Age criteria for the african elephant: loxodonta a. africana
TL;DR: Thirty age groups are described and illustrated, which are related to the progress of eruption and wear of the six teeth in each side of the lower jaw, which indicate an upper age limit of about 60 years, which is compatible with fuller information on Indian elephants.
Abstract: Summary
1. The paper is based on a collection of 385 lower jaws of the African elephant (Loxodonta a. africana Blumenbach) from western Uganda.
2. Thirty age groups are described and illustrated, which are related to the progress of eruption and wear of the six teeth in each side of the lower jaw.
3. Correct identification of individual teeth in the series is essential and several checks are described. Thus, when length is plotted against width for the six teeth the points fall into six well - defined groups. Frequency distributions of laminary indices and lamella numbers support the belief that teeth have been correctly identified, but overlapping, distributions preclude identification on these characters alone.
4. The presence of abnormal seventh molars in four jaws is described.
5. Chronological ages have been assigned to the relative age groups. Information on age and growth of captive animals has been considered and the general form of the growth curve established. Arbitrary estimates of the intervals between successive age groups were made and subsequently checked against growth and seasonal ridges on the roots. These indicate an upper age limit of about 60 years, which is compatible with fuller information on Indian elephants.
6. Growth curves support the validity of the ages assigned. Asymptotic heights at shoulder (∞) are respectively 317 cm and 298 cm for males from Murchison Falls and Queen Elizabeth National Parks. For females no distinction is made (because the sample from the latter area is small) and ∞ is 272 cm.
7. Growth in weight has also been established but shows no significant differences between the two populations. The mean maximum weight of females is 2766 kg (6100 lb), and of males 5450 kg (12000 lb). Growth apparently continues throughout life.
8. Tusk growth is analysed. There is a linear increase in weight of female tusks from eruption at 1–3 years up to the oldest group, with an indicated mean combined weight of 17.7 kg (39 lb) at 60 years. Male tusks show an increasing rate of growth throughout life to a mean combined weight of about 109 kg (240 lb) at 60 years.
Big tusks are generally the result of prolonged growth; extremely big tusks probably result from prolonged and above average rate of growth.
9. Seasonal and annual incremental layers on the root 3 of the teeth are briefly described; these give an objective estimate of the chronological intervals between the relative age groups.
10. Field age criteria are presented which are derived from these growth curves.
11. The age at puberty in the female elephant is discussed and compared with earlier conclusions. There is evidence of a retardation in recent years in the Murchison Falls National Park (South bank) population and of a lengthening of the mean calving interval. This considerable depression of the reproductive rate, which is almost certainly density dependent, agrees with the observed lower recruitment in this population.
12. Survivorship curves constructed from material representing 325 natural deaths are presented for the two populations. If estimates of the age at puberty and the reproductive rate are taken into account, the expected differences in recruitment are found.
13. The calculated mean expectation of life is less than 15 years.
14. Mean individual weight is estimated at about 3800 lb.
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References
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TL;DR: Growth curves, when conventionally plotted as length on age, are difficult to compare and classify; the usual mathematical methods of fitting them, such as the logistic and the Gompertz are rather laborious and incon venient for application to large numbers of individuals.
Abstract: Growth curves, when conventionally plotted as length on age, are difficult to compare and classify. Moreover, the usual mathematical methods of fitting them, such as, the logistic and the Gompertz are rather laborious and incon venient for application to large numbers of individuals. Fortunately, for many purposes, it is unnecessary to describe the whole growth curve; for the part below the inflection point is completed early and the part above the inflection point—the “? self-inhibiting― phase, covers the period of life when differences in growth are likely to be most striking. That phase of the growth curve can be appropriately represented by a straight line, the charac teristics of which can be treated statistically, by the following graphic method: Using arithmetic graph paper, with body length represented along both the x axis and along the y axis, plot length at ages 1, 2, 3, 4, 5@ n on the x axis against length at ages 2, 3, 4, 5, 6. n + 1, respectively, on the y axis. For several species on which I have found published length data, these points fall along a straight line. This line can be regarded as a sort of transformation of the usual growth curve, and in the following discussion I will call it that. The nine examples given in Figures 1—3are based on average lengths of large samples. When lengths of individual specimens are plotted by this method, a straight-line relationship is still obvious, though the points deviate more widely from the linethan when averages are used. These deviationsdoubtless result from several causes, among which random variations in environmental experience and errors of observation readily suggest themselves. For a few species the published growth data failed to produce a straight line. In these cases, the course of growth may differ from that in other animals; or the observed anomalies may reflect some artifactual effect in the data. Among those species for which this “? transformation― results in a straight line, the growth increments corresponding to equal time intervals, for example, be tween years of age (12 —? 11,13 —? 12,14 —? i@, @l,—? i@), have the following inter relations; where 1,, refers to the length at any given age, i.e., at the end of any given time interval :2
656 citations
216 citations
TL;DR: While working on the elephant seal in 1949, a new and accurate method of determining age, depending upon cyclical variation in the rate and manner of calcification of the teeth, was developed.
Abstract: FOR estimating the age of mammals such widely differing characters as coat colour, size, skull proportions and sutures, ossification, numbers of corpora albicantes, changes in the lens of the eye, etc., have been used; but such methods are laborious and frequently yield only an approximate result. While working on the elephant seal (Mirounga leonina) in 1949, a new and accurate method of determining age, depending upon cyclical variation in the rate and manner of calcification of the teeth, was developed. This makes possible determination of age, to within a month, up to at least twenty years in the male, and thirteen years in the female.
193 citations
133 citations
TL;DR: The findings are discussed with reference to the phylogenetic position of the genus, the probable role of the corpus luteum in pregnancy, and the significance of the results in relation to the conservation of existing wild elephant populations.
Abstract: Between December 1946 and December 1948, and January to March 1950, 150 elephants made available in the course of control work carried out by the Uganda Game Department were examined in greater or less detail according to circumstances. Eighty-one were females, of which sixty-seven were adult and thirty-one had an embryo in the uterus. All the dissections were carried out in the field, and the present account includes observations on the terrain, the food of the elephant, and other aspects of its ecology. Linear measurements of the carcasses and photographs of the molar teeth provide a guide to the age of specimens. Tusk growth is nearly similar in males and females until puberty, after which those of females generally cease to grow. The reproductive organs of the male are briefly described; those of the female are described in more detail, and discrepancies between existing accounts are considered in the light of this relatively extensive series of specimens. The mode of formation of the ovarial sac is unusual and is described from foetal, neonatal and adult specimens. There is marked hypertrophy of the interstitial tissue of the foetal gonads during the later stages of gestation. Breeding occurs at all times of year, but mating is possibly more frequent in the period December to March than at other times. Both sexes reach maturity at 8 to 12 years, and the female continues to breed until old age. Parturition is followed by a lactation anoestrus, after which the female undergoes a number of brief oestrous cycles until pregnancy ensues, lactation being continued throughout the subsequent gestation period. The interval between parturition and subsequent conception is normally of the same order of duration as the gestation period, and the normal calving interval appears to be rather less than four years. The ovarian cycle of the adult is characterized by the occurrence of multiple ovulation and the presence of many apparently active and histologically indistinguishable corpora lutea in both ovaries at all the stages of pregnancy which were encountered. It is probable that the corpus luteum of pregnancy develops from one of a number of follicles which ovulate under the same hormonal stimulus, and that it persists together with the accessory corpora lutea, some of which arise from follicles which ovulate and some from follicles which luteinize without ovulating. The corpora lutea are replaced about mid-pregnancy by a second set, which are formed by the luteinization of all the follicles with antra in both ovaries; some at least of the larger ones ovulate while many smaller ones do not. Follicular growth is suppressed in the later stages of pregnancy. The cycle of events bears some resemblance to that which occurs in the mare, and the comparison is discussed in detail. The ovarian periphery is characterized by numerous subsurface crypts and papillose projections which increase the area of the germinal epithelium. A description of the placenta and foetal membranes is in preparation, and preliminary study reveals a striking similarity to Hyrax , particularly in the quadri-lobulate allantois. The findings are discussed with reference to the phylogenetic position of the genus, the probable role of the corpus luteum in pregnancy, and the significance of the results in relation to the conservation of existing wild elephant populations.
123 citations