species-specific racemization rates are essential for accurate age estimation. Age models using endogenous fatty acid (FA) ratios have been successfully derived for killer whales (Orcinus orca), and humpback whales (Megaptera novaeangliae). Preliminary results using a single FA ratio for Cook Inlet belugas (Delphinapterus leucas) correlated with age from tooth GLG for physically immature animals. Future Hohn et al. (2016) Online Early Version NAMMCO Scientific Publications, Volume 10 work using two FA ratios in belugas is expected to provide more precision in relative age. It may be possible to use bone density as an indicator of relative age in beluga and narwhal flippers. The method would need to be calibrated with reference to GLG in beluga teeth and validated AAR ages in narwhal. The recording of historic hunting artifacts recovered in bowhead whales in Alaska has presented an opportunistic and potentially remarkable insight into longevity of this species (which may exceed 100 years if the interpretation of the age of the artifact is correct). Micro-CT scanning demonstrated potential for investigating internal structure of teeth and other hard tissue specimens. Because there is no destruction of the specimen and 3-D viewing is possible, this technique could be applied to specimens that are difficult to interpret from thin sections are rare, and therefore, not possible to section. Count...

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Ecological Aspects of Reproduction of Marine Mammals

Lockyer

2002

Marine Mammals

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Age determination in the dugong, Dugong dugon (Müller)

Cited by 13 publications

References 9 publications

Degenerate dentition of the dugong (Dugong dugon), or why a grazer does not need teeth: morphology, occlusion and wear of mouthparts

Degenerate dentition of the dugong (Dugong dugon), or why a grazer does not need teeth: morphology, occlusion and wear of mouthparts

Report of the Workshop on Age Estimation in Monodontids

Ecological Aspects of Reproduction of Marine Mammals

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